electronics world · frame giving +5v 35a, -5v 1.5a, +12v 4a (8a peak), -12v 1.5a, massive...

ELECTRONICSWORLD+ WIRELESS WORLDNOVEMBER 1993 £1.95

FREETexas Instrumentscharge -pumped op -amp

AUDIODistortion in theoutput stage

DIGITAL DESIGNWorking withPLA & PLD logic

APPLICATIONSSingle chipdata radioREVIEWDigital filterdesign underWindowsCOMPUTINGDSP withoutthe maths

HISTORYSpark transmittertechnology

aS

Denmark DKr. 70.00Germany DM 15.00

Greece Dra 760Holland DN. 14

Italy L 7300IR £3.30

Spain Pts. 780Singapore SS 12.60

USA $6.70

SOR DISTRIBUTION

A REED BUSINESS PUBLICATION

ODOIOIOOI1)I00I0I00

I 001010111I II0I000Id 11101010

01011000Q II0I03010I I:IOICOOI

I )IIII0

LPN ROOM

-JR

.

Trig

11

IOI0II0II

*101110100010130101110110

OII0I0IitI.101101131

,* 010IIII.100 *1101011

00100101 III

1111010011 0

- .4 '0'0

esmc=3imlimmec)co

cp

40% Windows EDA software discount See inside for details

THE WORLDS No.1 BEST SELLINGUNIVERSAL PROGRAMMING AND TESTING SYSTEM.

The PC82 Universal Programmer and Tester is aPC -based development tool designed toprogram and test more than 1500 ICs. The latestversion of the PC82 is based on the experiencegained after a 7 year production run of over100,000 units.

The PC82 is the US version of the SunshineExpro 60, and therefore can be offered at a verycompetitive price for a product of such highquality. The PC82 has undergone extensivetesting and inspection by various major ICmanufacturers and has won their professionalapproval and support. Many do in fact use thePC82 for their own use!

The PC82 can program E/EPROM, Serial PROM,BPROM, MPU, DSP, PLD, EPLD, PEEL, GAL, FPL,MACH, MAX, and many more. It comes with a 40pin DIP socket capable of programming deviceswith 8 to 40 pins. Adding special adaptors, thePC82 can program devices up to 84 pins in DIP,PLCC, LCC, QFP, SOP and PGA packages.

The unit can also test digital ICs such as the TTL74/54 series, CMOS 40/45 series, DRAM (evenSIMM/SIP modules) and SRAM. The PC82 caneven check and identify unmarked devices.

Customers can write their own test vectors toprogram non standard devices. Furthermore itcan perform functional vector testing of PLDsusing the JEDEC standard test vectors createdby PLD compilers such as PALASM, OPALjr,ABLE, CUPL etc. or by the user.

The PC82's hardware circuits are composed of 40set pin -driver circuits each with TTL I/O control,D/A voltage output control, ground control,noise filter circuit control, and OSC crystalfrequency control. The PC82 shares all the PC'sresources such as CPU, memory, I/O hard disk,keyboard, display and power supply.

A dedicated plug in card with rugged connectingcable ensures fast transfer of data to theprogrammer without tying up a standard parallelor serial port. Will work in all PC compatiblesfrom PC XT to 486.

The pull -down menus of the software makes thePC82 one of the easiest and most user-friendlyprogrammers available. A full library of fileconversion utilities is supplied as standard.

The frequent software updates provided bySunshine enables the customer to immediatelyprogram newly released ICs. It even supportsEPROMs to 16Mbit.

Over 20 engineers are employed by Sunshine todevelop new software and hardware for thePC82. Not many competitors can boast of similarsupport!

Citadel, a 32 year old company are the UK agentsand service centre for the Sunshine range ofprogrammers, testers and in circuit emulatorsand have a team of engineers trained to givelocal support in Europe.

* More sold worldwide than any other ofits type.

* UK users include BT, IBM, MOD, THORNEMI, MOTOROLA, SANYO, RACAL

* High quality Textool or Yamaichi zeroinsertion force sockets.

* Rugged screened cabling.* High speed PC interface card designed

for use with all PC models from XT to486.

* Over 1500 different devices (includingmore than 100 MPU's) supposed.

* Tests and or identifies a wide range oflogic devices.

NOW SUPPLIED WITH SPECIAL VALUEADDED SOFTWARE (worth over £300 ifbought seperately):

* MICROTEC disassemblers for Z8, 8085,8048. 8051, 6809 & 68HC11

Our stocked range of own manufactured andimported Sunshine products include:

* Super fast EPROM Erasers.1, 4 & 8 gang EPROM 8Mbit productionprogrammers.

* Battery operated portable EPROMprogrammers.

* "In circuit" Emulators." Handy pocket IC testers.

ORDERING INFORMATION

PC82 complete with interface card,cable, software and manual only £395

Please add £7 carriage (by overnight cornier) forUK orders, £20 for export orders, and VAT whereapplicable.

ACCESS, MASTERCARD, VISA or CWO.Official orders are welcome from Governmentbodies & local authorities.

Free demo disk with device list available.

* Software supplied to write own testvectors for custom ICs and ASICs etc.

* Protection circuitry to protect againstwrong insertion of devices.

* Ground control circuitry using relayswitching.

* One model covers the widest range ofdevices, at the lowest cost.

* No need to tie up a slow parallel port.

* Two year free software update.

* Speed optimised range ofprogramming algorithms.

* NATIONAL SEMICONDUCTOR OPALjrPAL/PLD development software.

* BATCH SOFTWARE for productionprogramming.

CP[CITADEL PRODUCTS LTDDEPT. WW, 50 HIGH ST.,EDGWARE, MIDDX. HA8 7EP.

Phone now on: 081 951 1848/9

Access

VISA

CONTENTS

Cover dlustrationKevin Clarkson

FEATURES

CLEAR HIGHWAY FOR DIGITALTELEVISION 8,2Although there are still no signs o' it in theshops, a new TV technology will shortlymake your video recorder and TV setobsolescent. Not only will picture qualityvisibly improve, but the availability of moreprogramme channels will provide a newimperative to broadcasters. Tom Woodfordreports on a digital TV revolution.

WORKING WITH PROGRAMMABLE LOGIC 905Programmable logic devices are essential to compactlogic design and have been so for a long time. Theysave component count and board area and provideadaptability of circuit function. Despite this utility theiroperation is not always well understood. In the first partof a new series on logic design Geoff Bostock explainsthe workings of programmable logic.

READER SERVICES OFFER: 902Texas Instruments charge -pumped TLE2662 op -ampMany op -amp applications process signals which swingabout ground. This requires the designer to add anegative supply rail to the system. Frank Ogden reportson a new op -amp package which generates its own.

WINDOWS SUPPORT FOR DSP DESIGN 912Want to develop DSP applications under Windows?You could try DSPworks and QEDesign. Apart fromthe user graphics, what else distinguishes them asksAllen Brown.

EXPERIMENTING WITH DSP 920The conventional way to learnabout DSP is to tackle thesubject with maths. Which isprobably the reason for somany otherwise competentdesign engineers falling downwhen presented with thesubject. Jean -Jacques Dauchotmaintains that the best way tounderstand DSP is to get holdof a development system andexperiment.

DISTORTION IN POWER AMPLIFIERS 928Class B output stages differ in at lest three differentways presenting some intractable design problems. ButClass AB proves to be no answer says Douglas Self inhis continuing series on audio amplifier design

USING RF TRANSISTORS 946Motorola RF applications engineers Norm Dye andHelge Granberg spell out the important performanceparameters affecting transistor matching networks.

THE SPARK THAT GAVE RADIO TO THE WORLD 865It seems incredible to modern technologists that theearly radio engineers could achieve up to 60 per centpower conversion efficiency in spark gap transmitters.George Pickworth has conducted tests based onreconstruction of their work. His examination usingmodern test equipment has produced some fascinatingresults

REGULARS

COMMENTPicture of opportunity

883 NEW PRODUCTS 951Roundup of the best in new products in our exclusiveat -a -glance guide

UPDATE 884Digital chips to change the face of radio? Narrowspectrum semiconductor laser. Plus a report from theEuropean Microwave Conference.

RESEARCH NOTES 888Sulphur chemistry recharges battery technology, Soundtreatment for pollution, Robots glimpse new view ofmachine vision,

CIRCUIT IDEAS 898Economical 27MHz phase modulator, independenton/off long period astable, low loss lamp dimmer, twowire level indicator, proportional indicator display.

DISCOUNT SOFTWARE OFFER 911

LETTERS 917Golden hearing, Wire swapping, Frequencies please,Pause for reflection, Genius in the genes andoverprocessed radio.

DESIGN BRIEF 956Ian Hickman shows how to make noise work for youand looks at the design of an economical semiconductorsource operating up to 1000MHz.

APPLICATIONS 960Low cost radio data receiver, current conveyor circuitsand lowpass/notch filter.

In next month's issue:Do it yourself spectrum analysis. There is nothinglike a spectrum analyser -o help things along if youwork or play with R.F. There is also nothing like theprice tag. Ian Hickman presents a good performance,penny pinching DIY design.Also next month: a single chip PC.

DECEMBER ISSUE IS ON SALE NOVEMBER 25

November 1993 ELECTRONICS WORLD + WIRELESS WORLD 881

Surplus alwayswanted for cash! THE ORIGINAL SURPLUS WONDERLAND! Surplus always

wanted for cash'

LOW COST PC SPECIALISTS - ALL EXPANDABLE - ALL PC COMPATIBLE8088 XT - PC99

256k RAM - expandableto 640k

4.7 Mhz speed

Factory burnt -in Standard 84 key

keyboard 360k 5-1/4" floppy 12" green screen 2 serial & 1 parallel ports included

MS-DOS 4.01 In good used condition

Optional FITTED extras: 640K RAM £39. 12' CGA colourmonitor with card £39. 2nd 5-1/4' 360K floppy £29.95. 20mbyte MFM hard drive £99.

only Egg 00_ (F)FLOPPY DISK DRIVES

286 AT - PC286

640k RAM expandable 2 serial & 1 parallelwith standard SIMMS ports

12 Mhz Landmark speed MS-DOS 4.01 20 meg hard disk Co -processor socket 1.2 meg 5-1/4" floppy Enhanced 102 key 1.4 meg 3-1/2" floppy keyboard

EGA driver on board Clock & calendar withbattery back up

BRAND NEW AND BOXED!

only E249 .00,The

the PC286 and £39.00 for the PC386.he

Philips 9CM073 is suggested for the PC286 and the

f

C M8873 for the PC386. Either may use the SVGA MTS-9600if a suitable card is installed. We can fit this at a cost of £49.00

POWER SUPPLIES51/4 " from £22.95 -3 /2" from £21.95! Power One SPL200-5200P 200 watt (250 w peak).Semi open

frame giving +5v 35a, -5v 1.5a, +12v 4a (8a peak), -12v 1.5a,Massive purchases of standard 51/4 and 31/2" drives enables us +24v 4a (6a peak). All outputs fully regulated with over voltageto present prime product at industry beating low prices! All units(unless stated) are removed from often brand new equipment protection on the +5v output. AC input selectable for 110/243and are fully tested, aligned and shipped to you with a 90 day vac. Dims13' x x 2.5'. Fully guaranteed RFE. £85.00 (6)guarantee and operate from standard voltages and are of stand- Power One SPL130. 130 watts. Selectable for 12v (4A) or 24 vand size. All are IBM;PC compatible (if 31/2' supported). (2A). 5v @ 20A. ± 12v @ 1.5A. Switch mode. New. £59.95(B)3.5" Panasonic JU363/4 720K or equivalent £29.95(B) Astec AC -8151 40 watts. Switch mode. +5v 0 2.5a. +12v f&3.5" Mitsubishi MF355C-L. 1.4 Meg. Laptops only' £29.95(B) 2a. -12v @ 0.1a. 6.1/4' x 4' x 1-3/4'.New £22.95(B)

386 AT - PC386

2 meg RAM expanded 2 serial & 1 parallelby slots ports

20 Mhz with 32k cache. MS-DOS 4.01Expandable to 64k Co -processor socket

40 meg hard disk Enhanced 102 keyboard 1.2 meg 5-1/4" floppy Kwik Disk Accelerator VGA card installed Software - FREE

BRAND NEW AND BOXED!

onlyE425 .00(,MONITORS

14" Forefront Model MTS-9600 SVGAmultisync with resolution of 1024 x 768.0.28pitch. 'Text' switch for word processing etc.Overscan switch included. Ideal for the PC -386 or PC -286 with SVGA card added. Alsocompatibe with BBC, Amiga, Atari (includingthe monochrome high resolution mode), Ar-

chimedes etc. In good used condition (possible minor screenbums). 90 day guarantee. 15" x 14' x 12'. Only £159(E(

14" Philips Model CM8873 VGA multisync.:: with 640 x 480 resolution. CGA, EGA or

VGA, digitaVanalog, switch selectable.'il. Sound with volume control. There is also ai: special 'Text' switch for word processing,

3.5" Mitsubishi MF355C-D. 1.4 Meg. Non laptop £29.95(B) Greendale 19ABOE 60 watts switch mode.+5v 0 6a,±12v 0 j:,:b-..:;:::::::*e:s::'7''''if: spreadsheets and the like. Compatible with5.25" EXTRA SPECIAL BRAND NEW Mitsubishi MF501B 1a,+15v 0 la. RFE and fully tested.11 x 20 x5.5cms. £24.95(C) '''''' IBM PC's, Amiga, Atari (excluding the

360K. Absolutely standard fits most computers £22.95(B) Conver AC130. 130 watt hi -grade VDE spec.Switch mode.+tv monochrome high resolution mode), BBC, Data cable Included in price. @ 15a, -5v @ 1a,±12v @ 6a.27 x 12.5 x 6.5cms.New. £49.95(C) Archimedes etc. Good used condition (possible minor screen

Shugart 800/801 SS refurbished & tested £175.00(E) Boshert 13090.Switch mode.ldeal for drives & system. +Sy@ 6a, bums) 90 day guarantee. 15' x 14' x 12'. OnlyShugart 851 double sided refurbished & tested £275.00(E) +12v @ 2.5a, -12v 0 0.5a, -5v 0 0.5a.£139(E)C29.95(&) Philips 9CM073 similar (not identical) to above for EGA/CGAMitsubishi M2894-63 double sided switchable Famell G6/40A. Switch mode. 5v @ 40a.Encased £95.00(C(

hard or soft sectors- BRAND NEW £250.00(E) Famell G24/5S. As above but 24v et 5a. £65.00(C)PC and compels. 640 x 350 resolution. With Text switch withamber or green screen selection. 14' x 12' x 13-1/2" £99(E)

Dual 8" drives with 2 mbyte capacity housed in a smart case KME 10" high definition colour monitors. Nicetight 0.28 dot pitch for superb clarity andmodem styling. Operates from any 15.625 khzsync RGB video source, with RGB analog andcomposite sync such as Atari, CommodoreAmiga, Acorn Archimedes & BBC. Measuresonly 13.5' x 12' x 11'. Also works as quality Tv wan our huti

BBC Model B type computer on a board. A major purchase, Telebox. Good used condition. 90 day guarantee. Only..£125 (E)allows us to offer you the PROFESSIONAL version of the BB., KME as above for PC EGA standard £145 (E)

computer at a parts only price. Used as a front end graphics Brand new Centronic 14' monitor for IBM PC and compatibles

system on large networked systems the architecture of the BE at a lower than ever price Completely CGA equivalent. Hi-resMitsubishi 0.42 dot pitch giving 669 x 507 pixels. Big 28 Mhzboard has so many similarities to the regular BBC model B that bandwidth. A super monitor in attractive style moulded case.Full

we are sure that with a bit of experimentation and ingenuity mary 90 day guarantee. Only £129 (E)useful applications will be found for this boardll It is supplied NEC CGA 12' IBM-PC compatible. High ..... .::,,.,complete with a connector panel which brings all the I/O to '0' quality ex -equipment fully tested with a 90and BNC type connectors - all you have to do is provide +5 and day guarantee. In an attractive two tone± 12 v DC. The APM consists of a single PCB with most major ribbed grey plastic case measuring 15'L xic's socketed. The ic's are too numerous to list but include a 13'W x 12'H. The front cosmetic bezel has6502, RAM and an SAA5050 teletext chip. Three 27128 been removed for contractualEcnEPROMS contain the custom operating system on which we reasons. Only Igu (E)have no data, On application of DC power the system boots and 20" 22" and 26" AV SPECIALSprovides diagnostic information on the video output. On boast Superbly made 'UK manufacture. PIL all solid state colourDIP switches and jumpers select the ECONET address and monitors, complete with composite video & sound inputs. Attrac-enable the four extra EPROM sockets for user software. App:c. five teak style case. Perfect for Schools,Shops,Disco, Clubs.dims: main board 13' X 10'. VO board 14' x 3'. Supplied tested In EXCELLENT little used condition with full 90 day guarantee.with circuit diagram, data and competition entry form. 20"....£135 22"....£155 26"....£185 (F)Only £29.95 or 2 for £53 (B)

with built in power supply! Ideal as exterior drives! £499.00(F)End of line purchase scoop! Brand new NEC D2246 8' 85megabyte of hard disk storage! Full CPU control and industrystandard SMD interface. Ultra hi speed transfer and access timeleaves the good old ST506 interface standing. In mint conditionand comes com . tete with manual. Onl£299 E

THE AMAZING TELEBOX!Converts your colour monitor into a

QUALITY COLOUR TV!!

TV SOUND& VIDEOTUNER!

The TELEBOX consists of an attractive fully cased mainspowered unit, containing all electronics ready to plug into a hostof video monitors made by manufacturers such asMICROVITEC, ATARI, SANYO, SONY, COMMODORE,PHILIPS, TATUNG, AMSTRAD and many more. The compositevideo output will also plug directly into most video recorders,allowing reception of TV channels not normally receivable onmost television receivers (TELEBOX MB). Push button controlson the front panel allow reception of 8 fully tuneable 'off air' UHFcolour television or video channels. TELEBOX MB covers vir-tually all television frequencies VHF and UHF including theHYPERBAND as used by most cable TV operators. Compositeand RGB video outputs are located on the rear panel for directconnection to most makes of monitor. For complete compatibility- even for monitors without sound - an integral 4 watt audioamplifier and low level Hi Fi audio output are provided as Trio 0-18 vdc bench PSU. 30 amps. New £ 470

Fujitsu M3041 600 LPM band printer £2950 t,,standard.Telebox ST for composite video input monitors £32.95 DEC LS/02 CPU board £ 150 pitTelebox STL as ST but with integral speaker £36.50 Rhode & Schwarz SBUF TV test transmitter tri25-1000mhz. Complete with SBTF2 Modulator £6500 ...44tTelebox MB as ST with Multiband tuner VHF -UHF -Cable. Calcomp 1036 lameo drum 3 pen plotter& hyperband For overseas PAL versions statey logicyser

£ 650 gtt......£ 375 gtt5.5 or 6mhz sound specification. £69.95 1.5kw 115v 60hz power source £ 950 Top quality 19' rack cabinets made in UK

Telebox RGB for analogue RGB monitors (15khz) £69.95 Anton Pillar 400 Hz 3 phase frequency converter 75Kw PGA ilt. by Optima Enclosures Ltd. Units featureShipping code on all Teleboxes is (B) Newton Derby 400 Hz 70 Kw converter PGA : 41 designer, smoked acrylic lockable front

RGB Telebox also suitable for IBM multisync monitors with RGB Nikon PL -2 Projection lens meter/scope £750 ... door, full height lockable half louvered backanalog and composite sync. Overseas versions VHF & UHF call. Sekonic SD 150H 18 channel Hybrid recorder £2000

SECAM / NTSC not available. HP 7580A A1 8 pen high speed drum plotter £1850door and removable side panels. Fully ad-justable internal fixing struts, ready

Kenwood DA -3501 CD tester, laser pickup simulator £ 350 punched for any configuration of equipment mounting plus readymounted integral 12 way 13 amp socket switched mains distribu-

Brand new and boxed 230 volts uninterruptable power supplies lion strip make these racks some of the most versatile we havefrom Densel. Model MUK 0565-AUAF is 0.5 kva and MUD Microllne 183. NLQ 17x17 dot matrix. Full width. £139 (D) ever sold. Racks may be stacked side by side and therefore1085-AHBH is 1 kva. Both have sealed lead acid batteries. MUK Hyundai HDP-920. NLO 24x18 dot matrix full width. £149 (D) require only two side panels or stand singly. Overall dimensionsare internal, MUD has them in a matching case. Times from Oume LetterPro 20 daisy. Qume OS -3 interface. £39.95 (D) are 77-1/2"H x 32-1/2'D x 22'W. Order as:interrupt are 5 and 15 minutes respectively. Complete with full Centronics 152-2 9 x 7 dot matrix. Full width. £149 (D) Rack 1 Complete with removable side panels ..... ..£275.00 (G)operation manuals MUK £249 (F) MUD......£525 (G) Centronics 159-4 9 x 7 dot matrix.Senal. 9-1/2' width £ 99 (D) Rack 2 Less side panels £145.00 (G)

1992 Winter Issue of Display News now available - send large SAE - POCKED with bargains)

BBC Model B APM Board£1 00 CASH FOR THE

MOST NOVELDEMONSTRATABLE

APPLICATION!

SPECIAL INTEREST

CALL FOR PRICING ON NTSC VERSIONS!

Superb Quality 6 foot 40u

19" Rack Cabinets

No Break Uninterruptable PSU's

:0041. .0110. 4100 0...

-EEC TROPliff

BRAND NEW PRINTERS

MAIL ORDER & OFFICESOpen Mon -Fri 9.00-5.30

Dept WW. 32 Biggin Way.Upper Norwood.

London SE19 3XF.

LONDON SHOPOpen Mon -Sat 9-5.30Thursday till 9.00pm

215 Whitehorse Lane.South Norwood.London, 5E25 .

DISTEL © The OriginalFree dial -up database!

1000's of itemsninfo on lineV21. V22 & V22 bis

081-679-1888

Massive ReductionsVirtually New, Ultra Smart!

Less Than Half Price!

ALL ENQUIRIES

081167914414Fax- 081-679-1927

Akk

All prices for UK Mainland. UK customers add 17.5% VAT to TOTAL order amount. Minimum order £10. PO orders from Govemment,Universities,Schcols & Local Autho lieswelcome -minimum account order £33. Carriage charges (A)=E2.00. (A1)=E3.75. (B)=E5.50. (C)013.50. (13)=E11.50. (E)=E14.00 (F).£18.00 (G)=Call . Scotland surcharge: call.All goods supplied subject to our standard Concitions of Sale and unless otherwise stated gparenteed for 90 days. All guarantees on a rehire to base basis. Rights reserved tochange prices & specifications without prior notice. Orders subject tostock. Quotations willingly given for higher quantities than those stated. Bulk surplus always wanted for cash.

882

CIRCLE NO. 100 ON REPLY CARD

November 1993 ELECTRONICS WORLD+WIRELESS WORLD

COMMENT

EDITORFrank Ogden

081-652 3128

DEPUTY EDITORJonathan Campbell

081-652 8638

CONSULTANTDerek Rowe

DESIGN & PRODUCTIONAlan Kerr

EDITORIAL ADMINISTRATIONLorraine Spindler

081-652 3614

ADVERTISEMENT MANAGERCarol Nobbs

081-652 8327

SALES EXECUTIVEPat Bunce

081-652 8339

ADVERTISING PRODUCTIONShirley Lawrence

081-652 8659

PUBLISHERSusan Downey

EDITORIAL FACSIMILE081-652 8956

CLASSIFIED FACSIMILE081-652 8931

SUBSCRIPTION HOTLINE0622721666Quote ref INJ

SUBSCRIPTION QUERIES0444 445566

NEWSTRADE DISTRIBUTIONENQUIRIESMartin Parr

081 652 8171

BACK ISSUESAvailable at £2.50

081-652 3614

cia REEDV1.01 Pain-TING

Picture of opportunityThe European electronics industry hasn'thad much cause for celebration in

recent years. The consumer interestssuffered badly at the hands of the Japanesewhile the ending of the Cold War took thesteam out of the defence business. Just sixmonths ago, its great hope for a newgeneration of broadcasting based on theMAC analogue TV standard fell apart asdigital broadcast strategies began toemerge.

But it has become clear that theopportunity presented by digital televisionwill be massive... Enough to replace theailing defence interests with market drivencivilian business while at the same timecontributing to technology at the first stageof its development.

There is good evidence that the initiativewill not be lost on this occasion. Some 85European broadcasters, equipment makers,satellite operators, network carriers,research organisations and Governmentdepartments have signed a memorandumof understanding to establish world classdigital TV standards and infrastructure inEurope by the end of the decade. Collectedinterests cover all aspects of digital video:origination, production, networking tosatellite and terrestrial broadcasting.

The initiative will be called the digitalvideo broadcasting project (DVB) and thefirst services to be run under its unifiedstandards will be on cable and satellite bythe end of 1995. This will be followed bydigital terrestrial services some two tothree years later.

The mix of interests contained in theMemorandum will ensure that it eitherdisintegrates spectacularly or forms thebasis of a world digital broadcastingstandard. For instance Japanese interestsare represented by Matsushita, Sony, JVC

and Toshiba. Given that the compressionelement of the package relies heavily onthe US driven MPEG-2 technology, it islikely to succeed all over the world.

It is almost impossible to overstate thesignificance of this announcement toEuropean electronics. The start point for allaspects of this venture are at least equaland possibly favourable to local interests.For instance, it seems likely that terrestrialbroadcast modulation standards will usecoded orthogonal frequency divisionmultiplexing, a close relative of spreadspectrum modulation, and pioneered byNTL in this country. The sameorganisation has also made an impressivecontribution to MPEG and its workfeatures prominently in Rupert Murdoch'ssatellite broadcasting plans. TomWoodford has written a comprehensivearticle on the technology in this issue.

Real technical advances in digital TVtechnology have been made by Europeanelectronics companies such as Philips,Thomson, Nokia and Grundig, all partiesto the Memorandum. They will make newequipment which, unlike MAC based sets,we will want to buy along with the rest ofthe world.

Unified digital TV technology willexpand vastly the number of channels andtypes of service which broadcastersprovide. Information on demand willcreate a new market for business anddomestic terminals, essentially TV setswith digital storage facilities and two-waycommunications channels built-in. It willoffer new business opportunities from newtechnology leading to the development of anew communications infrastructure.

It would be hard to find a more optimisticpicture on any other channel.

Frank Ogden

Electronics World + Wireless World is published monthly By post, urrent issue £2.25, back issues (if available) £2.50.Orders, padmants and general correspondence to L333, Eleztronics World + Wireless World, Quadrant House, TheQuadrant, Sutton, Surrey SM2 5AS. Telex:892984 REED BP G Cheques should be made payable to Reed BusinessPublishing Goup.Newstrade: IBC Marketforce, 071 261-5138Subscripbons: Quadrant Subscription Services, Oakfield House, Perymount Road, Haywards Heath, Sussex RH16 3DH.Telephone 0444 441212. Please notify a change of address. Subscriptzn rates 1 year (normal rate) £30 UK and £35 outside UK.USA: $116.0C airmail. Reed Business Publishing (USA), Suoscriptior s office, 205 E. 42nd Street, NY 10117.Overseas advertising agents: France and Belgium: Pierre .Aussard, 18-20 Place de la Madeleine,Paris 75008. United Statesof America Ray Barnes, Reed Business Publishing Ltd, 205 E. 42nd Street, NY 10117.Telephone (212) 867-2080. Telex23827.USA mailiig agents: Mercury Airfreight INernational Ltd Inc, 10(b) Eiglehard Ave, Avenel NJ 07001. 2nd class postage paidat Rahway N, Postmaster. Send address changes to above.Printed by BPCC Magazines (Carlisle) Ltl, Newtown Trading Estate, Carlisle, Cumbria, CA2 7NRTypeset by Marlin Graphics 2-4 Powersc-oft Road, Sidcup, <ent DA14 5DT©Reed Bu ;iness Publishing Ltd 1992 ISSN 0959 8332


UPDATE

Digital chips to change the face of radioA new class of dsp based processing chips

rA can replace traditional analogue radioarchitecture with direct digital processing.Developed by the US company HarrisSemiconductor for the portabletelecommunications market, the devicesperform filtering, second local oscillator andquadrature demodulation functions withoutreducing the signal to baseband as inconventional receivers.

The 16bit 52Msample/s processing rateallows the construction of filter equivalentfunctions with more than 100dB ofattenuation at a knee frequency of 13MHz.

Being a true digital architecture, the radiodsp family is programmable allowing designof system functions under software control.This flexibility includes the construction ofseparate I/Q channels for data recovery.

The company has also produced a frontend chip with a 2.2dB noise figure rfamplifier (at 900MHz) integrated with a+10dBm intercept double balanced mixer onthe same piece of silicon. A similar devicefor 1.8GHz is being developed.

Although hand-held radio is the intendedapplication, the multiple function dsp chipswill find use elsewhere. For instance theHSP50016 comprises a direct digitalsynthesiser with internal sine lookup table,mixer and two lowpass filters tunable with aresolution of 0.009Hz. The local oscillatorfunction is claimed to be spurious free downto -102dB below carrier level. And the filterfunction is claimed to have less than 0.04dBof ripple in the passband. It provides acomplete downconversion subsystem on achip.

2.2db noise factor: HFA 3500 silicon front end

Other dsp based devices released initiallyinclude a 52Msample/s half -band filter and aserial i/o filter with more than 140dB ofstopband attenuation.

Placing specialist radio functions in dsp

chips will eliminate much of the analoguesignal chain and its associated set upadjustments. It also reduces the need forblock filtering; complete data recovery canbe made with very few high frequencyconversions stages.Frank Ogden

Glint in Du Pont's eye: The first merchantaccelerator chip in the world for theOpenGL 3D graphics standard may belaunched next year by Du Pont Pixel.Nicknamed Glint, it will be able tomanipulate images like the one above at upto 300,000 Z -buffered Gourand-shadedtriangles a second. High level 3Dmanipulation instructions are taken by thechip and performed on objects stored in a setof off -chip buffers. It will run in Unix andWindows NT host systems. The first versionwill not handle geometry transformations;this will be integrated into later versions ofGlint, hopefully by 1996. A colour -mapchip, due for launch in 1995, will beintegrated into Glint by 1997.

884 ELECTRONICS'WORLD + WIRELESS WORLD November 1993

UPDATE

P6 is out of ordermore details have been released aboutthe P6, Intel's planned successor to

its Pentium (i586) chip. The P6, or i686,is in development and is scheduled forvolume production in 1995.

It will be built with 0.6ttm features inan attempt to pack more than five milliontransistors onto a single chip. Initialversions though may be in a multi -chipset.

Speed will be 133MHz and about200Mips. There will be four integer andtwo floating point processors.

Out of order instructions will be able tobe executed with the processors trying topredict which instructions it will receive.A DX version will be capable of runningin multiprocessor systems and the LXversion will be for single processor desk-top systems.

Engineers musthave green fingers

The Engineering Council is putting UKengineers and technicians in the front

line for safeguarding and improving theenvironment.

With the launch of the Code ofProfessional Practice on Engineers andthe Environment, the 290,000 engineerson the council's register were called uponto make the environment a keyconsideration in every project theyundertake. The code comes into effect inMarch.

The announcement coincided with thenews that Anthony Convery of CountyTyrone had won the council's 1993Environment Award for Engineers fordeveloping a machine to recycle wasteconcrete from ready -mix lorries and on -site concrete mixers.

A commendation was given to aninexpensive radar for insect pest forecastand control developed by Joseph Riley,Alan Smith and Douglas Gregory of theNatural Resources Institute in Kent.

* For the second year running a girl haswon the Engineering Council's YoungEngineer for Britain 1993 award. LucyPorter, 16, of Bath invented a swingexerciser for children with special needswho are unable to use their legs. TheMountbatten prize for the best projectusing electronics went to SamanthaHaines, 18, from Guildford for aphysiotherapy aid. And the best user ofinformation technology in a projectaward was won by Stuart Cowley, 18, fora lubrication advice service.

Laser linewidths cut to 3.6kHzA semiconductor laser with a spectral

linewidth of 3.6kHz, 3000 timesnarrower than conventional semiconductorlasers, has been developed by Hitachi.

This narrow bandwidth may make itsuitable for use in ultra -high speed coherentfibre optic communications systemsoperating at 200Gbit/s or more.

Inside the laser is a stack of multipleInGaAsP layers on an InP substrate. Infra-red radiation is emitted at a wavelength of1.55µm and output of 55mW.

Narrow wavelength distributed feedbackdiode lasers have a diffraction grating etchedonto the device. This sets up a pattern ofmultiple interfering wave trains that cancelout except in a narrow frequency range. Butthe resulting bandwidth of about l()MHz istoo wide for coherent fibre opticcommunications.

To get round this, Hitachi has adjusted thepitch of the diffraction grating on the deviceso that the grating spacing is slightly longerin the centtr:. of the resonator. Theinterference pattern produced results in amuch narrower bandwidth.

The company also uses a strained layermultiple quantum well structure withalternate layers having different latticeconstants.

Laser light

Strained -layer MOW

1.2mmp -electrode

n -electrode

Inp Substrate \

Corrugation -pitch -modulateddiffraction grating

241.08nm 11/4 241.0nm

Phase adjustmentregion(0.36mm)

Structure of semiconductor laser withnarrow spectral linewidths.

Level playing field wanted for pcbsEurope's pcb makers are lobbying theEuropean parliament in a bid to give pcbs

the same protection in Europe assemiconductors. Brian Haken, executivedirector of the UK's Printed CircuitInterconnection Federation, said Europeanpcb makers have a disadvantage comparedwith the Japanese when it comes to gettingmoney from the banks.

He said that "Japanese board makers canborrow at low preferential interest rates and

for longer than their European counterparts.All we want is a level playing field."

He pointed out that Sony had receivedfinancial assistance from the EC to establisha pcb plant in France.

Miti, Japan's industry body, has targetedpcbs and semiconductors as two crucialareas for future growth and it plans todouble Japan's income from pcbs in the nextfive years.

Transistor breaks noise barrierreduction has started of a redesignedP high electron mobility transistor, which

maker Toshiba claims has a lower noiselevel than any other on the market. Noiseoutput is 0.45dB at I2GHz.

The biggest source of noise in this type oftransistor k resistance in the channel layer,normally made of GaAs. Toshiba has usedInGaAs, adjusting the level of indium

dopant to make a lattice with minimalresistance.

The crystal structure has also beenimproved in the AIGaAs layer, whichsupplies electrons to the channel layer. Thismakes the electron flow 40% higher than inplain GaAs devices.

Mass production is scheduled to startNovember reaching 100,000 pieces by April.

Work ethic for wireless communicatorMotorola is to use Microsoft's At Worksoftware in a new wireless personal

communicator.The company has not announced when

these communicators will be out or whattheir price will be.

But Bob Growney, executive vice

president, said that "developing wirelesspersonal communicators based onMicrosoft's hand-held system allows us toleverage their strength in desk -top softwareto provide a pragmatic solution for today'smobile professional".


UPDATE

GaAs moves down commercial pipelineThe move from military to commercialapplications for GaAs and the design of

antenna arrays rather than simple aperture orwire types were the two most notable trendsat September's European MicrowaveConference in Spain.

GaAs technology has largely come of agein the form of MMICs. Until recentlymicrowave applications for GaAs have beenmainly as discrete devices, particularly themesfet and low noise high electron mobilitytransistor. These devices have beenintegrated into planar technology circuits toform hybrid modules.

But GaAs is also a suitable substratematerial for microwave transmission linesand so the complete MIC can be formedmonolithically.

With the prospects appearing for consumerand commercial applications, the rewards interms of numbers sold is very high. Inmilitary contracts a "large number" was stillseveral orders of magnitude below that ofpresent prospects.

A paper from E Pettenpaul of Siemensclaimed an estimated market of 20 milliondirect broadcast satellite receivers by 1995for Europe alone. And large scale use ofpersonal and mobile communications in the900MHz and 1.8GHz bands is estimated at100 million units in Europe by 2000.

For office use, including wireless lans,there is a GaAs MMIC effort in all theallocated bands to 60GHz and above.

A paper by N Diehl of Daimler-Benzpointed out that another vast application formicrowave communications is mobilecomputing. For example, test or calibrationengineers would be able to perform complexanalysis and checks on machinery,equipment and installations, and have fullreal time access to all data on suchequipment.

There seems little doubt that in a few yearsthere will be a steady growth in intelligentvehicle communication systems - again apotential market for 100s of millions ofsensors. Some aspects of such links in the5.8GHz band were presented in a paper byBucks and Grabow. On higher frequenciesto 60GHz there are also applications forautomatic collision avoidance and high-speed train links.

In all these systems the market volumesare so high that the pressure on microwaveGaAs MMIC technology to achieve lowcost, reliable performance and small size isvery high.

On antenna design, some present andcertainly future satellites will have narrowspot beams that are intelligently switchablein direction. Thus arrays are needed thathave the advantage of being able to combinea total transmit power from one amplifierper array element, or perform spatial signalprocessing using a separate receiver in eachelement.

Incorporating attenuators and phaseshifters with these functions lets the beamsbe steered and shaped.

Applications also include satellite tosatellite links. But such arrays have 100s to10.000s of individual elements and, to beviable for consumer or commercial use, thecosts of the microwave circuits in eachelement must be dramatically small. Again,the emphasis is on ingenious circuit design,accurate performance modelling, and a low-cost manufacturing technology.

The conference also saw a selection ofpapers looking at possible applications forsuperconducting materials with a criticaltemperature above 77K. These includedmicrowave components as high -Q circuitelements, non -dispersive signal processingcircuits, or low -loss small antennas.

Another developing field with wideapplications is that of the interaction ofmicrowaves and optical systems. Forexample, a paper from D Wake of BritishTelecom talked of a microwave transmitterneeding no electrical power and a fibre opticinput. It used video pattern data to frequencymodulate a 4.1GHz microwave oscillator,which in turn drove a laser. The I'm output ofthe laser then passed into a dispersive delayline to generate harmonics of the microwavefrequency plus modulation.

The optical signal is converted tomicrowaves using a zero bias edge coupledphotodiode with the seventh harmonic of28.7GHz selected and transmitted to asuperhet receiver. All power requirements inthe transmitter section were derived from theinitial optical signal. Possible applicationsare links in lans for broadband access.

At the associated exhibition, Thomson-CSF announced that it is acquiring thetravelling wave tube and coaxial tubebusiness from Siemens. Also announced wasthat Eesof is merging with Hewlett-Packardsubject to government approval. Eesofsimulation software is used for microwavecad. Mike Hosking

Vodafone wins cellularsurvey

Vodafone provides a more reliableservice than Cellnet according to a

survey of cellular networks by industrywatchdog Oftel.

Some 29,000 attempts were made to maketwo min phone calls from mobile to fixednetworks and vice versa.

On mobile to fixed network calls 97.1%were connected and completed on Vodafonecompared with only 95% on Cc Ilnet.

And on fixed network to mobile callsVodafone again came out on top with 95.1qset up and completed compared with only94.3% on Cellnet.

Beeb dabbles withdigital

TheBBC has started engineering tests

of digital audio broadcasting (dab)using high power transmitters in theLondon area.

A 10kW erp transmitter at CrystalPalace is being joined by 1kW erptransmitters at Alexandra Palace, Reigateand Wrotham. They will operate at226MHz.

Survey vehicles will measure the fieldstrengths of each transmitter and the waythey work together to form a singlefrequency network.

Following the tests the BBC expects toproduce proposals for introducing dabservices in the UK. The plan is fornational and local dab services tobroadcast terrestrially using vhffrequencies.

Joint project forcommercial gps

GEC Plessey Semiconductors andCanadian Marconi are jointly

developing receiver technology forcommercial gps applications.

GEC will be responsible for makingand distributing the MicroGPS family ofglobal positioning engines. And Marconiwill offer a customisation service forthose who want gps functions in otherequipment.

Ray Gleason, GEC's marketingdirector, said that among the technicaladvantages of MicroGPS is the "very fast15GHz bipolar process that enables low-cost low -power gps rf technology tobecome available for the first time to thecommercial market place".

The family will be available as standardoem modules for direct plug-inapplications.

Audio compressionfor comms ICs

Enfield firm Silicon Systems has beenlicenced to use California -based DSP

Group's Truespeech audio compressionalgorithm in its communication ICs forIan, modem, wireless and multimediaproducts.

The algorithm can compress a lminvoice file down to 60Kbyte with nonoticeable degradation. This compareswith about 960Kbyte for standard audiocompression algorithms.

The firm has also started to integrateDSP Group's Pine dsp technology in theICs to make them suitable for mobilecomputers, personal digital assistants andother portable computing applications.

Silicon Systems can be contacted on081-443 7061.

886 ELECTRONICS WORLD + WIRELESS WORLD November 1993

AMAZING PC BASESALE

WE HAVE ACQUIRED A SELECTION OF HIGHQUALITY AMSTRAD PC BASE UNITS AT MEGADISCOUNT PRICES. LOOK WHAT YOU CAN BUYFROM ONLY £19.00!

UNTESTED AMSTRAD PC BASE UNITSCOMPLETE WITH MOTHER -BOARD,VIDEO CONTROLLER, DISK CNTRLR,& 5.25" DRIVE(S).(Keyhoud.

AMSTRAD 1512SD £13.00 REF: EW/AMI9PIAMSTRAD 1 5 12DD £25.00 REP: EW'/AM25P1AMSTRAD 1640SD £25.00 REF: EW AM25P2AMSTRAD 1640DD £30.00 REF LW AM3OPIIN MMMMMMM MMMMMMMM NEW or REFURBISHED PC BASESCOMPLETE WITH KEYBOARD,MOUSE, and 5.25" DRIVE.RUNS UNDER MS-DOS VER 3 (DOS not .applied)

All sold guaranteed as new. All youneed is a power supply unit & monitor.

AMSTRAD 1512SDAMSTRAD 1512DDAMSTRAD 1640SDAMSTRAD 1640DD

£49.00£59.00£69.00£79.00

REF: EWIAM49P1REF: EWIAM59131REF: EW /AM 69P 1

REF: EW/AM79131

WM WM la ft ,, LIMITED OFFER44#.. IBM COMPATIBLE 4*.

LAPTOP COMPUTERSFROM ONLY .E99.00(,.._

IN AGAIN IN STOCK AT A SUPERB DISCOUNT PRICE!FULLY IBM COMPATIBLE LAPTOP COMPUTERS

OFFERING EITHER 512K OR 640K MEMO 12Y.FLIP UP GREEN SUPERTWIST LCD SCREEN.

FULL 'QWERTY' KEYBOARD,RS232 PRINTER PORT

VIDEO OUT.RUNS ON BATTERIES/

DC SUPPLY/MAINS ADAPTER. * MS-DOS 3.1 RUNS THESE UNITS 41' ar yaw -JENNE oil-

AMSTRAD LAPTOP OPTIONSAMSTRAD PPC 1512 SD (512k memory Single 3.5" disc drivel

AMSTRAD PPC 1512 DD (5)2k memory Two 3.5" disc drive)

£99.00 EW/AM99P1

£109.00 EW/AM100P1

AMSTRAD PPC 1640 SD (640k memory one 3.5" drive modem) £129.00 EW/AM129P1

AMSTRAD PPC 1640 DD (640k memory two 3.5" drive modem) El 39.00 EW/AM139P1

MAINS POWER SUPPLY FOR ALL ABOVE LAPTOP UNITS ONLY £10.00

AMAZING CIBM COMPATIBLE

COMPUTER BASELIMITED OFFER -

OMPUTER BARGAINSVAT,

EONLY g99.00,,,us,,

UNITS,,, VAT)

HURRY WHILE STOCKS LASTAMAZING SALE OF

BT ANSWERPHONESAs NEW, fully guaranteed BT

Product as LESS than Half theoriginal retail price!!!

RESPONSE 200 AND 400 MODELSFilch Response Unit is supplied with aMicro cassette. PSU and User Details. Thefollowing features are found on the 400Model and the 200 has almost as manyfeatures.: -Micro Cassette Ren 1.0.Call Screening Memo FacilityCall Count Remote FacilityAnswer only 20 MemoriesLast No recital Variable volumeOn hook dialling Hands free speachBT Network Services PABX CompatibleMute Facility LCD Display

RESPONSE 200 L35.99RefiEW36P1RESPONSE 400 L49.99Ref:EW49P1

(plus vat)

10 WATT SOLAR CELL(3" x 1") 14.5v/700mANow available by mail orderCoated with exceptionally efficient amorphoussilicon these glass solar cells have an almosttimeless lifespan and will not suffer withdiscolouration. There are possibly hundreds 01uses for these cells, a few of which could be: forCar Battery Charging, for useon Boats or onCaravans, in fact anywhere a portable 12Vsupply is required. Several of our overseasMediterranean customers with homes in remotehilly sites, use these solar cells as a daytimepower source to backup generators. The solarcells can be connected in series or parallel to givehigher voltages or larger current capacity.REF: EW34P2

PRICED at only

E33.95PLUS an additional £2.00 special packaging charge

mmlutAA cooris ORDER'!11201s.foavFaNwrr,:040OwlyNtlattsrlIp3.6L 00005sr .pplAk4g:ip.x-cTT149.pg CONUJTIQNB Iii

31,11AM3':111q.8S 01-1-ftR33/15 g7:AnD0 r.rARANTR5,0 (OR 30 DAYS.

Ru3EgVED '10 -CHANGE 1(71:;..S

kv1'111<ILT (R NLITICF

o IW1:r.kS SEM:1-E.r-rro sTact: QtIM ATIONSAt IN61, Y V1:,N FOR (:UA.,-TrrmsIFIJOSE.STATED:t-:

BULL ELECTRICAL250 PORTLAND ROAD HOVE SUSSEX

B/43 5QTMAIL ORDER TERMS: CASH PO OR CHEQUEWITH ORDER PLUS £3.00 POST PLUS VAT.

PLEASE ALLOW 7 -, IS DAYS FOR DELIVERY

)51:, OM )1:RS WEI.:2O!,.11- AmWM

.-Ax o27; 7:',3 +17

PORTABLE RADIATIONDETECTORSPECIAL OFFER

£49.99 (plus vat)

NEVIER OFFERED BEFORE We cannow supply a unique handheld personalportable Gamma and X -Ray detector. ThisRadiation detector contains two GeigerTubes has a 4 digit LCD display with a piezospeaker, giving an audio visual indicationThe radiation detectors detect high energyelectromagnetic quanta with an energyfrom30K eV to over 1.2M eV and a measuringrate 5-9999 UR/h (sampling rate 2555) or10-99990 NR/h (sampling rate 2.55) Sourcesof radiation could be Granite Kerbstonesold Luminous Watch dials or even aJewellery shop where mineral ore is sold torock collectors. A piece of uranium Orewould be idealOnly £49.99 Each Ref: EW5OP I

TURN YOUR SURPLUS STOCK INTOCASH, IMMEDIATE SETTLEMENT.WE WILL ALSO QUOTE FORCOMPLETE FACTORY CLEARANCE.

Mt. CU MITCH MORE IN OUR 1993CATALOGUE PLEASE SEND 41P, A4SIZED, SAE FOR YOUR FREE COPY.Alt. OUR PRICES ARE NET OF V A 'f

CIRCLE NO. 102 ON REM CARD

ELECTRONICS WORLD+WIRELESS WORLD November 1993 887

RESEARCH NOTES

Sulphur chemistry recharges battery technologyC cientists have developed an aqueousOcathode cell based on solid sulphur with atheoretical storage capacity several timesthat of conventional aqueous systemcathodes based on nickel, manganese,mercury or silver.

The room -temperature battery could be asignificant step forward in the search fornew, more efficient, energy storage, fuelledby applications as diverse asenvironmentally friendly vehicles and therapid growth of cordless communications. Ineach case the requirements are broadlysimilar: high energy storage per unit weight,good safety, room -temperature working,long life and low cost.

So far, no battery has met all theserequirements.

The highest energy systems use eithermolten electrolytes, or expensive orenvironmentally -unfriendly metals for theelectrodes. Many other promising room -temperature aqueous systems are beset withtechnical problems. Established technologieshave weight penalties, environmentaldisadvantages, modest capacities or highcost. But that could change with theannouncement by Dharmasena Peramunageand Stuart Licht of Clark University in

Worcester, Massachusetts, of what lookslike a promising new room -temperaturebattery using an aqueous cathode based onsolid sulphur.

Their research follows on from earlierstudies into the use of aqueous sulphidesolutions - unusual in that they will dissolveelemental sulphur. Sulphur is normallyinsoluble and non -conducting at roomtemperature. The resulting polysulphideshave been used successfully in experimentalrechargeable polysulphide cathode/tin anodecell.

But the latest development takes thisapproach a stage further with thedevelopment of a cathode capable of directreduction of elemental sulphur at roomtemperature. It makes use of solid sulphur incontact with a fully saturated solution ofpolysulphide. The theoretical storagecapacity of this composite sulphur cathode isseveral times larger than that ofconventional aqueous system cathodes basedon nickel, manganese, mercury or silver.

Experimental batteries using analuminium anode with the new sulphurcathode have a 40% greater capacity thanthe earlier experimentalaluminium/polysulphide batteries. Open

Sound treatment for pollutionA coustic agglomeration is a useful

rltechnique for separating smoke, ashand even fog. But no-one knew how itworked. Until, that is, researchers, led byDr Gary H Koopmann of the Center for

Acoustics and Vibration at PennsylvaniaState University, announced they had foundthe answer.

Koopmann and his team constructed asmall, controlled experimental set-up withtwo face-to-face loudspeakers operating inphase, so that the air between them movedback and forth, rather than beingcompressed by the sound waves. Usingcommercially available 81.tm beads (smallerbeads agglomerate naturally), theydispersed small amounts in the form of acloud falling through the chamber. Avariety of sounds from 600 to 1000Hz weretested, but 800Hz was found to provide thebest agglomeration.

Key feature of the experiment was avideo camera that recorded the scene at 30frames/s. Frame by frame examinationrevealed that, as the particles fell throughthe sound field, the larger ones appeared tobe pursued by smaller ones travellingslightly faster. Eventually the smallerparticles caught up with the larger ones andcoalesced.

circuit terminal voltage is also a healthy1.28-1.30V.

As for an overall comparison with existingcommercial aqueous batteries, the sulphurcathode system is said to develop220W.Hr/kg - even at relatively highdischarge rates - compared to 110 forzinc/air systems and up to 95W.Hr/kg foralkaline manganese batteries.

Peramunage and Licht say they areoptimistic of further improvements.

Charged Discharge

Solid sulphur cathode in charged state (left) anddischarging state (right).

The Pennsylvania researchers believe thatthis phenomenon is a scaled -down versionof what happens when a car gets into theslipstream of a lorry; the car tends to getsucked along. With suspended particles, theacoustic wind causes the smaller ones to"slipstream" larger particles and to bepulled closer before eventually collidingand clumping together.

"Not only did we see the particles comingcloser together and joining, but there is alsoa cascade effect. Once two particles join, athird smaller one will draught theagglomerated larger particle and eventuallyjoin," says-Koopmann.

Acoustic agglomeration plants normallygenerate sounds at the 160dB level,horrendously loud, but fortunately confinedto chambers that prevent too much escape.The aim of such techniques is to increaseparticle size to above 201.1m, where they caneasily be filtered out using conventionaltechniques. One of the main applications isthe removal of fly ash from the waste stacksof coal -burning plants.


JPG Electronics

IT It, 31,1111 -9 1111i 11,1 1191 gt..1 14/ t ..i 1, X Xl .' . , 2 1 lk .1111, 11,1/ ,

Yellow . 1 11. t la 1 1110071 II 111p

High intro..., led. green en vcIlow Sinni ...:114, rat h1110 . dip. 10911 1 1

(../Ible 11(N. 1p each. £5.95 pc, 111111/. 149.50 pei Suit lau light gun 111111111.111,1 N1111 .1 1.1 11111Q 4,1

10.0(81 11'3 ,.hp gni, a signal when p.mSmall stepping mob. -1 phase 12, 7.5' step 511 Hit-kering bglir w illi outpul

ohms i lbwS..011027 stepping motor &wet t hip 11.95 D1.-10. totivertor Reltabilit, 1110111'1 1.. 121' . I

High quality ['hoot resist coppri Clad rpm, glass 20010a inn :101/4 1111/111 10 outpt : Imam I,

boards data. .04.9S eat It ol tow k of Ili... 0 0

Ihniensions single sided ,lotible sided Flom t ouottd used 7 digit 240, ai S0111,x4 int hes 01(95 11.117 QWF RI L kes boat d 58 la-, go.til tpialtt, ,,,ot

IS inches 12.10 1'1,0 . .. ..

1x12 inches 1:5.37 A111,1, A.29":"- "10: wilting 00'0'1 I h 7 "011112x 12 int hes 110.66 -oh 6 0800 ilia hod, 6.3mns tiliall 189 i 10

Rechargeable balletic, 12011 011iiaahos id 10A A ( H P 7 1 .4.-% 51100A0 with stadia Pol,csIct t spat ittits Nix pr 22.Stnw- Icad pit, h

500mAll. it/ 110 tags ........... ... _II SS 0.901250,th 1811 cad] I 1p...10114 01. pit,. 4

AA 700mAll 11.9-, COW] Il 1.8.AI I 12 20 1012505 It 20p oath 15p. 1011 101. 1111111.

C 2 All o,,1,,,,],,Mile[ 1/111'211.2 .411 12.60 2.201 2746th .30(1 eat!, 20p 100 t I ', 10011.

lag, 13.611 P P 3 8 . 1 V 3 301 100,dc ... :101,e:till 211p...1101+ 1-.t. 1.101 .

1) 4.A11 ,.,,l, soidet 110,11.411 ... .11.95 101 SO, lapolaiboil,- trol, tit axial ',sub 1St

tags ..£1.95 Sub 1: with solder eat li 7 Xi/ 100110

1/2.0 A w Ith .older tags. ./2.74/ 112201 2,11, polves0.1 axial lead, . I Sp, .1,11.7 Sp

tags 11.55 1/3.. will, tags (Philip, 104,AAA ( 11 P I 61 1:1V1 .111/7, Philip, 123 ll'Ill, N/1111 .1111111111111111 .119.11 1,111, 111,1

1801111Al( 11.75 11' 6 2.210 1111, 114)1,111 251. loo -Standard charger charges -1 AA tell, in 5 hours or Philip, 1110 set ICS 22016:i, axial. 111(1

41:s oi Ds in 12-14 hours+ lzP11:1t 1.2. 3 or 4 tells et. 11 lip.. 1111111+may he rhatgeti at a time/ 15.95 %Wilda,' .AVX i mum( tapacitinc all Strtii taw 11

High pow, i hinge., as above butt hat gds the Cs and 1040 1041p1. I 514,1. 220p1. 10,0111.1,1110,0 lopUs,n S hot. s. A.As. Cs and Hs itnist he Charged in vic 11 5p...11104 3.5p 114000

2,0 I. £111115 snow ,,unptes.00n 111111111, 11,11

Special cater,. plc-. hut I. ha asailah1111, 111 id 370s.a. 111011,1 14.111 1.11/..111tor whalt , i 0.1 1,10-

F cell, 32,11a 1 L VII 1.1111 .9/11111.9 begs itintaining 1111 IN !NI £5 9,10 1.1'1 "III., IllH7111111. .£3.95 1.2, /4.30 '.5,1, II 512:1901 120ohni 4,p am 11 211p 11111+

.1 2 z 16 ''''I'll,,, liHOoltni 2l1 metal 1.1m Trxrrol 1p 1 lit/ ./ 21. 1111111 r

1.24 11415 Solid carbon Few,. irs ,c1, low mitt, tam c gleal I,Stick of 1 17100006111M dia with led & Ida, k leads RE i iri lots -27.4.112,.4, toiohtn 21, 251.

4.8v 15115,at 111 5p cat. I% 1110 1

4 cell battery 94x250101 dial 11/21 t c11,1 13 51/ IS, 11,1V12 a 1 arige . it 0 25,, OS, Is. and 2,, solidComputer grade itipat not, wuli .,,t,, winnuals tarlion reSIN11/1,.1/11'.1,1 1,1111i '1.11' 101 119

3000001211v 124,0 Intelligent -I thgit A1,11.0000,, it tS, ' 110111 1 15"1 0-41

8 7 0 0 0 u 1 III , . 1 1 » S 6 1411 0 0 111 LED displai. 1'2 pill 0.ii in. li ...Ai 1., k. Ne.-

15v 12 !IX 111000,11 111s 11 X0 5800164 111.91,,pc In.121 11.1 .121-,0

01),.. .. £195 each 12.00. 304 11.,a i.hecti £1101

7 segment i 0111011111 anode led chspla, 120im 10.45 AMP 27256.3 11,101113 .... 12.00 ca 6 1 I 25 100.1.M293 I A I 5 tI low drop out 5, ruglilalOr 10220 DIY swift h 3P1:0 12 pin (ERG SD( 4:1 0211 60p

packtit /0 /45 eat h .10p...1004.7812 and 1912 12v IA regulators... 120.00 per 100 Disk drive boxes ha 5.25 disk drive W1111 1,1oilt for.,1.M3'371 Tlei raw variable regobittn 11.110 (11 10 pow 1.1. 111/1/11.. light gte, plastit.

100, 67,226/W217mm 17 45 110 0 ini IliGaAs 1144: low leakage turtent 08871 . 112.95 each 11 ..... I hell'( ithiastimi ,,,,,,,,,,,,,I

(09.95 104-.17.95 100, 1.\"2101, gr. 1r1rs 30,11100o dm .10/ .1 w 1, tri 1111

852511 I' t 11.1111Ie I most et . 1015 lit 57,0 tad.. w ill al, ,...1k as a Iletill lighi topIra ..... U. ..........1:4.95 eat h 17 ',II pi, Imoper 100 :£2312, hatters tot c a, .11.111115 or lighters 751,

744.507, hex inveritit 1111 1/41 pea 11111 1',.d8718 tat, 131.1111,., 11111

1di,,onlrolld ....121511

All products advertised are new and unused unless otherwise elated.Wide range of CMOS Tyr. 74HC 741 Linear Tranne.tors kits. Rechargeable batteries, castritors, nails etc

alwaas in stork. Please add 11.95 wit., aril, p&p. VAT include,' in all price,

JPG Electronics, 276.278 Chatsworth Road, Chesterfield S40 2BHAccess/Visa (0246) 211202 Cal rs welcome

( IRCLE NO. 1010N REPLT (AR)

Ericsson :s MT is used in over50 countries world-wide

(Multi -DeviceProgrammer

00'1

Fast Programming - Intelligent Algor-thmsConnects direct to printer portOn line "HELP" SystemEasy to use menu driven softwareSupports a wide range of devices

All without adaptersIncluding:-

EPROMs E2PROMs Flash EPROMsPLDs GALs PALCEs8748 and 8051 families including 87C751

Additional modules include: -Serial E2PROMs (93C.. and 24C..)Microchip PIC and Zilog Z86 microcontrollers

New parts added all the timeContact SMART Communications for our full range of programmers

including stand -a one programmers. gang programmersand our comprehensive universal device programmer

Tel: 081-441 3890

Fax: 081-441 1843SMAKI

COMMUNICATIONS


Our commitment to Training does notCommitmert to training is essential in the rapidly changing communicationsworld. At Ericsson the importance of training has long been recognised.Since the early I 98Ils Ericsson has developed Technology Wsed Training(TB -O which all/lOS S personnel to be trained where and %A hen the user

needs it.

Ericsson's Tiff presents complex and difficult training material in aninteresting and exciting way. It is a self -paced, interactive, 1.ser-friendlyand cost effective method of enhancing technical competence.

Ericsson's generic range of IBM PCT' compatible coursewareincludes the following courses:- Introduction to Telecommunications ISDN Overview and ISDN Advanced OSI & Data Networks and OSI Advanced X.25 and Related Protocols and X.25 Advanced C7 Signalling System Part I and Part 2

Understanding Modems PCM Principles Cellular vlobile Radio X..100 Overview

For further information please contact your local Ericsson office or

Marketing Department,Ericsson Systems Expertise Limited,Adelphi Centre, Upper George's Street, Dun Laoghaire, Co. Dublin, Ireland.Tel: + 353 1 2800455. After 5pm: + 353 1 2843030. Fax: + 353 1 280591.4.

ERICSSON



RESEARCH NOTES

Robots glimpse improved vision processingIf robots could flick their cameras aroundin the same way as humans switch their

gaze back and forth, then they could make amuch better job of image processing - with alot less memory. That is the conclusion ofresearch currently in progress at theUniversity of Rochester in New York.

Mary Hayhoe, associate professor ofpsychology and a member of theUniversity's Center for Visual Science, hasbeen trying to understand why human visionis so markedly superior to that of robots,even though we mortals can only see clearlyin the very centre of our visual field. Why isit that robots are fooled by something assimple as a change in lighting, when they areequipped with edge -to -edge razor-sharpcameras and megabytes of digital image -processing capability?

Hayhoe and her colleagues discovered that

the key to human image processing is eyemovement. Unlike the robot eye, whichstares continuously at a scene, the humaneye constantly flicks around. These shortjerky eye movements, known as saccades,are how we circumvent the need for massiveamounts of image storage and processingpower.

"Eye movements provide a really efficientway to do things," says Hayhoe. Instead ofkeeping track of every detail in theenvironment, you use the world as yourmemory. You don't get information untilyou need it."

Other workers at Rochester have built onMary Hayhoe's work and produced anumber of versatile robots that mimic theway humans study their visual field. Insteadof boosting processing power to enable theirrobots to see every detail in their

Why lightning is forkedWby does lightning zig-zag its wayacross the sky rather than travelling in

a more -or -less straight line? As with manyapparently simple questions, the answer isstill being investigated. But plasmaphysicists at Moscow's Lebedev Institute ofPhysics and the Los Alamos Laboratory inNew Mexico think they have the solution.

Finding a single theory to explain whylightning forks, why it generates x-rays andeven why it takes place at all has beenextraordinarily difficult. Numerousmeasurements of electric fields inthunderclouds show them to be too week toaccelerate electrons to the speed necessaryto create atmospheric breakdown. To createan ionised trail for lightning to follow, anelectron has to gain enough acceleration toovercome the loss of energy it experiencesevery time it hits an air molecule.

But Robert Roussel -Dupre and hisassociates in the USA and Russia have nowformulated a theory that provides a coherent

explanation for all the above phenomena.According to the Roussel-Dupre's team, alightning strike is initiated when a cosmicray entering the Earth's atmosphere fromouter space collides with an air molecule,ejecting a fast-moving electron.

If the cosmic ray imparts enough energyto that electron, then the electric fieldstrength in a typical thundercloud is quiteenough to accelerate the electron further,keeping it moving as it hits and breaks apartair molecules. Every collision creates anavalanche of high-energy electrons, each inturn accelerated by the electric field andleaving behind a trail of ionised airmolecules.

According to Roussel -Dupre, thisavalanche rumbles downwards for about100m before it peters out, leaving a pool ofelectrically charged particles with its ownassociated field. The process might well stopthere except that there are large numbers ofcosmic rays that can re -trigger it.

environment - the usual approach to roboticvision - the Rochester group adopt anapproach which they call "active vision."With this technique the robot uses sensoryinput from its environment to make itsdecisions, including the ability to move itseyes.By using artificial saccades, theRochester robots simplify the imageprocessing task enormously andconsiderably enhance their ability to makesense of the visual field. With no remotecontrol, and in real time, these robots havebeen able to dodge tennis balls, manipulatetoys and search for identified objects such ascereal boxes.

Saccades - humans make over 100,000every day - are vital in our ability to makesense of the world. Our eyes move so fastthat we have the illusion of being able to seethe whole of our visual field in sharp focus.Tests at Rochester have shown that whenpeople are asked to copy a pattern ofbuilding blocks, they don't rely on an imagestored in the brain. Instead they makehundreds of saccades, through which theycompare the original with the duplicate theyare making. As Hayhoe puts it, "you don'tjust look once at a scene and then replicateit. Instead, your eyes are constantly goingback and forth, picking up little bits ofinformation again and again."

Traditionally artificial intelligence hasassumed that huge amounts of memorisedinformation are necessary for even thesimplest pattern recognition tasks. But if theRochester robots can successfully duplicatethe full range of human eye movements, thenit may, one day, be possible to perform evencomplex tasks without resorting to the usualelaborate models of the world

After a pause of only a few microseconds,a new cosmic ray collision sends a fast-moving electron through the pool of chargedparticles, creating another avalanche andanother ionised trail. This new trail is linkedto the first one, but heads off in a differentdirection.

This step by step conducting stairwayheads rapidly ground -ward until it is closeenough for a streamer to head up and closethe circuit.

It is a fascinating theory that explains boththe forked nature of lightning and also thelarge scale - often 300m - over which itoperates.

The researchers' mechanism furtherexplains the emission of x-rays, which arethought to result from the high energyelectrons generated by each successiveavalanche.

Research Notes is written by John Wilsonof the BBC World Service.


SMALL SELECTION ONLY LISTED - EXPORT TRADE AND QUANTITY DISCOUNTS - RING US FOR YOUR REQUIREMENTS WHICH MAY BE IN ETDCK

Marconi TF2008 - AM -FM signal generator - Also sweeper - 10Kcis -510Mc/s - from £350tested to £500 as new with manual - probe kit in wooden carrying box.HP Frequency comb generator type 8406A - £400.HP Sampling Voltmeter (Broadband) type 3406A - £200.HP Vector Voltmeter type 8405A - £400 to £600 - old or new colour.HP Synthesiser/signal generator type 8672A -2 to 18GHz £4000.HP Oscillographic recorder type 7404A -4 track - E350.HP Plotter type 9872B -4 pen - £300.HP Sweep Oscillators type 8690 A & B + plug -ins from 1 0Mc./s to 18GHz also 18-40GHz. P.O. R.HP Network Analyser type 8407A + 8412A + 8601A - 100Kc/s -110Mds -£500-E1000.HP Down Converter type 117108 -.01-11Mc/s - £450.HP Pulse Modulator type 11720A -2-18GHz -£1000.HP Modulator type 8403A - £100-£200.HP Pin Modulators for above -many different frequencies -£150.HP Counter type 5342A - 18GHz - LED readout -£1500.HP Signal Generator type 8640B - Opt001 + 003 - .5-512Mc/s AM/FM -£1000.HP Amplifier type 8447A - .1-400Mcis £200 - HP8447F .1-1300Mc/s £400.HP Frequency Counter type 5340A - 18GHz £1000 - rear output £800.HP 8410 -A -8 -C Network Analyser 110Mc/s to 12GHz or 18GHz - plus most other units anddisplays used in this set-up -8411A -8412 -8413 - 8414 -8418 - 8740 - 8741 - 8742 - 8743- 8746 - 8650. From £1000.HP Signal Generator type 8660C - .1-2600Mc./s AM/FM - MOO. 1300Mcis £2000.HP Signal Generator type 8656A -0.1-990Mc/s. AM/FM - £2000.HP 86998 Sweep PI -0.1-4GHz £750- HP8690B Mainframe £250.Racal/Dana 9301A-9302 RF Millivoltmeter -1.5.2GHz - £250-£400.Racal/Dana Counters 9915M -9916 -9917 - 9921 - £150 to £450. Fitted FX standards.Racal/Dana Modulation Meter type 9009 - 8Mc/s - 1.5GHz - £250.Racal - SG Brown Comprehensive Headset Tester (with artificial head) Z1A200/1- £350.Marconi AF Power Meter type 893B - £200.Marconi RCL Bridge type TF2700 -E150.Marconl/Saunders Signal Sources type - 6058B - 6070A - 6055B - 6059A - 6057B -6056 -£250-C350. 400Mc/s to 18GHz.Marconi TF1245 Circuit magnification meter + 1246 & 1247 Oscillators -£1004:300.Marconi microwave 6600A sweep osc., mainframe with 6650 PI - 18-26.5GHz or 6651 PI - 26.5-40GHz - £1000 or PI only £600.Marconi distortion meter type TF2331 -£150, TF2331A - £200.Microwave Systems MOS/3600 Microwave frequency stabilizer - 1GHz to 40GHz Elk.Tektronix Plug -Ins 7A13 -7A14 -7A18 - 7A24 -7A26- 7At 1 -7M11 -7511 - 7D10 -7S12 -S1 - S2 - S6 - S52 - PG506- SC504 - SG502 - SG503 - SG504 - DC503 -DC5013- DD501 -WR501 - DM501A - FG501A - TG501 - PG502 - DC505A - FG504 - P.O.R.Alltech Stoddart receiver type 17/27A - .01-32Mc/s - £2500.Alitech Stoddart receiver type 37/57 -30-1000Mc/s - £2500.Alitech Stoddart receiver type NM65T - 1 to 1 OGHz -£1500.Gould J3B Test oscillator + manual - £200.Infrared Binoculars in fibre -glass carrying case - tested -£100. Infra -red AFV sights £100.ACL Field intensity meter receiver type SR - 209 - 6. Plugs -ins from 5Mc/s to 4GHz - P.O.R.Tektronix 491 spectrum analyser - 1.5GHz-40GHz - as new - £1000 or 101AcJs40GHz.Tektronix Mainframes - 7603 - 7623A - 7633 - 7704A - 7844 - 7904 - TM501 - TM503 -TM506 - 7904 - 7834 - 7104.Knott Polyskanner WM1001 + WM5001 + WM3002 + WM4001 - £500.Alltech 136 Precision test RX + 13505 head 2 - 4GHz - E350.SE Lab Eight Four - FM 4 Channel recorder - £200.Ailtech 757 Spectrum Analyser - 001 22GHz - Digital Storage + Readout - £3000.Dranetz 606 Power line disturbance analyser - £250.Precision Aneroid barometers- 900-1050Mb - mechanical digit readout with electronic indicator- battery powered. Housed in polished wood carrying box - tested - £100-£200-C250. 1.2 or 3.HP141T SPECTRUM ANALYSERS- ALL NEW COLOURSTESTED WITH OPERATING MANUALHP1417+8552A or B IF -8553B RF -lkHz-110Mc/s-AIF -£1300 or B IF - £1400.HP141T+8552Aor B IF -8554B RF-100kHz-1250Mc/s-A IF- £1400 or B IF -E1500.HP1417 + 8552A or B IF -8555A RF - 10Mc/s-18GHz-A IF - C2400 or B IF - £2500HP141T+8552A or B IF -8556A RF - 2GHz-300kHz-A IF -A IF - E1200 or B IF -C1300.HP8443A tracking generator/counter - 100kHz-110Mc/s - £500.HP8445B tracking pre -selector DC-18GHz - £750.HP ANZ UNITS AVAILABLE SEPARATELY - NEW COLOURS - TESTED.HP141T mainframe - £550 - 8552A IF - £450 - 8552B IF - £550 - 8553B RF - 1kHz-110Mc/s -£550 - 8554B-RF - 100kHz-1250Mds - E650 - 8555A-RF - 10Mc/s-18GHz -E1550.HP 3580A LF-spectrum analyser - 5kHz to 50kHz - LED readout - digital storage - £1600 withinstruction manual - internal rechargeable battery.Tektronix 7D20 plug-in 2 -channel programmable digitizer - 70 Mc/s - for 7000 mainframes -£500 - manual - £50.Datron 1065 Auto Cal digital multimeter with instruction manual - £500.Racal MA 259 FX standard. Output 100kc/s-1Mcis-5Mc/s - internal NiCad battery - £150.Aerial array on metal plate 9"n 9' containing 4 aerials plus Narda detector -.130-11GHz. UsingN type and SMA plugs & sockets - ex eqpt -£100.EIP 451 microwave pulse counter 18GHz - £1000.Marconi RF Power Amplifier TF2175 - 1.5Mc/s to 520Mc/s with book -£100.Marconi 6155A Signal Source -1 to 2 GHz - LED readout - MOO.Schlumberger 2741 Programmable Microwave Counter - 10Hz to 7.1GHz - £730.Schiumberger 2720 Programmable Universal Counter 0 to 1250Mc/s - £600.HP 2225CR Thinkjet Printer -£100.TEK 576 Calibration Fixture - 067-0597-99 - £250.HP 8006A Word Generator -£150.HP 1645A Data Error Analyser -£150.Texscan Rotary Attenuators - BNC/SMA 0-10-60-100DBS -£50-E150.HP 809C Slotted Line Carriages - various frequencies to 18GHZ - £100 to MOO.HP 532-536-537 Frequency Meters - venous frequencies -£150-£250.Ban & Stroud variable filler EF3 0.1Hz-100kc/s + high pass + low pass - E150.S.E. Lab SM215 Mkl 1 transfer standard voltmeter- 1000 volts.Alltech Stoddart P7 programmer - £200.H.P. 6941B multiprogrammer extender. £100.Fluke Y2000 RTD selector + Fluke 1120A IEEE -488 -translator + Fluke 2180 RTD digitalthermometer + 9 probes. £350 all three items.H.P. 6181 DC current source. £150.H.P. 59501A - HP-IB isolated D/A/power supply programmer.H.P. 3438A digital multimeter.H.P. 6177C DC current source. £150.M.P. 6207B DC power supply.H.P. 741B AC/DC differential voltmeter standard (old colour) £100.H.P. 62098 DC power unit.Fluke 80 high voltage divider.Fluke 431C high voltage DC supply.Tektronix M2 gated delay calibration fixture. 067-0712-00.Tektronix precision DC divider calibration fixture. 067-0503-00.Tektronix overdrive recovery calibration fixture. 067-0608-00.Avo VCM163 valve tester +book £300.H.P. 5011T logic trouble shooting kit. £150.Marconi TF2163S attenuator - 1GHz. £200.PPM 8000 programmable scanner.Fluke 730A DC transfer standard.B&K 4815 calibrator head.

B&K 4812 calibrator head.Famell power unit H60/50 - £400 testedH.P. FX doubler 938A or 940A - £3130.Racal/Dana 9300 RMS voltmeter - £250.H.P. sweeper plug -ins - 86240A - 2-8.4GHz - 86260A - 12.4-18GHz - 86260AH03 - 10-15GHz - 8629013 -2-18.6GHz. 86245A 5.9-12.4GHz.Teiequlpment CT71 curve tracer -H.P. 461A amplifier - lkc-150Mc/s - old colour -E100.H.P. 8750A storage normalizer.Tektronix oscilloscopes type 2215A - 60Mc/s - c/w book & probe - £400.Tektronix monitor type 604 - £100.Marconi TF2330 or TF2330A wave analysers - £100-£150.HP5006A Signature Analyser £250 + book.HP10783A numeric display. £150.HP 3763A error detector. £250.Racal/Dana signal generator 9082 - 1.5-520Mc/s - £800.Racal/Dana signal generator 9082H -1.5-520Mcis - £900.Claude Lyons Compuline - line condition monitor - in case - LMP1 +LCM1 £500.Efratom Atomic FX standard FRT - FRK - .1-1-5-10Mc/s. £3K tested.Racal 4D recorder - £350- £450 in carrying bag as new.HP8350A sweep oscillator mainframe + HP11869A RF PI adaptor - £1500.Alitech - precision automatic noise figure indicator type 75 - £250.Adret FX synthesizer 2230A - 1Mc./s. E250.Tektronix -7S12-7S14-7711-7S11-SI-S52-S53.Rotek 610 AC/DC calibrator. £2K + book.Marconi TF2512 RF power meter - 10 or 30 watts - 50 ohms - £80.Marconi multiplex tester type 2830.Marconi digital simulator type 2828A.Marconi channel access switch type 2831.Marconi automatic distortion meter type TF2337A -£150.Marconi mod meters type TF2304 - £250.HP 5240A counter - 10Hz to 12.4GHz - £400.HP 3763A error detector.HP 8016A word generator.HP 489A micro -wave amp -1-2GHz.HP 8565A spectrum analyser - .01-22G1-lzHP 5065A rubidium vapour FX standard- £5k.Fluke 893A differential meters - £100 ea.Systron Donner counter type 605413- 20Mcls-24GHz - LED readout -E1k.Takeda Riken TR4120 tracking scope + TRI604P digital memory.EG&G Parc model 4001 indicator + 4283 signal averager Pl.Systron Donner 6120 counter/timer A+ B + C inputs - 18GHz - Elk.Racal/Dana 9083 signal source - two tone - £250.Systron Donner signal generator 1702 - synthesized to 1GHz - AM/FM.Systron Donner microwave counter 6057- 18GHz - Nixey tube - £600.Racal/Dana synthesized signal generator 9081 - 520Mc/s -AM-FM. £600.Famell SSG520 synthesized signal generator - 520Mc/s - £500.Ferns!! TTS520 test set - £500 - both £900.Tektronix plug -ins - AM503 - PG501 - PG508 - PS503A.Tektronix TM515 mainframe + TM5001i mainframe.Cole power line monitor T1085- £250.Claude Lyons LCM1P line condition monitor - £250.Rhodes & Schwarz power signal generator SLRD-280 - 2750Mc/s. £250-£600.Rhodes & Schwarz vector analyser - ZPV+ El +E3 tuners - .3-2000Mc/s.Bell & Howell TMA3000 tape motion analyser - E250.Ball Efratom PTB-100 rubidium standard mounted in Tek Pl.,Ball Efratom rubidium standard PT2568-FRKL.Trend Data tester type 100 - £150.Famell electronic load type RB1030-35.Fairchild interference analyser model EMC -25 - 14kc/s-1GHz.Fluke 1720A instrument controller+ keyboard.Marconi 2442 - microwave counter -.26.5GHz -£1500.Racal/Dane counters - 9904 - 9905 -9906 -9915 -9916 -9917 - 9921 - 50Mc/s - 3GHz -E100-£450 - all fitted with FX standards.B&K 7003 tape recorder - £300.B&K 2425 voltmeter -£150.B&K 4921+4149 outdoor microphone.Wlltron sweeper mainframe 610D -HP3200B VHF oscillator - 10-500Mot - £200.HP3747A selective level measuring set.HP3586A selective level meter.HP5345A electronic counter.HP4815A RF vector Impedance meter c/w probe. £500-£600.Marconi TF2092 noise receiver. A, B ar C plus filters.Marconi TF2091 noise generator. A, I3 or C plus filters.Tektronix oscilloscope 485 - 350Mc/s - £500.HP180TR, HP182T mainframes £300-E500.Bell & Howell CSM2000B recorders.HP5345A automatic frequency convertor - .015-4GHz.Fluke 8506A thermal RMS digital multirneter.HP3581A wave analyser.Philips panoramic receiver type PM7800 - 1 to 20GHz.Marconi 6700A sweep oscillator +6730A -1 to 2GHz.Wiltron scaler network analyser 560+3 heads. Elk.R&S signal generator SMS - 0.4-10a0Mc./s -£1500.HP85588 spectrum ANZ Pi - .1-15011Mc/s - o/c -E1000. N/C -£1500 -To fit HP180 seriesmainframe available - £1 00 to £500.HP8505A network ANZ + 8503A S parameter test set + 8501A normalizer - £4k.HP8505A network ANZ + 8502A test set - £3k.Racal/Dana 9087 signal generator - I 300Mos - 22kRacal/Dana VLF frequency standard equipment. Tracor receiver type 300A differencemeter type 527E+ rubidium standard type 9475 - £2750.Marconi 6960-6960A power meters with 6910 heads - 1 OMc/s - 20GHz or 6912 - 30kHz-4.2GHz - £800-E1 000.HP8444A-HP8444A opt 59 tracking generator El k-C2k.B&K dual recorder type 2308.HP8755A scaler ANZ with heads ElkTektronix 475 - 200Mc/s oscilloscopes - £350 less attachments to £500 c/w manual, probes etc.HP signal generators type 626 - 620 - frequency 10GHz-21GHz.HP 432A -435A or 8-436A - power meters +powerheads - 10Mcds-40GHz - £200-£280.HP3730B down convertor - C200.Bradley oscilloscope calibrator type 192 - £600.Spectrascope SD330A LF realtime ANZ - 20Hz-50kHz - LED readout - tested - £500.HP8620A or 8620C sweep generators -£25010 El k with IEEE.Barr & Stroud variable filter EF3 0.1Hz-100kcis + high pass +low pass - £150.Tektronix 7L12 analyser - .1Mcis-18GHz -£1500- 7L14 ANZ - £2k.Marconi TF2370 spectrum ANZ -110Mc/s -E1200-E2k.Marconi TF2370 spectrum ANZ+TK2373 FX extender 1250Mc/s+trk gen - £2.5k-E3k.Racal receivers -RA17L-RA1217-RA1218-RA1772-RA1792 - P.O.R.Systron Donner microwave counter 6057 - 18GHz - nixey tube - £600.HP8614A signal gen 800Mc/s-2AG1iz old colour £200, new colour £400.HP8616A signal gen 1.8G1-12-4.5GHz old colour £200. new colour £400.

ITEMS BOUGHT FROM HM GOVERNMENT BEING SURPLUS. PRICE IS EX WORKS. S.A.E. FOR ENQUIRIES. PHONE FOR APPOINTMENT OR FOR DEMONSTRATIONOF ANY ITEMS. AVAILABILITY OR PRICE CHANGE. VAT AND CARR., EXTRA.

ITEMS MARKED TESTED HAVE 30 -DAY WARRANTY. WANTED, TEST EQPT - VALVES - PLUGS & SOCKETS - SYNCROS - TRANSMITTING & RECEIVING EQPT. ETC.

Johns Radio, Whitehall Works, 84 Whitehall Road East, Birkenshaw, Bradford BD11 2ER. Tel. No. (0274) 684007. Fax 6511160.



BROADCAST

Clearhighwayfor digitaltelevisionAlthough there are still nosigns of it in the shops, a

new TV technology willshortly make your videorecorder and TV setobsolescent. Not only willpicture quality visiblyimprove, but theavailability of moreprogramme channels willprovide a new imperativeto the broadcasters. TomWoodford* reports on adigital TV revolution.

*Tom Woodford has spent much of his adult life inthe semiconductor industry and now runs aconsultancy specialising in communications projects,radio and data broadcasting. Someday soon he plansto move to France, to sail, write and grow tomatoes.

Current TVbroadcasttechnologyhas its origins

before the Second World War. It predatesmagnetic tape recording, radar, stereo, anddigital watches. With a few minor improve-ments - like better resolution, some sort ofcolour, and less fuzzy sound - you watch TVwhich is little different from Baird's andBlumlein' s.

In thirty years of research the only identifi-able achievement was MAC, which FortressEurope believed would protect it from the FarEastern invasion when the drawbridge wasraised in 1993. Proving again that democracyis a poor method of choosing winners, the realthreat was not a land attack from the Orient,but a Sky -borne raid from the Antipodes.

While Europe discovered that DMAC wasnot the consumer dream of the 1990s, theAmericans and Japanese were having the oddskirmish about high -definition standards. Allwas pretty quiet until a small US start-up,SkyPix, hit the market with a vapourwarelaunch of a fully digital DTH TV broadcastsystem in mid -1991. SkyPix would deliversome 64 TV programmes direct to the homeby packing five "or more" digital channelsonto each of sixteen high -power satellitetransponders. Cable operators and terrestrialbroadcasters would be out of businessovernight...

Suddenly hundreds of developmentsappeared in a rash of similar announcements.Presumably this was what SkyPix had hopedsince, the day after its own launch to the press,it was rumoured to be phoning around the

industry trying to buy into any working sys-tem. Like schoolchildren in their first com-munal shower, the industry had unwillinglybeen exposed to itself, only to find that every-one had been developing the same things,none of which yet actually worked.

With the secrecy and embarrassment lifted,the world was thrust into a new television era.Digital compression became public know-ledge, although still unattainable. Digital TVbecame a reality, while yet still undefined.

Digital video compression is unlike the datacompression used (for example) in fileexchange by modem or in PC hard -disk utili-ties like Stacker or SuperStor. PC Data com-pression uses coding techniques to eliminateredundant data. On recovery, the data is re-assembled exactly in its original form.However, in any system of video or audiocompression some of the original informationis deliberately thrown away in the coding pro-cess; it is lost forever and is never recoverable.

The advent of digital video had a reverseeffect on programme makers, who returned tosilver halide technology. The "InspectorMorse" TV series was filmed in 35mm;Super -16 format is more common. Producersof high -value programmes want to ensure thattheir work is stored for the future with mini-mum loss of quality. They feel that currentelectronic storage is inadequate.

Given that TV pictures are already a feeblerepresentation of a real image, what is theenthusiasm for digital compression, and whyhas it suddenly become the technological hotspot?Squeezing a bunch of lemonsIn a universe with limited RF spectrum,


BROADCAST

Squeezing a bunch of lemonsIn a universe with limited RF spectrum,straight digital transmission is a relative non-starter as an alternative to analogue tech-niques. A 625 -line video picture with a rea-sonable resolution of 400 vertical lines(S -VHS) requires 250,000 samples per frame.At 25 frames per second, and eight bits persample, this will require at least 50 megabitsper second to transmit. Add some colour andsome sound, and 60Mb/s is not unreasonable,but this still only gives a high -end -consumerpiCture quality.

Full studio broadcast standards wouldrequire over 140Mb/s, or at least 150MHz ofbandwidth. This compares with the 6MHz orso that a broadcast PAL signal needs inconventional vestigial-sideband AM.Nevertheless, the perceived benefits of digitaltransmission - picture accuracy, dynamicrange and noise immunity - have made it avery desirable objective, and this has spawneda vast amount of research into data compres-sion algorithms.

Much of a video signal is the same fromframe -to -frame; in real life very few largechanges occur in a twenty-fifth of a second.Obviously it should be possible to transmitonly the differences between frames, and

r-- 1 rL _ _ L_1

avoid the redundant burden of repeated infor-mation. There are some potential logistic prob-lems with this approach, particularly "appear-ances" (see box) but the major difficulty is theactual transmission medium itself. (For thetime being, "transmission" will be taken toinclude storage for subsequent replay)

Simple compression techniques are suc-cessful where high transmission powers areavailable to guarantee adequate signal-to-noiseratios at the receiver. With any sequential, dif-ferential system, a burst of noise can mask asignificant change in one area of a picture.This error will remain until the damaged areais subsequently updated, which could poten-tially be many minutes.

In the world of terrestrial TV it is common-place to bung a few megawatts up a big stickto broadcast distances of a few kilometres; forsatellites only fifty watts are available to trans-mit tens of thousands of kilometres.Conversely, the satellite engineer has over36MHz of bandwidth to play with comparedto his terrestrial colleagues' eight or so, andmultipath is not a problem with less receivedsignal power than the sound of a burning can-dle.

In practice it is terrestrial and cable broad-casting, with severe multipath, adjacent-chan-

The mpeg data streamstructureThe general form of the MPEG streamcomprises two layers. The System Layercontains timing and other informationused to demultiplex the audio from thevideo and subsequently to synchronise thetwo.

The Compression Layer contains thecompressed video and audio data streams.Audio coding will be covered in a laterarticle.

Within the video stream there is anhierarchical data structure. The videosequence contains a sequence headercode, one or more groups of pictures, andan end -of -sequence footer.

Picture Groups are strings of one ormore pictures which allow access into aSequence.

A Picture consists of three rectangularmatrices representing the Luminance (Y)and the Colour Difference (Cb and Cr)values. The luminance matrix has an evennumber of both rows and columns. Thecolour -difference matrices are each halfthe size of the luminance matrix in bothaxes, so there are one each Cb and Cr forevery four Y values. The Y and C values

VIDEO SEQUENCE

PICTURE GROUP

r

I

PICTURE

SLICE

MACROBLOCK

BLOCK OF8 x 8 PIXELS

are arranged as 8 x 8 sets known as Blocks, soa chrominance block describes a picture areafour times bigger than a luminance block.

The X and C Blocks are arranged intomacroblocks, each of which contains one Cbblock, one Cr block and four Y blocks.

nel and local interference potential, where thegreatest difficulties are found.

Broadcasters see it as essential that compat-ibility among all delivery methods is ensured,or the commercial burden of standards con-version will invalidate any likely benefit. Thisargument has been the justification for themany new, rival TV standards worldwide.HDTVT. HD Divine. Spectre. Sterne. System2000. Race 203 and Diamond are only a veryfew of the more prominent. However, therecent pre-emptive strikes by DirecTV in theUS and by Rupert Murdoch in Europe haveforced an uncharacteristic unity, and the de -facto future standard has become MPEG bydefault.

It would appear that the American systemhas won, but in reality the world's commercialgrown-ups have just noticed that their techni-cal children are still playing long after theirbed -time, and have imposed some discipline.

MPEG plus, plus plus, plus minusThe Motion Picture Experts Group of ISO, theInternational Standards Organisation, grew outof JPEG, the Joint Photographic ExpertsGroup. JPEG was formed to define standardsfor digital storage, processing and display ofstill pictures on the (then) growth technology

L _ _ J

Contiguous macroblocks are ordered fromleft to right and top to bottom into Slices.Slices are fundamental to MPEG errorhandling. Slices with errors are discardedby the decoder, which can skipimmediately to the start of the next slice inthe data stream. The number of slice sub-divisions of the data stream is thus a trade-off between error concealment and ultimatepicture quality.

Macroblocks form the basis for motioncompensation, by adding a motion vectorrelating the position difference between themacroblock being coded and its reference,plus an error term relating the contentdifference. For a macroblock within a B -Picture there are four possible codings;Intracoding with no motion compensation,forward prediction using the nearestprevious I- or P- picture as reference,backward prediction referencing the nearestfuture I- or P- picture, and bi-directionalprediction using the nearest past and futureI- or P- pictures. Backward prediction canbe used to overcome appearances byproviding the uncovered, new informationin advancex


BROADCAST

ihrt1. DCT Coefficient x 8 DC Term

3. DCT Coefficient 8 8 4 Coefficients

.111\5. DCT Coefficient 8 x 8 9 Coefficients

7 (left). DCT Coefficient 8 x 8 64 Coefficients

that

moved. 2. DCT Coefficient 8 s 8 Layer 1 contribution

4. DCT Coefficient 8 x 8 Layer 2 contribution

two a' Ali6. DCT Coefficient 8 x 8 16 Coefficients

DCT demonstration: This still image has been storedas a 720 by576 image and cut into 90 by 72 blocks. Each block is an 8 by 8, framebased, pixel area. These blocks were discrete cosine transformed toproduce 64 coefficients to 12 -bit accuracy.

The series of images show the effect of individual contributions ofselected coefficients to full accuracy in reconstructing the final picture.

The images are numbered from 1 to 7. The first image shows the resultof using just the DC term. The second image does not display a differenceimage but the picture information carried in three coefficients of the firstlayer from the DC term The third image shows the combined image ofthe previous two, a total of four coefficients. The images then progressthrough the layers until all 64 coefficients are used eventually to obtain acomplete picture.

Paul Burfield, BBC Research Department.


BROADCAST

of Personal Computers, and MPEG followedto continue the work in the area of picturesthat moved.

Originally MPEG was an occasional, typicalgathering of like-minded engineers, evaluatingcompression methods and discussing the var-ious possible applications of digital video.Participants would attend one of the routinemeetings bringing a tape of their latest video,which had defeated the current state-of-the-artcompression algorithms. Everyone wouldhave a jolly good laugh, and then go up thepub to chat about it. By this process of intel-lectual attrition the MPEG algorithms weresteadily refined, until a level of performancewas reached which the consensus agreed wasadequate.

It is important to understand that these earlydevelopments originated in the PC environ-ment, and were limited by the (late 1980s)standard PC bus and clock speeds with a max-imum data rate of 1.5Mb/s. Most of the par-ticipants had their backgrounds in informationtechnology, and their objective was to achievea reasonable performance in reasonabletimescales, aimed at the multi -media markets.

Hardware evolution progressed in parallelwith the specification and standardisation pro-cess, so that demonstrable systems existed andkept pace with the theoretical work, in partic-ular the essential operational silicon building -bricks. Like the DMAC development, theMPEG specification was an evolving sum-mary of what had already been achieved, orwas about to be.

By early 1991 the MPEG standard hadreached a performance level which the major-ity of contributors considered adequate, andMPEG 1 was effectively defined, althoughstill only in its "travelling draft" form.Multimedia consumer products were releasedto the market, in particular Philips CD -Interactive or CDi, although PC expansioncards offering MPEG-1 capability had alreadybeen available for some time.

Meanwhile, the professional TV broadcast-ers had been pursuing their own digital path-way. Starting from the minimum data rate ofaround 140Mb/s, their approach was to seehow much this could be reduced while stillretaining acceptability. By the late 1980s itwas felt that 25 - 35Mb/s was looking promis-ing, and working systems were built to provethe point to the doubters.

Casting around for available hardware, somedevelopers "discovered" the MPEG-1 sub-systems and were delighted to find that muchof the silicon would work at much higher datarates than the 1.5Mb/s for which it was speci-fied. These engineers were looking to upgradeexisting links for broadcast distribution net-works, and had only a passing interest in con-sumer markets.

Simultaneously, the programme makerswere evaluating the new digital technology, toestablish its viability as a lower -cost replace-ment for VHS tape and to expand cable net-works. They were stunned by the picture qual-ity which could be achieved in only 1.5Mb/s,and started to wonder what might be possible

Discrete cosine transforms, run lengthencoding and quantizationThe MPEG algorithms use numerous stagesin the source coding process. The obviousfirst stage for a digital system is to digitisethe analogue original. This implies inherentquantization into a finite number of pixels,each with a finite number of grey levels forthe luminance information, and similarlylimited chroma steps. The resulting array ofpixels is then subdivided into blocks of 64pixels, which are then translated to thefrequency domain by Discrete CosineTransformation.

DCT is usually explained in a heavilyjargonised, esoteric form. This may bebetter understood by considering it as delta -modulation and coding in pairs; the imageblock is coded as a series of transitions fromone grey level to the next. If the change inluminance between any pixel pair is large,the transformed equivalent pixel is white. Ifthere is ro change, the transform is black.There are obviously shades of grey inbetween these two extremes.

As luck would have it, the average videopicture has few hard contrast transitionedges in proportion to the total picture area,so the DCT version tends to have a largenumber of very black pixels, and the few,very white pixels tend to occur in specificgroups. The statistics necessary todemonstrate this are beyond the scope ofthis box, but anyone who wants to provethe point and has a couple of years to sparecan try pausing their home VCR on atypical tape, and then inspecting theresulting frozen video frame to perform aquick DCT in their head.

The resulting DCT form of a frame haslarge groups of all -black or all -white pixels,or long sequences of small changerepresentations, so the frame can be furthercomp-essed by Run -Length coding in pairs.

In simple terms this means that, if thereare 1000 identical pixels in a string, thenone could transmit a coded message saying"here follows 1000 identical pixels, all

black", which is obviously a shortermessage than all the 1000 original pixels,and a lot less boring.

For a smooth transition from black towhite over a series of pixels, a similarcoded message saying "the next 500 pixelsincrease by only one bit from one to thenext..." is an equally efficient simplification.

The MPEG system interposes anadditional step before run -length coding, byfirst zig-zag scanning the array of DCTpixels. This tends to produce long runs ofsimilar or identical transformed pixels, andincreases the RALC efficiency. Again, this issomething to try for yourself at home on atypical TV frame or two.

The run -amplitude -length coding is alsoof variable word length, so that the morecommonly occurring sequences haveshorter codes, which further increases thecoding efficiency. Conversely, some blocksneed to be coded much more accuratelythan others. A smooth transition needs to betransferred as such, because the eye is morecritical of harsh edges where they shouldn'toccur than of blurred edges which ought tobe sharp.

Since the original stage of the entirecoding process is to divide the picture intoblocks, it is vital that the edges of the blocksshould join seamlessly in the final, re-assembled picture. The MPEG algorithmmodifies the amount of quantisation foreach 16 x 16 "macro -block" of pixels toovercome this, and this additional processis also used to allow smooth adaptation tochanges in transmission bit rate.

Since this only describes the codingprocess used for one typical pair of videoframes in very simple terms, you will notnow be surprised that real-time MPEGencoding of raw video has only justbecome a reality. Indeed, one could beforgiven for wondering if there is enoughraw silicon in the world to construct all thenecessary MPEG encoders.

at only slightly higher data rates which wouldfit into their existing five or six megahertzbandwidth.

In the worldwide climate of de -regulation,telecomms operators were also evaluating dig-ital TV, particularly for the embryonic pay -per -view and video -on -demand domesticmovie services, but also with an eye on thevery lucrative news gathering market. PTTshave transmission standards at 1.2 and 8 Mb/s,and thus they were also following the twinperformance paths. Would 1.2Mb/s giveacceptable quality for consumers, and could8Mb/s be good enough for broadcast feeds?

TV setmakers, still smarting from theEuropean MAC disaster and equally wary ofthe continuing unresolved acrimony overwidescreen and high -definition formats, were

only too pleased to join in with anything thatlooked half sensible.

Apparently MPEG was already exploring allthese areas, and it was natural for the variousTV -oriented interest -groups to want to join in.

The original MPEG meetings typicallyattracted around fifty attendees. During 1992the number of Representatives grew, and thegathering in Sydney earlier this year drew 270Delegates. MPEG is now unofficially calledMP/G, where the "I" stands for "Interested".

With this level of world-wide participationthe speed of MPEG progress has accelerated,and now exceeds the ability of the politiciansto keep up. With MPEG-1 effectively anestablished standard, although still officially adraft, the various Interested bodies have movedonward to the next generation, MPEG-2.


BROADCAST

Picture codingThe MPEG standard defines three type of pictures within the codedstream: Intra, Predicted and Bi-directional.

Intra Pictures, or "I -Pictures" are coded using only informationpresent in the picture itself and therefore provide possible random-access points into the compressed video stream. I -Pictures use onlymoderate levels of compression coding, typically two bits per codedpixel.

Predicted Pictures, or "P -Pictures" are coded with reference to thenearest, previous I -Picture or P -Picture. This is referred to as"Forward Prediction", and allows higher levels of compression thanI -Pictures by using motion compensation. P -Pictures are used bysubsequent P -Pictures and B -Pictures for prediction, and thus canpropagate coding errors along the data stream.

Bi-directional Pictures, or "B -Pictures" use both a past and a futurepicture as a reference. By using bi-directional prediction some noisereduction is also achieved by the resultant averaging.

Although B -Pictures use the highest possible compression, theycannot propagate errors since they are never themselves used as areference.

The MPEG algorithm allows the encoder to choose the number andpositioning of I -Pictures within the data stream, depending on theoriginal video composition (number of cuts and scene changes) andon the specific need for random accessibility.

Where random access is paramount I -Pictures occur typically twiceper second.

2

B

ACTUAL PICTURE ORDER

B

4

P

BB

6

B

TRANSMITTED DATA STREAM ORDER

4

P

2

B B

7

P B

7

P

aB

The algorithm also determines the number of B -Pictures betweenany pair of P -Pictures or I -Pictures, depending on the video materialcontent and also the encoder's memory capacity. Typically, two B -Pictures will occur between successive I- or P- pictures.

The MPEG encoder re -arranges pictures into a different order fortransmission. Most importantly, the reference pictures needed toreconstruct any B -Pictures must be sent before the B -Pictures whichactually use them as a reference. This re -arrangement or re -orderingof the video sequences requires complex re -synchronising with thesound signal in the receiver..

With the broadcasters coming down from140Mb/s and the Ms going up from 1.2Mb/sthe inevitable clash occurred at around 15Mb.If the momentum of MPEG were not to belost it was essential that some new Peg wasput in the ground to mark the direction foronward development;

MPEG-1 silicon was already operating quitehappily at 15Mb/s and faster, and was grow-ing offshoots. The leader in MPEG silicontechnology, Californian C -Cube Microsystemsdeveloped its CL450 decoder with much ofthe actual algorithm soft -loaded as microcode.This has allowed amendments and upgrades to

basic MPEG-1 to be demonstrable almost assoon as it evolves.

This flexibility, and the higher data rates,could be used either to improve resolution orto reduce compression artifacts, or a bit ofboth. The speed upgrades had already becomeknown as MPEG-Plus, and with multipleenhancements there is also MPEG Plus -Plus.

The confusion increased with the require-ment that MPEG-2 should be backwards -com-patible, and hence the parallel existence ofMPEG-2-Minus...

At these various higher data rates, MPEG-1has demonstrated performance equivalent to

Timing and synchronisationThe MPEG system performs large amountsof signal processing before transmission andafter reception but before display. Althoughthe audio and video components aremultiplexed together in the data stream, theyuse totally different coding techniques. Inparticular, the video frames must betransmitted re -ordered, so the audio andvideo data components at any point in thestream may be totally unrelated. The MPEGstandard provides suitable timing referencesto allow the audio and video to be re -synchronised by the decoder.

The System Clock Reference is a sample ofthe 90kHz MPEG system clock. Thisprovides 7.8 x 109 clocks in a 24 -hour day.An SCR is transmitted as a 33 -bit value, socan therefore identify any one particularclock cycle in a 24 -hour period. SCRs areinserted into the data stream by the encoderat least once every 0.7 seconds. The systemdecoder in the receiver extracts the SCRs

and passes them on to the video and audiodecoders to update their own internalclocks.

A potential time difference of nearly asecond between the video and audio wouldbe totally unacceptable, so the system alsotransmits Presentation Time Stamps. Theseare effectively 33 -bit "clapper -board"markers which can identify related sound orvision Presentation Units to within onesystem clock tick. PUs are specific decodedvideo pictures or decoded audio sequences.

The encoder inserts a PTS into the datastream at least once every 0.7 seconds toidentify specific video frames and audiosequences which must occur together. Thevideo decoder checks incoming PTSmarkers against the current SCR beforedisplaying a picture. If the PTS is "early" theprevious picture is repeated; if it is "late" apicture is discarded.

existing systems. At 2Mb/s, picture quality issimilar to domestic VHS, and approachesbroadcast PAL standard at about 12Mb/s. Inbetween is Betacam SP used in SNG, ataround 8Mb/s. Since MPEG-1 already appearsto have reached the various targets of theinterested participants, what then is MPEG-2?

Until early September this was not a simplequestion since participants are party to non-disclosure agreements. The main improve-ments in MPEG-2 appear to be the possibilityfor flexible, seamless, dynamically variabledata rates rather than the nominally fixed1.5Mb/s of MPEG-1. In addition MPEG-2makes better use of the temporal redundancyin interlaced TV pictures, which was notexploited in the non -interlaced IT origins ofMPEG-1, and MPEG-2 is defined to be fullycompatible with telecommunications networksdata rates. Draft specifications of MPEG-2 arenotionally available from standards bodiessuch as BSI, but these all date from earlier thisyear and are already obsolescent.

MPEG has about five meetings a year, withsome ad -hoc gatherings in between as

required. The Spring meeting in Sydney setout MPEG-2 in outline, and these standardswere chilled at the July meeting in New York,in preparation for being frozen in the Koreameeting in early November.

At the International Television Symposiumat Montreux in June the Europeans apparentlycapitulated, finally buried MAC and adoptedMPEG as the future standard. A EuropeanLaunching Group meeting was planned forSeptember to lay out a co-ordinated plan forthe introduction of MPEG-2 by mid -1997. Itappeared that America had indeed won thedigital race.


BROADCAST

Mapping out a digital highwayHowever, in a pre-emptive strike at the end ofAugust, Rupert Murdoch announced thatBSkyB would operate an MPEG-2 digital ser-vice by the end of next year. Sky will workjointly with the UK's NationalTranscommunications Ltd (the old IBA'stechnical wing), Comstream, Thompson andNews Datacom, who provide the existingVideoCrypt conditional -access system. TheMurdoch digital service will therefore be vir-tually identical to the Hughes DirecTV systemin the US, scheduled for launch in mid -'94.Thompson and C -Cube are the technical andmanufacturing resource behind DirecTV.

BSkyB will undoubtedly use the potentialcompatibility to good effect. In late AugustMurdoch purchased Delphi Internet Services,one of the top five US on-line data suppliers.He has announced deals for interactive sys-tems with telecom operators, particulary BT,and with the Kirch Group in Germany forPay -per -view services. Significantly, all theselected partners are commercially indepen-dent; there are no government influences orstate monopolies in BSkyB's Digital future.

NTL's involvement follows from its System2000 digital transmission system, which theyhave been selling highly successfully as abroadcast feed since late last year. The devel-opment for Murdoch will probably be entirelynew, as an MPEG-2-based consumer system.The contract expects hardware in the retailmarket no later than the end of 1994. With thefinal stages of MPEG-2 definition onlyexpected after the meeting next November,these are tight timescales indeed for NTL, anorganisation with limited experience in con-sumer product technology.

C -Cube is confident that it will have work-ing MPEG-2 silicon available by Christmas,and volume product at consumer prices (under$50) early in 1994. The apparent lead of C -Cube may be because R & D head Didier LeGall is also chairman of the MPEG videocommittee.

NTL's significance is real-time MPEGencoding. At the end of 1991 the best avail-able encoders took around 200 minutes to pro-duce just one minute of programme output. Bymid '92 this overhead time was down to about70 minutes, and below 15 minutes by a yearago. While a dramatic improvement, this wasstill quite impracticable for any broadcast sys-tem.

Encoding was also a two -stage process, witha first pass to identify and edit out any hotspots which would defeat the MPEG algo-rithms. However, NTL was demonstratingreal-time encoding before the end of last year,and shipping product to customers soon after.C -Cube did not deliver real-time encodersuntil last month, and at reputedly very muchhigher prices.

It is difficult to understand why BSkyBshould want to move so quickly to digital,with a dominant installed base ofPAL/Videocrypt customers. Perhaps it is sig-nificant that none of Murdoch's chosen asso-ciates are manufacturers; they are developers

Movement prediction and appearances

Quite a tot of the information in any givenTV frame is similar to a previous orsubsequent frame. The MPEG system usesthis sequential redundancy to transfer somepictures in a simplified form representingonly their differences from some referencepicture previously or yet to be transmitted.

This technique has excellent potential forproblems, in particular with visualdiscontinuities known as "appearances".

The classic example is a static picturecontaining a black circle, which is actuallythe mouth of a tunnel from where, suddenlyand unpredictably, bursts an express train.More subtle is the side view or an aircraft'swheels at touch -down when t ley (suddenlyand unpredictably) start to rotate,accompanied by a puff of smoke. Theopening of a door to reveal a hithertoundisclosed scene beyond is less sudden,but equally unpredictable.

Conversely, it is easy to detect consistentmovement within a sequence of pictures byseeking groups of blocks which change onlyin their relative position to the overallpicture from frame to frame. This can be

used to predict the future position of amoving group of blocks, and code asequence of frames accordingly. Thistechnique is known as "MovementPrediction" or "Motion Compensation", andit can improve compression ratios by afactor of three or higher. It can also createmore serious problems...

I have actually seen a video of a horserace finish in which, in the digitallycompressed version, a different horse wins.A wide-angle view of an applauding crowdcan also create intolerable (but amusing)artefacts, since the overall movement ofcountless clapping hands is virtuallyrandom. Stormy seas or fields of wheat areequally incoherent.

A predicting algorithm needs to be able todecide when to give up trying and to waitaround and see what happens next. Theoverall algorithm also needs to transmitwhole pictures every so often, to allow thedecoder to recover from transmission errorswhich would otherwise propagate endlesslyfrom frame to frame.

and specifiers. While the litigation betweenthe old BSB and its DMAC receiver suppliersstill rumbles on, BSkyB is being careful not toincur any implied commitment to eventualsales of hardware. It is likely that Murdoch isprotecting himself against the future, by tryingto force it to look the way he wants. When,and how quickly, he follows his own lead willbe intriguing.

Perhaps the biggest concern is the short-termreplacement of VHS tape by Video CD.Nimbus is planning to have its add-on videodecoder for audio CD machines on the marketby the end of 1993. The Gang of Four(Philips, JVC, Sony and Matsushita) plan toenter the market with their rival "white book"CD -K machines early next year. Whicheversystem wins, either promises a drastic reduc-tion in the cost of video rental by eliminatingcheap, back -room piracy. With a common for-mat on both sides of both the Atlantic andPacific, the costs of programming must alsofall. The quality improvement over tape willbe dramatic and immediate for the ordinaryconsumer, with a price penalty which is low,or even zero.

The installed base of domestic TVs whichcan accept direct RGB inputs is small.Domestic RGB VCRs are non-existent. Aswith DMAC, the majority of viewers willwatch their MPEG-broadcast TV as conven-tional PAL, SECAM or NTSC via compositevideo or even UHF. To time -shift a satellitemovie they will certainly have to use an infe-rior analogue medium. Without the cost -

reduction benefits of digital, and extra featureslike video -on -demand and interactivity, it willbecome increasingly difficult for broadcastersto compete with the better quality and estab-lished convenience of renting a movie on CDfrom the local video store.

DirecTV and Digital Sky will be satellite -based, of course. With restrictions on coverageareas and due consideration for domestic con-sumers, the last European PAL transmitterwill probably not be switched off until 2015 oreven later. Much work has yet to be complet-ed on alternative terrestrial transmission tech-nology, although it looks as if NTL is againthe leader with its OFDM Spectre develop-ments. Whatever system is adopted to replaceAM for terrestrial broadcast, it will be deliv-ering digital programmes created using (bythen) long-established technology. In twentyyears' time every home could have a fibre -optic connection, and UHF broadcast maynever be upgraded at all...

At Montreux, it was suggested that MPEGactually stands for Maximising Profit andEfficiency Gains. MPEG offers the ability forbroadcasters to pack five, six or more TVchannels into the space occupied now by onlyone. As far as the average TV viewer is con-cerned, this will mean only More, not Better,until he has saved up to buy his new MPEGtelevision in some three years' time. One won-ders how much extra he will have to pay forspiked feet?


CIRCUIT IDEASSEND YOUR CIRCUIT IDEAS TO THE EDITOR, ELECTRONICS WORLD, QUADRANT HOUSE, THE QUADRANT, SUTTON, SURREY SM2 5AS

DO YOU HAVE A f100 CIRCUIT?, EACH MONTH'S TOP CIRCUIT IDEAAUTHOR WILL RECEIVE .£100. ALL OTHER PUBLISHED IDEAS WILL BEWORTH f25. WE ARE LOOKING FOR INGENUITY AND ORIGINALITYIN THE USE OF MODERN COMPONENTS

Economical 27MHz phase modulatorThis circuit phase -modulates a clock

I signal, a process finding application inPM and FM transmitters and in clock jittertesting. It exploits the properties of 74HCcmos gates that (a) input logic thresholdincreases with increasing V, (b)propagation delay increases with increasingV and (c) V is allowed to vary between2V and 6V.

Triangular modulation of 1Vpk-pk issuperimposed on the nominal 4V derivedfrom the 4.5V battery via the diode, whichcatches the modulating input and results in a

V varying between 4V and 5V. There issufficient noise immunity in 74HC

and 74HC logic to allow correctdrive to the following stage withthese levels.

Since the effects of varyingVcc on propagation delay and

logic threshold are in the samesense only on falling edges of the

clock input, both inverted and non -inverted clock signals are used, the timingfrom the rising edges being eliminated in the74HC74, configured as a pair of divide -by -two flip-flops. A 74HC86 Ex -Or sectioncombines the two outputs V5 and V6 toprovide the circuit output at up to 27MHz.

Two of the spare gates in the 74HC86 willmake the 27MHz crystal oscillator and thetriangular -wave generator was made fromspare Schmitt inverters, with a buffer, ataudio frequency. A 4.5V supply isconveniently obtained from three alkalinemanganese cells. I found it necessary to usea ground -plane hoard layout.Laurence RichardsonHers hamSurrey

At very low cost, an audio waveform phase -modulates a clock signal of up to 27MHz. Onlynegative -going input edges are used, since the

properties of the cmos logic exploited in thecircuit have a tendency to cancel on rising

edges.

27MHzclock

0input V1

74HC14

F omtwo-phasecrystal osc 0

V227MHzinvertedclock Up

Modulation1.0V pk-pk

74AC74 74HC86

V3

V4

Vcc

'L'Vcc 4.0V plusmodulation

TIMING DIAGRAM

V1

v2

V5

0CLP

1

Inhibit

PRD

0CLR

s,

1N4001

Vcc....L -114.5V

"700q

V3

V4

V6

EXORPhasemodulatedoutput

Vcc4.5V

1=:=1

.1720E1 Too

V5

V7

V6

V7

V7 = (V5 716) + (GT V6)


CIRCUIT IDEAS

Independent on/off for long -period astableA stable multivibrators using 555 timer

TAICs are flexible in that frequency andduty cycle are independently adjustable but,when long and independent on/off periodsare needed, large and costly capacitors mustbe used. This circuit avoids the problem andgives periods up to several hours.

An 4020 14 -stage binary counter dividesthe timer output, its Q14 and \Q14 outputsconnecting Ralf and R,,,, at alternatetransitions to give independent on and offperiods. Output Q1 gives an indication of theoutput duration.Devadoss JohnHindustan Cables LtdHyderabadIndia

D1,D2 = 1N4148Ton 5 mins for Ron = 100kToff 50 mins for Rofff = 1M

Roff

Low -loss lamp dimmerOnce having shut the car door in adark car -park and thereby

extinguished the internal light, you can'tfind the keyhole to lock it. But thiscircuit dims the light slowly until thedoor is locked.

Transistor Tr2 drives the lamp and inturn is driven by the 3524 regulatingpulse -width modulator. With the doorswitch closed (door open), C3 is fullydischarged, Tr1 fully conducting and C1shorted. Pin 2 of the PWM, the non -inverting input, is high and the lampfully on.

Closing the door and thereby openingthe switch causes C3 to charge throughR5,6, holding Tr1 in saturation for about aminute. When Tr' cuts off, CI chargesslowly through R7, bringing pin 2 of thePWM to 0.6V, and slowly dimming thelamp.

If matters were left there, one wouldhave to wait for the lamp to go outcompletely, which would take sometime, so the relay is actuated by the 12Vcontact on the lock to charge C3 quicklythrough R. Diode Di and C2 preventinterference when the engine is being

started.The driver transistor needs no heat sink

since it runs in hard switching.Yves Delbrassine,Hovenierslanden 3,8200 Bruges,Belgium

This principle is, of course, not limited todimmng car lighting; low -loss drive forhigh -power loads is common, although it isnot often seen described for such simpleprojects. Among the possibilities that springto mind is a miniature crystal oven using thePWM to drive a power transistor - Ed.

INPUTS

Doorswitch +12V contactJ1

0 0con2

K1

o o o

Pulse -widthmodulatorautomatically dimsinternal car lighting,giving time to kickthe doors before thelight goes out.

R1

47k

POWER

Gnd. +12V Input

J2........I.....0 0con2

LAMPS

+12V Lamp Lampt

0 0.13

con2

R5 Tr1

680k

470k

RF

C1 221., 25VTant

D1

BC557c

Door open = Gnd to doorswitch input

C3 47p 25V

Tent.

1 N 4 1 4 8

R7 1M

16

Ins

NI

D1 1N4007

C2 -- 1000 p25V

15 101 41 51

Vref V n SD +CS -CS

SG3524

CA

CB

EA

EB

Cext Rext Osc Comp7 6

C4

1p

25V

3I

4k7C5

9

3 47kR4

820p

TR2

BUZ11a

014Vout


CIRCUIT IDEAS

Two wire level indicatorUsing one IC, this two -wire remote -reading instrument indicatesthat water in an earthed vessel is at or above one of four levels.

If all sensing electrodes are unwetted, all Nand outputs are low andthe meter reads virtually zero. As an electrode touches water, its gategoes high and the meter reads a current Vcc/Ri. A rising water levelcauses more gates to contribute to the current.

The optional regulator and voltage -setting resistor R4 allow full-scale to be adjusted by shorting all the electrodes to ground.K N N Narayanan and C V Raman NagarBangaloreIndia.

Proportion indicatorTo show the ratio of one of several inputs to the total of all inputsas a percentage, the obvious solution involving a microprocessor

can be simplified by the use of three A -to -D converters, whichperform all the functions of digitising, ratio determination and drivingthe percent display.

The non -inverting, summing op -amp pair adds the inputs - three,in this case, as an illustration - the sum being taken as the referencevoltage for all A -to -Ds and the individual inputs being fed to Vin(hi) ofeach converter. Display 1 now reads

Vin(hi)/Vref(hi),orVi/(Vi + V2 + V3),

and similarly for the other inputs. If the right-hand decimal point in the"tens" position is turned on, the display shows a percentage.

This circuit will handle a total input of 0.2-4.5V and give threereadings per second; although three inputs were used in the prototype, itshould work with any number. +5VM S Nagaraj 1N4148

ISRO Satellite CentreBangalore 1N4148

-5V

Indicator shows ratioof each input as apercentage of totalinput. Circuitreplaces more exoticmicroprocessor -based arrangements.

V1 10k0.1%

V2 10k0.1%

1A,M,11 X 10

?\tv/161

10k0.1%

+12v

V3 10k OP -070.1%

12V

R2

2IC

3

R1

R2

6IC1

4

R1

R2

8

IC110

R1

R2

12

13IC1

14

Sensng electrode

230V50Hz

IC2

ti

12V1000p 16V

Gnd electrode

101 CD4011IC2 7805R1 see textR2 10k .25W

M1

_L720n 7n 11nl 7100p

470k 100k

INT BUFF A/z Cref Cref Osc3 Osc2 Osc1

In HI ICL7107

Ref HI

In LO Ref LO Common Gnd V V+

470k

220n 7711 1-1101-ni

-5V 1 +5V

700p100k


In HI ICL7107

Ref HI

In LO Ref LO Common Gnd V

10n

AMA,1M

10k 0.1%

0-MAAr-la(0.1%

OP -07

155k6%

705%

720n470k

7n [lir]

-5V I +5V

700p100k


In HI ICL7107

Ref HI

In LO Ref LO Common Gnd V- V+

10n

-5V I +5V

Vcc5V to 12V

Display - 1

%E1

5 1.9

Display - 2%E2

32 -1-1

Display - 3%E3

I57


SCHEMATIC DRAWING FORWINDOWS

ISIS ILLUSTRATOR combines the high functionality of our DOS based ISIS products with thegraphics capabilities of Windows 3. The result is the ability to create presentation qualityschematics like you see in the magazines. ILLUSTRATOR gives you full control of line widths, fillstyles, fonts, colours and much more. When the drawing is complete, transferring it your WP orDTP program is simply a matter of cutting and pasting through the Windows Clipboard.

FeaturesFull control of drawingappearance including line widths,fill styles, fonts, colours and more.

Curved or angular wire corners. Automatic wire routing and dot placement.

Fully automatic annotator Comes complete with component libraries.

Full set of 2D drawing primitives + symbollibrary for logos etc.

Output to Windows printer devices includingPOSTSCRIPT and colour printers.

ILLUSTRATOR+ adds netlist generation, bill ofmaterials etc. anc is compatible with mostpopular CAD software for DOS & Windows.

From£99

CADPAK - Two Programs forthe Price of One.ISIS SUPERSKETCHA superb schematic drawingprogram for DOS offering WireAutorouting, Auto Dot Placement, fullcomponent libraries, export to DTP andmuch more.

Only£79

Exceptionally easy and quick to use. For example, youcan place a wire with just two mouse clicks - the wireautorouter does the rest.

PCB IIHigh performance manual PCB layout package forDOS. Many advanced features including curved tracks,auto track necking, DXF export, Gerber and NC filegeneration, Gerber viewing and more.

Graphical User Interface with intuitive "point and do"operation gives unparalled ease of use.

cocerzerElectronics

ISIS and ARES for DOS - TheProfessional's ChoiceISIS from £275ISIS DESIGNER+ forms the ideal front end of yourCAD system, providing schematic capture, netlisting,bill of materials and electrical rules checks. Advancedfeatures include automatic annotation, hierarchicaldesign and an ASCII data import facility. Put simply,DESIGNER+ is one of the easiest to learn and mostpowerful schematics packages available for the PC.

ARES from £275The ARES range of advanced PCB design productslinks with ISIS (DOS or Windows) and otherschematics programs. Working from a netlist, AREShelps you get it right first time with each connectionautomatically verified against the schematic.

ARES AUTOROUTE adds multi -strategy autorouting,whilst for the ultimate in performance, ARES 386 goesup to 400% faster with unlimited design capacity.

Call us today on 0274 542868 orfax 0274 481078 for a demo pack.

Combination, multi -copy andeducational discounts available.

14 Marriner's Drive, Bradford, BD9 4JT.CIRCLE NO. 197 ON REPLY CARD

ELECTRONICS WORLD +WIRELESS WORLD November 1993 901

COMPONENTS

Many op -amp applications process signals which swingabout ground. This requires the designer to add anegative supply rail to the system. Frank Ogden reportson a new op -amp package which generates its own.

1 OUT1 IN -1 IN+

VCC-VOUT

VREFOSC

VIN

DW PACKAGE

(TOP VIEW)

VCC+2 OUT2 IN -2 IN +

CAP-GNDCAP +

FB/SD

TLE2662 pinout

Charge pumpconverter internalblock diagram

F13,SD

OSC

VREF

Charge pumped op -ampsupplies the missing rail

Most portable communications andinstrumentation designs must draw theirpower from a single battery or supply rail.The input signals which they process are

usually referenced to ground. Logic level input signalspose little problem; they swing from ground towards thepositive rail allowing the signal conditioning circuitry tooperate from a single supply. Provided of course that thereare enough volts on the supply rail to provide headroomfor the signal being processed.

Most other signals swing around ground. Designerstraditionally deal with these either by using cmos op -ampssuch as the TLC271 which include the negative rail in theircommon mode range or by putting in an extra power blockto provide a negative supply rail referenced to ground.

Using op -amps with extended common mode range isnot always a good idea. They will tolerate a below -groundswing of just a few hundred millivolts. Exceeding this, forinstance during a transient, incurs a real danger of devicelatch -up. However, the provision of a proper negativesupply rail allows fully symmetrical signal handling andextended dynamic range at the expense of power supplycomplexity and board area.

Texas Instruments provides an answer to this dilemma inthe TLE2662. Incorporating a pair of high output drive,jfet input op -amp blocks together with an adjustablecharge pump negative rail generator, it allows the designof single 5V rail signal processing system with aninput/output drive capability of 7Vp-p about ground withina single device package. The allowable supply voltagerange of the converter system extends to 15V providingthe amplifier blocks with ±15V supply rails and 25Vp-poutput swing about ground.

REF2.5 V

OSC

vcc

JCAP)

CINt

O

I Drive I

CAP -

Drive I

I Drive I-

GND

COUTt

VouT

1 OUT

1 IN -

1 IN+

vcc

VOUT

VREF

OSC

VIN

Amplifier Block

6

Switched -Capacitor

Block

'

15VCC+

15 2 OUT

14 21N-

13

2

11

Functional block diagram

Suitable for modems, PCMCIA cards, portable phones,VCOs, level shifters, battery chargers and data acquisitionsystems, the device comes in a wide bodied SMD package.

The amplifiersThe identical amplifier blocks exhibit fairly typical jfet op -amp performance with 2V/µs slew rate, 25mA output drivecapability and a millivolt of input offset voltage. Howeverinput bias current is just 3pA making the amplifiers highlysuitable for electrometer type applications. The equivalentinput noise current is also very low, about lfA'Hz. Fulloutput swing bandwidth extends to 140kHz at a supplyvoltage of ±5V. Quiescent no load current drain is about600pA.

The voltage converterThe bipolar charge pump voltage converter doesn't shareany pins with the amplifier blocks allowing total systemseparation if required. It will deliver up to 100mAprovided that dissipation considerations are taken intoaccount. Since the associated amplifiers would draw nomore than about 6mA in small signal, high impedance loadapplications, the converter may be configured to supply auseful amount of current to other parts of the system. Anextra pair of external diodes will allow its configuration asa boost converter to increase the available positive railvoltage to the amplifier section or other external systems.

The converter block also includes a 2.5V referencewhich may be used to regulate the output voltage through aresistive divider associated with a feedback/shutdown pin,or as an external reference for other circuitry.

2 IN

CAP

GND

CAP r

FBISD


Fig. 1. Basicapplicationcircuit showing adirect signalconnection From

between the Preamplifier

amplifiers andthe internalnegative railpower supply.Low level signalconditioningapplicationswould normallyrequire extradecouplingbetweenconverter andamplifiersections.

RF

RF

RL

2

Filter

3

= 4

_-0

1N4933

COOT 7

1OUT

1IN-

1IN.

VCC-

VOUT

VREF

osc

VIN

VCC+

2OUT

2114-

2114.

CAP

GNI)

CAP.

FB/SD

To ADC

16

5V

15 FtF

4 RIN Signal

3

2

11

10 "="

j_CIN

The power convener generally operates most efficientlyat the internal oscillator frequency of 25kHz. However,this frequency may be raised, lowered or locked to anexternal clock with the appropriate placement of anadditional external capacitor. The converter may also bestrobed for interleaving with data acquisition operations. Itcan also be temporarily shut down. Converter supplycurrent reduces to about 80pA under shutdown conditions.

Design considerationsAlthough the circuit blocks of the TLE2662 allow greatversatility in system design, the high switching currentspresent in the converter section require careful handling.Many applications will be able to use a direct connectionbetween the power converter and amplifier section: thisbasic arrangement can lead to 25kHz switching rippleappearing on the op -amp outputs amounting to a few tensof millivolts. A simple LC filter comprising a 50pEsurface mount inductor feeding a 220p.F capacitor in eachamplifier supply leg will reduce output ripple by a coupleof orders of magnitude.

Alternatively, the strobe facility on the power convertersection may be used to stop the oscillator during sensitivedata acquisition operations.

Attention should be given to decoupling adequately themain power supply to the converter at pin 8, Vin,particularly where long circuit tracks are involved. Alsobear in mind that the converter ground return, pin 11,carries switching currents which could upset signal circuitsif taken to a signal grounding point.

Typical applicationIn its most basic configuration, the switched capacitorsection of the TLE2662 provides the negative rail for theamplifiers in a single supply system. As shown in Fig. 1,the 5V positive supply is connected to Vc, (pin 16) and Vin(pin 8). The negative output voltage, Vout, from the chargepump (pin 5) connects to the amplifier negative supplypoint, Vcc- (pin 4). Only three external components arenecessary not counting the components associated with thesignal handling functions of the amplifiers: storagecapacitors Ciro C0.1 and a small Schottky diode to preventVou, rising above ground during startup. Once the negativerail is established, it provides no further function. Asshown one amplifier is connected an inverter driving aresistive load while the other forms part of an ADC systemusing the TLE2662 internal reference.

The second circuit, Fig. 2, shows the converter section

FromTransducer

Shutdown

rar'

set up to provide a regulated negative outputvoltage rather than the simple of dual of the supplyinput voltage. Its value is determined by the ratioof R1 to R2 and, assuming a Vref of 2.5V, is givenby:

R, = R,

VoVREF 40mV +I

2

RI should be 201a2 or greater since the referencecurrent is limited to ±100p.A. R2 should be in therange 100k52 to 300ka Frequency compensationis accomplished by adjusting the ratio of Cin to

READERSERVICESOFFERTo obtain your freesample of theTexas InstrumentsTLE2662 chargepump dual op -amp, fill in andsend off the specialreply card locatedbetween pages936 and 937 ofthis issue. Thisreader servicesoffer is beinghandled directly byTexas Instruments.Our editorial officeis unable to assistin any queriesrelating to it.

COOT100 uF Tantalum

161 OUT vc c

21 IN - 2 OUT

15i(

3 141 IN. 2 IN -

your - VCC- 2 IN13

R112

VOUT CAP-

R2 6CIN

VREF GNI)1+

10 uFTantalum

10OSC CAP

6VIN

9VIN F B/SD R3

2.2 uF

1411_

Shutdown

Cow, a normal ratio of about 10:1. Capacitor C1, requiredfor good load regulation, should be 2nF for all outputvoltages.

TLE2682This is a higher speed derivative of the 2662 offering atypical slew rate of 40V/µs and a gain bandwidth productof 10MHz. For instance, settling time to 0.1% on a 10Vstep (1k11//100pF load) is about 400ns. In other respects ithas similar characteristics to the TLE2662.

R4

Restart

Fig. 2. The basicregulator function.Vout, referenced toground (pin 11) mustbe less than the totalof the supply voltageless the voltage dropacross the internalcharge pumpswitches.


H -P Oscilloscope

HAWLETI: 54800A loo VIM& PACKARD OSCILLOSOMI 2 CNANNGL

HIS Hewlett-Packard oscilloscope combines the feeland display of a top line analogue instrument with the

precision and programmability of digital electronics.This DSO is easy to use because it was designed byelectronics engineers for electronics engineers.

Electronics World is looking for freelance authors who

can bring applied electronics design alive for other electronics

professionals through their writing. We want to commissionarticles on circuit design using the wealth of moderncomponents now available to electronics engineers. Possible

areas of interest could be RF, microwave, audio, video,consumer electronics, data acquisition, signal processing and

computer peripherals.All articles accepted for publication will be paid for - in

the region of several hundred pounds for a typical designfeature.

The author- of the best script received over the periodJune I, 1993 to May 30, 1994 will receive an HP54600Aoscilloscope in addition to the normal author's fee.

The judging panel will be drawn from ElectronicsWorld and Hewlett-Packard.

TRIGGER

Aul:) Molar

VERTICALVolts/Om Von/DA

A Hewlett-PackardHP54600A

100MHz digitalstorage scope, could

be yours when 0 Uwrite fo Electronics

d + Wireless4

the journal thatdesign engineers pay

to read.

For further details about our quest fof

the best call or write to:

Frank Ogden, Editor, ELECTRONICS WORLD

Quadrant House, The Quadrant, Sutton

SM2 5AS. Tel 081-652 3128

DESIGN

WORKINGwith programmable logicProgrammable logicdevices are essential tocompact logic designand have been so for along time. They savecomponent count andboard area and provideadaptability of circuitfunction. Despite thisutility their operation isnot always wellunderstood. In the firstpart of a new series,logic designer GeoffBostock explains theworkings ofprogrammable logic.

programmable Logic has come of age.It is at least 21 years since the firstproms (programmable read onlymemories) came to the market.

It may seem perverse to start a series on pro-grammable logic by mentioning memorydevices, but one of the most common uses ofproms is as logic devices. After all, everycombination of input signals to a prom willresult in a well defined set of output signals -exactly how a combinatorial logic devicemight be defined. Conversely, even a 2 -inputnand gate could be described in 'memorynotation' as:

ADDRESS DATA0 1

1 1

2 1

3 0

One prom manufacturer, MonolithicMemories Inc. (now a subsidiary of AMD),even went as far as calling proms PLEs (pro-grammable logic elements) when used in logicapplications. If proms can be used as logicdevices, why is there a need for pals, GALs,FPLAs and all the other PLDs (programmablelogic devices) which have mushroomed ontothe market? Indeed, why not just use TTL orcmos logic? By the end of the series I willhope to have answered these questions.

Proms as logic devicesExamination of the prom structure, Fig. 1a,shows how they can operate as logic devices.The 5-input/8-output prom is a real devicemarketed by AMD as a 27S/9, National as a745288, Philips as 825123 and Texas as an185030, etc. The five input signals are fullydecoded into 32 internal lines. Each line driveseight transistor bases; their emitters are con-nected via fuses to the input side of one of theeight output buffers.

Viewed as a memory, the five inputs definean input address; this sends one of the internallines high. Any of the outputs connected viaan intact fuse will be pulled high also; theinverting output buffer making a low appearon the corresponding output pin. Conversely,a blown fuse will let the output line stay low,sending the output high. Thus the pattern ofblown fuses determines the output data corre-sponding to any particular input address.

The alternative way of describing the promis to call the input decoder a fully decodedAND -array, and the output section a pro-grammable OR -array. Line 0 in Fig. 1 a isthus:

!A4 & !A3 & !A2 & !Al & !AOwhere ! represents an inversion and & the andfunction. The lines driving the output buffersare wire-ORed, where the fuses are intact, soan output function formed by leaving the fuses


DESIGN

31

300

29

0- 5 LINE TO32 LINE

DECODER00- - -- FIXED AND

ARRAY1 OR ARRAY0-0

bbbbFig. la. Prom architecture

--0

OR -ARRAY

0

Fig. lb. FPLA architecture

on lines 3 and 17 intact, but blowing out allthe others could be written:

00 =!00 = !A4 & !A3 & !A2 & Al & AO# A4 & !A3 & !A2 & !Al & AO

where # represents the OR function. Note that00 is inverted, because the output buffer isinverting.

We could equally well represent this logicfunction by a Karnaugh Map. Every cell in afive -bit Karnaugh Map corresponds exactly toone of the internal decoder lines so, if a logicfunction fits one it can be implemented in aprom. The Karnaugh Map for the above func-tion is shown in Fig. 2. Note that we are onlytalking about combinatorial functions here.

It does not matter if the logic is defined asactive -low, as here, or active -high. In the lattercase the cells would be defined by 'H'sinstead of 'L's.

Proms are usually defined by a truth table,rather than equations or a Karnaugh Map. Thetruth table for the above equations would be:

0 1 2 3 4

0000 - 01 01 01 00 01 ....0010 - 01 00 01 01 01 ....

and so on, where addresses and data are inhexadecimal.

In practice, several software packages forPLD design include an assembler for proms.This allows logic to be defined as Booleanequations, and assembled into a format suit-dble for prom programmers. We will look atPLD assemblers and programmers in moredetail later on.

One of the earliest applications for promlogic was in address decoding. Fig. 3a showsthe memory map of a fairly simple, hypothet-ical microprocessor system, including somememory -mapped i/o, one port being read only,the other read/write. The enable signals for thevarious peripherals can be derived from theupper four address lines and the read/!writeoutput from the processor.

This logic may be converted directly to thetruth table in Fig. 3b, more or less by inspec-tion. For example, A15, Al4 and Al3 all lowwill address any location in the lowest 8K ofthe map. The only complication is the ramspace, which needs to be split into three seg-ments for addressing purposes.

To convert this truth table into a hex-asciitable, which is the format needed for loadinginto a prom programmer, we must first allo-cate pins to signals. Let us assume that R/!W

A question of notationMany designers prefer to describe logic circuits by a circuitdiagram, although most PLD assemblers require Boolean logicequations as their data source. Computer aided design systemswith schematic capture usually have interfaces to the popular PLDassemblers, so direct conversion of circuit diagrams to logicequations is possible. If this is not available, the conversion mustbe done by hand. Figures 7a and 7b illustrate this process for asimple circuit.

The first step is to eliminate double inversions, then the circuitcan be redrawn without the constraints of standard logic familypackages. The internal signals can be labelled with their logicequations, starting from the inputs. By carrying this process

through to the outputs, the logic equations for the outputs can bededuced.

Internal signals which become too complicated can be redefinedas a single symbol. Most PLD assemblers allow substitution ofstrings or internal signals by logic equations defined in terms ofinput signals. They will then perform Boolean algebra on theresulting complex logic equation. The most likely snag is that thechosen target device will not have sufficient capacity for theresulting equations. The way round this, assuming that theassembler has performed some minimisation, is to redefine theactive levels of the outputs with most and terms, if the deviceallows this, or try a different device with higher and term capacity.


DESIGN

AND -ARRAY

Fig. 1c. pal architecture

is the most significant address line and Al2the least significant; also assume that the out-puts are assigned in order from proml as 00to I/02 -WRITE as 07. The output data for 00low and all other outputs high is 'FE', for 01only low it is 'F'D' and so on.

Prom) is selected when A15, Al4 and Al3are low irrespective of R/!W and Al2, whichcorresponds to addresses 0000, 0001, 0010and 0011; similar reasoning will determine theactive addresses for the other outputs andallows us to construct the prom table of Fig.3c.

This is a fairly elegant one -chip solution fora circuit which would otherwise take five gatepackages, or a 3 to 8 decoder and two gatepackages.

However, prom logic does suffer fromdrawbacks. Firstly, each additional inputrequires the number of memory cells to bedoubled. Further, the number of inputs andoutputs in a particular prom is fixed with, usu-ally, either four or eight outputs. As memorysize increases, so do cost, power consumptionand delay time. Thus, while proms may besuitable for simple logic circuits, they soon runout of steam in more complex situations.

The FPLA solutionThe major prom drawback of doubling in sizefor each extra input comes about because theinputs are fully decoded. This is clearly awaste of resources in our example abovebecause six of the outputs only need a singlecombination of inputs decoded while the othertwo need just three.

In an FPLA (field programmable logicarray) the input decoder is programmable aswell as the output or -array. This architecture isshown in Fig. 1 b. Thus, in the PLSI00, thefirst commercial FPLA, only 48 input combi-

FIXED OR-ARRAY

24K

16K

3K

I/O - 2I/O - 1

32K RAM

8K PROM

8K PROM

0 0 0 0 1 1 1 1 A4

0 0 1 1 1 1 0 0 A3

0 1 1 0 0 1 1 0 A2

0 0

0 1 L

1 L

0

Al AO

8K PROM

Fig. 3a. Memory mapfor simplemicroprocessor system

Fg. 2. Kamaugh Map for promlogic function

R/ch? A15 A14 A13 Al2 I/0-2 READ ACTIVE 0/P

H H H H H I/0-2 READ 07 (7F)

L H H H H I/0-2 READ 06 (BF)

XHHHLI/0.1 05 (DF)

X H H L X

03 (F7)X HL X X ,RAM -CE

X L H H X

L H H L X

04 (EF)L H L X X RAM -WE

L L H H X

X L H L X PROM 3 02 (FB)

X LL H X PROM 2 01 (FD)

X LL L X PROM 1 00(FE)

Fig. 3b. Address decoder truthtable for simple microprocessorsystem

0 1 2 3 4 5 6 7 8 9 A B C D E F

000_ FE FE FD FD FB FB EF EF EF EF EF EF EF EF DF BF

001 FE FE FD FD FB FB F7 F7 F7 F7 F7 F7 F7 F7 DF 7F

Fig. 3c. prom programming table for address decoder

nations are decoded from the 16 inputs com-pared with the 65536 decoded lines in a theo-retical 256k prom, with 16 inputs.

On examining the structure of the and -array,we find that each and -gate (usually called anand term or product term) has two connectionsto each input line, one to the 'true' signal andone to its complement. By leaving the appro-priate fuse intact, any signal or its complementcan be present in any product term.

In our memory map example, leaving thethree complement fuses of A15, Al4 and Al3intact - and blowing all the other fuses - willprovide the decode signal for proml.

To connect the decode signal to an output,the appropriate fuse in the or -array betweenthis product term and the 'proml' output mustbe left intact and the fuses to the other output

lines blown. Left like this, the output will behigh whenever these three address lines arelow, and low at all other times; this is just theinverse of what we programmed into theprom.

There are two ways out of this problem. Oneis to use Boolean Algebra and rewrite thelogic as:px n1 = A15 # A14 # A13The other way is to make use of the pro-

grammable inverter which is usually found inFPLAs and many other PLDs. It is an exclu-sive -or gate, shown in Figure 4, with one inputfrom the or -array and the other to a pull-upwhich is grounded via a fuse. With the fuseblown the logic is inverted, if unblown it is notaffected.

The format for entering this data into a pro -


DESIGN

Fig. 4. Programmablepolarity circuit

grammer, in order to blow the desired fuses isa dedicated truth table, although it is moreusual to use a logic compiler with logic equa-tions these days. Nevertheless, an FPLA truthtable is a useful way of representing a logicfunction, and may still be used to by-passlogic compilation.

Fig. 5 shows the FPLA truth table for ourmemory map decoder. It has two halves; thereis a section for defining the product terms, anda section for connecting the or -array and set-ting output polarity.

An 'IT in a signal column connects the'true' fuse to that term, an the comple-ment. A 'don't care', that is no connection atall, is shown by the symbol. Putting '0'would cause both fuses to be left intact, so theand gate would see both polarities at once; itwould, therefore, always be low which is aninactive state. The combination of Hs and Lsis the logic condition which will cause theproduct term to be active; that is to go high.

In the or -array, each column represents anoutput. The box at the head of each columndefines the action of the programmable invert-

er. An 'H' means no inversion (active -high)and an 'L' causes inversion (active -low). Toattach a product term to an output via the or -array, an 'A' is placed in the box where theproduct term row and output column intersect.A in this box means that the fuse at that or -array intersection is to be blown.

The memory map example shows that thesame logic which used 32 product terms in afully decoded prom, needs only twelve termsin an FPLA. The PLS100, though, has sixteeninputs, eight outputs and 48 product terms, soits resources are very under -used. Even ifthere were other logic functions to be includ-ed, all the outputs are used up so the rest ofthe FPLA is redundant in this application. ThisFPLA shares one of the drawbacks of proms,namely, a fixed number of outputs leading toan inflexible allocation of logic resources.

The next generation of FPLA, the PLSI53and PLSI73, overcame this by using the bi-directional i/o structure of Fig. 6. Each FPLAhas ten i/o pins and, respectively, eight andtwelve inputs, with 32 product terms. If aPLSI73 were used for the memory mapdecoder, there would be seven inputs, two i/opins and 20 product terms available for anoth-er logic function. However, the same FPLAcould be used in an application requiring 20inputs and just two outputs, for example.

An additional set of product terms must beprogrammed to define the direction of dataflow through each i/o pin. An unprogrammedPLSI53/173 has low levels on all the and gateoutputs. The three state buffer on each i/o hasan active -high control so, before program-ming, all the buffers are disabled and each i/opin acts an input. If all the fuses in a productterm are blown the and -gate will be uncondi-tionally high; in this case the buffer is alwaysenabled. If a logic function is programmedinto the product term, the buffer will beenabled when the logic function is true.

INPUTS OUTPUTS

14 13 12 f li 13 07 05 05 04 03 02 01 05

ACTIVE LEVEL L L L L L LL L

H H H H H A -.

H..A . ...-HHH L ..A .... .

- H H L - .A ...- H L - - . ,. A

-LHH- . , A.LHH L- ..A . ..L H L - - . , . A . . , ,

L L H H- . . A .

- L H L- , , . A .

- LLH-. . , ..A .

- L L L -Fig. 5. FPLA programmingtable for address decoder

PROM, PAL or FPLA?There are three architectures commonlyused for implementing combinatorial logicfunctions in programmable format: prom,FPLA and pal. Although proms aredesigned to be used in memory applica-tions such as program storage and look -uptables, they are equally suited to use aslogic devices. Every possible input com-bination can be programmed to give a spe-cific output. Any logic function which canbe written as a truth table can also, in prin-ciple, be programmed into a prom; theonly restriction is the number of inputsand outputs which the prom supports.

An alternative approach is draw theKamaugh Map for the logic function.Every cell in the Kamaugh Map can beprogrammed individually into a prom,because the inputs are fully decoded. Allthe decoded lines are or-ed together in theor -array, via fuses, which transmit a highto the output when the line is addressed,but leave it low if the fuse is blown.

Adding an input to a prom doubles thenumber of fuses needed in the or- array. Inan FPLA the input decoder is also pro-grammable, so only 'active' input combi-nations need to be programmed. Thus,while a ten -input prom has the equivalentof 1024 and -gates in its input decoder,FPLAs typically have only 32 or 48 pro-grammable and -gates.

If a logic function has a truth table withmore than 48 lines, there might be prob-lems fitting it into an FPLA. The only wayround this problem is by logic minimisa-tion. For simple functions it may be pos-sible to draw Kamaugh Maps for eachoutput and reduce the number of logicterms by combining map cells. For morecomplex functions it may be necessary touse a minimisation program on the logicequations for the function.

FPLAs possess the property of beingable to allocate any and -term to any one ormore outputs. However, many circuits,particularly address decoders, need eachand -term for only one output. Thus theprogrammable or -array can be replaced byfixed or -gates without adversely affectingthe utility of the device. This is the prin-ciple of pals.

Apart from simplicity, there is a gain inperformance from this approach. The or -array consumes power and adds capaci-tance to the decoded and -term lines; palsnormally run cooler and faster thanFPLAs.

The chief drawback is the limitation inand -terms per output. There are, at most,only seven or eight and -terms or-edtogether for each output, in simple com-binatorial pals, so functions needing morethan this would require an FPLA.

,H18 ELECTRONICS WORLD + WIRELESS WORLD November 1993

DESIGN

It should be noted that, even when the out-put is enabled, the i/o pin is still connected tothe and -array. Any output function can, there-fore, be fed back and combined with input sig-nals. The FPLA can implement multi -levellogic in this way, or make latches and flip-flops as we shall see further on.

The code for entering control logic in truthtable format is just the same as in the mainlogic array, with the addition of the symbol '0'to denote both fuses left intact. Thus, a controlterm for a dedicated input will usually consistof a row of Os.

PALs -a simpler wayWhile FPLAs offer a more flexible solutionthan proms for programmable logic, re-exam-ination of Fig. 5 shows that they can be unnec-essarily complicated. Although each productterm is available in the or -array to be gatedinto any output, in this application every prod-uct is used in only one output. In other wordsthe programmability of the or -array is wasted.Each output could just as well use a fixed or -gate with the product terms shared betweenthe outputs.

This is just the structure of a pal; pal standsfor programmable array logic, and is illustrat-ed in Fig. lc. PALs were introduced byMonolithic Memories Inc. in the mid 1970s.The first pals occupied a 20 -pin package andcontained just sixteen product terms. Thesewere shared among the outputs so that a twooutput pal had eight terms per output, a fouroutput device just four terms, and so on. Asimilar 24 -pin family was also made available.

Pals have a very logical numbering system.For example, a PALI4H4 has fourteen inputsand four active -high outputs, while a

PAL16L6 has sixteen inputs and six active -low outputs.

Apart from being simpler to understand andto use, pals have performance advantages overFPLAs. A fuse array is a high capacitancestructure which introduces propagation delayinto the logic path. Removing the or -array infavour of a fixed or -gate saved 5ns in the firstpal family, compared with the equivalentFPLA. Also, cutting down the number ofproduct terms made a significant reduction inpower consumption.

The first pal families suffered from therestrictions of fixed input and output numbers,and fixed output polarity. While adequate forsimple circuits, even our simple memory maplogic would not fit the pal with the appropriatei/o count, the PALIOL8. This is because twoof the outputs need three product terms, butthe PALIOL8 has only two terms per output.

Introduction of more complex pals, such asthe PALI6L8, overcame these drawbacks.This pal has eight product terms per output,but one of these controls the three -state outputin the same way that bi-directional outputs arecontrolled in FPLAs. Six of the eight outputsare bi-directional, so i/o flexibility is availableas well as increased logic power. There arestill only ten direct inputs, but the fed backinputs make a total of sixteen into the wholearray.

CONTROLTERM

Fig. 6. Bidirectional i/o circuit

PAL16H8 and PALI6P8 (programmablepolarity) were also made but better solutionscan be found now, as we shall see in a laterarticle, so only the PAL 16L8 remains in cur-rent production.

Our address decoder will fit into a such adevice, but truth table entry is not a preferredmethod of designing pals. Once personal com-puting became commonplace, MMI intro-duced a pal assembler called palasm. Thedesigner uses logic equations to define the cir-cuit and palasm assembles this into a file tothe jedec specification. The jedec file can beloaded into a pal programmer. which blowsthe correct fuses in the pal to reproduce thelogic in hardware.

Given that the tools exist we just have todefine our circuit as logic equations. We canillustrate this by writing the logic equations forthe memory map example. Each line of thetruth table is a single and -term; where an out-put contains more than one line of truth table,the various and -terms are or-ed together.

!07 = !RNW & A15 & A14 & A13 & Al2!06 = RNW & A15 & A14 & A13 & Al205 = A15 & A14 & A13 & !Al2!04 = !TINY/ & A15 & A14 & !A13

# !RNW & A15 & !A14# !RNW & !A15 & A14 & A13

!03 = A15 & A14 & !A13# A15 & !A14It !A15 & A14 & A13

!02 = !A15 & A14 & !A13!O1 = !A15 & !A14- & A13!00 = !A15 & !A14 & !A13

Note that the above equations would notassemble in palasm because that uses a dif-ferent syntax: * for and, + for or and / forinvert. These symbols are used for arithmeticfunctions in some other assemblers which arenow available.

For completeness we should mention theother combinatorial pals which are still avail-able. The PAL20L8 is a 24 -pin version of thePALI6L8 it has fourteen dedicated inputs butis identical in every other way. Another 24 -pindevice is the PAL2OLIO; this has only fourproduct terms per output, one for control andthree for logic. It has twelve direct inputs, twodirect outputs and eight bi-directional terms.

While these devices are still being made, itis likely that most will be phased out in favour

of the cmos generic pals, which we will exam-ine in the third article. The exception may bethe 5ns and 7ns pals, which are still easier tomake in bipolar than cmos technology.

Design entry methodsThe standard way of defining logic for anycombinatorial PLD is in terms of Booleanequations. Many assemblers are now avail-able. Some are dedicated to a particular PLDmanufacturer such as AMD (palasm),National (Opal) and Philips (snap), while oth-ers are marketed for universal use. Examplesof universal software suppliers are Data I/O(abel), Isdata (LOG/iC), Logical Devices(cupl) and OrCAD (OrCAD-PLD). Manywork stations also feature PLD assemblers.

Most software now includes features such aslogic expansion, minimisation and simulation.The former allows many functions to be writ-ten as compact equations, with brackets andmulti -level logic definition, while the lattergives the designer confidence that the finishedproduct will do the job for which it is intend-ed. Simulation will usually result in the pro-duction of test vectors. These instruct the pro-grammer how to functionally test the PLDafter programming. Occasionally, a devicewill be programmed correctly but will notfunction because of some small fault in thedevice, which cannot be tested before pro-gramming.

However comprehensive the software, thecorrect logic data must be entered in order toguarantee a working PLD. We have seen howa truth table can be converted into logic equa-tions but, very often, the logic is not readilydefined as a truth table.

The first step in any design is partioning...deciding which input and output signals are tobe included in the logic block. If the totalnumber of signals is no more than twenty two,and there are ten or less outputs, it is likelythat the logic will fit into one of the devicesdescribed so far if we allow only combinato-rial logic.

The relationship between the input and out-put signals must eventually be defined bylogic equations but some designers may not becomfortable taking that step directly. Theother common way of visualising logic is witha logic diagram, or schematic. A logic


DESIGN

3 to 8

decoder

schematic is, perhaps, the traditional way ofdefining a logic system as the components areclearly laid down with their interconnectionsdrawn in. Often, the components are func-

> 00, tional blocks from a standard logic familywith a scattering of single gates and inverters.

1, 0

17 0

I, 0

0 02 A simple example is shown in Fig. 7a.Schematic capture software will convert

-D° 0 03logic schematics directly to logic equations ina format suitable for most of the standard logicassemblers. If schematic capture software is

-77/6 0 06 not available, the designer is then faced with

Fig. 7a. Typical logic circuit drawn for TTL or cmos implementation

I 0

3 to 8DECODER

Y3 V,

V2 Y2 Y2

I s 0

1,

LEN

DualD latch

17 0

LEN

Ir

D LATCH

the task of converting the data manually. Thisis not as traumatic as it may appear. Fig. 7bshows the first stage, which is to label a sim-

02 plified logic schematic with internal signalnames.

The second stage of the conversion is todefine the internal signals in terms of input

O oe signals and 'earlier' internal signals, thus:YO = !I1. & !12 & !13Y1 = !I1 & !I2 & 13Y2 = !I1 & 12 & !13Y3 = !I1 & 12 & 13LEN = !14 & !15 & YO

If the PLD assembler can handle internalsignals which are neither inputs nor outputs,

0 07 LEN can be left unexpanded; otherwise itmust be expanded to:LEN = !I4 & !I5 & !Il & !12 & !13

0 0. The output signals may now be written interms of input and internal signals. 01 to 06should cause no problems, unless 02 and 04need further expansion by hand,!02 = 15 # !Y2 becomes:!02 = 15 # I1 # !I2 # I3 and !04 =

15 # !YO becomes:!04 = 15 # I1 # 12 # 13 by the usual

01 de Morgan conversions.07 and 08 are outputs from a dual D -latch,

which is not a combinatorial circuit, but can0 o2 be built from combinatorial components. Fig.

8 shows the schematic of a D -latch built fromnand gates, and the corresponding Karnaugh

o3 Map. The logic equation for the D -latch is:Q =D & LE # Q & !LE # D & Q

0The third term (D & Q) looks superfluous0

but links the other two terms on the KarnaughMap. Without it there would be a danger ofglitches when the latch changed state; as ageneral rule, overlapping terms in a Karnaugh

OsMap will prevent glitches. The only problemis that the design is now untestable without

o adding a control signal to allow the gates to be0tested individually.

We can complete the derivation of the logicequations by substituting 16 and 17 for D, 07and 08 for Q, LEN for LE; thus 07 becomes:

Lui- - D -LATCH

0 07

Fig. 7b. Typical logic circuit after compaction for Boolean logic equations

0

Fig. 7c. Logic equations derived from Fig. 7b

!01=Y3#I4!02=!Y2#15!03=Yl#I4!04=!YO#I5!05=14&I5!06=14&!1507=I6&LEN#070LEN#I6&0708=I7&LEN#080LEN#I7&08


DESIGN

Fig. 8a. Circuit diagram ofD -latch (with deglitchterm)

LE

07 = 16 & LEN # 07 & !LEN # 16 & 07

If expansion is necessary, the followingresults:

07 = 16 & !I1 & !12 & !13 & !14 &

!i5# 07 & Il # 07 & 12 # 07 & 13# 07 & 14 # 07 & 15 # 07 & 16

In most cases, expansion will not be neces-sary and the complete set of equations can beleft as in Fig. 7c.

Design methods for sequential circuits areusually quite different from those illustratedabove, and device architectures are more com-plex. These topics will be covered in nextmonth's article.

ProgrammingThe only issue left unresolved is program -

Fig. 8b. Karnaugh map ofD -latch

ming. Programmers come in all shapes andsizes, from large universal stand-alonemachines to small dedicated units which arePC driven. Because the design will probablyhave been done on a PC, the data has to betransferred to the programmer. A standard for-mat has been agreed between device manu-facturers, design software houses and pro-grammer makers.

This jedec standard numbers each fuse inthe device and the design software will pro-duce a file with a string of is and Os indicatingwhich fuses are to be blown and which leftintact. This file is downloaded into the pro-grammer which addresses the device to beprogrammed with the correct fuse locations,according to the data in the file.

Test vectors can be appended to the pro-

gramming data and most programmers canuse this to functionally test the finished device.A small proportion of devices will not workcorrectly even when the correct fuses havebeen blown. This is because the device cannotbe fully tested by the manufacturer before anyfuses have been blown. Unless the device ismade in an erasable technology, which manyare now, the fuses cannot be blown beforeleaving the factory.

For similar reasons, a small proportion ofdevices will not program correctly either.Although programming failures can be due tomanufacturing defects, they can also becaused by the programmer being out of cali-bration or by poor socket contact. For this rea-son., users performing their own programmingshould ensure that their programmer is keptwell maintained. A fall in programming yieldcan indicate a need for corrective action.

Many users of programmable logic buy theirPLDs ready programmed, or use a specialistsub -contractor. This has the advantage ofremoving yield problems, and the need forinvesting in equipment which has to beupgraded as new devices come onto the mar-ket. Once the design is proved, buying PLDsthen becomes as transparent as buying stan-dard logic and easier than masked semi -cus-tom, because PLDs are mass-produced stan-dard devices, unlike masked ASICs.

EXCLUSIVE SOFTWARE OFFER FOR ELECTRONICS WORLD READERS

40% off PCB and sdiessatic deur peuigageQuickroute 2.0 for Windows 3/3.1 Professional Edition for only £59 (normally £99)

Quickroute 2.0 Professional Edition is a high quality easyto use PCB and schematic design system. It includessimple schematic capture, auto -router tools, Gerberimport and export, and NC -Drill export features.A comprehensive set of editing tools, built-in hyper -texthelp, and support for more than 150 printers and plottersmake this one of the most attractive packages available.As a special offer to our readers we are selling thissoftware for only £59 compared to its normal pr ce of£99. Add £5 for postage and packing if ordering fromoutside the UK. But be quick, the offer ends on 14thDecember.

To makes sure you get your copy of this software, fill inthe form right and rush it to POWERware SoftwareDesign, 14 Ley Lane, Marple Bridge, Stockport, SK65DD, UK:

-... there is no doubt that running under

Windows puts it ahead of the field and makes

it a visually exciting package", Martin

Cummings, EW + WW, July 1993

Name

Address

Post Code

Please debit my credit card for £59 (UK)/ £64 (overseas)*

Card type: Visa/Mastercard*

Number 0000 0000 000J JUDD

Expiry date SignatureOR I enclose a cheque payable to POWERware for £Cheque number* Delete as appropriate

Please note that this offer is being handled directly byPOWERware. Please address all correspondenceandqueries direct to the company. POWERware's telephonenumber is 061-449 7101.

November 1993 ELECTRONICS WORLD + WIRELESS WORLD

PCENGINEERING

Fig. 1. WindowsDSPworks featuresare accessed viadrop -down menus.Background windowis that of a squarewave with addedGaussian (normally)distributed noise(which hascontrollable meanand variance).

WINDOWSsupport for DSP design

DSPworks and QEDesign 1000 are available as a single packagefor digital filter design. But, apart from running under Windows,

what else distinguishes them, asks Allen Brown?

The number of digital signal processing (DSP) softwarepackages running under Windows is still small. ButMomentum Data Systems of Costa Mesa, California

has added to that total with the release of two Windows pack-ages for DSP design and analysis. QEDesign 1000, aimed atdesigning digital filters, and DSPworks, for signal analysis.

DSPworks is a general purpose digital signal processingsoftware package that allows many of the well known signalprocessing tasks to be carried out on data derived from anexpansion card or previously stored in a disc file. Its easy -to -use graphics allow data to be displayed in a variety of formats.

One immediate piece of good news is that DSPworks doesnot need a dongle: the bad news is that QEDesign 1000 does.That said, once it is connected to the ever growing donglestring protruding from the back of your PC, you should be upand running in no time. (QEDesign 1000 will actually work

GeneratorSinusoidal...

Operation

Square...Triangular...Swept Sine...gait Sample...Unit Step...Window Functions...Sinc Function...Ramp Function...Ea' Function...Noise Functions...

0.00011

-1.00011

-2.0000

-3.0000

-4.0000

-5.0000

I

1024 pts t 8000 Hz; REAL32 Binary

18.719 1 438 56.156 74.87'.

without the dongle but it will not output the filter coefficientsto disc).

In DSPworks, every waveform or function generated getsits own window, with the individual waveforms selectedfrom a drop -down menu.

Reflecting the importance of DSP window functions, alarge selection are available with DSPworks - including theKaiser Bessel window, indispensable for designing finiteimpulse response filters (FIR) using the window technique.

Another broad choice is that of formats for the waveformgenerated, spanning 32 -bit floating numbers, binary or asciicharacters. Considerable control can be exerted over the dataformats by using the utilities menu to, for example, round,truncate and convert formats. Conversion is useful when dataare to be used with other applications packages.

Waveforms that have been generated or imported can thenbe manipulated, with options including a smooth or movingaverage. QUANTISE FIXED POINT enables data to be quantised.This is useful when simulating the behaviour of digital filtersimplemented on fixed point processors (eg MotorolaDSP56000), which can differ significantly from floatingpoint simulations.

File names are allocated to the generated waveforms, andstored on disc as they are created. Whether this is a confi-dence measure or a method of reducing the amount of ramrequired, it is certainly a convenient safeguard.

Time domain signal processing operations include all thestandard functions, with an oscilloscope option available tousers with an appropriate expansion card resident in the PC.SIGNAL FILTERING is only useful if data from QEDesign 1000is present.

In this case, QEDesign 1000 would have been used for thedesign of the digital filter, followed by code assembly thenanalysis of performance either using disc data or real-timedata from an expansion card.

Of the frequency options, as with the time options, somecan be performed with disc data while others are only offeredwhen real-time data is available from a DSP card. In effect,


PC ENGINEERING

QEDesign allows a PC and DSP card to act as a real-timespectrum analyser with 2-d spectral displays and 3-d water-fall displays.

DSP expansion cardsTo get the most out of DSPworks, a DSP card is must - mostengineers working in the field of DSP will probably have atleast one DSP card at their disposal anyway.

Card manufacturers represented include Ariel, Lough-borough Sound Images, Sonitech, DSP Research and DataTranslation, a list that shows ample support for cards hostingTexas Instruments and Motorola chips. But for cards hostingAnalog Devices ADSP-2100 series chips, support is lacking,a deficiency that should be rectified since Analog Devices iscapturing a sizeable part of the telecomms DSP market.

If the card has analogue I/O facilities, DSPworks also pro-vides options relating to sample rate and channel selection.For example the Ariel DSP32C card has sampling ratesadjustable from 2kHz to 100kHz.

A DSP card can be used in a number of ways. For exam-ple, where signal behaviour in given frequency regions is ofinterest, a digital filter could be placed between the incomingdata and the display on the screen. Orthe expansion card could act purely asa digital filter, digital data derivedfrom its A -to -D converter being pro-cessed and the output digital datastream being passed to its D -to -A togenerate a filtered analogue output.

QEDesign 1000QEDesign 1000 is a specialisedWindows software package, solely fordesigning digital filters. The user isasked, through dialogue boxes, tospecify filter parameters, and tilt'appropriate filter coefficients are pro-duced. Various filter characteristics (egtransfer function and impulseresponse) are plotted in individual win-dows, giving instant visual access tofilter performance.

In practice, digital signal processorsare frequently used to perform filteringtasks and part of the course of design-ing a digital filter is to determine theappropriate coefficients.

One interesting feature of QEDesign 1000 is the use ofdouble precision (64 -bit floating point) in design calculations.In design of very large filters, with many tens of taps, thenumerical rounding effects can be significant. For examplethe Equi-ripple design method uses the Remetz exchangealgorithm which is recursive and very sensitive to numericalprecision. But it means that a maths coprocessor is indis-pensable (maths coprocessors for 33MHz 386 -PCs can befound for under £60 and every engineering PC should haveone anyway).

Choosing coefficients for a digital filter is somewhat sim-ilar to choosing the Rs and Cs in an analogue filter.QEDesign 1000 presents seven plotting areas on the screen,and when a filter has been designed the results are displayedin the seven regions using the tile option from the windowcommand.

File Wldaw fienerator

f -F

OperationSignal statisticsArithmeticReciprocal...Square...Square root...trigonometricExponential...Flip...Shift_Join...Extract..Smooth_Sample and had...Difference...Quantize fixed point...

frequency Utilities

1024 pts 1111 8300 Hz; REAL32 Binary5.0000

3.0000

1.0000

1.0000

3.0000

5.00000.000 20.070 56.156

chan_ Lunn

1024 pts 80101Hz; REAL32 Bina5.0000 --

3.0000

1.0000

-1.0000

-3.0000

-5.000053.00 81.08

004"wsi4,1"10

109.16

Window Eenecator Operation

chan_1.tim

3inr Wave

1024 pts @ MI Hz; REAL32 Bin5.0000

3.0000

7.0000

1.0000

0.0000

-1.0000

-2.0000

-3.0000

-5.00000.000 28.078 56.156

DSPworksTime

Signet Filtering...Frequency

Autocrirrelation...Cross correlation...

Decination...Inter' olation...fast Fourier Transtonr,...

Waveform Display... CtrItQscil oscope... Oil+

Ill -AI 37 Hill Ir.

0.1000

0.0000

-0.1000

-0.2000

-0.3000

-0.4000

-0.50000.000 28.08 56.156

ling In'Sl

IIR filter designQEDesign 1000's infinite impulse response (IIR) filterdesign is based on the impulse invariant technique, usingmodels of analogue equivalent filters. The models areButterworth, Tschebychev, Elliptical and Bessel, all familiarto analogue filter designers.

EASIER CODE GENERATION

Part of QEDesign 1000 is an optional codegenerator(s) which is not only tailo-ed to a selectedDSP processor, but also to a proprietary PCexpansion card.

Once satisfied with the design of a digital filter, auser can avoid the task of coding in assemblylanguage for a specific processor by using theoptional code generator.

Code gene-ators are not rew - Atlanta SignalProcessing, with their digital filter design package,provided a code generator for the -exas InstrumentsTMS32010 in 1983. But they are c3nvenient,especially when designed to work with specific PCexpansion cads. MomentLm Data Systems arecurrently proiucing code generators for several wellestablished commercial expansion cards: eg theAriel DSP32C board. But the software developmenttools (assemblers and linkers) will still be needed forthe processor to produce e>ecutable code.

Fig. 2. DSPworkshas severalprocessingoptions. Smooth isshown is thebackground.

Fig. 3. Timedomainprocessingoptions areinstantlyavailable. Screenshows the effectof applying theautocorrelationfunction to anoisecontaminated sinewave.

November 1993 ELECTRONICS WORLD 913

PC ENGINEERING

Elle Window fienerator Qperation lime

chan 4.1irn CEO

1024 pts @ 8000 Hz; REAL32 Binary2.0000

1.0000

0.0000

-1.0000)1 II

-2.00000.000 28.078 56.156

Dtit'worksFrequencyInverse ITT...

utilities

Magnitude Display... Ctrl+EMagnitude Display 12D1...Magnitude Display 13D]...Phase Display...Power Display...

Spectral Display2-0 Spectral Display...3-D Spectral Display...

CtritS

1024 pts @ 8000 Hz; CREAL128RECT(W) Binary40.0

20.0

0.0

-20.00.0000 1.0000 2.0000 3.0000 4.0000

Fig. 4. A DSP card allows real-time frequency processing to be achieved

Fig. 5. QEDesign 1000 choice of filter types is large.

file Window DesignIIR Design

Log Magnil

AnalysisFilter

Qpflons EtonCID

EIR Design (Windows'J FIR EquIripple Design

ighltude

11,111 Lowpass...I 111111---------1

Hlghpass...Bandpass...

-20d111 Bandstop... .1100

Difterentiator...Multlband...

Anal IHilbert Transform...Arbitrary Magnitude...

.600

Halfband...Raised Cosine...

-60d11 Root Raised Cosine...Arbitrary Grn, p Delay...

11111

.4 17

:111180dB

-100dB Ii .1,.1 1.21. tt111111

25000 51111110 25000 50000

! I' I lit OUE NCY HMI r

Filter Designfile Window Design Analysis QptIone Start

Log MagnitudeldB1

0411

-20d13'

-40dB

-6111dEil

-8048

100dB025000 50000

Group Delay

1.34E-3

1.01E-3

6.72E-4

3.36E-4

0751100 cntinni

PI

0

pip

PI0 ?s000

fl

too

50000

2.00

1.511

1.00

11.511

00 1.495

Impulse Respo

6.774E-2

3.387E ?

0 14411"."'

-3.3871-

-6.774E0 1.495

2.99

1.000

SYSTEM REQUIREMENTS

386 or 486 PC with VGA monitorMaths coprocessor (advisable)Expansion card hosting DSP chip (strongly advised)

DELIVER US FROM DONGLES

What happens if a user has several softwarepac<ages, each requiring a dongle? The result is aribbon cable and a string of cascaded dongles.Thee must be a better solution.

One alternative that would still prevent multiplecop es of software from being made is a greater useof the cd-rom.

The cd-rom drive is continually falling in price(the Mitsumi L0005S is now available for under£12')) and over the next year will become acommon peripheral in PCs.

But it is not only cost that will act as a drivingforce, there are hard disc advantages too.

H storically, the problem with computers hasbeen their insatiable appetite for memory. Nomatter how much memory a computer has, it willnever be enough.

TFe dos memory limit managed to stem thisproblem for several years forcing softwareprocucers to work within the 640kbyte boundary.But the advent of Windows, memory managersand dos extenders has brought multi-Mbyte PCsoftware packages.

Many commonly used software packages takeup several megabyte of hard disc space, (forexample Visual C++ from Microsoft takes up40Mbyte of hard -disc and can take up to an hourto install). A 386 -PC or 486 -PC with only a single100Mbyte disc will soon become inadequate.

By issuing software on cd-roms (either 12cm or8cm:, which can be executed directly, it will beposs ble to save on hard -disc space, save time bynot Faving to install it, while giving a high degreeof protection against illegal copying. Theargument against using cd-roms usually relates tothe data transfer rate from disc to ram which ismuch less than for hard -discs.

But imaginative use of cache techniques canminimise the problem - bearing in mind that cd-rom s read-only.

If monthly music magazines can generate give-away cds then I'm sure, with a little imagination,software manufacturers can distribute theirproducts on CDs.

AB

SUPPLIER DETAILS

DSPworks £500 + VAT, QEDesign 1000 £800 +VATDSPviorks Plus (Both packages) £1200 + VAT.Bore Signal Processing, 39 Hawkswell Close,Woking, Surrey GU21 3RS. Tel: 0483-740138 Fax:0483 740136.

Fig. 6. Graphical results of an IIR filter design displayed in theseven plotting areas.

ELECTRONICS WORLD + WIRELESS WORLD November 1993

PC ENGINEERING

Filter profile parameters are entered by the user and, beforethe calculations begin proper, the package estimates the num-ber of taps to realise the design. Results are shown in theseven plotting areas - quite an attractive feature really (Fig.6) - showing frequency magnitude (linear), frequency mag-nitude (dB), phase response, zero -pole plot, group delay, stepresponse and impulse response. The coefficients can not beaccessed directly, though they can be printed from the savedfile.

Most IIR filters are implemented on fixed point processorsand so there are certain conventions regarding their realisa-tion. An IIR filter can have many tens of taps. But it is nor-mally configured as biquadratic structures cascaded in aseries (see diagram), maximising stability of the filter. Filtercoefficients are provided in groups of five for the five mul-tiplications for each biquad.

Should the need arise to implement the filter on a floatingpoint processor. QEDesign 1000 also provides appropriatefloating point coefficients.

In many applications where digital filters are required, lat-tice filter structures are the best choice. Unfortunately in thisversion of QEDesign 1000 there is no provision for design-ing lattice filters: it would be nice to see this deficiency reme-died in future versions.

FIR filter designFinite impulse response filters can be designed in severalways, and QEDesign 1000 supports window and equi-rippletechniques.

All linear phase FIR filters are derived from a sine (FT)profile and truncating the function causes a problem. In thewindow design method, a window is applied to a function tominimise sharp truncation by softening its end values. Manywindows can be used. In the frequency domain they have theeffect of improving attenuation in the stop band regions -usually at the expense of broadening the pass band regions.

QEDesign /000 offers no less than 17 window functions.In response to the filter profile parameters, the package givesa choice of window function with the number of tapsrequired to realise the filter requirement.

As in IIR filter design, results are displayed graphically.showing frequency magnitude (linear), frequency magnitude(dB) and impulse response. The other method of FIR filerdesign relies on the work done by Parks and McClellan in1973. It is basically a curve fitting method, giving a mini-mum number of taps for a given filter profile.Computationally, it is quite intensive and does not alwaysfind a set of solutions (filter coefficients). But the techniquedoes make design of multiband filters relatively easy.

The result is three plots showing the filter's characteristics.Other options in the FIR design menu include differentia -

tors and Hilbert Transformers (HT) - HTs being useful forgenerating quadrature components of waveforms. Givensin(FT), the HT will produce cos(FT) which can be used inquadrature amplitude modulation (qam) schemes.

QEDesign /000 also has a facility to analyse the behaviourof transfer functions. Transfer function parameters areentered (either in the Z or S domain) and pole zero values arecalculated. Quite complex transfer functions can be ana-lysed, and the package will then design a biquadratic cascadeready for direct implementation of the transfer function.

On the whole, QEDesign /000's design path is wellthought out and easy to learn. But it offers little more thanthe standard features generally found on digital filter designsoftware. What would be really useful is a FIR multirate fil-ter design feature for when sampling rate of the input deviceis different from processing rate. Cascading multirate FIR fil-ters can save a lot of computational effort: maybe we shallsee this in a future version.

Biquadratic structure with five multiplications, two delayelements and adders.

Competitive marketLooking at both packages, engineers designing FIR and IIRdigital filters will certainly find something to attract them.

But there is also a lot of other software on the market per-forming very similar tasks with lower price tags - some iseven free. I also feel the product is a little weak in not offer-ing substantially more than its competitors.

Even so, as a suite, DSPworks, QEDesign 1000 and a codegenerator, running under Windows makes an attractive pack-age. The added facility of linking the product with a range ofDSP expansion cards is particularly appealing.

The overall result is that the package is a well put togeth-er product that will surely prove a useful asset to the DSPengineer.

USER MANUALS

Curiously, the manuals, one far each package, are not actuallybound as finisbed products. They come in A4 ring binders withthe impression that as more options are, purchased, new pagesare added to the binder. The result is oat the product looks tobe still in a stale of flux.

In reality, for most software produc-_s, no sooner has VersionX been installed than Version X+1 is -eleased, rendering theuser manual oLt of date. At least with a ring binder updatedchapters can be inserted as appropriate.

Layout of the manuals is good with lots of screen shotsshowing how to access the various op:ions.

The Windows common user interface makes leaming easier,but in general -he detail is rather thin, with the feeling that themanuals are mist readable by users Ixtio are very familiar withdigital filter.

New users of these devices will need to have a good priorunderstanding of the nature of digital filters before launchinginto the product. What would have been useful here is agreater use of -eferences to readable bxts on the subject suchas Digital Sigral Processing: A Practical Approach by E CIfeachor and Jervis (Addison-Wesley 1993).


COMPUTER ICSP8271 BBC DISC CONTROLLER CHIP EX EQPT f20SAA5050 TELETEXT CHIP EX EQPT £52817A-20 (2K x 8) EEPROM ex eqpt. £227C64-25 used/wiped f1.50 100+ £1D41256C-15 256Kx1 PULLS 9 FOR £580C31 MICRO £2P8749H MICROD8751-8 NEWMK48Z02-20 ZERO POWER RAM EQUIV 6116LPNEW 4164-15USED 41256-15USED 4164-15BBC VIDEO ULA8051 MICROKS82C55-250 SAMSUNG 89/90 1100 AVAILABLE9 x 41256-15 SIMM8 x 4164 SIP MODULE NEW

£5£10

£4£1£1

60p£10

£1.25C3

£10E8

27128A 250ns EPROM USED £2 NEW £2.3027C1001 -20Z NEW 1M EPROM £6FLOPPY DISC CONTROLLER CHIPS 1771 £16FLOPPY DISC CONTROLLER CHIPS 1772 £17.5068000-8 PROCESSOR NEW £6HD6384-8 £5ALL USED EPROMS ERASED AND BLANK CHECKED2716-45 USED 100/£12732-45 USED £2100/£12764-30 USED £2 100/£1.6027C256-30 USED C227C512 USED1702 EPROM EX EQPT2114 EX EQPT 50p 4116 EX EQPT6264-15 8k STATIC RAMGR281 NON VOLATILE RAM EQUIV 6116Z80A SIO 0

£3.50£5

70p£2£5

£1.25TMS27PC128-25 ONE SHOT 27C128 El ea 100/£7080387-16 CO PROCESSOR (OK WITH 25MHz 386) £357126 31/2 DIGIT LCD DRIVER CHIP £2 ea2816A-30 HOUSE MARKED £22Mb SIMMS FOR IBM RS6000 RISC MACHINE £65 eaIBM PART NO. 68X6271 PANASONIC PART NO.MN4B40512S85 512K X 40TMS9000NL PROCESSOR £20TMS9901/2/3NL, TIM9904NL £4.50 eaHM6167LP-8 65pKM28C65-25 SAMSUNG 89/90 1100 AVAILABLE £3

REGULATORSLM338KLM323K 5V 3A PLASTICLM323K 5VA METALSANKEN STR451 USED IN AMSTRAD MONITORS78H12ASC 12V 5A78M05 5V 0.5ALM317H T05 CANLM317T PLASTIC TO220 variableLM317 METAL7812 METAL 12V 1A7805/12/15/24V plastic 25p 100+ 20p 1000+ 15p7905/12/15/24 plastic 25p 100+ 20p 1000+ 15pCA3085 T099 variable reg, 2/£1L387 5v 92A WITH RESET OUTPUT Elea f50/100

CRYSTAL OSCILLATORS2M4576 3M6864 5M0 5M76 6M144 7M000 7M3728 8M0009M216 12M000 14M3181 14M7456 17M5476 17M6256 16M25718M000 20M000 23M587 24M000 25M000 25M175 27M027M038 28M322 32M000 35M4816 40M000 44M4444 44M90048M000 64M000 1M000 1M8432 4M000 10M000 16M00018M432000 19M0500 20M0500 38M10000 56M6092

£1.50 each

£6£2£3£5£5

7/£1£1Cl

f2.20fl

CRYSTALS4M0256 10M368 17M6256 18M432 25M000 28M4694 31M469648M000 55M500 111M80 112M80 114M318 114M80 1 MO1M8432 2M000 2M4576 2M77 3M00 3M2768 3M5795453M58564 3M93216 4M000 4M19304 4M433619 4M608 4M91525M000 5M0688 6M0000 6M400 8M000 8M488 9M8304 10M24010M245 10M70000 11M000 12M000 13M000 13M270 14M00014M381818 15M000 16M000 16M5888 17M000 20M00021M300 21M855 22M1184 24M000 34M368 36M7562536M76875 36M78125 36M79375 36M80625 36M8187536M83125 36M84375 38M900 49M504 54M19166 54M741657M75833 60M000 69M545 69M550 £1 each

TRANSISTORSMPSA92 10/E12N2907A 10/f1BC477, BC488 10/£1BC107 BCY70 PREFORMED LEADSfull spec £1 £4/100 £30/1000BC557, BC238C, BC308B £1/30 £3.50/1002N3819 FETS short leads 4/£1

POWER TRANSISTORS0C29 £1.35 eaP POWER FET IRF9531 8A 60V 3/£1N POWER FET IR F531 8A 60V 2/£12SC1520 sim BF259 3/£1 100/£22TIP 141/2 El ea TIP 112/42B 2/C1SE9301 100V 1DA DARL SIM TIP121 2./E1PLASTIC 3055 OR 2955 equiv 50p 100/£352N3773 NPN 25A 160V £1.60 10/14

TEXTOOL ZIF SOCKETS28 PIN USED £3 40 PIN NEW £10SINGLE IN LINE 32 WAY CAN BE GANGED FOR USE WITHANY DUAL IN LINE DEVICES COUPLING SUPPLIED 2/£1.50

CAPACITORS COMPUTER GRADE24,000pF 50V10,000pF 100V SPRAGUE/PHILIPS

QUARTZ HALOGEN LAMPS12V 50wan LAMP TYPE M312 £1 ea HOLDERS 130p ea24V 150 WATTS LAMP TYPE A1/215 £2.50 each

MISCELLANEOUSSINCLAIR SPECTRUM +2 PSU 9V 2A £3.95 (£2)MINIATURE FERRITE MAGNETS 4x4x3mm 10/£120 ASSORTED SLIDERS + ROTARY POTS £2

KEYTRONICSTEL. 0279-505543FAX. 0279-757656

P 0 BOX 634BISHOPS STORTFORD

HERTFORDSHIRE CM23 2RX

100nF 63V X7R PHILIPS SURFACE MOUNT 30K available£42/4000 box

1ONF 63V X7R PHILIPS SURFACE MOUNT 160Kavailable £30/4000 boxETHERNET 4 PAIR TRANSCEIVER CABLE. BELDEN TYPE9892 £60 for 50 metresSWITCHED MODE PSU 40 WATT UNCASED QTY.AVAILABLE +5v 5A, +12V 2A, 12V 500mA FLOATING

£9.95 (£2)SIM RS 361-018 Each pair foil screened + overall braidedscreen £300 for 305 metre drum+ plus PVC outer sheath. ON 305 metre drums330nF 10% 250V X2 AC RATED PHILIPS 60KAVAILABLE f20/100220R 2.5W WIREWOUND RESISTOR 60K AVAILABLE

£50/1000CMOS 555 TIMERS 2/£12/3 LITHIUM CELLS AS USED IN COMPACT CAMERAS £2.50ea.ICM7126CPL CMOS 31/2 DIGIT LCD DRIVER CHIP flea36 CORE 7/0.2mm OVERALL SCREENED f50/100mLITHIUM CELL 1/2 AA SIZE 2 FOR £1PASSIVE INFRA RED SENSOR CHIP + MIRROR + CIRCUIT

£2 eachEUROCARD 21 -SLOT BACK PLANE 96/96 -WAY £25 ea"PROTONIC 24 VARIBUS" 16.7"x 5" FIBREGLASSMULTILAYER PRH PCBEUROCARD 96 -WAY EXTENDER BOARD 290x 100mm

£10 ea"PROTONIC 24" c/w 2 SUPPORT ARMS/EJECTORS.DIN 41612 96 -WAY A/8/C SOCKET PCB RIGHT ANGLE £1.30DIN 41612 96 -WAY A/B/C SOCKET WIRE WRAP PINS £1.30DIN 41612 64 -WAY NC SOCKET WIRE WRAP PINS £1DIN 41612 64 -WAY NC PLUG PCB RIGHT ANGLE £1DIN 41612 64 -WAY NB SOCKET WIRE WRAP (2 -ROW BODY)

flBT PLUG + LEAD 3/f113A MOULDED PLUG + 2m lead £1MIN. TOGGLE SWITCH 1 POLE c/o PCB type 5/£1LCD MODULE sim. LM018 but needs 150 to 250V AC for display40 x 2 characters 182 x35 x 13mm £10TL431 2.5 to 36V TO92 ADJ. SHUNT REG 2/£16-32 UNC 5,16 POZI PAN SCREWS £1/100

NUTS £1.25/100PUSH SWITCH CHANGEOVER 2J£1RS232 SERIAL CABLE D25 WAY MALE CONNECTORS

£5.90 ea (£1.30)25 FEET LONG, 15 PINS WIRED BRAID + FOIL SCREENS

INMAC LIST PRICE £30LCD DISPLAY sim Hitachi LM016L £6.50AMERICAN 2/3 PIN CHASSIS SOCKET 2/£1HUMIDITY SWITCH ADJUSTABLE £2WIRE ENDED FUSES 0.25A 30/£1NEW ULTRASONIC TRANSDUCERS 32kHz £2/prAlso available 28 slot van -bus backplane same size +Price NEWPOWERFUL SMALL CYLINDRICAL MAGNETS 3/£1BNC 500HM SCREENED CHASSIS SOCKET 2/£1SMALL MICROWAVE DIODES AEI 0C1026A 2/£1D.I.L. SWITCHES 10 -WAY El 8 -WAY 80p 4/5/6 -WAY 80p18OVOLT 1WATT ZENERS also 12V & 75V 20/£1VN1OLM 3/£1MIN GLASS NEONS 10/£1RELAY 5V 2 -pole changeover looks like RS 355-741 markedSTC 47WBost £1 eaMINIATURE CO -AX FREE PLUG RS 456-071 2/£1MINIATURE CO -AX FREE SKT RS 456-273 2/£1.50DIL REED RELAY 2 POLE n/o CONTACTS CCPCB WITH 2N2646 UNIJUNCTION WITH 12V 4 -POLE RELAY

£1400m 0.5W thick film resistors (yes four hundred megohms) 4/£1STRAIN GAUGES 40 ohm Foil type polyester backed balco gridalloy £1.50 ea 10+ flELECTRET MICROPHONE INSERT £0.90Linear Hall effect IC Micro Switch no 613 SS4 sim RS 304-267

£2.50 100+ £1.50HALL EFFECT IC UGS3040 + magnet flOSCILLOSCOPE PROBE SWITCHED x 1 x 10 £121 pole 12 -way rotary switch 4/£1AUDIO ICS LM380 LM386 TOA 2003 Cl ea555 TIMERS £1 741 OP AMP 6/f1ZN414 AM RADIO CHIP 80pCOAX PLUGS nice ones 4/£1COAX BACK TO BACK JOINERS 3/C14x4 MEMBRANE KEYBOARD f1.50INDUCTOR 209H 1.5A 5/£1125" PANEL FUSEHOLDERS 3/f1CHROMED STEEL HINGES 14.5x 1" OPEN £1 each12V 1.2W small w/e lamps fit most modern cars 10/£1STEREO CASSETTE HEAD £2MONO CASS. HEAD £1 ERASE HEAD 50pTHERMAL CUT OUTS 50 77 85 120°C fl eaTHERMAL FUSES 220°C/121°C 240V 15A 5/£1TRANSISTOR MOUNTING PADS TO-5/TO-18 £3/1000TO -3 TRANSISTOR COVERS 10/£1PCB PINS FIT 0.1" VERO 200/£1TO -220 micas + bushes 10/50p 100/E2TO -3 micas + bushes 15/£1Large heat shrink sleeving pack £2IEC chassis plug filter 10A £3POTS SHORT SPINDLES 2K5 10K 25K 1M 2M5 4/£140k U/S TRANSDUCERS EX-EQPT NO DATA fl /orLM335Z IOMV/degree C E1LM234Z CONST. CURRENT I.C.£1BNC TO 4MM BINDING POST SIM RS 455-961 £1BUTTON CELLS SIM. AG10/AG12 4/E1MIN PCB POWER RELAYS 10.5v COIL 6A CONTACTS 1 p oledo £1AVEL-LINDBERG MOULDED TRANSFORMER TYPE OB1015+15V 10VA QTY. AVAILABLE £2 eaBANDOLIERED COMPONENTS ASSORTED Rs, Cs, ZENERS

E5/1000LCD MODULE 16 CHAR. X 1 LINE (SIMILAR TO HITACHILM10) E5KYNAR WIRE WRAP WIRE £1/REELOPI1264A 10kV OPTO ISOLATOR £1.35 ea 100 £1 ea'LOVE STORY' CLOCKWORK MUSICAL BOX MECHANISMMADE BY SANKYO fl eaTelephone cable clips with hardened pins 500/£2

DIODES AND RECTIFIERSAl 15M 3A 600V FAST RECOVERY DIODE 4/£1

1N5407 3A 1000V 8/C11N4148 100/£1.501N4004 SD4 lA 300V 100/£31N5401 3A 100V 10/£1BA158 1 A 400V fast recovery 100/£3BY127 1200V 1.2A 10/£1BY254 800V 3A 8/£1BY255 1300V 3A 6/£16A 100V SIMILAR MR751 4/£11 A 600V BRIDGE RECTIFIER 4/£14A 100V BRIDGE 3/£16A 100V BRIDGE 2/f110A 200V BRIDGE £1.5025A 200 V BRIDGE £2 10/£1825A 400V BRIDGE £2.50 10/£222KBP02 IN LINE 2A 200V BRIDGE REC 8/£1

SCRSPULSE TRANSFORMERS 1:1+1 £1.252P4M EOUIV C106D 3/£1TICV106D 800mA 400C SCR 3/£1 100/£15MEU21 PROG. UNIJUNCTION 3/£1

TRIACS DIACS 4/0NEC TRIAC ACO8F 8A 600V TO220 5/E2 100/£30TXAL225 8A 500V 5mA GATE 2/£1 100/E35BTA 08-400 ISO TAB 400V 5mA GATE 90pTRAL2230D 30A 400V ISOLATED STUD £5 eaTRIAC 1A 800V TLC3817 16k AVAILABLE

5 FOR £1 £15/100

CONNECTORSD25 IDC SOCKET FUJITSU £234 -way card edge IDCCONNECTOR (disk drive type) £1.25CENTRONICS 36 WAY IDC PLUG £2.50CENTRONICS 36 WAY IDC SKT £4.00BBC TO CENTRONICS PRINTER LEAD 1.5M £3CENTRONICS 36 WAY PLUG SOLDER TYPE £4USED CENTRONICS 36W PLUG + SKT £3

PHOTO DEVICESHI BRIGHTNESS LEDS COX24 RED 5/C1SLOTTED OPTO-SWITCH OPCOA OPB815 £1.30

TIL25777N 50p

81 PHOTO TRANSISTOR £1TIL38 INFRA RED LED 5/£14N25, OP12252 OPTO ISOLATOR 50pPHOTO DIODE 50P 6/£2MEL12 (PHOTO DARLINGTON BASE n/c) 50pLED's RED 3 or 5mm 12/£1 100/£6LED's GREEN OR YELLOW 10/£1 100/£6FLASHING RED OR GREEN LED 5mm 50p 100/(40HIGH SPEED MEDIUM AREA PHOTODIODE FIS651-995 £10 ea

STC NTC BEAD THERMISTORSG22 220R. G13 1K, G23 2K, G24 20K, G54 50K, G25 200K.RES 20°C DIRECTLY HEATED TYPE £1 eaFS22BW NTC BEAD INSIDE END OF 1" GLASS PROBE RES20°C 200R fl eaA13 DIRECTLY HEATED BEAD THERMISTOR 1k res. ideal foraudio Wien Bridge Oscillator f2 ea

CERMET MULTI TURN PRESETS 3/4"10R 20R 100R 200R 250R 500R 2K 2K2 2K5 5K 10K 47K 50K100K 200K 500K 2M 50p ea

IC SOCKETS14/16/18/20/24/28/40 -WAY DIL SKIS £1 per TUBE8 -WAY DIL SKITS £2 per TUBE32 -WAY TURNED PIN SKTS. 7k available 3 for £1SIMM SOCKET FOR 2 x 30 -way SIMMS £1

SOLID STATE RELAYS40A 250V AC SOLID STATE RELAYS £10

POLYESTER/POLYCARB CAPS330nF 10% 250V AC X2 RATED PHILIPS TYPE 330.... E20/100100n, 220n 63V 5mm 20/£1 100/£31n/3n3/5n6/8n2/10n 1% 63V 10mm 100/£51On/15n/22n/33n/47n/66n 10mm rad 100/£3.50100n 250V radial 10mm 100/£3100n 600V Sprague axial 10/C1 100/£6 (£1)292 160V rad 22mm, 292 100V rad 15mm 100/£101On/33n/47n 250V AC x rated 15mm 10/£119 600V MIXED DIELECTRIC 50p ea1p0 100V rad 15mm, 190 22mm rad 100/£6

RF BITSMARCONI MICROWAVE DIODES TYPES DC2929, DC2962,DC4229F1'F2 £1 EAXTAL FILTERS 21M4 55M0 £2 eaALL TRIMMERS 3 for 50pVIOLET 5-105pFYELLOW 5-65pF RED 10-110pF GREY 5-25pFSMALL MULLARD 2 to 22pF 3 FOR 50p £10/100TRANSISTORS 2N4427, 2N3866. 2N5109 80p

ea.CERAMIC FILTERS 4M5/6M'9M/10M7 60p eaFEED THRU' CERAMIC CAPS 1000pF 10/C1SL610 £56 VOLT TELEDYNE RELAYS 2 POLE CHANGEOVER £2(BFY51 TRANSISTOR CAN SIZE)2N2222 METAL 5/E1P2N2222A PLASTIC 10/E12N2369A 5/£1

PLESSEY ICS EX -STOCKSL350G SL360G SL362C SL403D SL423ASL521B SL523C SL541 B SL850C SL1021ASP8655 SP8719DG

MONOLITHIC CERAMIC CAPACITORS10n 50V 2.5mm 100/£4.50100n 50V 2.5mm or 5mm 100/£6100n ax short leads 100/£3100n ax long leads 100/£5100n 50V dil package 0.3" rad 100/E81pF 50v 5mm £6/100

SEND £1 STAMPS FOR CURRENT IC + SEMI STOCK LIST -ALSO AVAILABLE ON31/2" FLOPPY DISK

MAIL ORDER ONLYMIN. CASH ORDER £5.00. OFFICIAL ORDERS WELCOME

UNIVERSITIES/COLLEGES/SCHOOLS/GOVT. DECARTMENTSMIN. ACCOUNT ORDER £10.00

P&P AS SHOWN IN BRACKETS (HEAVY ITEMS) OTHERWISE 95p

ADD 171/2% VAT TO TOTALELECTRONIC COMPONENTS BOUGHT FOR CASH


ELECTRONICS WORLD+WIRELESS WORLD November 1993

Golden earingI was interested to read PhilDeniss's response to Ben Duncan'sarticle on op -amp distortion (Letters,EW + WW, October), butdisappointed to note that he chose towrite off the "claims of the goldeneared or subjectivist club" with suchfacility and derision. The mostvaluable tool in any scientificresearch programme must surely bean open mind. And certainly the factthat we can't - yet - measure orquantify something that we canotherwise positively identify doesn'tinvalidate its existence. It simplymeans that we have to work harderto identify an appropriatemeasurement methodology.

Over the last ten or so years I haveworked with Ben on thedevelopment of a number ofcommercial power amplifierdesigns. From that experience Iwould now rank "developmentallistening" as being as valid in thedesign of an amplifier as is the questfor product safety, long-termreliability, applications suitabilityand an acceptable cost ofproduction. Indeed I find it strangeto find myself writing to defend apractice which I had alwaysassumed to be a "given" in thedevelopment of any audio product -by definition a device which willalways be employed subjectively.

However, at the risk of invitingderision from Phil Deniss and themany other members of hisobjectivist club, I'll describe theway in which I employ my own"golden ears" . Where mydescription is incomplete it isbecause I don't currently understandthe mechanisms involved, I hopethat one day encephalography willperhaps tell us more.

My listening tests are carried outin Ben's sitting room, using asystem which has remainedessentially unchanged for the lasteight years. My source material,both vinyl and CD, consists of tracksthat I know well, chosen forinstrumental or vocal content,performance quality or for someother aspect which I either like orhave found useful.

At the start of each session (asession may last for several days) Ispend as much time as I feel I needto in re-establishing a model of ourreference system in my head. Duringthis time I find I can either switch

from general "listening ' toanalytical "hearing"' or I can't.Colds, coffee, cigarettes and fatiguecan all make a difference, but not ofdegree. t's either yes or no. If theanswer is yes, then the referenceamplifier is swopped for theamplifier to be tested.

I set myself no time limits, remainrelaxed, and play music, in anyorder which comes to mind that Iknow will highlight a particularaspect of amplifier performance.Both amplifier channels are alwaysin the same mod state, and I listen instereo at levels ranging from veryquiet to very loud. Because thesedays we don't usually start listeninguntil we've confirmed channel -to -channel amplitude matching ofbetter than +0.05dB on the AudioPrecision, and because our designsusually include the type and make ofpassive components which we knowfrom experience can be expected tosound good, listening to the effectsof each circuit or component changecan often be quite prolonged . Longenough, in fact, for me to constructwhat I can only describe as a mentalsonic map of what I ant hearing.Longer if I am enjoying theexperience.

"Hearing" is probably too limiteda description of what seems tohappen. Like others have reported, Ifind I can mentally chop up thesource material to concentrate on avoice, or an instrument or afrequency band. But sense of visionalso seems to play a part as well . Asan example I should cite a testamplifier which incorporated aparticularly low -quality presetpotentiometer, positioned as aCMRR [rimer across the invertingand non -inverting inputs of itsdifferential front end stage . At anylistening level I experienced quiteinvoluntary, rapid and independentmovement of each eye (behindclosed lids), and eventually becamequite nauseous as a result - Ipresume - of trying to resolve twosets of continuously -variable error -laden information into one stableand coherent image.

That the preset was the cause ofthe problem was later confirmed byAudio Precision testing, in whichbanging the pcb (and even shouting"hoi" at the preset) were shown tocause significant step changes in itsvalue. Similar vision -related effectshave been noted at other times, too.

LETTERS

Wire swappingWith regards to Roger Castle -Smith's (EW + WW, July) and RAWoolley's (August) letters concerning swapping live and neutral leadsto an amplifier, Woolley's explanation of what happens in thetransformer is very clear but the closing remarks make me put pen topaper.

First, most common components have tinned iron lead -outs, whichwill be affected by the magnetic field present in the amplifier. Theeffect of the trick is thus to reduce the various forms of distortion inthese components. That is why high -end manufacturers all useexpensive components with copper lead -outs and often outboard powersupp ies.

Secondly, the little hum actually created by the magnetic field maynot be audible as hum, but different levels in two components of a hi-fichain must be equalised by way of the only connection between thetwo - the signal connection. Consequently, the signal transfer will begiven less than perfect conditions, which will affect the sound.

In most cases it is more important to connect all components in a hi-fi chain with the same orientation of live and neutral than it is toconnect each and every component with the right orientation.

Hope this will cast some light on this piece of folklore, as Woolleyprefers to call it.Bjorn JerleBirkerod, Denmark

One commonly -used fet driver stagedesign is usually drawn to include acomponent we now refer to as thesea -sickness capacitor.

Lack of space precludes adescription of several otherrecurring physical effects (all, ofcourse, brain -centred) and myapparent ability to retain mentalperformance "maps" test -to -test. Inany event by now Phil Denisshimself may be feeling quitenauseous. Nevertheless, and despitetheir subjective nature, our listeningtests are as rigorous as we can makethem. Only one change is ever madebetween tests, I note my impressionsduring each test, and each iterationof the amplifier under test issubjected to the same suite of AudioPrecision analyses from which hardcopy output is compared.Interestingly this last will oftenproduce no discernible differencesunder static testing, and it is largelythis that prompted Ben's latestresearch into areas of harmonics anddynamic performance. We want tomeasure and explain the differencesI hear - it makes good commercialsense to be able to do so - but wecan't find them all. Yet.

I made the observation earlier thatI don't understand the mechanismsinvolved in this, although naturally Iam curious to find out more. Interms of their application, though, I

don't think it matters that much. I'mconfident that I can - with referenceto my experience as a studio and livesound balance engineer - use myodd physiology/training/ears toachieve the "best" sound obtainablefrom any well -designed audioproduct. The fact that our products,once finalised, tend to sound "good"on systems ranging from mid -rangedomestic to pro audio studiomonitoring and touringreinforcement leads me to suspectthat our procedures do have somevalidity.

The statement that "the vastmajority" of people apparently can't"hear" the same things does notmatter much either. I remainconvinced that such a listener willbenefit from our work, albeitunconsciously at an emotional level.(Sorry to introduce emotions, Phil.More difficult -to -measuremechanisms at work.) In ourdeliberately casual, unpressurisedand completely random user tests,most subjects have reported anenhanced sense of listening comfortor satisfaction when auditioning ourproducts.

I'm happy with that.Jerry MeadMead & CompanyRoystonHerts


LETTERS

Not on, 10-4While I ant concerned that the hugeamount of money people haveinvested in equipment with the 88 to108MHz broadcast band may have

to be augmented by purchases ofdigital broadcast equipment with apossible lesser technical shelf life, Iam concerned that another aspect ofthe use of the EM spectrum seems tobe totally ignored.

I am referring to the use ofcommunications equipmentavailable to the general public forprivate purposes.

Here in these islands the onlylegal two-way radiocommunications equipmentavailable to the public is theinefficient and interference -prone27MHz fm citizens' bandequipment. A more uselessallocation could hardly have beenchosen into which to dump hundredsof thousands of users throughoutEurope.

In the US citizens can buy mobileand portable equipment withminimal paperwork and licenceformalities that operate in the 150 or460MHz regions. Australia, I think,still has a uhf citizens band withrepeater facilities. Are governmentsafraid to let radio communicationsequipment become available to allcitizens? Think of the safety, timeand frustration saving aspects inhaving portable or mobilecommunications available. Use,identification and frequency controlof such equipment could be easilycontrolled by credit-card type smartcards to minimise abuse of theairwaves.

With two blocks of frequencies afew megahertz apart in the upper vhfor uhf part of the spectrum, unit tounit or repeater use could make life

easier for many people.Surely with encryption,

scrambling, digital and spreadspectrum techniques the military donot effectively use all the 225 to400MHz spectrum? Time for themto hand most of it over and let thepublic have access to the spectrumas well.

Just who is using all the vhf anduhf frequencies. Surely even 0.5%of the spectrum could be used by(theoretically) 100% of the people?The 27MHz allocation is unusable.So why were we given it?Des WalshCork, Ireland

Genius in thegenesThe article "Geniuses are made notcreated" (EW + WW, October)repeats a common major logicalerror. Evidence - howevercomprehensive - that topperformance always implies highmotivation and hard practiceprovides no proof for the converse.

Neither does the fact that manywith high potential ability fail tomaximise their ability prove thatoutstanding success may beachieved without high inherentpotential.

Despite the continuing natureversus nurture argument there ismuch evidence for major geneticdifferences between individuals inanimals and humans for physical,intellectual and personalitycharacteristics.

For a wide range of physical skillseven small differences in bodyconformation have major effects onextreme performance. The samebody type does not produce topperformance in all sports. Individualcases prove nothing. Top performers

Pause for reflectionIf, before reading Ian Hickman's article about rf reflections (EW +WW, October), I had known little about the theory and practice oftransmission lines, I might have gained the impression by reading itthat most transmission lines have phase or wave velocities of200,000km/s and that somehow a coaxial configuration leads to this.

He states that "in practice any substantial increase [in velocity]proves to be impossible". What he does not point out is that thisparticular velocity applies only to transmission lines with solidpolythene (or equivalent) dielectrics.

Transmission lines (coaxial and balanced) used by broadcastingengineers and others frequently have wave velocities in excess of290,000km/s, which is due to the small amount of dielectric materialused to separate the two conductors. In my opinion 290,000km/s is asubstantial increase on 200,000km/s.

He also says that the "values of L and C per metre in free space arethe lowest that can ever be achieved, giving v = c and 4 = 37752".Surely he means that the product of the values of L and C per metre islowest when the conductors are separated by free space, giving v = c. Land C themselves may have any values, within reason. The ratio L/Cdetermines the 4 of the line, which, in theory, may also have anyvalue.Dick MantonPurley, Surrey

at national or international level arenot random samples but highly selfSelected for motivation and inherentability. Small children normallypersevere only with skills thatprovide satisfactory rewards.

First born children tend to producea much higher proportion of thosewho achieve outstanding success inlife. The normal diversion ofconcentrated parental attentionfollowing the birth of a second childsuggests rejection and leads manyfirst boms to make special efforts toregain a starring position.

Evidence from animals shows thatsimilar training does not give similarresults for all. Some breeds, strainsand individuals do much better thanothers. Underlying differences inability usually show early in life.

In domestic animals widedifferences of behaviour occurbetween individuals treateduniformly and kept in a singlegroup. Different breeds, especiallyin dogs, tend to have inherentbehaviour characteristics.

Siblings, even in a similarenvironment, usually differ widely.This fact contrary to much popularbelief supports rather than denies theargument for genetic causes.

The mathematician NorbertWiener quoted the case of his ownbrother. Their father had believedthat his special teaching system hadproduced Norbert's outstandingskills. He was highly disappointed tofind that, for his younger son, thesame system produced only normaladequate competence.

The success reported by ProfessorEricsson refers to the somewhatspecial and narrow skill inremembering a sequence ofnumbers. However, a memory for3000 digits suggests an unusualbrain quality far beyond the averageof 80 more widely achieved by hardpractice.

Competence for any skill requiressufficient practice so that the skillbecomes largely unconscious andautomatic. Any need for consciousthought usually worsensperformance. Small changes intarget skills create major problems -Konrad Loren wrote at length onthis point.

Extreme levels of performancerequire hours of regular practice.How does this concentration ofinterest affect the wider range ofskills?RG SilsonTring 1-lerts

Over processedradioGM Non hem me, mother? There's aline for radio nostalgia fans. It wasthe catch -phrase of comedyventriloquist Sandy Powell whoused it to see if he could be heard atthe back of the hall. If Sandy wasworking in radio today, he could be

sure we can hear him. Very loud -but not so clear.

My own sense of nostalgia onlygoes back a couple of decades, butat last it's official, The 1970s areback! This is the best news in agesas it means all my furniture hascome back into fashion.

A Quad II, an ultralinear pair ofKT66s allied to a distortion -cancelling pair of EF86s in a cleverphase-splitter used to give me "theclosest approach to the originalsound" for years.

But not any more. To be honest, itsounds dreadful. Legal beaglesdown at Quad can save their sealingwax, there is nothing wrong with thetuner. Your only crime was todesign it properly.

The problem lies in the audioprocessing that has slowly changedthe sound balance since Mott theHoople was in the charts. It startedwith wide -band compression. TheBBC led the field with a limiter thatgently reduced the dynamic range ofall audio frequencies present by thesame amount, giving an overallimpression of loudness enough tocounter reasonable domestic noise.

Then came the active systems. Abank of filters carve up the audiointo anything up to six pass -bands.These are compressed at differentrates preset by the broadcaster, thereconstituted audio then going fortransmission.

In pop radio, some DJs can settheir own processing at the deskleading to double compressioneffects which, as they have nomusical analogy, can lead to listenerfatigue simply due to the saturationof the sound.

Engineers say processing is hereto stay - it has grown to be anindustry in itself.

Radio marketing staff will tell youthat those who shout loudest get thelargest audience and so attract theadvertising revenue. That's fine upto a point but with CD and digitalaudio mass storage setting newstandards for source programmingand radios chasing fashion byincluding user settings forequalisation - Megabass and the like- this must be the time for thebroadcasters to reassess their use ofprocessing to allow the final level offidelity to align with the listenerslevel of investment in equipment. Inother words, you'll get what you payfor.

As it is, audio processing has hadthe effect of putting the traditionalhi -ti and the ghetto -blaster on amiddling common denominator.

With so much choice now inradio, isn't it time to move thetechnical goalposts?

Yes, we can hear you, Sandy. It'sjust that there seems to be rather alot of you.Robert EllisDerby


rPROMulator

/ Emulates up to 41 Mbit EPROMsvia one standardprinter port

/ Downloads 27256In 3 seconds

/ Accepts Intel Hex,Motorola S -Recordsand Binary files

ROM Emulator

FastFlexible

from only 9 9

/ Emulates 24, 28, 32,40 and 42 pin devices

/ Full screen editor

Other models availableup to 8 Megabits andwith bi-directionalcommunications

CALL FORFULL DATA SHEET

Tel: 081-441 3890Fax: 081-441 1843

t'i\Ak\wrrCOMMUNICATIONS


TELNETOSCILLOSCOPIMGOULD 054200 -DIGITAL STORAGE f.250HEWLETT PACKARD 1740A-100MHz DUAL

CHANNEL 8350HEWLETT PACKARD 1741A-100MH2 DUAL CHANNEL

WITH ANALOGUE STORAGE L350HEWLETT PACKARD 1744A.100MHz DUAL CHANNEL

WITH ANALOGUE STORAGEPHILIPS 3211-15MHz DUAL CHANNEL from f 150PHILIPS 3217-50MHz DUAL CHANNEL keen L250PHILIPS 3226-15MHz DUAL CHANNEL /corn L150PHILIPS 3240.50MHz DUAL CHANNEL. Rom L250PHILIPS 3261-120MHz DUAL CHANNEL from 325SOLARTRONSCHLUMBERGER CD1740-20MHz 4

RACAL DANA3100 SYNTHESIZER 40-130 MHz. 07505002 VVIDEBAND LEVEL METER LEBO

5003 DIGITAL MULITMETER f 1509000 MICROPROCESSINC TIMER COUNTER 500MHz f6009081 SYNTHESIZED SIGNAL GENERATOR 520Mliz f600

9242D PROGRAMMABLE POWER SUPPLY 25V -2A 02509246S PROGRAMMABLE POWER SUPPLY 259 10A 040093001 RMS VOLTMETER L2759300 RMS VOLTMERE. L2509141 IGR DATABR/DGE £5009084 SYNTHESIZED SIGNAL GENERATOR 35009475 RUBIDIUM FREQUENCY STANDARD f3 SR

HEWLETT PACKARD1615A LOGIC ANALYSERS f 200180TR WITH 8755B - SWEPT AMPLITUTDE ANALYSER

(RACK MOUNTED f3503300A FUNCTION GENERATOR WITH 3305A SWEEP PLUG-IN3400A RMS VOLTMETER 0150URSA BROADBAND SAMPLING VOLTMETER L1753710A IF BASERANO TRANSMITTER FITTEDWITH 3716A BIB TX37021 IFBASEBAND RECEIVER FITTED WITH37050 (DIFFERENTIAL PHASE DETECTOR)

3710A AND non MAKE UPMICROWAVE LINK ANALYSER

3762A DATA GENERATOR.3763A ERROR DETECTOR . L750 pan

3964A INSTRUMENTATION RECORDER AS NEWIMMACULATE CONDITION) L.500

f 1 51fLoili,

400 F AC VOLTMETER f 150400 E AC VOLTMETER [150

MARCONITF GTA 9A INILLIWATT POWER METER ..........[250

TF 893A AF POWER METER LSO

TT 1066196 FM SIGNAL GENERATORTF 1073 R F ATTENUATOR 0.100dB L70771245 Q METERIT 1247 20.300MHz OSCILLATOR. L250 for both

TF 2016A ARVIN SIGNAL GENERATOR IOKHZ-120MHz 0175

TF 208114 DIGITAL ERROR DETECTOR [250

MISCELLANEOUSADRET 740A 512MHz SYNTHESISERANRITSUME538C MICROWAVE SYSTEM

ANALYSER f3 SKDATMARK AUTOMATIC TRANSISTOR TESTER (COST

NEW 150K) NOW L6K

[1250

TEXTRON= 453-100MHz DUAL CHANNEL C250TEKTRONIX 475-200MHz DUAL TRACE £500TEKTRONIX 7313-100MHz 4 CHANNEL' ITH ANALOGUE

STORAGE Isom 1.350TEKTRONIX 7603-100MIR 4 CHANNEL . . from L350TEKTRONIX 7623-100MHz 4 CHANNEL WITH ANALOGUE

STORAGE from L500TEXTRON= 7904-500MHz 4 CHANNEL from L750TEKTRONIX 465 100MHz DUAL TRACE £400TEKTRONIX 4650 100MHz DUAL TRACE L450TEKTRONIX 468 1039411. DIGITAL STORAGE DUAL

TRACE L850TEKTRONIX 466 100MHz STORAGE £450TEKTRONIX 7704 250MFIz 4 CHANNEL from L650

9500/9515 UNIVERSAL COUNTERT=.IEL 5I2MHz 02009520 FREQUENCY COUNTER IONIliz 1759824 UHF FREQUENCY METER 0 2601114, (1509839 FREQUENCY COUNTER (UHF) 562MHz ..f1609901 50MHz UNIVERSAL COUNTER 150035 L1009903 50MHz UNIVERSAL COUNTER INER L1039905 FREQUENCY COUNTER - MN Hz L1259917 FREQUENCY METER (UHF FRFO COUNTER

560MHz) L1759919 FREQUENCY METER (UHF FRED COUNTER

10612) L2759932 INSTRUMENT INTERFACE 11259303 TRUE RMS R F LEVEL METER L650

41S E SWR METER E2756342A MICROWAVE FREQUENCY COUNTER - 18

GHZ 8125065IB TEST OSCILLATOR 0.10MHz L150701011 X -Y RECORDER L1508620C SWEEP OSCILLATOR (MAINFRAMES) £25086900 SWEEP OSCILLATOR WITH 894 F100 IN 18 12 4

00218750A STORAGE NORMALISERS L4003580A 5Hz-50KHz AUDIO SPECTRU A ANALYSERS (12503582A DUAL CHANNEL 25KFlz SPEC TRIM

ANALYSER L30003585A 20Hz-40MHz SPECTRUM AN aLYIE R L5K3760A DATA GENERATOR3761A ERROR DETECTOR

3779A PRIMARY MULTIPLEX ANALYSER Ilk8443A TRACKING GENERATOR.CCUN-ER [50084450 AUTOMATIC PRUSELECTOF . [7508011A PULSE GENERATOR . f 500

TF 209IB (WHITE) NOISE GENERATORTF 21392B (WHITE/NOISE RECEIVER

TF 2211/1 XY DISPLAYTT 2300 FM AM MODULATION ME TER17- 23300 FM AM MODULATION METERTr 2330 WAVE ANALYZER 20HZ 5CKfliTF 2370/1 110MHz SPECTRUM ANALYZERIT 2432A 560MHz DIGITAL FREQUENCY METERTT 2600A VIDEO VOLTMETERTF 2600 SENSITIVE VALVE VOLTMETER

L200

[350120.1£195

1100f1250

075

DATRON 4700 WITH OPTIONS 20 ilt11)90 C5 5KAVO RNI215.11112 BREAKDOWN. LEAKAGE 6 IONISATION

0600PHILIPS 6309 DISTORTION METER [250PHILIPS 5167 10MHZ FUNCTION GENERATOR I400WAVETEK 650 2MHZ VARIABLE PHASE SYNTHESISER £10

SEND LARGE SAE FOR LIST OF EQUIPMENT, TOO NUMEROUS TO LIST HERE

ALL EQUIPMENT IS USED, WITH 30 DAYS GUARANTEEPLEASE CHECK AVAILABILITY BEFORE ORDERING. CARRIAGE VAT TO BE ADDED TO ALL GOODS

TELNET UNIT 8, CAVANS WAY, BINLEY INDUSTRIAL ESTATE,COVENTRY CV3 2SF

Telephone: 0203-650702 Fax: 0203-650773

PRODUCTION/A.T.E._SECOND USER EQUIPMENT

HUGE SAVINGS PRICES1

SPECIAL OFFER - SCOOP PURCHASETETRONIX 2236-100 MHz Counter/laner/DMN. TEK 222 handheld Rugged 10 MHz Digital StorageDual Trace Portable Oullioscope Inteurated Oscilloscope Battery OperationCounterrnmer OMM, Ugletweight amp to use Size 66.1x3.4"x9.9 Depth TOTAL Weight 4.4Ibs.IrsV sensitivity Sns/Divisims Sweep Rare, 100 MHz Is the Optimum OscilkerApe for Field Ureice,canter, Gated Counter Measurements, Tin,. Several Powerful Futures Including Auto Aet-up,Channel AC Or DC Volts. (095 85232, Full Programmability and Floating

Manual I Probes extra Measurements 10 MS,s, Dual Digitizers 100 NsTEKTRONIX S76 Curve Tracer, nods Calibrated Giltsch Capture, Autoriuer, Sane Reference

Memory. Floatable -400V/CH, Complete WithDoplay Offset Power up so 220W. Stale Fawn toReadout (Call Carrying Case and Battery Charger, Power

Adapter (99S

ENVIRONMENTALTESTpitch

KANE MAY 1000 Hand held infratrate Infra RedThermometer 0°C to 1o00°C. Recorder Cup.. Variable

tone, Last reading Memory Carry cue (395

SHARTREE Soak Test Room Ansb. -60°r. (5,7508x0 It Internal Dimensions. Seivice and UK hstallatut

PLOTTERincluded.MONTFORD TSPKTELMI Thermal Shock Chamber .7C.0 to-.. 200C (2,475ALTITUDE TEST CHAMBER. atHomidity/Vacuurn. Configured to on (CallMIICROTON ESSI3 20 Litre POA

SCHLUMBERGER 1834-S AI Plotter L 1 SOO

OCE 613 DIE UNE PRINTER Perfect for Plus/Cir,sit Digs L9S0AARQUE 202 Dye iisi LP/5

GALLENKAMP TGC200. -70°C to 0203°C. 225Lives, Digital Programming LPOA PCB ASSEMBLYNERAEUS VTR 5036 Vacuum Drying Own. Temp.Range 40°- I NM L2,97SGALLENKAMP FESOT/IUMD1/1440 Clamber. TempRange -40C to 100°C CallGALLENKAMP OVR 200/910W Humid,/ Oven.Temp. Range Arnb. to 60.. Humidity Range 3 to 95%. 190Litres Working Volume LIMOANG WAY Apel Test Chamfer. -KM to + 110°C!mensal Dimensions 2500x2500x2900nen (CallLING VIBRATION System. Various modelsaulable (CallPROLAN PE 300F4SH Clinsatic Clumbet wrth hurnidit Y-WO t 17.5`C LS500NERAEUS UTS042E Laboutory Oven. Ambient to22.0.0 As new (1,500

PANASONIC AV NM20118 Anal Inserter. NewI991 6.000 Firs Run Tenn LoaderAinioader (POAROYONIC 410/401 Assembly Table withPrummur MallNARITA ECM 8400 Automats High Precision ICPlacer with Vision Systems 8 Board Conveyor MallMAMIYA ECM 83rd W. Table Top Machine with

,e, (CallMAM1YA ECM 0300. With Glue Dispensing Head.Component Squanng II PC Canpiner (CallPWP7000. Snell Marcel Pick 8 Place Machine MallSIEMENS HS 180 Line. Me Spud Surface MountAssembly Lone with Screen Pont.' and IR Oven (CallSVECIA PRINTER SSMPC Semi Automatic ScreenPrinter. 5SOn75Onvn Print Area t4,950

MISCELLANEOUS UNIVERSAL NULTIMOD iliMA LIB,500ROBIN AMBOTECH Anal/DIL

MARCONI 1871 Data Analyser (1.750MARCONI 1111311 AF POWI.Ft (275SIGMA MECHANICAL COMPARATOR MODEL201-13 "a°EPROM ERASER UV141 1 swing Pr.eciocl S -S0 Mon (45Eprom Eraser Stag SE100 Large r it, Accept 60Eirowts in Quick Action Slide in Drawer Timer up co 60nen (71EPROM PROGRAMMER! Universal Ec ring GP P6000 API 00 L I"Portable Safety Isolating Trarormer 5009. Input240VAC - Outpn 110VAC re Socket OSLane Voltage Cordrtion for M cm and PC C omputersImp. 204.276v output 240- ± 6% at 11W. L99.50HP11410011411B Network Analyser/Phut MagnitudeC Splay (4201419641011/8411A Network AnaNser/Plue Magnitude[Mislay L420NP11144713 RF emplder. (2751111.111447C Ampkfer "014P35401A Spectrum Analrer Interface . (ISOYELSONIC M4000 Ultratanic Welding mem. Mate000176mm. Weld rungs u- to 3kW. Stroke limitZrisrn LPOA

EKTRONIX AMSOIS Current Probe .ysurn withA6302 Probe BanctwAth Dcto 50MHt "A"RACAL ,euurncy Counte I. 1GHt L29SKERRY USC300f2H. Gleams Ptant Agnew (1,000

Inserter (CallASSEMBLY WORKFRAMES From (45COAXIAL CABLE/CUT & STRIP Bench Top L995AXIAL Lead Formng Machine L395NEVER 715 Autornatc Axial Lead Forming Machine.CompletelyDEK 245 Senn Automatic Printer. 2S4e203rnm Printsize 0.990KERSTEN Screen Pnnter 430x40Ornm frames sue 6re.,,,,...,,,,,. [CallTRESTON PA -40L Paternoster Assembly Station with10 shelves Motorized component tray, Anti AUKbiro MallFUJI 81I6 36 Feeder Stations. Controller. Loader/Unioader POADYNAPERT MIS3111.3IP5I I NIA 60 Way FeederBed, Vision System Various Feeder CombinauoroAvailable. LosdersAJnfteders Prke from (14,500DYNAPERT MPS2500 High Speed SMO PlacementMachine, wish Linear Feeder Bed. Full Spec Mutsu withCurrent Upgrade. Range of Feeders. Excellent Condruon.

Package Prices from 09,000CONTAX CS400A Light Guided Assembly Station. 10Component trays. rotary bin. I.C. feeder (CallWE IGHDATA MC Electronic Component CountingScales. As New L735PANASONIC N/441202A Radial Component,,,cert,,. (CallTOHO RCI4502 I, lot C-opping Ils,5ine 0995

SOLDERING/ WIRE BONDERSREFLOW HUGHES 1460-1I TAB Bonder Laceilent Coalition

ROTADIP RDO Solder Pa with Solder 2"ROTAD1P RIM" Solder Pa wan Solder (495HOLLIS ASTRA IV Dual Wave SolderMachne. Foam'loner with vanaNe control -Air Knife. Acnistable angle

'Mya L4,450ERARIUTT TEST7R CEMCO (475

-10T AIR Rework Station 000 L495

New 190 MallKUUCKE & SOFFA 14194. Gold Wire Bonder.Software DHYB2m 4"xil- X -Y Table. 43200 2 ChannelUltrasolic Generator. 815-1.00 Cruder CCTV System.Camera 8 Monitor. flourch 8 Lomb

Seer4Microscope Fibre Optic Ught Source. 14.930.

-40LUS FUTURE I SPfl Dual Wave Icler Machine.-emperature control. Foarnifluner wnh F taxer A. -knife. OSCILLOSCOPES;durable hour Conveyor (Call6.MI H D327 Buds Top, Sallee, Foam Flamer with

G. Controller, 3 Phase Solder Maanne (4.7S0;INSERT LOC-400-CU.Gernni Way . 10 Board,Automats Solder Filling. Four Flung Stmon with.7irculation Pump. Automat z Solder Refil LPOAJN1FLOW JEN 410 10' Fellow oven s new (CallELECTROVERT ECONOPAK 11 108 PLV WaveSolder Machine. Flux Conveer. Full Sober Pot. Carriers.Good Conditoon L4,975

HPS4501A Dgitzing 02,4S0TEIU201 Oral Storage 0695

TEK222 10MHz DSO Batt Portable 0995

TEKI3311100MHz 0975TEK2445 1SOMHz [1.550TEK2465A 350MHz (2,491PHILIPS 1120 200MHz DSO (2,495HP 54120T 20Gliz Digital (7.950

VITRONICS SMD) ION LeBow Oven with NitroC16,7genAtmosphere 50

SURF IRM300HP Reflow Dv. 04,950SURF UV/IR300 Curing/Peflow Oven 04,950ANALYSERS

SPECTRUM

SIGNAL SOURCES HP3582A 0.02Hz-25.5KHz L3,750

HP332.5A 0.21MHz Funcuon Generator Li msHP3335A 200141 to 81MHz SynthesizeeLevel

HP3585A 2014.-4001Hr 05,750MARCONI 2380,2382 40014Hy (4.950

GeneratorMP1N42A I OKHz to 1280MHz Signal Generator

L3,460(9,790 ATE SYSTEMS

HP83SOA/116211013 2-18.602Hz Sweep Generator (4,950HP86406 0 5 to 512MHz_ Signal Generator From [MS GENRAD 72134 Systems Can be coniigured to sus moss

POWER SUPPLIEShcations POA

MARCONI 510 Checkmate. I aDVS, I sIGT. !ACCIxICR. IKOMM. 1 aUTC. I aPWS Monitor. Printer.

FARNELL Ga. 6V 40A (45CLAUDE LYONS LVC ISO Lie Voltage Condiuoner.Output 24.09 2 5A. Input 20-276V 48-Eafil L195FARNELL L30-5. 10V SA Bench Top 05

Vacuum Pump. Keyboard MallHP3065 Config uredGENRAD 22n44

to suit From L13.0000Test Points (22.S013

GENRAD 2276E Board Test system (Call

MAINS METERSMONITORING RACAL 9919 UHF Frequency Meter (290

FLUKE 0520A GP IS Multirneter (495

CLAUDE LYONS Con,Lisse . :se i ondition HP34711A HP I B 81sItirneser (499

slos 0, I Cs-, 245 240V Print, As N.,. [695 HP535013 20Q-17 Counter 02.975

- If you have manufacturing equipment to sell,WANTED.

give us a call. We cal turn your under-utilised assets into cash.

Subscr be Now for Your FREE Copy

See latest issue of Buyers News for full listing and Terms & Conditions.Prices exclude VAT - Buyers Premium not included

ALTERNATIVE DISTRIBUTION (UK) LTDTel: 071-284 4074 (UK) Fax: 071-267 7363 (UK)

146 Camden Street, London NW I 9PFCIRCLE NO. 110 ON REPLY CARO

November 1993 ELECTRONICS WORLD+WIRELESS WORLD

CIRCLE NO. 111 ON REPLY CARO

919

COMPUTING

The conventional wayto learn about DSP is to

grasp fully the mathsfirst. Which is probablywhy so many otherwise

competent designengineers fall down

badly in applyingdigital signal

processing. Althoughthe basic algebra is

really quitestraightforward Jean -

Jacques Dauchotmaintains that the bestway to understand the

subject is to get hold ofa DSP development

system andexperiment...

Experimenting with

processing signals in a numerical formusing digital hardware offers signifi-cant improvements in reliability andstability over traditional analogue han-

dling methods. With the introduction ofmicroprocessors dedicated for digital signalprocessing, it is becoming economical to use.However, the use of digital signal processingtechniques requires considerable mathematicalskill.

Learning from books can be frustrating asthey tend to lean on mathematics in a big way.The best way to find out about DSP is to

experiment. Using a low cost DSP kit andsoftware developed by Tycho Designs andHippo Solutions, this article introduces twotypical uses of DSP: fir filtering and digitalsinewave generation.

Experimenting with FIRThe main advantages in using digital filters arethat filter characteristics are easily changed;they are stable against changes in temperature;they process low frequencies more effectively;frequency response characteristics can bemade to approximate closely to the ideal; they

can be made to have no insertion loss; linearphase characteristics are possible; reliable andrepeatable; no precision components or com-ponent matching; no timing required; superiorperformance.

There are two kinds of digital filters used:finite impulse response (FIR) and infiniteimpulse response (IIR) filters. Digital filterswith a finite impulse response can exactlyachieve linear phase, cannot become unstable,and can be easily realised on general purposeor customised hardware. IIR filters are moreefficient than FIR filters, and can generally


COMPUTING

give a sharper cut-off than an FIR filter of thesame order. Because IIR filter algorithm usesfeedback of a previous output signal, they arealso called recursive filters. Consequently,they have a non-linear phase response and canbecome unstable.

Which filter is better for a particular appli-cation depends on the hardware used for theimplementation of the filter. For example, theTexas Instruments TM320C series family ofsignal processors include a special instructionto facilitate the implementation of an fir filter.The combined use of the instructions LTD andMPY are specially geared in the design of thefir filter.

The fir filter is also known as a non -recur-sive filter or convolution filter. From the time -domain point of view, it is also called a mov-ing average filter. A fir filter works processingan output signal from the history of a numberof previous samples each time a new samplesignal is received. We can view the process offiltering through the changes in the differencesin level between consecutive samples. Theway the filter distinguishes between high andlow frequencies is by the rate of changebetween samples. Large differences indicatehigh frequencies and small differences indi-cate low frequencies.

Consider the filter design in Fig. 1 and sup-pose a sequence of samples of values 1, 8, 6,4, 1, 5, 3, 7 enter the system. The differencebetween consecutive samples ranges from 2 to7 . Using a coefficient value g of 0.25, the firstthree numbers enter the filter and are addedand multiplied: (1+8+6)x(0.25) = 3.75.

The next generation yields: (8 + 6 +4)x(0.25) = 4.50. After the entire sequence haspassed through the system, the result is a newsequence which is 3.75, 4.50, 2.75, 2.50, 2.25,3.75. The new inter -sample difference rangesfrom 0.25 to 2.25, and we have effectivelyachieved a low pass filter.

Filter by designTo begin with, coefficients for the filter mustbe calculated for a given set of parameters.The art of designing non -recursive filters is toachieve acceptable performance using as fewcoefficients as possible . Typically, a practicalfir filter will employ between 10 and 150coefficients. Theoretically, in order to achievean ideal response, a fir filter will have an infi-nite number of taps or coefficients, but in real-ity a fir filter will have a finite number of tapsdue to the limitation of processing time and ofthe hardware.

This truncation effect introduces errors, theeffect of which is ringing or rippling in thestop band region. Because an fir filter has afinite response, the actual amplitude responsewill be different to the theoretical value. Thiseffect is known as the Gibb's phenomenonand has the frequency response of what isknown as the rectangular window.

The spectrum of a rectangular window tendsto the sin(x)/x or sine, form. The method thatcan be used to reduce this effect is as follows.By multiplying the impulse response sequencewith another window function smooths the

INPUT

Fig,. I. FIR filter model OUTPUT

rippling in the stop band. There are severalwindow functions that may be used and thetwo common ones are the Hamming and theHanning widows.

Hanning 0.5(1- cos((2m)/N-1));Hamming 0.54-0.46cos( (2rn)/N-1)

The number of coefficients used in the filterwill depend on the order of filtering required,the cut-off frequency and the sampling fre-quency used. The relationship of the cut-offfrequency and the sampling frequency is animportant factor to be considered when decid-ing how many coefficients should be used inthe design. For the filter to be efficient, thelength of the delay line (ie the number of taps)must hold at least one complete cycle of sam-ples of the required cut-off frequency.

The calculations employed in the generationof filter coefficients are often complex and dif-ficult to understand. These filter coefficientsmay early be calculated using computer meth-ods, or may even be performed on a pro-grammable scientific calculator.

The Fourier transform method with win-dowing is the simplest method of designing alinear phase fir filter. The basic formulae usedto calculate the coefficients is

isn(2nW(M-n))H(n)= 0 n (M - I)n)

Where W = cut-off frequency divided by thesampling frequency, and M = 1/2(N-1) whereN is the length of the filter.

To achieve exact linear phase, an fir filterhas to have a unit -pulse response that is sym-metrical around the point (M-1)12. Fig. 2shows how the coefficients for a 20 tap filterare organised to achieve linear phase.Coefficients 10 to 19 are a mirror copy of thecoefficients 0 to 10.

H(0)H(1)

H(2)

H(3)

H(4)

H(5)

H(6)

H(7)

H(8)

H(9)

H(19)H(18)

H(17)H(16)H(15)

H(14)

H(13)

H(12)H(11)H(10)

Fig. 2. Linear phasefilters require a

symmetricalcoefficient structure.

Once the coefficients have been calculated,the formulae shown below is used to realisethe filter. Yn = X(N)*H(N) + X(N-I)*H(N-1)+ X(N-2)*H(N-2)+ X(N-n)*H(N-n) Yn is theoutput of the filter, X(N) is the oldest sample,X(N-n) is the newest sample and N is the

length of the filter. As the values of the coef-ficients are normalised using real numbersranging between -I<0<_I, they must be scaledto the processor's data word size. TheTMS320C10 DSP has a I6 -bit data wordlength, therefore all coefficient values must bescaled by multiplying them by 215 to obtainvalues ranging between: -32768 5_ 0 32768This process introduces rounding errors whichdegrade the performance of the filter further.A software package, FDesign, is to be used todesign the filter. Not only will it calculate thecoefficients, but it will generate the 320C/0code as well. The parameters necessary togenerate the filter coefficients are: the sam-pling frequency, the cut-off frequency, thenumber of taps, the type of window damping.

Once the coefficients have being calculated,the frequency response of the filter is calcu-lated and displayed in graphical form.

In this example, we wilI design a low passfitter for the developer. The specification ofthe filter will be as follows:

Sampling Frequency: 10 KhzCut off Frequency : 2.5 KhzBandwidth of signal : 5.0 KhzNumber of taps : 20Window type : HammingFilter coefficients calculated are shown

below:H100] = H[10] -1.39622e-03 ffd3

H,01] H[11) +6.36498e-03 00d0

H[02] H[12] +1.91480e-03 003e

HI03] H[131 -2.09039e-02 fd54

H:041 H[14] +3.14799e-03 0067

H)05] H[15] +5.00330e-02 0667

H106] H[16] -2.62335e-02 fca5

H107] H[17] -1.07157e-01 2249

H108] H[18] +1.18529e-01 Of2b

H(091 H[19] +4.74540e-01 3cbd

TMS320C10 program generated by FDesign whichis ready to be assembled and linked.idt

maskmaskl

'fir

equequ

filter'0

1

xn equ 2

x01 equ 3

x02 equ 4

x03 equ 5

x04 equ 6

x05 equ 7

x06 equ 8

x.07 equ 9x08 equ 10

x09 equ 11

x10 equ 12

xll equ 13

x12 equ 14

x13 equ 15

x14 equ 16


COMPUTING

x15 equ 17

x16 equ 18

x17 equ 19x18 equ 20

x19 equ 21

h00 equ 22hOl equ 23h02 equ 24

h03 equ 25h04 equ 26h05 equ 27

h06 equ 28h07 equ 29h08 equ 30

h09 equ 31h10 equ 32

hll equ 33h12 equ 34


h15 equ 37



yn equ 42

one equ 43

aorg 0

b startdata Ox7fffdata 0x8000data Ox0000data Ox0000data Ox0000data Ox0000data Ox0000data Ox0000data Ox0000data Ox0000data Ox0000data Ox0000data Ox0000data Ox0000data Ox0000data Ox0000data Ox0000data Ox0000data Ox0000data Ox0000data Ox0000data 0x0000Start of

coefficientsdata Oxffd3data Ox00d0

o db

-5 db

-10 db

it, db

-20 db

-25 db

-30 db

-35 db

-40 db

-45 db

-50 db

-55 db

-60 db

-65 db

-70 db

-75 db

-80 db

-05 db

-90 db

data Ox003edata Oxfd54data 0x0067data 0x0667data Oxfca5data 0xf249data OxOf2bdata Ox3cbddata Ox3cbddata OxOf2bdata 0xf249data Oxfca5data 0x0667data 0x0067data Oxfd54data Ox003edata Ox00d0data Oxffd3End of coefficientsdata Ox0000

tble data 0x0001

start lack tblelarp 0

lark 0,onemake tblr

sub onebanz make

ltd x13mpy h13

ltd x12mpy

ltdmpy

h12

xll

hll

ltd x10 mpy h10

ltd x09mpy h09

ltd x08mpy h08

ltd x07mpy h07

ltd x06mpy h06

ltd x05mpy h05

ltd x04mpy h04

loop bioz get ltd x03b loop mpy h03

get in xn,pa0zals mask ltd x02xor xn mpy h02sacl xnzac ltd x01

mpyIt x19mpy h19 ltd

ltd x18mpy h18

ltd x17mpy h17

ltd x16mpy h16

ltd x15mpy h15

ltd x14mpy 114

...4F111 Response!

2000 3000

Frequency in Hz

mpy

apacsackzalsxor

sacloutb

end

h01

xn

h00

yn,1masklyn

yn

yn,palloop

4000 5000

Loading a filter programThe filter program generated by fdesign mustbe assembled and linked using the Hippo solu-tion's DSP development package. The outputfile generated by the linker is in Motorola Srecord format. The developer is connected toan 8 -bit ADC+DAC circuit board via a 64 -

way backplane. The Developer's three channeltimer is used to generate the sampling fre-quency and the input and output anti-aliasingfiltering. The output of channel No. 2 is usedto generate a signal that is connected to theBIO pin of the 320C10, the channel is pro-grammed to generate a 10000Hz square wave.

The sampling frequency must be twice thatof the highest frequency being sampled.Channel No 1 and Channel No2 are used toclock switched capacitor filters which pro-vides anti-aliasing filtering, they must beclocked 100 times that of the highest fre-quency being sampled. The devcomms soft-ware is used to communicate with theDeveloper via the PC's serial port. Wheninvoked, it attempts to communicate with thedeveloper. Once communication has beenestablished, a success banner is displayed andthe Developer is ready to receive commandsand data.

The filter code is loaded with "Load Code",selected from the File menu or by hitting theF3. It takes about 5 seconds to transmit thecode to the developer.

Before the DSP is allowed to run its pro-gram, the timer has to be programmed. By hit-ting CTRL T, a control panel is invokedwhich allows the timer to be programmed.The following frequencies are programmedinto the timer:

Channel No. 1 500,000 HzChannel No 2 10,000 HzChannel No 3 500,000 HzWith an audio signal generator and an oscil-

loscope connected to the analogue board, theloaded fir filter code can be tested. The filterdesign generated earlier achieved 60dB atten-uation per octave. By varying the number offilter taps, the performance of the number oftaps, cut-off frequency and sampling fre-quency can easily be demonstrated.

Generating sine wavesSinewave generators are fundamental buildingblocks of signal processing systems in appli-cations such as communication, instrumenta-tion and control. In the past, engineersdesigned oscillators using analogue compo-nents with their inherent tendency to drift.Using DSP it is possible to produce stable,low distortion sine waves over a wide range offrequencies. Two methods of sinewave gen-erations using the TMS32010 will bedescribed.

The first frequency response plot left shows theGibb's effect using a rectangular window, thesecond plot right shows the effect reduced byusing a hamming window. The plots are of a 21taps FIR filter with a cut-off frequency of2500Hz using a sampling frequency of10,000Hz

)

ELECTRONICS WORLD + WIRELESS WORLD November 1993

COMPUTING

The developerThe developer is based on the TMS320C10 running at 20MHz.An 80C31 microcontroller is used as a master processor to the

DSP and its serial port is used to connect to an IBM PC. Asoftware package on the PC communicates to the DSP developerwhich allows DSP programs to be downloaded to the DSPprogram memory.

The DSP developer is constructed on a extended single eurocardwith all the 320C10 data, control and input/output signalsconnected to the 64 -way DIN connector.

The board includes a three channel timer chip controlled by the80C31 cpu which can be used for anti-aliasing, sampling rate, andreconstruction filtering. The three timer channels outputs areconnected to the 64 -way DIN connector. A backplane is availableto connect the DSP board to analogue/digital interface cardscomplete with 64 way DIN connectors.

The 80C31 has full access to the DSP program memory whichcan be loaded with a program or contents read. The output port ofthe 80C31 has control of the TMS320/ 0 reset line.

The developer comes with two software packages, the IBM PCDeveloper interface and real-time firmware in an EPROMplugged into the DSP developer board. The PC Developerinterface software is a set of windows and pop down menus whichallow the user to control the developer via the serial interfaceusing simple commands.

The software package used to develop the programs for the320C10 is the Hippo Solutions TMS320CXX development tools.Together with the Developer, it offers a complete and low costdevelopment system for the DSP chip.

The software system consists of a compiler, assembler, linkerand simulator. Broadly speaking, the compiler translates 'C'language subset source into assembly language. These sources are

combined with other assembly language sources, assembled andlinked into a single executable image which can be either splitinto high and low byte images with the provided utility `I.J1X' orloaded into the simulator or downloaded into the DSP Developerto be run.

On its own, the DSP developer board can do little. A suitableinput/output board must be connected to the developer via the 64 -way back plane. An eight -Dit adc/dac circuit is shown on Fig. xx.It uses the popular DAC800 dac chip and the Analog DevicesADC7575 analog ADC chip. Anti-aliasing filtering isaccomplished with a 2nd order low pass filter and an 8th orderclock tunable low pass filter using a MAX291 chip from MAXIM.The clocking frequency for the filter is provided by the 82C53timer channel 0 under the control of the 80C31 controller. Theclocking frequency must be a hundred times that of the highestfrequency being sampled.

Sampling is initiated by reading the ADC7575 which loads thecontents of the previous sample and starts the next samplingprocess. The ADC has a built in sample and hold circuit. Thesamphng period can be determined by the use of the 320CI0'sBlO pin connected to the output of the monostable. The 82C53timer 3 is programmed to trigger the monostable.

The output of the dac is connected to another MAX29I filtercircuit which reconstructs the signal and filters out the samplingfrequency. The conventional 2nd order filter circuit removes anyresidue clocking signal. The 82C53 timer 0 provides the clock forthe switching capacitor filter.

The DSP developer and the TMS3201X Software developmenttools can be obtained from Tycho Designs 38, Playfields Drive,Branksome, Poole, Dorset BH12 2EQ Phone 0202-736791. Pricesstart from about £100.

The first is the fast direct table lookup following format:method and the second is the use of IIR filters.

Direct table lookup sine generatorThe first algorithm is a simple, fast tablelookup process. The sine values of N angleswhich are uniformly spaced round the unit cir-cle are stored in a table. The values have the

INDEY SINE0 SINE( /N))

1 SINE( /N))

2 SINE( IN))

3 SINE( 3 * (360 IN))

N-2 SINE(N - 2 (360 /N)

A sine wave is generated by steppingthrough the table at a constant rate, wrapping

TABLE0 * (360

1 (360

2 (36)

0 dh

-5 db

-10 db

-15 db

-20 dh

-25 db

-30 db

-35 db

-40 db

-45 db

-50 db

-55 dh

-60 dh

-65 dh

-70 db

-75 db

-80 db

-85 db

-90 db

FIR Response

O 1000 2000 3000

Frequency in Hz

4000 5000

round at the end of the table when 360° isexceeded. What determines the frequency arethe step size in degrees between samples andthe time interval between successive samples(ie the sampling interval fs). The frequency isgiven by the equation:

f= step size/(fs x table size)The accuracy of the sine wave depends on thesize of the table, the greater the number ofsteps in the table the greater the accuracy is.To satisfy the Nyquist criterion there must beat least two samples generated for each sinu-soidal period. The values in the table are allnormalised using the two's complement hex-adecimal Q14 notation. The decimal valuesbetween +1.0 and -1.0 are multiplied by16384. Rounding is applied, rather than trun-cation to reduce further distortion. To run thesinewave generator into the DSP developer,use the assembler and the linker to build anexecutable .COD file from the following pro-gram.

B START

DELTA EQU 0

ALPHA EQU 1 ;Mask toconfine addresses to tableSINA EQU 2 ;Start

address of sine tableTEMP EQU 3

chase stepMASK EQU 4

part phase stepCFSET EQU 5

accumulator integer

;Integer part

;Fractional

;Phase


COMPUTING

LTD and MYP instructionsThe combined use of the LTD and MPY/MPYK instructions

implements a basic FIR filter tap.

LTD X1The load T register and Shift Data instruction (LTD) implementsthree key operations in parallel. During the execution of thisinstruction, the P Register is added to the accumulator, the TRegister is loaded with the data from the operand, and the datavalue is shifted to the next internal memory address.

MPYK and MPYThe MPYK instruction multiplies the contents of the T register bya signed 13 -bit constant and the result is loaded into the P register.

The MPY instruction multiplies the contents of the T register bythe contents of a specified data memory address, and the resultstored in the P register.

The following example illustrates the use of this powerfulinstruction in implementing FIR filters. The routine assumes anI/O device on Port 0 which inputs a sample. The TMS32010 thencomputes a number (Y), based on this and previous samples. Y isoutput to the I/O device on Port 1. The following symbols areused:

Y = output to I/O device on Port 1X1 = current sample taken at time "t"X2 = sample taken at t-1X3 = sample taken at t-2X4 = sample taken at t-3

X4 is at a higher address than X3; X3 is at a higheraddress thanX2, etc.

The formula is Y = 3*(X1) + 4*(X2) + 5*(X3) + 6*(X4)Data is shifted down one interval by LTD

Example:X1 EQUX2 EQUX3 EQUX4 EQUY EQU

1

2

3

4

5

START:IN Xl,PAOLT X4

shift data hereZACMPYK 6

LTD X3(X4)

MPYK 5

LTD X2

(X3)

MPYK 4

LTD X1-> (X2)

MPYK 3

APACSACLOUTB

Y

Y,PA1START

; Load T register no need to

Zero accumulatorMultiply 6 x (X4)

Move (X3) --> T and Move (X3)

Multiply 5 x (X3)

; Move (X2) --> T and Move (X2)

; Multiply 4 x (X2)

; Move (X1) --> T and Move (X1 -

Multiply 4 x (X2)

Add P Register to AccumulatorStore result to Y locationOutput resultdo it again

SIGN EQU 8

; Initialise generatorSTART LDP 0

LACK 0x80SACL SIGNLACK M1TBLR MASKLACK SINESACL OFSETZACSACL ALPHA

; Wait for hardwaretimerWAIT BIOZ SWAVE1

B WAIT

; Infinite Loop tooutput sine samplesSWAVE1 LAC ALPHA,8

SACH TEMPLAC TEMPADD OFSETTBLR SINALAC SINA,8ADDH SIGNSACH OUTV,0OUT OUTV,PAO

;Output this sample tothe DAC

LAC ALPHA;Save new phase valuefor next sample

ADD DELTAAND MASKSACL ALPHAB WAIT

SINE DATA #0

DATA #324DATA #646DATA #964DATA #C7CDATA #F8DDATA #1294DATA #1590DATA #187EDATA #1850

DATA #1E2BDATA #20E7DATA #238EDATA #2620DATA #289ADATA #2AFBDATA #2041DATA #2F6CDATA #3179DATA #3368DATA #3537DATA #36E5DATA #3871DATA #39DBDATA #3B21DATA #3042DATA #3D3FDATA #3E15DATA #3EC5DATA #3F4FDATA #3FB1DATA #3FECDATA #4000DATA #3FECDATA #3FB1DATA #3F4FDATA #3EC5DATA #3E15DATA #3D3FDATA #3042DATA #31321

DATA #39DBDATA #3871 ;

DATA #36E5DATA #3537DATA #3368DATA #3179DATA #2F6CDATA #2041DATA #2AFBDATA #289ADATA #2620DATA #238EDATA #20E7DATA #1E2BDATA #1B5DDATA #187EDATA #1590DATA #1294DATA #0F8DDATA #OC7CDATA #0964DATA #0646DATA p03-24

DATA #0000DATA #FCDCDATA #F9BADATA #F69CDATA #F384DATA #F073DATA #ED6CDATA #EA70

DATA #E782DATA #E4A3DATA #E1D5DATA #DF19DATA #DC72DATA #D9E0DATA #0766DATA #0505DATA #D2BFDATA #D094DATA #CE87DATA #0C98DATA #CAC9DATA #C91BDATA #C78FDATA #0625DATA #C4DFDATA #C3BEDATA #C2C1DATA #C1EBDATA #C13BDATA #0081DATA #C04FDATA #0014DATA #0000DATA #0014DATA #C04FDATA #0081DATA #0138DATA #C1EBDATA #0201

M1

DATA #C3BEDATA #C4DFDATA #0625DATA #C78FDATA #C91BDATA #CAC9DATA #0098DATA #CE87DATA #D094DATA #D2BFDATA #D505DATA #D766DATA #D9E0DATA #DC72DATA #DF19DATA #E1D5DATA #E4A3DATA #E782DATA #EA70DATA #ED6CDATA #F073DATA #F384DATA #F69CDATA #F9BADATA #FCDCDATA #7FFF

PEND

ArchitectureThe general architecture of the TMS320 processorfamily uses a modified Harvard architecture for

speed and flexibility. In a strict Harvardarchitecture, program and data memory lie in twoseparate spaces, permitting a full overlap ofinstruction fetch and execution. The TMS320family's modification allows transfers between

program and data spaces, thereby increasing theflexibility of the device. This modification permitscoefficients stored in program memory to be readinto the internal ram area, eliminating the need for aseparate coefficient rom. It also makes availableimmediate instructions and subroutines based oncommuted values.


COMPUTING

Then load the program into the developer.The following frequencies are programmedinto the timer:

Channel No 2 10000 HzChannel No 3 500000 Hz

Sinewave generation using IIR filters

One disadvantage using IIR filters is that theycan become unstable under certain conditionsThese conditions occur when the poles of thefilter function approach and extend past theunit circle. Without going into too muchdetail, poles and zeros determines thebehaviour and impulse response of a recursivefilter. If an pulse of finite time and magnitudeis injected into a second order IIR filter withits poles located within the unit circle, a

sinewave will be generated with its amplitudedecaying exponentially in time. However, ifthe same pulse is injected into the same typeof filter with its poles located outside the unitcircle, the same sinewave is generated. Butthis time, the amplitude of the wave willincrease exponentially in time until the filtersaturates. Now, if the poles of the filter arecalculated so that they reside on the unit circleand a pulse is applied, the filter will oscillateforever. The formulae to generate thesinewave is as follows:

Y[n] = (y[n-l] x (w))-(C2 x y[n-2]) + XnWhere nu] is the output of the filter y[n-l]

and An -2] are the direct form II IIR filterdelay elements.

C2 is the coefficient representing the radiusof the pole of the filter.

The frequency is calculated using the fol-lowing equation :w = 2it(Freq/Sampling Freq)

Example : Fs.,pling 10kHz, Fsinewave 500Hzw = 2 x cos(2n(500/10,000)) = 1.90211.w must be converted to Q14 notation, there-

fore w = 1.90211 x 16384 = 31164. Below is

A11 -A0/P42 -PAD

XIctxotr. X2./CLXIN

'

File :'-'.11ou Memorii

000E 0000081C 088000ZA H8000838 0080"

0046 08000854 00800062 00086078 0080007E 0080008C 0088089A 8000

808000808800.00000000080000000000000000800080

DSF Bpplicati

EFT128 CODCODE .CDFIR.CODTEST CODADC .COD

I ALT_Y

00000088000000000000t.eliO

Run

083800980038009800900098

Data Link

0000

Proc

il.AH

Timersy0000 0000

0880 0000 0000 0000 00008008 0080 BOOR 0000 00800080 00001 8000 0000 00000800 8000 8800 0800 00000808 0000 0080 0000 00000080 0800 0080 0000 )1,110

0

ValueIncStatus

13 it

!Timer Contra Ii Pane 11

Timer 1 Timer 2 Timer 3

0008 0000 rnitlil rOJOH MHO0000 0000 0088 0000 00080000 0000 0000 0000 00008800 8808 0000 0000 00000000 8808 0080 0800 00000800 0000 0008 0088 00000008 ',I18 0880 0800

Timerl Timer2 Timer3

=EMT 0010800 05000000000010 0000010 0000010Run Run Run

ESC to exit timer control

T2 freq : 0010000T3 status : RunningT3 freq : 0500080

a program written in 'C' and compiled withthe Hippo solution 'C' compiler and assem-bler. To demonstrate the filter will decay if theC2 is set m value of less then 1, change thevalue to 0.999999. You will see that the oscil-lation will decay. If the value of C2 is set to1.0001, the filter will go unstable. Severalsinewave can be generated simultaneously beduplicating the formulae variable and sinefunction stibroutine. Care must be taken not tosaturate the output of the DAC when addingthe resulting output value of each of the tones.

The following frequencies are programmedinto the timer:

Channel No 2 10,000HzChannel No 3 500,000Hz

#define cut#asmout r@0],01 \

/13

MUX

PC 1121

12

/18

MSTRUCTION

STAG))4x12

PROGRAMROMAEPRON

11.61U4XWORDS)

PROGRAM BUS 019 -DO

440 (16)

.4211 (Io)

LEGEND:

ACC. AuurnulatorARP Auxiliary reenter ciantaiARO . Auxiliary register 0AR1 Auxiliery revere, 1

DP . Data 9.3. Omm.,PC - Program counterP . P replete,T T register

ADDRESS

DATA RAM1144/266WORDS1

DATA

/16

)

SIMMERWIC

/32

/32

TI161

MULTIPLIER

P1321

MUX

ALU 1321

32

ACC 1321

/32

32

SNIFTER 10. 1, 41 16/

16

AO 0000 000001108 0000 00080000 0880 00000000 0888 00000880 0880 8000

f Status

rt

IsDSP ProgramMemory BankDSP Type

COM1OSNot RunningNot LoadedRank 1TMS320c10

The Developer has a three channel timerconnected to the backplane. Channel No 1 isused to clock a switched capacitor filter circuitused for anti-aliasing filter, channel No 2 is usedfor generating the sampling frequency andchannel No 3 is used to clock a filter circuit forthe reconstruction of the signal.

#endasm#define wait

#asmcopy 'wait.asm'\#endasm

int y1=0, y2=0; /* Oirect Form I:II8 filter delay elements */int OutVal; /* Output value*/

int A = +1.90211 ; /* 5C0 Hz 2cos(w)*/

int 02 = 1.0 /* Radius of the

pole */

main()

int impulse= 500;pulse amplitude */while (1)

wait ;

pin */out(OutVal, 0);

value */

/* DAC8000 binary offset DAC */OutVal=(sine(impulse)- 2048) >>

impulse =0 ; /* set pulsezero */

/* Initial

/* wait for the BIO

/ Output the

4;

TMS320C10 architecture DATA BUS16

1.) /1";

MOTORS - BATTERY 1-12V3 Different model motors, £1, Order Ref. 35Spin to start 3v dc motors for model aircraft etc. 5 for £1,Order Ref. 134Cassette motor 1.5-12v powerful speed increases withvoltage, £1, Order Ref. 224Mini cassette motor 6-9v working, £1, Order Ref. 944.High efficiency motor for solar cell working, £1, Order Ref.643.12v motor ex BSR record player, £1, Order Ref. 687.9v cassette motor, brushless, £1.50, Order Ref. 1.5P141/4ohp 12v dc motor Smiths, £4, Order Ref. 4P221/4hp 12v motor, Smiths, £6, Order Ref. 6P1Vehp 12v motor, Smiths, £8, Order Ref. 8P141/3hp motor (Sinclair C5), £15, Order Ref. 15P8

MAINS MOTORS WITH GEARBOXES

5rpm 60W £5, Order Ref. 5P5440rpm 100W, £6, Order Ref. 6P2150rpm 60W, £5, Order Ref. 5P1686Orpm 60W, £5, Order Ref. 5P171110rpm 60W, £5, Order Ref. 5P172150rpm 60W, Order Ref. 5P16920Orpm BOW, £5, Order Ref. 5P216500W motor with gearbox & variable speed selector100rpm upwards, £5, Order Ref. 5P2201 rev per 24 hours 2W motor, £1, Order Ref. 891 rev per 12 hours 2W motor, £1, Order Ref. 901 rev per 4 hours 2W motor, £2, Order Ref. 2P2391 rev per hour 2W extra small motor, 2 for £1, Order Ref.5001/2 rpm mini motor, £3, Order Ref. 3P641 rpm mini motor, £2, Order Ref. 2P3284rpm 2W motor, £1, Order Ref. 44615rpm 2W motor, £2, Order Ref. 2P32125rpm 2W motor, £2, Order Ref. 2P322200rpm 2W motor, £1, Order Ref. 175250rpm 2W motor, £1, Order Ref. 750

MAINS MOTORS

3/4 stack motor with 1/4" spindle, £1, Order Ref. 85Motor 11/2" stack with good length spindle from each side,£2, Order Ref. 2P55Motor 11/4" stack with 4" long spindle, £2, Order Ref. 2P203Motor by Crompton .06hp but little soiled, £3, Order Ref.3P4Jap made precision motor balanced rotor & reversible,1500rpm, £2, Order Ref. 2P12Tape motor by EMI 2 speed & reversible, £2, Order Ref.2P701/4hp 1000rpm, £8, Order Ref. 8P7

MOTORS - STEPPER

Mini motor by Philips 12v-7.5 degree step, quite standarddata supplied, only £1, Order Ref. 910Medium powered Jap made 1.5 degree step, £3, OrderRef. 3P162Very powerful motor by American Philips 10-14v 7.5degree step, £5, Order Ref. 5P81

LOUDSPEAKERS

2" round 50 ohm coil 1/2W, 2 for £1, Order Ref. 90821/4" 8 ohm, 2 for £1, Order Ref. 45421/2" 35 ohm, 2 for £1, Order Ref. 51431/2" 8 ohm, 2 for £1, Order Ref. 68261/2" 4 ohm with tweeter, £1, Order Ref. 89561/2" 6 ohm, Et, Order Ref. 89661/2' 8 ohm, with tweeter, £1, Order Ref. 8976"x4" 4 ohm, £1, Order Ref. 2425"x5" 15 ohm, £1 Order Ref. 9065"x3" 16 ohm, £1, Order Ref. 7257"x4" 16 ohm, 2 for £1, Order Ref. 6848", 15 ohm audax, £1, Order Ref. 5049"x3" 8 ohm 5W, £1, Order Ref. 1383" 4 ohm tweeter, £1, Order Ref. 433Goodmans 61/2" 10W 4 ohm, £2, Order Ref. 2P27Horn speaker 41/2" 8 ohm, £3 Order Ref. 3P8220W 5" by Goodman, £3, Order Ref. 3P14520W 4 ohm tweeter, £1.50, Order Ref. 1.5P9Amstrad 8" 15W 8 ohm with matching tweeter, £4, OrderRef. 4P57Cased pair of stereo speakers by Bush 4 ohm £5 per pair,Order Ref. 5P141Double wound voice coil 25W, ITT, £7, Order Ref. 7P12Bulkhead speaker, metal cased, £10, Order Ref. 104325W 2 way crossover, 2 for £1, Order Ref. 2240W 3 way crossover, £1, Order Ref. 23

MONITORS AND BITS

Philips 9" high resolution monitor, £15, Order Ref. 15P1Metal case for the above Philips monitor, £12, Order Ref.12P3Philips 9" high resolution tube Ref. M24 306W, £12, OrderRef. 12P76" electrostatic monitor tube Ref. SE5J31, £10, OrderRef. 10P104Mini scope tube face size 2"x21/2", electrostatic 3v heater1Kv in new metal shield, £10, Order Ref. 10P73

SOME POPULAR BARGAINSBATTERY QUICK CHARGER, into a flat battery thecharging rate would be 8-10A, this would fall away to about5A as the battery charges up or it can be switched to a lowerrate. Complete kit includes mains transformer, rectifier,capacitor, switch and metal case, £7.50, Order Ref. 7.5P20200W MAINS TRANSFORMER, secondary voltages 8v -0-8v, so you could have 16v at 12A or 8v at 25A. Could beideal for car starter charger, soil heating, spot welding,carbon rod welding or driving high powered amplifiers etc.£15, Order Ref. 15P1LCD 31/2 DIGIT PANEL METER, this is a multi rangevoltmeter/ammeter using the A -D converter chip 7106 toprovide 5 ranges each of volts and amps. Supplied with fulldata sheet. Special snip price of £12, Order Ref. 12P19500V INSULATION TESTER, we still have a few perfect BTbridge meggers £45, Ref. 45P2, also we still have someslightly imperfect but quite repairable. Faults would beperhaps bad case, battery cover missing, terminals broken,no one would have all these faults but could have one ortwo, £25. Order Ref. 25P15MINI TRANSFORMER, mini construction and resin filled,PCB mounting. Two versions, one with 2 X 15v secondarieseach rated at .75vA, Order Ref. 937; other with 2x18vsecondaries each rated at .7vA, Order Ref. 941, £1 each12V -0-12V 6VA PCB MOUNTING MAINS TRANSFOR-MER, normal 230v primary and conventional open windingconstruction, £1, Order Ref. 938AMSTRAD 3" DISK DRIVE, brand new. Standard replace-ment or why not have an extra one? £20, Order Ref. 20P28THIS COULD SAVE YOU EXPENSIVE BATTERIES, an in -car unit for operating 6v radio, cassette player, etc from carlighter socket, £2, Order Ref. 2P318MEDICINE CUPBOARD ALARM, or it could be used towarn when any cupboard door is opened, built and neatlycased requires only a battery, £3, Order Ref. 3P155FULLY ENCLOSED MAINS TRANSFORMER, on a 2m 3core lead terminating with a 13A plug. Secondary rated at6v 4A. Brought out on a well insulated 2 core leadterminating with insulated push on tags, £3, Order Ref.3P152, Ditto but 5A, £4, Order Ref. 4P69DON'T LET IT OVERFLOW, be it bath, sink, cellar, sumpor any other thing that could flood. This device will tell youwhen the water has risen to the pre-set level. Adjustableover quite a useful range, neatly cased for wall mounting,ready to work when battery fitted, £3, Order Ref. 3P156DIGITAL MULTI TESTER MG3800, single switching covers30 ranges including 20A ac and dc lOmeg input impedence,31/2 LCD display. Complete with lead. Currently advertisedby many dealers at nearly £40, our price only £25, OrderRef. 25P14ANALOGUE TESTER, input impedance 2K ohms per volt.It has 14 ranges, ac volts 0-500 dc volts 0-500, dc current500 micro amps at 250 milliamp, resistance 0-1meg-ohm,decibels 20 56dB. Fitted diode protection, overall size90x60x3Omm. Complete with test prods, price £7.50, OrderRef. 7.5P8LCD CLOCK MODULE, 1.5v battery operated, fits nicelyinto our 50p project box, Order Ref. 876. Only £2, Order Ref.2P307

SENTINEL COMPONENT BOARD, amongst hundreds ofother parts, this has 15 ICs all plug in so don't need de -soldering. Cost well over £100, yours for £4, Order Ref 4P67AMSTRAD KEYBOARD MODEL KB5. this is a mostcomprehensive keyboard, having over 100 keys including,of course, full numerical and qwerty. Brand new, still inmaker's packing, £5, Order Ref. 5P202SOLAR PANEL BARGAIN, gives 3v @ 100mA, £2, OrderRef. 2P324ULTRA SONIC TRANSDUCERS, 2 metal cased units, onetransmits, one receives. Built to operate around 40kHz,£1.50 the pair, Order Ref. 1.5P4INSULATION TESTER WITH MULTIMETER, internallygenerates voltages which enables you to read insulationdirectly in megohms. The multimeter has 4 ranges ac/dcvolts, 3 ranges dc milliamps, 3 ranges resistance and 5amps. These instruments are ex BT but in very goodcondition, tested and guaranteed OK, yours for only £7.50,with leads, carrying case £2 extra, Order Ref. 7.5P4MAINS ISOLATION TRANSFORMER, stops you getting toearth shocks, 230v in and 230v out. 150W upright mounting,£7.50, Order Ref. 7.5P5 and a 250W torroidal isolation, £10,Order Ref. 10P97MINI MONO AMP on pcb. Size 4"x2" with front panel holdingvolume control and with spare hole for switch or tone control.Output is 4W into 4 ohm speaker using 12v or 1W into 8ohm using 9v. Brand new and perfect, only £1 each, OrderRef. 495EXPERIMENTING WITH VALVES, don't spend a fortune ona mains transformer, we can supply one with standardmains input and secs. of 250-0-250v at 75mA and 6.3v at3A, £5. Order Ref. 5P1670-I MA FULL VISION PANEL METER, 23/4" square, scaled0-100 but scale easily removed for re -writing, £1, Order Ref.756

PCB DRILLS, 12 assorted sizes between .75 and 1.5mm,£1 the lot, Order Ref. 128.12V AXIAL FAN, for only £1, ideal for equipment cooling,brand new, made by West German company. Brushless sovirtually everlasting. Supplied complete with simple 12vtransistor circuit, £1, Order Ref. 918.

POWER SUPPLIES- SWITCH MODE

(all 230v mains operated)Astec ref. B51052 with outputs +12v .5A, -12v .1A, +5v3A, +10v .05A, +5v .02A unboxed on pcb size 180x130mm,£5, Order Ref. 5P188.

Astec ref. BM41004 with outputs +5v 31/2A, +12v 1.5A, -12v 1.5A, £5, Order Ref. 5P199Astec No. 12530 +12v 1A, -12v .1A, +5v 3A, uncased onpcb size 160x100mm. £3, Order Ref. 3P141Astec No. BM41001 110W 38v 2.5A, 25.1v 3A part metalcased with instrument type main input socket & on/off dprocker switch size 354x118x84mm, £8.50, Order Ref. 8.5P2Astec model No. BM135-3302 +12v 4A, +5v 16A, -12v0.5A totally encased in plated steel with mains input plug,mains output socket & double pole on/off switch size

400x130x65mm, £9.50, Order Ref. 9.5P4

POWER SUPPLIES - LINEAR

(all cased unless stated)4.5v dc 150mA, £1, Order Ref. 1045v dc 21/2A psu with filtering & volt regulation, uncased, £4,Order Ref. 4P63

6v dc 700mA, £1, Order Ref. 1036v dc 200mA output in 13A case, £2, Order Ref. 2P1126-12v dc for models with switch to vary voltage and reversepolarity, £2, order Ref. 2P39v de 150mA, £1, Order Ref. 7629v dc 2.1A by Sinclair, £3, Order Ref. 3P1519v dc 100mA, £1 Order Ref. 73312v dc 200mA output in 13A case, £2, Order Ref. 2P11412v 500mA on 13A base, £2.50, Order Ref. 2.5P412v 1A filtered & regulated on pcb with relays & Piezosounder, uncased, £3, Order Ref. 3P80

Amstrad 13.5v dc at 1.8A or 12v dc at 2A, £6, Order Ref.6P23

24v dc at 200mA twice for stereo amplifiers, £2, Order Ref.2P4

9.5v ac 60mA made for BT, £1.50m, Order Ref. 1.5P715v 500mA ac on 13A base, £2, Order Ref. 2P281AC out 9.8v (a' 60mA & 15.3v 150mA, £1, Order Ref. 751BT power supply unit 206AS, charges 12v battery andcuts off output should voltage fall below pre-set, £16, OrderRef. 16P6

Sinclair microvlslon psu, £5, Order Ref. 5P148

LASERS & LASER BITS

2111W laser, helium neon by Philips, full spec. £30, OrderRef. 30P1

Power supply for this in kit form with case is £15, OrderRef. 15P16, or in larger case to house tube as well, £18,Order Ref. 18P2.

The larger unit, made up, tested and ready to use,

complete with laser tube £69, Order Ref. 69P1

HEATING UNITS

Linear quartz glass tubes 360W, 2 in series for mains, £1,Order Ref. 907

1000W spiral elements for repairing fires etc. 3 for £1,Order Ref. 223

1000W pencil elements, 2 for £1, Order Ref. 3761.2kW mini tangential heater, ideal for under desk etc, £5,Order Ref. 5P23'2kW tangential heater, £6, Order Ref. 6P303kW tangential heater, £8, Order Ref. 8P2412' tubular heater, slightly storage soiled, £6, Order Ref.6P31

Water -proof heating wire, 60ohms per metre, 15m is rightlength for connecting to mains, £5, Order Ref. 5P109

The above prices Include VAT but please add £3towards our packing and carriage if your order is under

50. Send cheque or postal orders or phone & quotecredit card number.

M&B ELECTRICALSUPPLIES LTD

Pilgrim Works(Dept. WW),

Stairbridge Lane, Bolney,Sussex RH17 5PA

Telephone 0444 881965(Also fax but phone first)

926



ELECTRONIC ENGINEERS

REFERENCE BOOKThis reference bock is diviced into f ve parts:

techniques physical phenomena, materials antcomponents: electronic design and applications. The sixthedition was updated throughout to take into acacJntchanges in standards and materials as well as advancesin techniques. and was expanced to include newchapters on surface rrount tecinology. hardwa-e andsoftware design techniques, semi -custom electronics anddata commJnications.

6th Edition

ELECTRONICSENGINEER'S

s

REFERENCEBOOK

f

F F Mazda

Freidman Mazdahas worKed in theelectrcr cs andtelecom riunica-tons incustry forover twenty years.and is currentlyProduct andOperatonsManager. GenericNetworkManagement,with NorthernTelecon. He isthe author of sixtechni.-2.E1 books(translated intofour languages)and the editor oftheComm t_ -iicationsEngineersReference BookpublisiEd byButtermorth-Heiner ann.

CONTENTS:Techr iluesTrigorc-netricfunctions andgeneral formulae:

Calculus, Series and transforms; Matrices and detern nants:Electric circLit theory; Statistics. Piysical PhenomenaQuantities and units: Electricity: Light. Radiation. The ionosphereand troposphere. Materials and components Resistivematerials and components: Dielec:ric materials and components:Magnetic materials: Inductors and transformers; Relays;Piezoelectric materials and compcnents: Connectors; Printedcircuits: Power sources; Discrete semiconductors; Mc-owavesemiconduc-or devices: 3ptical digital integrated circJ -s. Linearintegrated circuits; Semiconductor memories; Microp-ccessors;Application -specific intecrated circuits; Electron microscopy:Digital design; Software engineering; Digital systems analysis;Control systems. Antenras and arays; Noise management inelectronic hardware, Noise and communication; Corrcuter aideddesign; Television and sound broadcast ng. ApplicalicnsCommunica-ion satellites: Point-to-point conmunicat ci, Fibre -optic communication; The integrated services digital network(ISDN): Local area networks: Radar systems; CompLtars andtheir application; Videotape retorting; Office commui cations;Medical electronics.

1006 pages PAPERBACK ISBN 07506 0809 9£42.50 (inc post & packaging)

6th EditionF F Mazda

* Now available to Electronics World & Wireless World readersin paperback.* Expert coverage of all aspects of electronics* Over 50 contrioutorE* For electronic engineers, technicians and students

Please supply me - copies of the ELECTRONICENGINEERS REFERENCE BOOK (ISBN 07506 0809 9) @£42.50 (INC POST & PACKAGING)

Add VAT at local rateNB ZERO RATE FOE UK & EIRE TOTAL

Business purchase: Please seed me the books list-ed with an invoice. I will arrange for my company to pay theaccompanying invoice within 30 days. I will alach my businesscard/letterhead and h ave signed the form below.

Guarantee: If you are not completely satisfied, books may bereturned within 30 de's in a resalable condition for a full refund.

Remittance enclosed £Cheques should be m ade payable to Reed Book Services Ltd.

Please debit my credit card as follows:

Access/Master Barclay/Visa

Amex Diners

Credit Card No. Exp date

NAME (Please print)

OF.GANISATICN

STREET

TCWN

COUNTY

COUNTRY

DATE

SIGNATURE

T3300

POST CODE

TELEPHONE NUMBER

VAT RATES6% Belgium, 25% Denmark, 5.5% France, 7% Germany, 4%Greece, 4% Ita y, 3% Luxembourg, 6% Netherlands, 5%Portugal, 3% Spain. FOR COMPANIES REGISTERED FORVAT, PLEASE 3UPP_Y YOUR REGISTRATION NUMBERBELOW (customers outside the EEC should leave th s partblank)VAT NO.

If in the UK please am 28 days for delivery. All prices are :.orrect attime of going to press but may be subject to change.

Please delete as approp riate. I do/do not wish to receive further detailsabout books, journals and information services.

Credit card orderaccepted by phone.Ca I 081 652 3614

Please retirn to: Lorraine Spindler, Room L333,Quadrant House, The Quadrant, Sutton, Surrey SM2 5AS

AUDIO

"Power tends to corrupt." First Baron Acton.

Class B output stages differ in at least threedifferent ways, presenting some intractabledesign problems. But class AB proves to be noanswer, says Douglas Self.

Distortionin power amplifiers4: the power amplifier stages

The almost universal choice in semi-conductor power amplifiers is for aunity gain output stage, and specifi-cally a voltage follower. Output stages

with gain are not unknowns, but they are notcommon. Most designers feel that controllingdistortion while handling large currents is hardenough without trying to generate gain at thesame time.

The first three parts of this series have dealtwith one kind of distortion at a time, due tothe monotonic transfer characteristics of smallsignal stages, which usually, but not invari-ably, work in class A2. Economic and thermalrealities mean that most output stages are classB, and so we must now consider crossoverdistortion, which remains the thorniest prob-lem in power amplifier design, and HFswitchoff effects.

It is now also necessary to consider whatkind of active device is to be used; jfets offerfew if any advantages in the small currentstages, but power fets are a real possibility,providing that the extra cost brings with it tan-gible benefit.

The class warThe fundamental factor in determining outputstage distortion is the class of operation. Apartfrom its inherent inefficiency, class A is theideal operating mode, because there can be nocrossover or switchoff distortion. However, ofthose designs which have been published orreviewed, it is notable that the large signal dis-tortion produced is still significant. This lookslike an opportunity lost, as of the distortionmechanisms discussed in the first part of thisseries, we now only have to deal withDistortion I (input stage), Distortion 2 (vas),

and Distortion 3 (output stage large signalnon -linearity). Distortions 4,5,6 and 7, as men-tioned earlier, are direct results of class Boperation and therefore can be thankfully dis-regarded in a class A design. However, classB is overwhelmingly of the greater impor-tance, and is therefore dealt with in detail.

Class B is subject to misunderstanding. Thestatement is often made that a pair of outputtransistors operated without any bias are work-ing in "class B", and therefore "generatesevere crossover distortion". In fact, with nobias each output device is operating for slight-ly less than half the time, and the questionarises as to whether it would not be moreaccurate to call this class C and reserve classB for that condition of quiescent current whicheliminates, or rather minimises, the crossoverartifacts.

A further complication exists; it is not gen-erally appreciated that moving into what isusually called class AB, by increasing the qui-escent current, does not make things better. Infact, the THD reading will increase as the biascontrol is advanced, with what is usuallyknown as "g, doubling" (ie a voltage gainincrease caused by both devices conductingsimultaneously in the centre of the output volt-age range) putting edges into the distortionresidual that generate high order harmonics inmuch the same way that underbiasing does.This important fact seems almost unknown,presumably because the gm doubling distortionis at a relatively low level and is completelyobscured in most amplifiers by other distortionmechanisms.

The phenomenon is demonstrated in Figs.la,b,c which shows spectrum analysis of thedistortion residuals for under biasing, optimal,

and over biasing of a 150W/851 amplifier at!kHz.

As before, all non-linearities except theunavoidable Distortion 3 (output stage) havebeen effectively eliminated. The over biasedcase had its quiescent current increased untilthe gm doubling edges in the residual had anapproximately 50:50 mark/space ratio, and sowas in class A about half the time which rep-resents a rather generous amount of quiescentfor class AB. Nonetheless, the higher orderodd harmonics in Fig. lc are at least 10dBgreater in amplitude than those for the optimalclass B case, and the third harmonic is actual-ly higher than for the under -biased case aswell. However the under biased amplifier,generating the familiar sharp spikes on theresidual, has a generally greater level of high-

order odd harmonics above the 5th; about 8dBhigher than the AB case.

Bearing in mind that high order odd har-monics are generally considered to be themost unpleasant, there seems to be a clear casefor avoiding Class AB altogether, as it willalways be less efficient and generate more highorder distortion than the equivalent class B cir-cuit. class distinction therefore seems to resolveitself into a binary choice between A or B.

It must be emphasised that these effects canonly be seen in an amplifier where the otherforms of distortion have been properly min-imised. The rms THD reading for case la was0.00151%, for case 1 b 0.00103%, and forcase lc 0.00153%. The tests were repeated atthe 40W power level with very similar results.The spike just below 16kHz is interferencefrom the test gear VDU.

This may seem complicated enough, butthere are other and deeper subtleties in class B.


AUDIO

Range: 0 dBmRes OW. .36 HzA:SWEPT SPECTRUM

01dBm

LogMag

10 dB/div

(a) -100

VBW: Off

mkr

4 -Mar -1992 1H: 45Swp lime: B.19 Sec

2 990 Hz -32.21 dBm

Cfri'vt 1,/

2 6Center: 10 000 Hz

AVERAGING AVG: 5

Range: 0 dBmRes BW: 36 HzA:SWEPT SPECTRUM

0dBm

LogMag

10 dB/div

(b) -100

VBW: OffMk r

10 Span: 20 000 Hz

4 -Mar -1992 16:41Swp Time: 8.19 Sec

2 950 HZ -30.55 dBm

2 4Center: 10 000 Hz Span: 20 000 Hz

AVERAGING AVU:U

Range: 0 dElm

Res BIN: 36 HzA:SWEPT SPECTRUM

(c)

VBW: OffMkr

01dBm

LogMag

10 dB/01v

4 -Mar -1992 17. 09Swp Time: 8.19 Sec

2 950 Hz -25.98 dBm

MI? ,mAlvv,v -

-100-100Center

AVEHA(,INc10 000 Hz

AVG. 5

10Span: 20 000 Hz

Fig. 1. Spectrum analysis of class B & ABdistortion residual. la). Under -biased class B;1b) Optimal class B; 1c) class AB.

Distortions of the outputI have designated the distortion produceddirectly by output stages as Distortion 3 (seePart 1); this subdivides into three categories.Mechanism 3a describes the large signal dis-tortion produced by both class A and B, ulti-mately because of the large current swings inthe active devices. In bipolars, but not fets,large collector currents reduce the beta leadingto drooping gain at large output excursions. Ishall use the term "LSN" for large signal non -linearity, as opposed to crossover andswitchoff phenomena that cause trouble at alloutnut levels.

Tne other two contributions to Distortion 3are associated with class B only; Distortion 3bthe classic crossover distortion resulting fromthe non -conjugate nature of the output char-acteristics, and is essentially frequency inde-pendent.

In contrast, Distortion 3c is switchoff dis-tortion generated by the output devices failingto turn off quickly and cleanly at high fre-quencies. This mechanism is strongly fre-quency dependent. It is sometimes calledswitching distortion, but this allows room forconfusion, as some writers use "switching dis-tortion" to cover crossover distortion as well.I refer specifically to charge storage turn offtroubles.

One of my aims for this series has been toshow how to isolate individual distortionmechanisms. To examine output behaviour, itis perfectly practical to drive output stagesopen loop providing the driving sourceimpedance is properly specified; this is diffi-cul, with a conventional amplifier, as it meansthe output must be driven from a frequencydependant impedance simulating that at thevas collector with some sort of feedbackmechanism incorporated to keep the drivevoltage constant.

However, if the vas is buffered from the out-put stage by some form of emitter follower, asdescribed in the last part, it makes thingsmuch simpler, a straightforward lowimpedance source (eg 5052) providing a goodapproximation of a vas -buffered closed loopamplifier. The vas buffer makes the systemmore designable by eliminating two variables- the vas collector impedance at LF, and thefrequency at which it starts to decrease due tolocal feedback through Cdom. This markedlysimplifies the study of output stage behaviour.

The large signal linearity of various kinds ofopen loop output stage with typical values areshown in Figs. 6-15. These diagrams were allgenerated by spice simulation, and are plottedas incremental output gain against output volt-age, with the load resistance stepped from1611 to Al The power devices are MJ802 andMJ4502, which are more complementary thanmany transistor pairs, and minimise distractinglarge signal asymmetry. The quiescent current


AUDIO

Fig. 2. Three types of emitter follower output stages.

(a)

Fig. 3. CFP circuitand quasicomplementarystages.

is in each case set to minimise the peak devi-ations of gain around the crossover point for80 loading; for the moment it is assumed thatyou can set this accurately and keep it whereyou want it. The difficulties in actually doingthis will be examined later.

There are at least 16 distinct configurationsin straightforward output stages not includingerror correcting3, current dumping4 orBlomley5 types. These are as follows:

Emitter FollowerComplementary Feedback PairQuasi ComplementaryOutput TriplesPower FET

3 types1 type

2 typesAt least 7 types.

3 types

Fig. 2Fig. 3Fig. 3Fig. 4Fig. 5

The emitter follower outputFigure 2 shows three versions of the mostcommon type of output stage; the double -emitter follower where the first follower acts

(b)

as driver to the second (output) device. I havedeliberately called this an emitter followerrather than a Darlington configuration, as thislatter implies an integrated device with asso-ciated resistors. As for all the circuitry here,the component values are representative ofreal practice.

Two important attributes of this topology are:The input is transferred to the output via two

base emitter junctions in series, with no localfeedback around the stage (apart from the verylocal 100% voltage feedback that makes anemitter follower what it is);

There are two dissimilar base emitter junc-tions between the bias voltage and the emitterresistor Re, carrying different currents and atdifferent temperatures. The bias generatormust attempt to compensate for both at once,though it can only be thermally coupled toone. The output devices have substantial ther-mal inertia and thus thermal compensation

(c)

represents a time average of the precedingconditions. Fig. 2a shows the most prevalentversion (type I) which has its driver emitterresistors connected to the output rail.

The type H configuration in Fig. 2b is at firstsight merely a pointless variation on type I,but in fact it has a valuable extra property. Theshared driver emitter resistor Rd, with no out-put rail connection, allows the drivers toreverse bias the base emitter junction of theoutput device being turned off.

Assume that the output voltage is headingdownwards through the crossover region; thecurrent through Rel has dropped to zero, butthat through Reg is increasing, giving a voltagedrop across it, so Tr4 base is caused to gomore negative to get the output to the rightvoltage. This negative excursion is coupled toTr3 base through Rd, and with the valuesshown can reverse bias it by up to 0.5V,increasing to 1.6V with a 452 load. The speed


AUDIO

(a)

Fig. 4. Three of the possible output tripleconfigurations.

up capacitor C. markedly improves this action,preventing the charge suckout rate being lim-ited by the resistance of Rd. While the type Icircuit has a similar voltage drop across Reg,the connection of the mid point of R1, R2 tothe output rail prevents this from reaching Tr3

base; instead Tri base is reverse biased as theoutput moves negative, and since charge stor-age in the drivers is usually not a problem, thisdoes little good. In the type II circuit thedrivers are never reverse biased, though theydo turn off. The important issue of output turnoff and switching distortion is further exam-ined in the next part of this series.

The type III topology shown in Fig. 2cmaintains the drivers in class A by connectingthe driver emitter resistors to the opposite sup-ply rail rather than the output rail. It is a com-mon misconception6 that class A driverssomehow maintain better low frequency con-trol over the output devices, but I have yet tosubstantiate any advantage myself. The driverdissipation is of course substantially increased,and nothing seems to be gained at LF as far asthe output transistors are concerned, for inboth type I and type II the drivers are still con-ducting at the moment the outputs turn off,and are back in conduction before the outputsturn on, which would seem to be all that mat-ters.

Type III is equally good as type II in reversebiasing the output bases, and may give evencleaner HF turn off as the carriers are beingswept from the bases by a higher resistanceterminated in a higher voltage approximatingconstant current drive; I have yet to try this.

(b)

Simple source followerfet output

Quasi -complementaryfet output

Fig. 5. Three mosfet output architectures.

The large signal linearity of the three ver-sions is virtually identical - all have the samefeature of two base emitter junctions in seriesbetween input and load.

The gain/output voltage plot is shown at Fig.6; with BJTs the gain reduction with increas-ing loading is largely due to the emitter resis-tors. Note that the crossover region appears asa relatively smooth wobble rather than ajagged shape. Another major feature is thegain droop at high output voltages and lowloads indicating that high collector currents arethe fundamental cause of this.

A close up of the crossover region gain for80 loading only is shown in Fig. 7; note thatno Vbias setting can be found to give a constantor even monotonic gain; the double dip andcentral gain peak are characteristic of optimaladjustment. The region extends over about±5V, independent of load resistance.

(c)

V.

v -

Full complementaryCFP fet output

Complementary feedback outputThe other major type of bipolar output is thecomplementary feedback pair (CFP) some-times called the Sziklai Pair, Fig. 3a. Thereseems to be only one popular configuration,though versions with gain are possible. Thedrivers are now placed so that they compareoutput voltage with that at the input. Wrappingthe outputs in a local negative feedback looppromises better linearity than emitter followerversions with 100% feedback applied sepa-rately to driver and output transistors.

This topology also has better thermal sta-bility, because the Vbe of the output devicesis inside the local feedback loop, and only thedriver Vbe affects the quiescent current. It isusually simple to keep drivers cool, and ther-mal feedback from them to the Vbias genera-tor transistor can be much faster and mechan-ically simpler.


AUDIO

OUTEF2C CIR: EF 0/P, MPSA42/92, 11J802/4502. 18/6/93Date/Time run 08/04/93 23:49:21 Temperature: 25.0

1.00.

LOAD.-16 SL

095

090

085

0.80+-60V -40V -2 0V

o . . DV(7)VIN

Fig. 6. Emitter follower large signal gain vs output.

-OV 20V

6 n -

5.7n.

4 sq.

OUTEF2C.CIR: EF 0/P, MPSA42/92, MJ802/4502. 18/6/93Dote/Time run: 08/04/93 23:39:07 Temperature: 25.0

1.00.

O 98

0,96

094

O 92

O 90+40V 60V -5 OV -4 OV

e V 0

-2 OVA DV(7)

2.95V

OV 2 OV 4 OV 5 OV

VIN

Fig. 7. Emitter follower crossover region gain deviations, ±5V range.

OUTPUT4C.CIR CFP 0/P, MPSA42/92,MJ802/4502, Re=0R22, Vbias= 18/6/93 OUTPUT4C.CIR CFP 0/P, MPSA42/92,MJ802/4502, Re=0R22, Vbias= 18/6/93Date/Time run: 08/04/93 23:54:32 Temperature, 25.( Date/Time run: 08/04/93 23:42.02 Temperature: 25.0

1.00T 100TLOAD

16 n.

095'

090,

085,

0.80+-60V -40V -20V

. DV(7)

6 se

570

4

-OV

VIN

20V

Fig. 8. Complementary feedback pair gain vs output.

Like emitter follower outputs, the drivers areconducting whenever the outputs are, and sospecial arrangements to keep them in class Aseem pointless. This stage, like emitter fol-lower type 1, can only reverse bias the driverbases rather than the outputs, unless extra volt-age rails outside the main ones are provided.

The output gain plot is shown in Fig. 8.Fourier analysis shows that the CFP generatesless than half the large signal distortion of anemitter follower stage. (See Table 1) Givenalso the greater quiescent stability, it is hard tosee why this topology is not more popular.

The crossover region is much narrower, atabout ±0.3V (Fig. 9). When under biased, thisshows up on the distortion residual as nar-rower spikes than an emitter follower outputgives.

40V 60V

O 98,

O 96

094

092

O 90+-2 OV -1 5V

130 V 0

-1.0V -0 5V0

OV 0 5V 1.0V 1.5V 2 OV. . . DV(7)VIN

Fig. 9. CFP crossover region ±2V, Vbias as a parameter.

The bad effects of gn, doubling as Vbiasincreases above optimal (here 1.296V) can beseen in the slopes moving outwards from thecentre.

Quasi complementary outputsThe original quasi complementary configura-tion7 was almost mandatory, as it was a longtime before pnp silicon power transistorsmatched the performance of the npn versions.The standard version shown at Fig. 3b is wellknown for poor symmetry around thecrossover region, as shown at Fig. 10. Aclose-up of the crossover region (Fig. 11)reveals an unhappy hybrid of the emitter fol-lower and CFP, as might be expected, and thatno setting of bias voltage can remove thesharp edge in the gain plot.

A major improvement to symmetry may bemade by using a Baxandall diode8 as shown inFig. 3c. This stratagem yields gain plots verysimilar to those for the true complementaryemitter follower at Figs 6, 7, though in prac-tice the crossover distortion seems rather high-er. When a quasi Baxandall stage is usedclosed loop in an amplifier in which distortionmechanisms 1 and 2, and 4 to 7 have beenproperly eliminated, it is capable of better per-formance than is commonly believed. Forexample, 0.0015% (1kHz) and 0.015%(10kHz) at 100W is straightforward to obtainfrom an amplifier with a negative feedbackfactor of about 34dB at 20kHz.

The best reason to use the quasi Baxandallapproach today is to save money on outputdevices, as pnp power transistors remain


AUDIO

EmitterFollower

CFP QuasiSimple

QuasiBax

TripleType 1

Simplemosfet

Quasimosfet

Hybridmosfet

8Q THD: 0.031% 0.014% 0.069% 0.050% 0.13% 0.47% 0.44% 0.052%Gain: 0.97 0.97 0.97 0.96 0.97 0.83 0.84 0.97

4Q THD: 0.042% 0.030% 0.079% 0.083% 0.60% 0.84% 0.072% 0.072%Gain: 0.94 0.94 0.94 0.94 0.92 0.72 0.73 0.94

Table 1. This summarises the spice curves for 4 and 8Q loadings. Each was subjected to Fourier analysis to calculateTHD results fora ±40V input.

QUASIICIR Ouasi-comp 0/P stage, voltage drive, perfect Vbias 30/4/93 OUASIl.CIP Quasi -comp 0/P stage, voltage drive, perfect Vbias 30/4/93

Date/Time run 08/05/93 20:32.10 Temperature: 25 0 Date/Time run. 08/05/93 21:13:21 Temperature 25.0

LOOT 1 00, -

LOAD

16 .0

moo- 6 n

0 95,

oa

090

0 85

0

-60V -40V -20V -0V. 0 . 0 dv(7)

20V 40V

2.B

60V

VIN

Fig. 10. Quasi complementary large signal gain vs output load resistance

somewhat pricier than npns. Given the tinycost of a Baxandall diode, and the absolutelydependable improvement it gives, there seemsno reason why anyone should ever use thestandard quasi circuit. My experiments showthat the value of R1 in Fig. 3c is not critical;making it about the same as R, seems to workwell.

TriplesWith three rather than two bipolar transistorsin each half of an output stage the number ofcircuit permutations possible leaps upwards.There are two main advantages if outputtriples are used correctly: better linearity athigh output voltages and currents; and morestable quiescent setting as the pre drivers canbe arranged to handle very little power, andremain almost cold in use.

However, triples do not automaticallyreduce crossover distortion, and they are, asusually configured, incapable of reverse bias-ing the output bases to improve switch -off.Fig. 4 shows three ways to make a triple out-put stage - all of those shown (with the pos-sible exception of Fig. 4c, which I have justmade up) have been used in commercialdesigns. The circuit of 4a is the Quad 303quasi complementary triple. The design of

0.98

096

094

092,

090+-20V -15V -10V -5V OV

VIN

Fig. 11. Quasi crossover region ±20V, Vbias as parameter.

triples demands care, as the possibility of localHF instability in each output half is very real.

Power fet outputsPower mosfets are often claimed to be a solu-tion to all amplifier problems, but they havetheir drawbacks: poor linearity and a high on -resistance that makes output efficiencymediocre. The high frequency response is bet-ter, implying that the second pole P2 of theamplifier response will be higher, allowing thedominant pole P1 be raised with the same sta-bility margin, and in turn allowing more over-all feedback to reduce distortion. However, theextra feedback (if it proves available in prac-tice) is needed to correct the higher open loopdistortion.

To complicate matters, the compensationcannot necessarily be lighter because the high-er output resistance makes the lowering of theoutput pole by capacitive loading more likely.

The extended frequency response creates itsown problems; the HF capabilities mean thatrigorous care must be taken to prevent para-sitic oscillation, as this is often promptly fol-lowed by an explosion of disconcerting vio-lence. Fets should at least give freedom fromswitchoff troubles as they do not suffer fromcharge storage effects.

5v 10V 15V

Three types of fet output stage are shown inFig. 5. Figures 12 to 15 show spice gain plots,using 2SK135/2SJ50 devices.

Most fet amplifiers use the simple sourcefollower configuration in Fig. 5a; the large sig-nal gain plot at Fig. 12 shows that the gain fora given load is lower, (0.83 rather than 0.97for bipolar, at 8c2) because of low gm. This,with the high on resistance, noticeably reducesoutput efficiency.

Open loop distortion is markedly higher;however large signal non -linearity does notincrease with heavier loading, there being noequivalent of "bipolar gain droop". Thecrossover region has sharper and larger gaindeviations than a bipolar stage, and generallylooks pretty nasty; Fig. 13 shows the difficul-ty of finding a 'correct' Vbias setting.

Fig. 5b shows a hybrid (ie bipolar/fet) quasicomplementary output stage9. The stage isintended to maximise economy rather thanperformance, once the decision has been made(probably for marketing reasons) to use fets,by making both output devices cheap n -chan-nel devices; complementary mosfet pairsremain relatively rare and expensive.

The basic configuration is badly asymmet-rical, the hybrid lower half having a higherand more constant gain than the source fol-

20V


AUDIO

OUTFET.CIR FET 0/P stage, voltage driveDate/Time run: 08/05/93 21722732

1.07

0,9

0.8

07

0.6.

4

0.4+ r r

-60V -40V -20V. > . v . . dv(7)

2SK135/25J50. 14/6/93OUTFET CIR FET 0/P stage, voltage drive, 2SK135/2SJ50 14/6/93Temperature: 25 0

Date/Time run. 08/05/93 21:32 19 Temperature 25 0

-0v

VIN

LOAD

--.- n.

20V

Fig. 12. Source follower fet large signal gain vs output.

40V

BIPFET.CIR Comp FET 0/P stage, BJT drivers 25K135/25J50. 15/6/93Date/Time run: 08/05/93 21744:04

1.007

0.95

0.90

0.85

0 80+-60V -40V -20V

o . . 0 dv(7)

60V

Temperature. 25 0

*

-0V

VIN

20V

Fig. 14. Complementary bipolar fet gain vs output.

lower upper half. Increasing the value of Re2

gives a reasonable match between the gains ofthe two halves, but leaves a dauntingcrossover discontinuity.

The hybrid full complementary stage in Fig.5c was conceivedl° to maximise performanceby linearising the output devices with localfeedback and reducing 1q variations due to thelow power dissipation of the bipolar drivers. Itis highly linear, showing no gain droop atheavier loadings (Fig. 14) and promises free-dom from switchoff distortion. But, as shown,it is rather inefficient in voltage swing. Thecrossover region (Fig. 15) still has some dubi-ous sharp corners, but the total crossover gaindeviation (0.96-0.97 at 8S2) is much smallerthan for the quasi hybrid (0.78-0.90) and soless high order harmonic energy is generated.

8

40V 60V

900m

700m+-15V -10V

12 0 V 0

-5V dv(7)

OV 5V

VIN

Fig. 13. Source follower fet crossover region ±15V range.

lOy 15V

BIPFET.CIR Comp FET 0/P stage, BJT drivers; 2SK135/2SJ50. 15/6/93Date/Time run: 08/05/93 21751723 Temperature: 25.0

980m r

960m,

940m,

920m,

900m,

880m

860m-5 OV -4 OV -2 OV OV

X V dv(7)VIM

Fig. 15. Complementary BIT fet crossover region ±15V range.

Next month: Controlling large signal non -linearity, crossover, and switch -off distortion.

References1. Mann R. The Texan 20+20 Watt StereoAmplifier. Practical Wireless, May 1972, p48.2. Takahashi. Design & Construction of High

Slew Rate Amplifiers Preprint No. 1348 (A 4)

20V 4.0V 5 OV

for 60th AES Convention 19783. Hawksford MO. Distortion Correction inAudio Power Amplifiers. )AES Jan/Feb 1981p27 (Error correction)4. Walker P. Current dumping audio amplifier.Wireless World 1975 pp60/625. Blomley. New Approach To class B.Wireless World, Feb 1971, p57 & Mar 1971,p127/1316. Otala. An Audio Power Amplifier forUltimate Quality Requirements IEEE Trans onAudio & Electroacoustics, Dec 1973, p5487. Lin, H. Electronics, Sept 1956 ppl 73/1758. Baxandall P. Symmetry in class B. Letters,Wireless WorldSept 1969 p416.9. Self D. Sound mosfet design. Electronics &Wireless World Sept 1990, p760.10. Self D. Mosfet audio output, letter,Electronics & Wireless World, May 1989,p524 (see also9.)


M & B RADIO (LEEDS)THE NORTH'S LEADING USED TEST/EQUIPMENT DEALER

OSCILLOSCOPES

475207 --TEKTRONIX 475 200MHZ DUAL TRACE WITHRROBES ..... 8400TEKTRONIX 466 100MHZ STORAGE 095TEKTRONIX SC504/TP4503/DM501 PORTABLE 80MHZ SCOPE +

iW ATSU I SS6 I 22 100MHZ 4 TRACE CURSO 1900HITACHI V222 20MHZ DUAL TRACE WITH MANUAL............... L225GOULD 054000 10M1 -1Z DIGITAL STORAGE L I 95

FARNELL DTC 12 I 2MHZ DUAL TRACE/COMPONENT TESTER (175FARNELL DT 12/5 12MHZ DUAL TRACEHP 17228 275MHZ MICROPROCESSOR CAL MEASUREMENTS......... L750HP I 725A 275MHZ OSCILLOSCOPES (AS NEW) £600TEKTRONIX 465A/B I 00MHZ DUAL TRACE PRICES FROM ............. £300

NICOLET 4094A DIGITAL OSCILLOSCOPE £500

SIGNAL GENERATORSMARCONI 2019 80KHZ TO 1040MHZ L1900MARCONI 70 IBA 80KHZ TO 520MHZ L1250MARCONI 2018 80KHZ TO 520MHZ SYNTHESIZED 7777. 7477. L750MARCONI 2008 10KHZ TO 520MHZ INC. RF PROBE KIT

MANUAL . 000MARCONI 2015/2171 SYNCHRONIZER 10MHZ TO 520MHZ (AS

NEW) . L325HP 864013 500KHZ TO 550MHZ OPT. 001... . . . L650HP 86 I 6A I 8GHZ TO 4.5GHZ ... L295HP 33108 0005HZ TO SMHZHP 4204A 10KHZ TO 10MHZ OSCILLATOR .L250HP 8165A 00 I HZ TO 50MHZ PROD SIGNAL GENERATOR............... L950ADRET 740A I OKHZ TO 1.IGHZ SYNTHESIZED L1500FARNELL SSG2000 I OKI-IZ TO 2GHZ SYNTHESIZED (AS NEW) L2250FARNELL 55G1000 10KHZ TO IGHZ SYNTHESIZED (AS NEW) £1500FARNELL 55G520 10MHZ TO 520MHZ & TTS 520 TRANSMISSION

I EST SET ..................................... . L800ADRET 20230A MHZ SYNTHESIZED SOURCE L 195POLRAD I I INSET 1.8 TO 4.6GHZ WITH MODULATOR.............. L400RHODE & SCHWARZ TYPE SMC I 4.8GHZ TO I 2.6GHZ ...._.. £500RHODE & SCHWARZ NOISE GENERATOR I TO 1000MHZ SKTU

,NEW. . SOWA VETE K 193 20MHZ SWEEP FUNCTION GENERATOR__ L295MARCONI 2020 50KHZ TO 520MHZ SYNTHESIZED . £500MARCONI 2000 20KHZ TO 20KHZ WITH METERED

ATTENUATOR.TEX SCAN V56011 SWEEP GENERATOR . £250SAY ROSA FREQUENCY OSCILLATOR MA30 10HZ TO

10KHZ (2S0EXACT 628 20MHZ PULSE/SWEEP FUNCTION

GENERATOR £650GIGAGR1101A 12 TO HIGHZ PULSE GENERATOR (NEW) (750

TEST EQUIPMENTE F RATON FRT ATOMIC FREQUENCY STANDARD L2500HP 5065A RUBIDIUM VAPOR FREQUENCY STANDARD [2000

MARCONI 2955 COMMUNICATIONS TEST SET 7777. 7777. L3000MARCONI 2305 MODULATION METER L2000MARCONI TF23038 MODULATION METER. L395MARCONI 2331 EXTORTION FACTOR METER . . . L250FARNELL LA520 RF AMPLIFIER I .5MHZ TO 520MHZ LISO

FARNELL TH8 TFUE EMS SAMPUNG RF METER (AS NEW) IGHZ 050TEKTRONIX 521A PAL VECTORSCOPE. L1000DYMAR 2085 AF FOWER METER f225BIRD TENULINE4343 100W 6DB ATTENUATOR (NEW) .L100NARDA 3022 B I DIRECTIONAL COUPLER IGHZ TO 4GHZ .......... L250NARDA 3001.30 DIRECTIONAL COUPLER 460MHZ -0 960MHZ L100AVO RM2IS US AC/DC BREAKDOWN TESTER L300ROTEK AC/DC PFECISION CALIBRATOR...._._..........L650EXACT 334 CURF.ENT PRECISION CALIBRATOR £195HP 11667A POWER SPLITTER (NEW) 18GHZ £600HP 11683A POWER METER CALIBRATOR.... _ 8300NARDA 769/6 I 5CW 600 HIGH POWER ATI- (NEW) L100

RACAL DANA 9:03 TRUE RMS RE LEVEL METER.. _ . £700RACAL DANA 6000 MICROPROCESSING DVM 4477.. _ 8300RACAL DANA 9000 MICROPROCESSING TIMER COUNTER

L275RACAL DANA 4118 IEEE STD 488 BUS ANALYSER L250RACAL DANA 1102 THERMAL PRINTER LI50RACAL DANA 9302 RF MILUVOLTMETER 10KHZ TO I 500MHZ 8400RACAL 930IA RF MILLIVOLTMETER I OKHZ TO 150C MHZ ...............8250RACAL 9008 MODULATION METER 8300RACAL DANA 1998 1 .3GHZ FREQ COUNTER/TIMES . 8750RACAL 9811 3GI- Z FREQUENCY COUNTER . L225RACAL 9921 3G1- Z FREQUENCY COUNTER L4043RACAL 9903 TIMER COUNTER. . L100RACAL 9904 TIMER COUNTER. L150RACAL 9915 10H2 TO 520MHZ FREQUENCY COUNTER.......... . L150RACAL 9919 1.1 GHZ FREQUENCY COUNTER/TIMER L32.5HP 435A POWER METER 8482H HEAD . £650

FARNELL 530/S ,Z)WER SUPPLY 0-30VOLT SAMP.................. .....845FARNELL 1330820 POWER SUPPLY 0-30VOLT 20A71._.......... 1100RACAL 9063 TWO TONE GENERATOR . L250FARNELL ELECTRONIC LOAD RB1030/35. L495FARNELL TRIPLE OUTPUT POWER SUPPLY TOPS X)FARNELL L50/0.7AMP POWER SUPPLY t95MARCONI TF2910/4 TV UNEAR DISTORTION ANALYSER .............. £750MARCONI TF2913 TEST LINE GENERATOR + INSERTER............... L750MARCONI TF2914A INSERTION SIGNAL ANALYSER_________ .. L750

FEEDBACK SS0603 SINE/SQUARE AUDIO OSCILLATOR .....L85FEEDBACK 602 VARIABLE PHASE OSCILLATOR. LI 45FEEDBACK 5E0611 I 2MHZ SWEEP FUNCTION GENERATOR..._. 045FEEDBACK TFA TRANSFER FUNCTION ANALYSE ... L295

HP 8405A VECTOR VOLTMETER & ACCESSORIES L850HP 8406A COME FREQUENCY GENERATOR 7777. 7777. L250HP 346813 DIGITAL MULI1METER £400HP 3466A DIGITAL MULTIMETER L200HP 8750A STORAGE NORMAUZER L395HP 3400A TRUE RMS VOLTMETER LI45

HP 340 .0 TRUE RMS VOLTMETER DIGRAL. (ISOHP 394A VARIABLE ATTENUATOR IGHZ TO 2GHZ. LB5HP 340.4A SAMPLING VOLTMETER ....................HALC` ON 511106/52181 UNIVERSAL TEST SYSTEM L650TEKTRONIX 576 CURVE TRACER & 172 PROGRAMME VEIL F TEST

PSI A1601 WAVEFORM.............._._............................._....£225HP I 0529A LOGIC COMPARATOR. 185I WATSIJI I GHZ FREQUENCY COUNTER. L325HP 5006A SIGNATURE ANALYSER ..L39SKEMO DPI PHASE METER IHZ TOWAYNE KERR CT496 LCR BRIDGE PORTABLE_MARC )NI TF2700 LCR BRIDGE PRICES FROM._ .L95

HP 33411 DISTORTION METER... ..L2S0FLUKE 33308 PROD CONSTANT CURRENT/VOLTAGE

CALBRATORUNACF114 FIELD STRENGTH METER .............................._._................._.....£65

PACIF C MEASUREMENTS 1 034A RF POWER 1MHZ TO.186 4Z . [450

PHILDS PM5565 VIDEO WAVEFORM MONITOR ............. L225BA LLA.NTINE 6125C PROD TIME/AMPLITUDE TESTSET. L500FERRO GRAPH RTS2/ATU I AUDIO TESTSET .L300TE KT -ON IX 1421 VECTOR SCOPE . t400TEKTRONIX 528A VIDEO WAVEFORM MONITC R... 000AILTH 533X- II CALIBRATOR. [400SIEMENS U2233 PSOPHOMETER (NEW). L500

SPECTRUM ANALYSERS

HP 857.815 I OMHZ TO I .5GHZ WITH 1827 MAINFRAME....... E1000HP 141 T (1552B IF 855413/8553B RF UNITS.

000HP 3540A 5KHZ TO 50KHZ ANALYSER (NEW) ,C£2217,50

BAK 2033 AUDIO ANALYSER I HZ TO 20KHZMARCONI 2370 I I OMHZ ANALYSER 6950HP 1411 T 1155311/8552B I IOMHZ WITH 8443A TRACKING GENERA TOR

(AS L2000HP 9444* RACKING GENERATOR TO 1300MHZ .......................t1000TEKTRONIX 492 50KHZ TO 18GHZ PORTABLE L5500TEKTRONIX 492AP I OKHZ TO 22GHZ (325GHZ)............................/7000HP 358181 WAVE ANALYSER I 5HZ TO 50KHZ (AS NEW)................... DISOHP 8505/1 NETWORK ANALYSER SOOKHZ TO I 300MHZ.................. MOO

RADIO EQUIPMENT11600

RACAL RA2309B/RA2295PHIUPS 88MHZ TO 108MHZ BROADCAST TX I OKW ........... L3000

L159EDDYSTONE 1990/3 RECEIVER 25 TO 1450ROCKWELL COLLINS HF8014A EXCITER (NEW)..................... L900

000RACAL RA I T/9/MA 1107 HE L1700REDIFON 5500 SYNTHESISED HE RECEIVER..._..__............ L500

BULK PURCHASE SPECIALS

MARCONI 1101 RC OSCILLATOR 20HZ TO 20KHZADCOLA 777 DESOLDERING STATION..

ALL PRICES PLUS VAT AND CARRIAGE86 Bishopsgate Street, Leeds LS 1 4BB

Tel: (0532) 435649 Fax: (0532) 426881

.C458100

'111. LE NO. (HON REPLY CARD

FIBRE -OPTICS EDUCATOR

Versatile trainingequipment foreducation andindustry.

FIBRE -OPTICS POWER METER

dBm and euWscale; battery life500 hours.

FIBRE -OPTICS MONITOR

For continuitytesting and voicecomms.

For further details contact:ELLMAX ELECTRONICS LTD.,Unit 29, Leyton Business Centre,Etloe Road, Leyton, London, E10 7BTTelephone: (081) 539 0136Fax: (081) 539 7746

[ELLMAXECTRONICS

10 OUTLET DISTRIBUTIONAMPLIFIER 4

A compact mains powered unit with one balanced inputand ten AC and DC isolated floating line outputs. Exemplary RF breakthrough specifications giving

trouble -free operation in close proximity to radio tele-phones and links..

Excellent figures for noise, THD, static and dynamicI MD.

Any desired number of outlets may be provided atmicrophone level to suit certain video and audio re-corders used at press conferences.

Meets IEC65-2, BS415 safety.*Advanced Active Aerial 4kHz-30MHz *PPM10 in -vision PPM andchart recorder *Twin Twin PPM Rack and Box Units *Stabilizersand Fixed Shift Circuit Boards for howl reduction *BroadcastMonitor Receiver 150kHz-30MHz *Stereo Variable EmphasisLimiter 3 *Stereo Disc Amplifier *Peak Deviation Meter *PPM5hybrid, PPM9 microprocessor and PPM8 IEC/DIN -50/+6dBdrives and movements *Broadcast Stereo Coders

SURREY ELECTRONICS LTDThe Forge, Lucks Green, Cranleigh,

Surrey GU6 7BG.Telephone: 0483 275997. Fax: 276477


November 1993 ELECTRONICS WORLD+WIRELESS WORLD 935

TELEUI51011Subscribe to the magazinethat experienced electronicsprofessionals never missWhatever your interest in the world of television electronics, there's awealth of news, advice and hard information for you in TELEVISION.

TELEVISION offers you a definitive guide to today's TV electronicsbusiness, keeping you up-to-date with new developments in TV, video andsatellite - whilst furnishing you with 'hands-on' advice and information onthe latest equipment.

EVERY MONTH - EVERYTHING YOU NEED TO KNOWOnce you are a subscriber to TELEVISION you'll enjoy a great informationadvantage. You'll be ahead of all of the latest product developments - you'llreceive inside information on important techniques and time -saving workmethods - and, importantly, you'll have access to the most comprehensivemarketplace for components and services in the UK.

Servicing solutions TV fault finding New Products VCR clinic Satellite TV Equipment reviews Readers' letters CD players casebook Components News and comment And much more!

Quite simply TELEVISION is the 'bible' of the television electronics industry - if you want to keepup with the competition, you can't afford to be without it.

SUBSCRIBING IS SIMPLEComplete the coupon and return it to us at TELEVISION, Reed Business Publishing, FREEPOST,9th Floor, Quadrant House, The Quadrant, SUTTON, Surrey SM2 5BR

Please send me TELEU151011One Year at a cost of £26

.1 Two Years at a cost of £49 SAVE £31 Three Years at a cost of £70 SAVE £8

Name

Job Title

Company

Address

Postcode

Telephone No.

Fax No.

Reed Business PublishingCompany Registered in England(registered number 151537)VAT no: 235723565

4 WAYS TO PAY1 , I enclose a cheque for £ made payableto Reed Business Publishing

2 Please charge my:Access Li Visa

_ Diners Club E] American ExpressExpiry Date

-__1 j_i LI LI

3 Please invoice me/my companyOrder No

4 Or alternatively just ring our credit card hot-line on0622 721666 and quote reference RJ3

Are you registered for VAT, Yes No -

If yes, please supply your registration Number

Please send a VAT receipt

Signature DatePrices apply to UK, Isle of Man. and Channel Islands only.

RJ3

-


936 ELECTRONICS WORLD +WIRELESS WORLD November 1993

HISTORY

George Pickworth traces the evolution ofthe rotary discharger, from simple

hemispherical electrode to the complexity ofMarconi's 300kW transmitter

The spark that gave

to the worldThe spark -electrode assembly, the dis-charger, was of vital importance to thethe spark transmitter, in the same way

as the thermionic valve was to the valve -typetransmitter.

Early dischargers were simply a pair ofhemispherical electrodes housed in a sounddeadening wooden box. But this design wassuperseded, in all but low power installations,by Wien's quenched gap - adopted almostuniversally by the Telefunken company - andby rotary type dischargers taken up by theMarconi company.

Evolution of the spark transmitter is essen-tially that of the discharger. In this article, wewill concentrate mainly on the rotary dis-charger, of which there two basic types: plain,using disc type electrodes to facilitate coolingand so reduce electrode erosion: and thoseemploying radial or transverse electrodeswhose role was to initiate and then quench adischarge after a given number of oscillations.These are referred to as either interrupters, orquenched -spark type dischargers.

As they were self cooling, rotary dischargerswere inherently suited to high power installa-tions. Their development stemmed fromexperimentation with different methods of

quenching the discharge, and from early hemi-spherical types to highly complex rotarydesigns - culminating in Marconi's 1914.300kW synchronous discharger

Resonating selectivityThe term "spark transmitter" described whatappeared to be a momentary electric dis-charge, and it became the generic name forthis type of transmitter. The discharge wasoscillatory with a duration corresponding tothe train of oscillations.

Perhaps "arc" would have been a slightlymore exact description, but this would havecaused confusion with quenched -arc continu-ous -wave systems. Spark transmitters weregeneralised as wave train transmitters.Amplitude of the wave train declined steeply -especially with early systems.

This was the principal reason for developingcontinuous wave systems: "syntony", a terminvented by radio pioneer Lodge to describereceiver selectivity by resonance, where oscil-lations progressively build up in amplitude inthe receiver tuner.

With spark transmitters, resonance, andtherefore syntony, is largely ineffective. Oneeffect of quench -type dischargers was to

431

a

increase the number of significant waves ineach train and so allow a small measure ofsyntony.

Even where syntony was not vital, forexample in maritime systems which did notrequire a long range and where the frequencyspan was large, quenching still greatlyimproved transmitter efficiency.

Quest for long rangeEarly in the history of radio, before the rela-tionship of wavelength and transmission dis-tance was appreciated, long range was syn-onymous with high power.

Engineers knew that high effective powercould best be obtained by storing energy andsuddenly releasing it by spark discharge - thebasic principle of spark transmitters.

Much of Marconi's early work in the questfor long range was with "unti.ned" systems,where energy was stored in the antenna andreleased by a spark discharge - virtually as an

The Caernarfon three turn, 2.0m diameterprimary circuit inductor -a single layer helixof stranded insulated wire wound around ahollow 300mm tube. The three sectionantenna coupling coil was supported on asquare section wooden beam.


HISTORY

electromagnetic pulse. The pulse. being ape-riodic, has no frequency, so cannot be tuned(syntony was out of the question).

Nonetheless, an EM pulse can contain anenormous amount of energy: inducing a cur-rent pulse in the receiver antenna; triggeringthe coherer (a sensitive relay); activating amorse-inker (powered by its own battery), andso registering a dot for each pulse.

Grouped pulses were used for Morse sig-nalling (Fig. 3).

Spark system principlesA capacitor suddenly discharging across aspark gap and through an inductor causes anoscillatory discharge at a frequency set bythe values of the capacitor and inductor.(Fig. 1).

In early spark systems, DC pulsesgenerated by an induction coil periodicallycharged the capacitor. But because of theshort duration of the pulses, capacity valuewas limited to that which could be charged(typically to 15kV) within the pulse duration- only a fraction of the coil's open circuitpotential.

Theoretically, an open circuit allows thepotential across the secondary of aninduction coil to rise to infinity when theprimary circuit is interrupted. So, to avoiddamaging the coil through a broken chargingcircuit, protection spark gaps were placedacross the coil's secondary winding.Induction coils were graded by maximumsafe open circuit spark length, for example6in or 12in.

Transformer systems give a much longerduration of each negative- or positive -goingAC half cycle than an induction coil pulse.Their longer charging period enables moreenergy to be stored, while still allowing thecapacitor to charge to typically 15-30kV.

When the potential reaches the pointwhere the air dielectric between the spark -gap breaks down - typically 4.0kV/1.0mmgap - ionisation dramatically reduces theresistance across the gap. Every dischargeinitiates a wave train, with the periodbetween each train setting the tone heardwith rectifier type receivers.

Induction coil -type transmitters had theirdischarge rate set by the interrupter -typically a few hundred Hz .

For the early transformer systems,employing fixed hemispherical electrodes,discharge repetition rates were set by the ACfrequency (bearing in mind that there aretwo discharges per cycle). High frequencyalternators, typically 500Hz, were generallyused with transformer systems.

In rotary dischargers, drive speed and thenumber of electrodes set the discharge rate.

Shock excitationInstead of discharging the capacitor directlythrough the tuned circuit, as with simplespark systems, it can be discharged throughan additional coil with very low inductanceand resistance, inductively coupled to thetuned circuit. Quickly quenching thedischarge so that the capacitor dischargesvirtually a single unidirectional pulse, shocks

More energy from tuned systemsMuch more energy could be stored in a capac-itor proper than in an antenna. So later tunedsystems discharged the capacitor through aninductor to generate a train of exponentiallydeclining oscillations. Frequency was set by thevalue of the capacitor and inductor (see box)

All the radiated energy first had to be storedin the capacitor so it had a large value. But totune the system to the maritime frequencies -500kHz and 1.0MHz - the inductor value waslow, typically a few turns of heavy gauge wire.

the tuned circuit into oscillation at itsresonant frequency. This was the effectexploited by Prof Wien and adopted by theTelefunken system under the name"quenched spark", Fig. la.

The quenched -arc system had its roots inElihu Thompson's 1892 "wave generator"which consisted of an arc lamp burning DCand shorted by an inductor and capacitor inseries. The oscillator generated continuousoscillations, so the arc appeared to burncontinuously - hence the name. But this toowas quenched and re -ignited every rf halfcycle (Fig. 2).Operation of the quenched arcis complicated and still not fully understood.But a simplified explanation is that thechoking coils, and in some cases a variableresistor, limit the rate at which the capacitorcan charge. Once the arc is struck, itsresistance falls to a low level. Current is thendrawn from the capacitor faster than it isreplaced, and potential falls to a point wherethe arc is quenched.

Resistance across the gap then reverts to ahigh level and the capacitor re -charges. Thecycle is repeated at a rate set by the resonantfrequency of the inductor/capacitor.Potential at which the arc is quenched is setby the gap -width, but to ensure quenching,ionised gases have to be scavenged.

Spark or quenched arc?As a general rule, early systems powered byhigh potential pulsed DC, generated by aninduction coil, can be considered as sparksystems.

Ordinary transformer -type sparktransmitters with hemispherical electrodesalso operated as true spark systems becausethe spark -gap was set so wide that dischargedid not occur until the capacitor hadcharged to operational potential.

Marconi's interrupter -type rotarydischargers also made use of shockexcitation. These were mechanical, so muchslower than the Wien quenched gap, whichwas a magnetic device. Quenching seems tohave occurred after a number of oscillations,depending on design of the interrupter andresonant frequency of the exciter circuit.However, subsequent oscillations declinedvery rapidly in amplitude after the initialpulse.

A similar shock effect would also havebeen significant with early spark transmittersemploying loosely -coupled antenna circuits.

Marconi's transmitters, with their multi -spark interrupter rotary -dischargers, seem tohave operated primarily in the shock

Originally, the antenna was connecteddirectly to the inductor, and energy was radi-ated as exponentially declining waves. But, atclose range, the large -amplitude first wave ofthe train shocked the receiver tuner into oscil-lation at the frequency to which it happened tobe tuned, known as "spark jamming".

At longer range, syntony was virtually nil.The amplitude of the waves declined toorapidly for resonance to be effective, thoughthe coherer could still be used as the detector(Figs. 4 and 4a).

excitation mode. But they may well haveoperated in quenched -arc mode during eachnegative- or positive -going half AC cyclewhen, in effect, the source current is DC.Systems employing fixed gap dischargersand energised by smooth high potential DCinvariably operated in the quenched arcmode.

Induction coilor transformer

Spark gap

tIsolating chokes

Fig. 1. Basic spark oscillator.

Oscillatory circuit

Ballast Reservoirresistor capacitor Resonant

circuit

Interruptor

Currentpulse

Fig. la. Wien's quenched spark adoptedby Telefunken.

Carbon rods

DC power supply

Isolating chokes

Tuningcapacitor

Oscillatory circuit

Fig. 2. Quenched arc oscillator generatingcontinuous oscillations, with the arcquenched and reignited every rf half cycle.


HISTORY

Loose antenna couplingIonisation dramatically lowers the resistanceacross the spark -gap. But as the gap is inseries with the capacitor and inductor, it dis-sipates appreciable energy. The logical way tominimise the loss is immediate transfer of theenergy by EM induction to a tuned -secondarycircuit, normally the antenna system.

The horizontal part of the antenna hascapacitance with earth, or ship deck, and inconjunction with the antenna coupling coil,creates a resonant circuit. The antenna's lowcapacitance value meant the secondary wind-ing normally had many more turns than theprimary. But, with small ships where thelength between the masts is limited, antennacapacity was increased by employing severalparallel wires.

When the antenna circuit was precisely intune with the primary circuit, the amplitude ofthe oscillations in the antenna circuit rose lesssteeply and declined more slowly than in theprimary circuit, radiating pear-shaped wavetrains. Although the amplitude of pear-shapedoscillation trains declined as a result of energybeing radiated, the reduction in number of sig-nificant waves was much less pronouncedthan with exponentially declining wave trains,allowing a very limited degree of syntony(Fig. 5, 5a, 5b and 5c).

Beats occurred if the primary and secondarycircuits were not tuned to precisely the samefrequency (Fig. 5d) but this problem wasavoided by shock excitation.

QuenchingEven a loosely -coupled antenna coil allowedsome energy to be re -transferred to the pri-mary circuit and dissipated by the spark -gap.The logical approach was to quench the dis-charge so that the spark -gap reverted to itshigh resistance state. By quickly quenchingthe discharge, the incidence of beat notes wasgreatly reduced.

In Wien's quenched gap, the discharge wasprobably quenched after less than six oscilla-tions, so the the secondary circuit was virtuallyshock excited. To all intents, this preventedgeneration of beats.

One way of quenching was to direct an air -blast across the gap to disperse the ionisedgases. As energy was transferred to the sec-ondary circuit, amplitude dropped to the pointwhere the air -blast prevented re -ignition of thearc after being quenched at the end of an rfhalf cycle. But the method posed practicalproblems and was not widely used.

Prof Wien's simple and elegant approach,developed in 1906, was to use the spark's ownmagnetic field to drive the discharge radiallyto a wide part of the gap where it was auto-matically quenched. This "quenched -gap" wasadopted almost universally by the TelefunkenCompany (Fig. 6a).

Essential feature of the Wien quenched gapwas its pile of pairs of discs, each pair sepa-rated by mica washers to create a spark gap.The discs all had a circular groove close to theperiphery, and their flat surfaces were parallel

InterrJpter

Induction coil

Fig. 3. Marconi's untuned system. Energy stored in the antenna was released by a spark discharge.

History replicatedThe earl y radiopioneers produced"oscillograms" usinga special camerafocused on a fairlywide horizontalspark gap. Duringdischarge, thephotographic platewould drop rapidlyso tracing the imageon a moving plate.

To produce theoscillograms shownin this article, Iconstructed smallscale reproductionsof each transmitter.The oscillograms,recorded with scopeand camera, areessentially the sameas early graphicrepresentations ofwave formsproduced by theearly workers andconfirm what theyhad intuitivelydeduced. The resultsalso give anindication of thephilosophies ofthose pioneers andtheir approach toproblem solving.

GP

Fig. 4. First generation tuned systemwith directly connected antenna.

Oscillatory circuit

Fig. 4a. Wave train radiated by early maritime spark transmitter. Directlycoupled antenna heavily damps the oscillations.

and silver plated to prevent formation of pim-ples than would short the discs (Fig 6).

During discharge, the magnetic field thatdeveloped around the axis of the pile drovethe sparks radially to the groove where gap -width was greater and the discharge was extin-guished. The number of pairs of discs in cas-cade depended on power requirements: for12.5kV this was typically 14.

The capacitor was discharged virtually as asingle unidirectional pulse, shocking thetuned circuit into oscillation at its resonantfrequency.

Marconi experimented with a similar devicebut rejected it in favour of his rotary -type

quenched -discharger where the gaps widenedafter each discharge.

Interrupter -type rotary dischargersEarly Marconi synchronous rotary dischargersconsisted of a hub with four radial electrodeswhich rotated between a pair of fixed rod -typeelectrodes. The hub was driven by a shaftextending from its complementary alternatorso the two rotated synchronously - hence thename.

Discharge commenced while the gaps werestill narrowing and potential of a half cyclewas increasing. Further narrowing as the elec-trodes rotated, reduced resistance across the


HISTORY

Fig. 5a. Oscillation train in a primary circuit. Antenna (secondarycircuit) is loosely coupled.

Fig. 5c. Wave trains radiated by a loosely coupled antenna.

Fig. 5. Second generation tuned system with looselycoupled antenna.

500 Hz

Transformer

Primary circuit

gaps as the amplitude of the oscillationsdeclined, and while energy was being trans-ferred to the secondary circuit. The gaps thenwidened and the draught created by the rotat-ing electrodes dispersed ionised gases,quenching the discharge and returning thegaps to a high resistance state (fig. 7b).

Rotary dischargers originally had four radi-al electrodes - corresponding to the alterna-

Fig. 5b. Oscillation train in a loosely coupled antenna circuit.

Fig. 5d. Oscillations in secondary circuit when not tuned toprecise frequency of primary circuit.

Horizontal antenna section

Capacity with ship's deck

`T-I

-L-

Secondary circuit

tor's four pole pieces, - aligning four timesduring each revolution. Rotation speed wastypically 25rev/sec (1500rev/min). Each rev-olution generated two cycles, so there werefour discharges/rev, 100 discharges/sec. Butthe corresponding tone produced by rectifierreceivers was too low to be heard through"static" interference. (Fig. 7b)

Multiple -spark dischargersTo raise the pitch of the tone, Marconiincreased the number of radial electrodes to 16or 32, depending on the model. But the ruggedfour pole piece alternator was retained so thatinstead of one discharge per ac half cycle,there were now four or eight discrete dis-charges (Fig. 8a).

Furthermore, the magnitude of successivedischarges varied according to the point oneach AC half cycle where discharge occurred(Fig. 8b).

Operation was primarily in the shock exci-tation mode. But it could also have been in thequenched arc mode because during each neg-ative- or positive -going ac half -cycle, thepower supply was in effect dc. The 16 radial -electrode model gave 16 discharges/rev - at25rec/sec 400 discharges/sec - while the 32electrode model gave 800 discharges/sec, pro-ducing a pleasant tone with rectifier typereceivers. But because energy available fromeach AC half cycle was distributed amongseveral wave trains, effective power was lessthan if the energy had been radiated as a singlewave train.

Maritime systems had the alternator drivenby a DC motor running off the ship's DC sup-ply. Terrestrial installations used a petrol


HISTORY

Spark gap

Cooling fins Mica washers

Elevation

Discharge driven radiallyby magnetic field to

grooves where extinguished

Plan

Fig. 6. Quenched spark system - Wien's quenched gap - showing two spark -gap sections.

Fig. 6a. Oscillation train in primary circuit witha quenching type discharger.

Fig. 7a. below. Quenched spark systemschematic with its rotating electrodes.

Fig. 7b. below right. Rotating electrodes.

Spark gap

Alternator

Rotating electrodes Static electrodes

engine, or mains power and a transformer - inwhich case the drive motor was synchronisedwith the mains supply.

The electrodes rotated in synchrony with thealternator, though this was not essential andthere was no noticeable difference in perfor-mance with transformer systems and an asyn-chronous drive motor. Indeed, the multipledischarger had it roots in an asynchronous ver-sion developed by Tesla for use with his"Magnifying Transmitter".

Only a limited degree of syntony was pos-sible, but this was of no great significancewith early maritime systems. More importantwas that the discharger was efficient and, inconjunction with thermionic valve regenera-tive receivers, remained in service with mar-itime systems until the 1930s when interfer-ence caused to other radio users could nolonger be tolerated.

Marconi -Mackie disc dischargerA scaled up version of the smaller maritimemultiple -spark discharger, capable of han-

DetectorsThe gradual rise in amplitude of the wavetrain greatly reduced spark janming. Butbecause the pulse effect was cramaticallyreduced, the coherer was almost uselessas a detector.

Fessenden, another giant in radiohis:ory, developed a liquid oe:ector whichwas also a relay type. With a battery andwill rf current present, it prcdticed aroaring sound in headphones. Massie'spoor contact or microphonic detector wasalso of the relay type and produced asimilar sound to the liquid detector.

Marconi's famous magnet c detectoralsp produced a sound in headphones.Be ng a rugged magnetic/mecnanicaldevice it was far better suited to shipboarduse than the liquid or microphonicdetector, though it was less sensitive.

Rectifier -type detectors, inc uding thesilicon detector and the audios valve,were experimented with by otherpicneers. But unlike relay tyoes and themagnetic detector, rectifier detectorsproduced a sound with a piedcorresponding to the wave t-ain repetitionrate. Pear-shaped wave trains producedan almost musical note, as ea:h wavetra n gently caused the earpie:ediaphragm to vibrate in sympathy with :hewave train repetition rate. But the firstwave of exponential wave tra ns virtual 'y"hammered" the diaphragm intovik ration.

With all rectifier -type detectors, and themagnetic detector energy to produce thesound was derived from the ern wavesant this limited sensitivity; th s in turnbrought about the development of highlysensitive headphones.

dling considerable power, is the Marconi -Mackie discharger. Largest example seems tohave been 60kW machines employed by mar-itime relay stations.

The assembly was installed in a brick"silence -cabin" with the drive shaft and flexi-ble coupling extending through the wall to thealternator.

Alternator

Insulated drive shaft

Common drive shaft

Drive motor


HISTORY

Spark gaps

Fig. 8a. Marconi's multiple spark discharger.

Strong discharge

Zero potentialno discharge

Static electrodes

AC half -cycle

Rotating electrodes

Weak discharge

Fig. 8b. Relationship of discharges to AC half -cycles - synchronised version.

Rod -type static electrodes were eventuallysuperseded by rotating side discs 300mmdiameter and 30mm thick. The main disc, orhub, was of solid copper 900mm diameter and30mm thick with 24 radial electrodes eachabout 200mm long. At its normal speed of25rev/sec the 24 radial electrodes gave 600discharges/sec.

12 transversestud electrodes

(5 shown)

Main disc

Side discs

-_1

J

Caernarfon synchronous dischargerNumerous operator manuals were produced toexplain the workings of maritime radio sys-tems. But very little meaningful technical datawere published on the super stations. Theywere one-off installations, and because of theirstrategic importance during the World War Iand the fact that they were used to signal to

Brick wall of silence -cabin

Alternator

Wooden frameworkTod ye

Insulated drive shaft motor

Fig. 9. Caernarfon synchronised discharger.

submerged submarines during that war, theywere shrouded in secrecy.

So, to fill gaps in known specifications,some assumptions have to be made.

The 300kW Caernarfon 21.4kHz transmit-ter had a discharger that evolved from of theearly maritime -synchronous -discharger. Butinstead of four radial electrodes, 12 copperstud electrodes, 10mm long, extended trans-versely from both sides of the periphery of a900mm diameter steel disc. These alignedwith a pair of slowly rotating copper sidediscs, each 300mm diameter.

The steel disc was coupled to the alternatorby a non-conductive shaft extending throughthe brick wall of the silence cabin, whichhoused the machine, to the 300kW singlephase alternator driven by a three-phasemotor drawing power from high voltagemains (Fig. 9)

Contemporaneous notes state that the alter-nator - and so the discharger - ran at 25rev/s(1500rev/min) and that AC frequency was150Hz. But they give little further technicalinformation. The assumption is that the alter-nator had 12 pole pieces and the dischargerhad 12 electrodes, giving 12 discharges/rev or300 discharges/s. To pack maximum energyinto each wave train, there was one dischargeper ac half cycle.

Wave trains would have been pear-shapedand contain about 25 waves of significantamplitude. Each wave had a period of 4611s,so the duration of the wave train was 1.175ms.Period between each wave train was 3.3ms.Keying was by breaking the capacitor charg-ing circuit, and the arc which developed whenthe circuit was broken, was quenched by an airblast at 2.0 psi.

The three turn, 2.0m diameter primary cir-cuit inductor consisted of a single layer helixof stranded insulated wire wound around ahollow tube 300mm in diameter. The multi -turn, three section antenna coupling coil ofstranded insulated wire was supported on asquare section wooden beam that allowed thecoil to slide axially inside the primary coil,and thereby adjust the degree of coupling.

The antenna was an inverted L and com-prised 10 parallel wires each 1300m long sup-ported by 10 tubular steel masts 130m highover an earth screen (9.0m above the ground.Antenna resistance was given as 0.6212 andmaximum antenna current as 220A.

Efficiency from alternator to antenna wasgiven as 30% in one document - but 60% inanother.

Two dischargers were completed in 1914,one of which seems to have been a stand-by.Although perfectly satisfactory in service,syntony was poor and in 1916 they werereplaced by the timed -spark transmitter whichradiated continuous but undulating waves.

Marconi continuous -wave transmitter will becovered in a future article.


Keep in touch

with ANTEX

Precision

SolderingAntex thermally balanced irons are

available with a wide selection of

soldering bits. There are also

adjustable temperature controlled

irons for low temperature work.

Solder Stations

with optional

digital

temperature

read-out are

also available.

Ask for Antex at leadingElectronic Distributors.

ANTEXAntex (Electronics) Ltd. -2 Westbridge Industrial Estate, Tavistock, Devon PL 19 8DETelephone: (0822) 613565 Fax: (0822) 617598


SYSTEM 200 DEVICE PROGRAMMER

SYSTEM: Programs 24,28,32 pin EPROMS, EEPROMS,FLASH and Emulators as standard,quickly, reliably and at low cost.

Expandable to cover virtually any pro-grammable part including serial E2, PALS,GALS, EPLD's and microcontrollers from allmanufacturers.

DESIGN: Not a plug in card but connecting to the PCserial or parallel port; it comes completewith powerful yet easy to control software,cable and manual.

SUPPORT: UK design, manufacture and support. Sameday dispatch, 12 month warranty. 10 daymoney back guarantee.

m VISA

MOP ELECTRONICS Ltd.Park Road Centre

Malmesbury, Wiltshire. SN16 OBX. UKTEL. 0666 825146 FAX. 0666 825141

ASK FOR FREEINFORMATION

PACKGERMANY 089/4602071NORWAY 071-17890ITALY 02 92 10 35 54FRANCE (1169.30.13.79Also from VEROSPEED UK


"... there is no doubt that running under Windows puts it ahead of theand makes it a visually attractive package." Electronics World +

Wireless World July 1993High Quality PCB and Schematic Design for Windows 3/3.1 and DOS

IMINII

et

0=fmlel:)

'It,o_Ai,2,_1_0.,_0 Supports over 150 printers/plotters including 9 or ?fm,,, _,_,,,'';7,-'`'""'""'"'lINI011atralini fft- N ar, al X ,.0 - 1 NI10 ' 1 CiWiiri! .P44.4 J

24 pin dot-matrix, DeskJet, LaserJet, Postscript,and HPGL. Professional Edition imports GERBER 9files, and exports GERBER and NC DRILL files. -csolil

0 Up to 200,000 pads/track nodes depending onrimo.iiii..4 - -

memory. Simple auto -router and schematic captuletools,i,SPICE'

with compatible net -list output. `4NIMI..4 0-16 -

DODO=

0 Low cost DOS version (reduced features) alsoavailable. Ring for full details!

1:/ .0 111-1,

- , I/ 411,A

- Iri.--1

"Quickroute provides a comprehensive and effective introduction to PCBdesign which is a pleasure to use" Radio Communication May 1993.

from

£39POWERware, Dept EW, 14 Ley Lane, Marple Bridge, Stockport SK6 5DD, UK.

14.1, Ring us on 061 449 7101 or write, for a full information pack.POWER were

Quickroute is available for Windows :7:13.1 in Professional (£99.00) and Standard (£59.00) editions,Software .. Design and for DOS with reduced features (£39.00). All prices inclusive. Add £5 P+P outside UK.


November 1993 ELECTRONICS WORLD+WI REUSS WORLD 943

COMMUNICATIONSERVICES VIASATELLITE

OR AND FET

'MANUALRSTJN

INSTRUMENTATIONAND TEST GEAR

CIRCUITS MANUAL

Programmable LogicHandbookGeoff BostockLogic circuit designers areincreasingly turning toprogrammable logic devices as ameans of solving problems. Thisbook, for the establishedelectronics engineer, student andtechnician, is a thoroughintroduction to programmablelogic. Geoff Bostock will take youto a level where you, as adesigner, can take full advantageof the growing product range ofASICs and other self -programmable arrays used incomputer and control systems.Paperback 256 pages.Price £19.95 0 7506 0808 0

Understand Electrical andElectronic MathsOwen BishopPeople who find maths difficultoften have, as a result, difficulty

in grasping electrical andelectronics theory. This book hasbeen written to help suchstudents to understand themathematical principlesunderlying their subject so thatthey can go on with confidenceto tackle problems in practicalcircuits. Paperback 256 pages.Price £14.95 0 7506 0924 9

CIRCUIT MANUALSRay MarstonA series of books dealing withtheir subjects in an easy -to -readand non -mathematical manner,presenting the reader with manypractical applications andcircuits. They are specificallywritten, for the design engineer,technician and the experimenter,as well as the electronics studentand amateur. All the titles arewritten by Ray Marston, afreelance electronics designengineer and international writer.

Op -amp Circuits ManualPaperback 224 pagesPrice £13.95 0 434 912077

Audio IC Circuits ManualPaperback 168 pagesPrice £13.95 0 434 912107

CMOS Circuits ManualPaperback 192 pagesPrice £13.95 0 434 912123

Electronic Alarm CircuitsManualPaperback 144 pagesPrice £13.95 0 7506 00640

Timer Generator CircuitsManualPaperback 224 pagesPrice £13.95 0 434 912913

Diode, Transistor and FETCircuits ManualPaperback 240 pagesPrice £13.95 0 7506 0228 7

Instrumentation and Test GearCircuits ManualRay MarstonModern instrumentation and testgear circuits of value to theindustrial, commercial, oramateur electronic engineer ordesigner make up this book.Almost 500 outstandingly usefuland carefully selected practicalcircuits are in here. This is onebook you must have if you needaccess to practical workingcircuits ranging from simpleattenuators and bridges tocomplex digital panel meters,waveform generators, and scopetrace doublers. Paperback 400pages.Price £16.95 0 7506 0758 0

Logic Designers HandbookAndrew ParrEasy to read, but none the lessthorough, this book on digitalcircuits is for use by students andengineers and provides anaccessible source of data ondevices in the TTL and CMOSfamilies. It's a 'DesignersHandbook' that wil live on thedesigner's bench rather than onthe bookshelf. The basic theoryis explained and then supportedwith specific practical examples.Paperback 488 pages.Price £25.00 0 7506 0535 9

Digital Audio and CompactDisc TechnologyLuc Baert, Luc Theunissen &Guido VergultEssential reading for audioengineers, students and hi-fienthusiasts. A clear and easy -to -follow introduction and includes atechnical description of DAT(digital audio tape). Contentsincludes principles of digitalsignal processing, sampling,quantization, A/D conversionsystems, codes for digitalmagnetic recording, principles oferror correction, the compactdisc, CD encoding, opto-electronics and the optical block,servo circuits in CD players,signal processing, digital audiorecording systems, PCM, Video8, R-DAT and S-DAT. Paperback240 pages.Price £16.95 0 7506 0614 2

NEWNES POCKET BOOKSA series of handy, inexpensive,pocket sized books to be kept byyour side and used every day.Their size makes them an ideal'travelling' companion as well.

Newnes ElectronicsEngineer's Pocket BookKeith BrindleyHardback 319 pagesPrice £12.95 0 7506 0937 0

Newnes Electronics AssemblyPocket BookKeith BrindleyHardback 304 pagesPrice £10.95 0 7506 0222 8

Newnes Television and VideoEngineer's Pocket BookEugene TrundleHardback 384 pagesPrice £12.95 0 7506 0677 0

Newnes Circuit CalculationsPocket BookT DaviesHardback 300 pagesPrice £10.95 0 7506 0195 7

Newnes Data CommunicationsPocket BookMichael TooleyHardback 192 pagesPrice £12.95 0 7506 0427 1

Newnes TelecommunicationsPocket BookJE Varrall & EA EdisHardback 400 pagesPrice £12.95 0 7506 0307 0

Newnes Z80 Pocket BookChris RobertsHardback 185 pagesPrice £12.95 0 7506 0308 9

Newnes 68000 Pocket BookMike TooleyHardback 257 pagesPrice £12.95 0 7506 0309 7

Newnes Electrical PocketBook21st editionE A ParrPaperback 526 pages£12.95 0 7506 05138

Newnes Electric CircuitsPocket Book Linear ICRay MarstonHardback 336 pagesPrice £12.95 0 7506 0132 9

Newnes Guide to Satellite TVD J StephensonA practical guide, withoutexcessive theory of mathematics,to the installation and servicing ofsatellite TV receiving equipmentfor those professionallyemployed in the aerial rigging/TVtrades. Hardback 256 pages.Price V 7.95 0 7506 0215 5

Newnes Practical RFHandbookIan HickmanPressure on the RF spectrumhas never been greater and it'speople with knowledge and skillsof RF design who are now indemand in the electronicsindustry to design, produce,maintain and use equipmentcapable of working in thiscrowded environment. Thispractical introduction to modernRF circuit design will equip youwith the necessary RFknowledge and skills to enableyou to compete effectively in theindustry. Paperback 320 pages.Price £16.95 0 7506 0871 4

Troubleshooting AnalogCircuitsR A PeaseBob Pease is one of the legendsof analog design. Over the years,he's developed techniques andmethods to expedite the often -difficult tasks of debugging and

troubleshooting analog circuits.Now, Bob has compiled his'battle -tested' methods in thepages of this book. Based on hisimmensely popular series in EDNMagazine, the book contains awealth of new material andadvice for Digital/Analogelectronics engineers on usingsimple equipment totroubleshoot. Paperback 217pages.Price £14.95 0 7506 16326

PC -Based Instrumentation andControlM TooleyDo you need information toenable you to select thenecessary hardware andsoftware to implement a widerange of practical PC -basedinstrumentation and controlsystems? Then this book is foryou. Paperback 320 pages.Price £14.95 0 7506 1631 8

Electronic Circuits HandbookM TooleyProvides you with a uniquecollection of practical workingcircuits together with supportinginformation so that circuits canbe produced in the shortestpossible time and withoutrecourse to theoretical texts.Paperback 345 pages.Price £24.95 0 7506 0750 5

Communication Services viaSatelliteG E LewisDBS is already with us, and willcreate a series of new technicalproblems forengineers/technicians intelevision and communicationservices. This book gives you thesolutions to these problems by:

AUDIO ICCIRCUITS MANUAL

R MARSTON

explaining how the systemfunctions; describing severalactual systems and givi igseveral analyses and designrules. You can't afford to bewithout this invaluabletechnology update if you're asystems design engineer, serviceengineer or technician.Paperback 400 pages.Price £25.00 0 7506 0437 9

Digital Logic DesignBrian HoldsworthAs one of the most successfuland well established electronicstextbooks on digital logic design,this book reflects recen:developments in the digital fields.The book also covers newfunctional logic symbols andlogic design using MSI andprogrammable logic arrays.Paperback 448 pages.Price £19. 50 0 7506 0501 4

The Circuit DesignersCompanionT WiliamsThis compendium of practicalwisdom concerning the real -world aspects of electronic circuitdesign is invaluable for linearand digital designers al ke.Hardback 320 pages.Price £25 00 0 7506 1142 1

Credit cardordersaccepted byphone

081 652 3614

MICROPROCESSOR TroubleshootingARCHITECTURE laAND SYSTEMS DI mi, Atimo Analog,,,sc,cisc, DSP

ANDn.oircuits

IECH ADIOS Yt

Steve Heath

rReturn to: Lorraine Spindler, Room 1_333, Quadrant House,The quadrant, Suttor, Surrey SM2 5AS

Please supply the following titles:

I Qty Title ISBN Price1 Programmable Logic Handbook 075,16 0808 0....19.95

Understanding Electrical & Elec Maths 075.36 0924 9....14.95Op -amp Circuits Mania] 04 34 912077 13.95

I nudio IC Circuits Manual 04 14 912107 13.95r--.1.MOS Circuit Manua, 0434 912123 13.95I Electronic Alarm Circuits Manual 0753,) 0064 0....13.95

Power Control Circuit; Manual 0753,-) 06908 13.95Timer/Generator Ciro. its Manual 0434 91291 3....13.95

Diode, Transistor & FE T Circuits Man 075)) 0228 7....13.95I Instrumentation & Tes: Gear Circuits Man _07533 0758 0....16.95I Logic Designers HandbookI Digital Audio and Compact Disc

Newnes Elec Engineers Pkt BkNewnes Elec Assembv Pk Bk

07533 0535 9...25.000753'306142...16.950 75(.6 0937 0 ..12.9507505 0222 8...10.95

I Newnes TV ani Video Eng Pkt Bk 0750.3 0677 0...12.95I( Newnes Circuit Calculations Pkt Bk 07505 0427 1 ....10.95

0750 5 0308 9....12.9507505 0307 0....12.9507505 0308 9....12.95

I--ixlewnes 6800C Pkt BI. 07505 0309 7....12.9507505 05138 12.9507506 0132 9 12.95

07505 0215 5 17.9507505 0871 4 16.95

Troubleshootirg Anal ag Circuits 075% 16326 14.9507506 1631 8 14.95

1-=.1ectronic Circuits Handbook 07506 0750 5....24.9507506 0437 9....25.00

Digital Logic Design . 07506 05014 19.50

1-Newnes Electrical Pk 3kNewnes Electric Ciro_ its Pocket BkNewnes Guide to Satelite TVJewnes Practical RF Handbook

L

Newnes Data Commcnications Pkt BkNewnes Telecommunications Pkt BkNewnes Z80 Nt Bk

3C -Based Instrimentation and Control

t=ommunication Servi:es via Satellite

PLEASE ADD £2.50 FOR FOSTAGEAdd VAT at local rateNB ZERO RATE FOR UK & EIRE TOTAL

Busiress purchase: Please send me the books listed smith an invpice. I willarrange for my company to pay the accompanying invoice within 30 clays. I

will zttach my business ca d/letterhead and have signed the form below.Guarantee: If you are not completely satisfied, books may be returnedwithin 30 clays in a resaleable condition for a full re'und.

Remittance enclosed £Checues should be made payable to Reed Book Services Ltd.Please debit my credit card as follows:

Access/Master BardayNisa Amex Diners

Cred t Card No. Exp date

NAtv,E (Please print)

ORCANISATION

STREET

TOWN

COL NTY POST CODE COUNTRY

DATE TELEPHONE NUMBER

SIGNATURE

T3000VAT RATES6% Belgium, 25% Denmark, 5.5% France, 7% Gemany, 4% Greece, 4"/Italy, 3% LuxemboJrg, 6% Netherlands, 5% Portuga , 3%, Spain. FORCOMPANIES REGISTERED FOR VAT, PLEASE SUPPL Y YOURREG STRATION NUMBER BELOW (customers outsic e the EEC should leavethis part blank)VAT NO.If in :he UK please allow days for delivery. All p-i :es are co-rect at time ofgoin4 to press but may be subject to change.Please delete as ap3ropriate.I do/do not wish to reci.we further details aboutbook, journals and information services.Reec Business Pub ishing - Registered Office - Quay iant Hse The QuadrantSutton Surrey SM2 5AS Registered in England 151537

1

RF ENGINEERING

USING RF TRANSISTORS2: Putting a figure on low power devices

Continuing the seriesbased on their book Radiofrequency transistors:principles and practicalapplications, Norm Dyeand Helge Granberg showhow to select a low powertransistor with exactly theright parameters.

Norm Dye is Motorola's productplanning manager in the SemiconductorProducts Sector, and Helge Granberg isMember of Technical Staff, RadioFrequency Power Group (SemiconductorProducts) at Motorola. Their rf transistorsbook includes practical examples fromthe frequency spectrum from 2MHz tomicrowaves, with special emphasis onthe UHF frequencies .

RF Transistors: Principles and practicalapplications is available by postalapplication to room L333 EW+WW,Quadrant House, The Quadrant, Sutton,Surrey, SM2 5AS.Cheques made payable to Reed BooksServices. Credit card orders accepted byphone (081 652 3614).288pp HARDBACK 07506 9059 3 Cost£19.95 + Postage £2.50

One of the most useful means of spec-ifying a linear device is to use scat-tering parameters, commonly referred

to as S -parameters, in reality voltage reflectionand transmission coefficients when the deviceis embedded into a 50L1 system.

Magnitude of the input reflection coefficient1S111 is directly related to input VSWR by theequation

VSWR = (1 + IS/ /I)/O - IS/ /1)

Likewise magnitude of the output reflectioncoefficient IS221 is directly related to outputVSWR (Fig. 1). Square of the magnitude ofthe input -to -output transfer function 1S2212 isalso the power gain of the device, referred toon data sheets as "insertion gain". Note thatIS2212 is the power gain of the device when thesource and load impedances are son. Animprovement in gain can always be achievedby matching device input and outputimpedances - almost always not 5012 - to

Radio FrequencyTransistors

dm/ l'rai

nve and I Mgt.. Granberg

500 through matching networks. The largerthe linear device, the lower the impedancesand the greater is the need to use matchingnetworks to achieve useful gain.

Another gain specification shown on lowpower data sheets is "associated gain", withthe symbol GNF. It is simply the gain of thedevice when matched for minimum noise fig-ure. Yet another term is "maximum unilateralgain", Gu,,. As expected, Gumax is the gainachievable by the transistor when the inputand output are conjugately matched for maxi-mum power transfer (and S/2 = 0.). Gu. canbe derived using scattering parameters:

Gumax = 1S2112 (I - 1S1112) - Is2212)}

Simply stated, this is the 5051 gain increasedby a factor which represents matching theinput, and increased again by a factor repre-senting matching the output.

RF low power transistors are often used aslow noise amplifiers, leading to several tran-sistor data sheet parameters related to noisefigures. NF,in is defined as the minimumnoise figure that can be achieved with the tran-sistor. Achieving this NF requires sourceimpedance matching which is usually differentfrom that required to achieve maximum gain.So design of a low noise amplifier is always acompromise between gain and NF.

A useful tool in aiding this compromise is aSmith Chart plot of constant gain and noisefigure contours, drawn for specific operatingconditions - typically bias and frequency (Fig.2). These contours are circles, either totally orpartially complete within the confines of theSmith Chart.

If the gain circles are contained entirelywithin the Smith Chart, then the device isunconditionally stable: if portions are outside,then the device is "conditionally stable", andthe device designer must investigate instabil-ities, particularly outside the normal frequen-cy range of operation.

Where the data sheet includes noise param-eters, a value will be given for the optimum


RF ENGINEERING

The intercept point is a usefulconcept in that it allows the valueof distortion for any signal level to

be determined.Second order distortion products can

be shown mathematically to haveamplitudes that are directlyproportional to the square of the inputsignal level. Third order distortionproducts have amplitudes that areproportional to the cube of the inputsignal level. The conclusion is that aplot of each response on a log -log scale(or dB/dB scale) will be a straight linewith a slope corresponding to the orderof the response.

Fundamental responses will have aslope of 1, the second order responseswill have a slope of 2, and the thirdorder responses a slope of 3. Note thatthe difference between fundamentaland second order is a slope of 1, andbetween fundamental and third order isa slope of 2. So for second orderdistortion, a 1dB change in signal levelresults in a 1dB change in second orderdistortion, but a 2dB change in thirdorder distortion. Using the curvesshown in the figure, if the output levelis OdBm, second order distortion is at-30dBc and third order distortion is at-60dBc. Change the output level to-10dBm and the second orderdistortion should improve to -40dBc(-50dBm) but third order distortion willimprove to OdBc (-90dBm).

Thus, a 10dB decrease in signal hasimproved second order distortion by10dB, and third order distortion by20dB.

The intercept point is defined as thepoint on the plot of fundamentalresponse and second (or third) orderresponse where the two straight linesintercept each other. It is also that value

Intercept pointof signal (hypothetical) at which thelevel of jistortion would equal theinitial signal level.

For example, if at the point ofmeasurement, second order cistortion is-40dBc and the signal level is -10dBm,then the second order intercept point is40dB alcove -10dBm or +30cBm. In thefigure, +30dBm is the value cf outputsignal at which the fundamertal andsecond order response lines cross. Thebeauty of :he intercept point is thatonce it is known , the value ofdistortion for any signal level can bedetermined, provided it is in a region ofoperatic n governed by themathematical relationships stated

IMDs greater than 63dB belowthe carr er.

Similarly, to determine third orderintercept point, measure third orderdistorticn at a known signal level. Then,

take calf the value of the distortion(expressed in dBc) and add to the sigr allevel For example, if the signal level is+10cBm and the third orde- distortion is-40dBc, the third order intercept pointis the same as the second weerinter..-ept point or 10dBm + 20dB =30dEm. Both second order and thirdorde- intercept points are it ustrated.

In general, the intercept points forsecond and third order distortion will bedifferent because the non-Wearities thatcreate second order distortion areusua ly different from those that createthird order distortion. However, theconcept of the intercept point is stillvalic: the slopes of the responses arestill . , 2, and 3 respectively. All thatneecs to be done is to specify a secondorde- intercept point different from thethird order intercept point.

Furd2mental,secprid order andthiod )rderamplifier responsecurves.

40-

100

INTERCEPT PINT

FUNDAMENTA L

)/ 11

1

2ND ORDER

131

3RD ORDER

-toPIN. INPUT POWER (dBm)

input reflection coefficient to achieve mini-mum noise figure, f' or sometimes Fop,. Butremember, matching this value of input reflec-tion coefficient means far less gain is likely tobe available than is achievable by the transis-tor.

Input reflection coefficient for maximumgain is normally called rms while the outputreflection coefficient for maximum gain isnormally called riviL.

Another important noise parameter is noiseresistance, 1?, expressed in ohms. Sometimesin tabular form, this value may be normalisedto 5052, in which case it is designated r. Thesignificance of r can be seen in the formula:

NF = NF, + - To!' / 1(1 - Ir12) Il+r12}

which determines noise figure NF of a tran-

sistor for any source reflection coefficient r, ifthe three noise parameters NF,,,, r and To(the source resistance for minimum noise fig-ure) are known (Table 1).

The locus of points for a given NF turns outto be a circle - the NF. circle being a point.So by choosing different values of NF, a seriesof noise circles can be plotted on the chart.

INPUT

O

LINEAR

TWO -PORT

OUTPUT

O

_fp4 REFERENCE PLANES

$ot - INPUT REFLECTION COEFFICIENT . bt 22 0,Sg2 - OUTPUT REFLECTION COEFFICIENT b2 ILI 0

112

FORWARD TRANSMISSION COEFFICIENT b2 22 0,512 REVERSE TRANSMISSION COEFFICIENT b

at

Fig. 1. Using scattering (S)parameters to specify a lineardevice.


RF ENGINEERING

+i150

- j100

Va - V

- 3 rnA1 2002 1,110

-AEA OF INSTAMLITY

(A) F = 2 GHz (B) F = 4 GHzFig. 2. Gain and noise contours. Solid circles represent gain, and dotted circles representnoise figures.

tel

2.0

1.0

r11w/0

Fig. 3. Small signal current vsfrequency.

II- SLOPE REGION

12

e, to

8

E 6

4

Izec

0

2

0

II

IR Oa tT f

VcE = 6V

2 3 5 7 10 20 30 40

Ir. COLLECTOR CURREHT(rnA)

EXTRAPOLATED GAIN

1dB GAINCOMPRESSION POINT

UNEAR GAIN

INPUT POWER IN DBM

Fig. 4. Gain -bandwidthproduct vs collectorcurrent.

Fig. 5. Linear gain and the ldBcompression point.

Table 1. Typical noise parameters for theMRF942 transistor.

VcE IC f NFm,n GNF(VdC) (mA)(MHz) (dB) (dB)

ro(mag,ang)

RN NF50c1(0) dB

6 3 1000 1.3 16 0.36 Z 94 17.5 1.72000 2.0 11 0.37 L-145 15.5 2.64000 2.9 8.0 0.50 Z 134 21.5 4.3

15 1000 2.1 19 0.25 Z 150 13 2.62000 2.7 14 0.26 Z 173 16.5 3.14000 4.3 9.0 0.48 L -96 47 5.4

r can be measured by measuring noise fig-ure for F.; = 0 and applying the above equa-tion.

A parameter found on most rf low powerdata sheets is commonly called the currentgain -bandwidth product, f1. Sometimes it isreferred to as the cut-off frequency, because itis generally thought to be the product of lowfrequency current gain and the frequency atwhich the current gain becomes unity. Whilethis is not precisely true (Fig. 3), it is closeenough for practical purposes. It is true that f,is an excellent figure -of -merit , becoming use-ful in comparing devices for gain and noisefigure capability.

High values of f, are normally required toachieve higher gain at higher frequencies -other factors being equal.

To the device designer, high f, specs meandecreased spacings between emitter and basediffusions, and shallower diffusions - factorsthat are more difficult to achieve in making anrf transistor.

The complete rf low power transistor datasheet will include a plot of f, versus collectorcurrent. Such a curve (Fig. 4) will increasewith current, will flatten, and then begin todecrease as I increases thereby revealing use-ful information about the optimum currentwith which to achieve maximum device gain.

Another group of characteristics associatedwith linear (or class A) transistors has to dowith the degree to which the device is linear.Most common are terms such as "P,, 1dBgain compression point" and "third orderintercept point" (ITO). P0, 1dB gain com-pression point is simply the output power atwhich the input power has a gain associatedwith it that is 1dB less than the low powergain. In other words, the device is beginningto go into saturation, where increases in inputpower fail to realise comparable increases inoutput power(Fig. 5).

Importance of the ldB gain compressionpoint is that it is generally accepted as thelimit of non -linearity tolerable in a 'linear"amplifier and points to the dynamic range ofthe low power amplifier. On the low end ofdynamic range is the limit imposed by noise:on the high end is the limit imposed by "gaincompression."


Electronic DesignsSchematic Design and Capture

....IOW Ste

Create your schematics quickly andefficiently using EASY -PC Professional.Areas of the circuit can be highlighted onscreen and simulated automatically usingPULSAR, ANALYSER Ill and Z -MATCH IIour simulation programs

Digital and Analogue Simulation

Hi

www

Modify theconfigurationand changecomponentvalues untilthe requiredperformanceis achieved.

PCB Design

The design, complete with connectivity, canthen be translated into the PCB. Theconnectivity and design rules can bechecked automatically to ensure that thePCB matches the schematic.

ight First Time?

Affordable Electronics CADEASY- PC: Low cost PCB and Schematic CAD £98.00

EASY- PC Professional: Schematic Capture andPCB CAD. Links to ANALYSER III and PULSAR.

£195.00

PULSAR: Low cost DOW Circuit Simulator- 1500 gate capaciy.

£98.00

PULSAR Professional: Digital Circuit Simulator- 50,000 gate capacity.

£195.00

ANALYSER III: Low cost Linear Analogue CircuitSimulator - 130 nodes

£98.00

ANALYSER III Professional: Linear AnalogueCircuit Simulator - 750 nodes

£195.00

Z -MATCH U: S-nith Chart Program for R.F. Engineers £195.00

No penalty upgrade policy. Prices exclude P&P and VAT.

Number One Systems Ltd.Ref WW. Harding Way, St. Ives,

Huntingdon, Cambs. PE17 4WR, UK.

For Full Information Please Write, Phone or Fax.

Tel: 0480 461778Fax: 0480 494042


WE HAVE THE WIDEST CHOICE OFUSED OSCILLOSCOPES IN THE COUNTRY

TEKTRONIX 7000 SERIES OSCILLOSCOPESDual Trade Plug-in with TB from £200

Many Plug-in options available. 4 Traces;Differential etc. PLUG -INS SOLD SEPARATELY

CHASE HER 2000 INTERFERENCE MEASURING It _CEIVER WITH MAINS

NETWORK E1750

DATRON 106IA - 61/2 digit True RMS AC.0 liner- El ISO

DATRON 1065 MutIlmeter 514 digit AC DCOnms IEEE £540

HEWLETT PACKARD 34904 Bench Multimete 51(0 digit AC DC Ohms £200

PHILIPS PIA2534 Multifunction 0MM 612 digit PIET IEEE £450

MARCONI Digital Frequency Meter 74306 10Hz 8CMHz £115

MARCONI Dtgital frequency Meter 2431A 1011, 2EDMHz E150

MARCONI Universal Counter hoer 14370C 1001410 E175

MARCONI Universal Counter Timer 2438DC(52010-1, £225

HP 331I4 Function Generator 0 111z-IMIll Sine Salln C115

FEEDBACK FG600 Sine/So 1100 OIHE-10010Q £60

MULTIMETERS Hand Held M135532 ranges AC IC 10 Amps Diode

Transistor Tester. Free counter. £3250

TEITININIX 2231 Dual Trace 100MHE Delay Sweep C000

PHILLIPS 3065 1,1 Channels 100MHZ Dual TB ITH 8-i l E700

TEKTRONIX 475 Dual Trace 100 MHz Delay Sweet, 0550

HP. 17273 Dual Trace 604160 Delay Sweep £450

H.P. 17154 Oual Trace 200Mlin Delay Sweep...E500H.P. 1740A Dual Trace 100MHz Delay Swoop E400

TEKTRONIX 2215 Dual Trace 60MHz De, ay Sweep- C4511

PHILLIPS MA3217 Dual Trace 508111, Delay Sweep C400

HISACMI 0422 Dual Elate 4111112 .gdzs

IWATSU SS5705 3 Channel 40MHE Delay Sweep £400

TRIO CS1830 Dual Trace SOMME Delay Sweep E300

KIKUSUI 5530 Dual Trace 3518110 . .C1110

GOULD 001100 Dual Trace 30MHE .. . . .C160

TEKTRONIX 166 Dual Trace 100 MHz Storage C450

GOULD OS300 Dual Trace 20MR, E200

GOULD OS2508 Dual Trace 15MHz . E115

HITACHI V223 Dual Trace 20 MHz Delay Sweep£000

11110 IS 1UST A SAMPLE. MANY OTHERS 111114411

FARRELL ELECTRONIC LOAD RE11030. 35 11. 3 Amp 35 Volt E600

HP 8690 Sweep Ox with 86974 Plug( in 26 5.4G111 £3110

RACALIANA RF Power Meter 9104 . £400

RACALIDANA 9341 Databndge Automatic 1 C R El/ £350

WAYNE KERR 0905 Automatic Precision Bridge Oe% C900

WAYNE KERR 6605 Automatic Component Bride 0 1% £350

FARRELL POE TV5701112 708 56300.100 C300

FARRELL PSU H60125 0-60V 0-15Amps Metered £400

FARRELL PSU L30E 0-3011 OSArnps Metered £00

FARRELL 1330 10 !JAM, 20Amps .. LER

FARRELL 030 10 0-300 I °Amps £200

El P 61090 0 3206, 0 0 lAmps Metered £115

A

MARCONI TF1700 UniversalVO

Characteristic Meter VCLCR

Bridge Batter) tom £050

M163 E300

FARNELL tA510 liF Power Amp 1 5-520MHz 300.11 I115

RACAL 9100 Absorption Wattmeter IMHzIGHE Pi £100

PHILLIPS PM5I93 Programmable synthesizer:Function Generator

0 1Mt1,5010111EEE4841 As new E1500

MARCONI 2019 Synthesoed MAFIA SI Gen 130KHE- 1040M14 C2000

MARCONI 0022 AM/FMSig Gen IRBIL ICHZ £1200

MARCONI 2018 Synthesized AALETA 514 Gen 801010-510MHE `IP/IIANA 35ID Microwave frequency Counter 10HE-18G111 C950

RACAL 9911 Frequency Counter 3GKE. . £30

P.339 Distortion Measunng Son IONEITOKHE £1500

ACALOANA 1991 Nanosecond Universal Counter £80

RACAL 9302 Millivol1meter True MS 1010K-1 EGA, [45RACAL 9301A Rf Melivolltmeter True RMS 10K11,1 5G11, £300

1[41 9009 Automatic Mod Meter 10MHzI 5GH1 Wide Deviation E25

TONS PG73N Pulse Gen PRO 1HE-20MH1 [ISO

ARCONI 2610 True RMS Voltmeter . £800

ORD BicrnatIon K5000D Logic Analyser £500

FARRELL PSG52011 Synthesised Sig Gen AM FM 100K111.520MHE £60

CABER LSG216 AMEM Sig Gen 0 1 -30MHE g 15-115MHE £4111)

KEITILEY 191 51:2 Me Autoranging Microvolt WM with IEEE [ISO

FARRELL Isolating Transtrmers

GU500 240. 500VA. unused C50

NEW EQUIPMENTHAMEL OSCILLOSCOPE 441005 Triple Trace 10111111 Delay Timebase . £1147

NAMES OSCILLOSCOPE HM604 Dual Trace 60MIt Delay Sweep E653

HAMER OSCILLOSCOPE HM203 7 Dual Trace /0MIY4 Component Tester E362

HAMER OSCILLOSCOPE HM205 3 Dual Trace 10111, Digital Storage C653

All other models available Ill osc,rlosrop5 s uoOlretl mlb 2 MOW,

SPECTRUM ANALYSERSHP 14:1 with 85556 & IF Plug-in 108111E-113GHE £1800HP :4 IT with 85548E 85518 50010E-1250Mhz £1000

HP.;' wan 85541. & 8552A 5001;HE-1250MHz £1000

HP 111T with 85564 & 85528 20110-300100 £1000

HP 1401 with 85531 & 85524 1111E-110MHE LIMMARCONI 1E2370 3014E-110MHz E1500

HP 1820 with 8558E1100112-1500MHz £1500

Ii 3582A 0 02HZ-25 5682 E1000

BLACK STAR EQUIPMENT (P11 a 110,174 ES1

APOLLO 10-100MHz Counter rimer RalloTenodirme Int, .. r' 0200

APOLLO 100-100MHz (As above with more lunc60ns1 1315

METEOR 100 FREQUENCY COUNTER 100/411, 1119

METEOR 600 FREDUENCE COUNTER 600MHz 1145

METEOR 1000 FREQUENCY COUNTER 1GHE 1199

IUPET0R 500 FUNCTION GEN 0 1HE- SIXISHE Sine ST Tr. E119

ORION COLOUR BAR GENERATOR PART/Video E229

All other Bina Star Cooly mere available

OSCILLOSCOPE PHONES Swrtchable 8 18 10 (P&P 131 E'.1

Used Equipment - GUARANTEED. Manuals supplied If possible.This is a VERY SMALL SAMPLE OF STOCK. SAE or Telep one for lists. Please check availability before ordering.

CARRIAGE all units C16. VAT to be a ded to Total of Goods and Carriage.

STEWARTAilk 110 WYKEHAM ROAD, READING,

of READINGBERKS RG6 1PL VISA

Telephone: (0734) 268041. Fax: (0734) 351696Callers Welcome 9am-5.30pm Monday to Friday (until 8pm Thursday)

R.S.T. LANGREX R.S.T

SUPPLIES LTDOne of the largest stockists and

distributors of electronic valves, tubesand semiconductors in this country

Over 5 million items in stock covering more than6,000 different types, including CRT's camera

tubes, diodes, ignitrons, image intensifiers, IC's,klystrons, magnetrons, microwave devices, opto

electronics, photomultipliers, receiving tubes,rectifiers, tetrodes, thryatons, transistors,

transmitting tubes, triodes, vidicons.

All from major UK & USA manufacturers.

Where still available.

Obsolete items a speciality. Quotations by return.Telephone/telex or fax despatch within 24 hours

on stock items. Accounts to approved customers.Mail order service available.

LANGREX SUPPLIES LTD1 Mayo Road, Croydon, Surrey CR0 2QP

Tel: 081-684 1166Telex: 946708

Fax: 081-684 3056


November 1993 ELECTRONICS WORLD +WI RELESS WORLD


949

L.

Finally an upgradeable PCB CADsystem to suit any budget ...

CaptureBcar,-Capture - Scnematie Captu-e

Direct netts' tiff< '.o- Board.Mal*T2For...ard anr ota_ion with part -aluesFull ur'do/redo acility (50 ope-aticms)Sing e -sheet. m ilti-paged and hierarcr tca= resignsSm»th scrcilIngkite Igent wifes (automatic jurrtions)Dyramic connectivity informattnAuto vatic on -lire annotationInto aced on-th t. -f y htraiy edt>rCort 3SL° sensiiv editingExteefsive ccrnp)nent-tased power coltr.:1Bac< annotwion frpri 3oarcilfilaker2

£395

111111111 1 1111 1 11111111111111111111111111

MakerBoardMakerl - Entry level

Pas CB and schematic drafting

Surface mount support90, 45 and curved track corners

E95 Ey and intuitive to use

Ground plane fillCopper highlight and clearance checking

BoardMaker2 - Advanced levelAll the features of BoardMakert plusFull netlist support - OrCad. Schema, Tango. CadStarFull Design Rule Checking - mechanical E electricalTop down modification from the schematicComponent renumber with back annotatiorReport generator - Database ASCII, BOMThermal power pane support with full DR:,

£295

RouterBoardRouter - Gridless autorouter

Simultaneous mu ti -layer routingSMD and analogue supportFull interrupt, resime, pan and zoom while routing

Output drivers - Included as standardPrinters - 9 & 24 pin Dot matrix. FIPLaseilet and PostScriptPenplotters - HP, Graphtec, Roland & HoLstonPhotoplotters - Al Gerber 3X00 and 4X00Excellon NC Drill .1 Annotated drill drawing 3 (BM2)

Call for info or fullevaluation kit

Tsien (UK) LimitedTel (0354) 695959Fax (0354) 695957

£200

-41"411111111k....

tsienTsten (UK) Ltd, Ayletasy Nov.seenny Road, Chatter., Certbridde PE16 6UT

(1k) ' \(.1. 12- (J\ HI Pt) 11:1)

Custom metalworkgood & quick!

Plus a wice range of rack-mountinccases etc. from stock.

Send for our new = t Catalogue.

NIS

IIA EREIALIISI ...IS (MS

k IPK Broadcast Systems3 Darwin Close Real ng Berks RG2 OTBTel: (0734) 311030 Fax: '0734) 313836

THIS IS THECOUPONthat brings the 1993-94

I CATALOGUEI140 pages, A4, copiously illustrated, bangup to date and with bonus vouchers. Senccheque/PO for £1.50

I that brings the

I SERVICECATALOGUE

nna.)

Iwith choice of very wide ranges of famous -name qualityelectronic components and associated gear sent promptly onreceipt of your order. A service

I that

1ELECTROVALUE LTD., 3 CENTRAL TRADING ESTATE, STAINES TW18 471Telephone 0784 442253 Fax 0784 460320

I enclose Cheque/PO OrdenCredit Card Novalue £1 50 for your 1993-94 CATALOGUEI

Name

-7;171.01 /ralueIhave been providing constructors with continuously since 1965.With this Catalogue, you will find our service the best ever. Sendfor your copy NOW!

IAddress

I IPost CodewwJ1

950

:.-IRCLE NO. 1230N REPLY CARD CIRCLE NO. 124 ON REPLY CARD


NEW PRODUCTS CLASSIFIED

ACTIVE

Asics8000 -gate PLD. EPF8820 is amember of Altera's Flex8000 family ofhigh -density programmable logicdevices in 0.8 micron technology.EPF8820 contains 820 registers andhas 152 user i/o pins in 208 -pin quadflat pack, 192 -pin PGA and 192 -pinball grid array packs. Averagebenchmark speed is 40MHz AlteraLtd. 0628 488811.

A -to -D & D -to -AconvertersCodec. In Mitel's MT9125 adaptivedifferential pulse -code modulator, two64kb/s PCM channels arecompressed into two 32kb/s ADPCMchannels and ADPCM to PCM, TheADPCM algorithm conforming toCCITT G.721 and ANSI T1.303-1989.It also supports a 24kb/s (3 -bit word)algorithm CCITT G.723. The deviceneeds only 50mW for dual -channelworking. Mitel Semiconductor, 0291430000.

Discrete active devicesAutomotive fets. Low -voltage powermosfets from IR are particularlysuited to the car electronics market.The 60V IRFP064 has an onresistance of 9mQ, and a currentrating of 70A, while the IRFZ48handles 50A with an on resistance of18ma Two further devices, IRFZ46and IRFP048, are meant for use intraction and transmission control,UPSs, DC -DC converters and motorcontrol. International Rectifier, 0883714234.

SM, p -channel mosfet. New in theSupertex family of p -channelenhancement -mode mosfets withgate thresholds of 1V maximum is theLP0701LG, a surface -mountedversion of the TO92 LP0701N3 andLP0701ND die. Drain -sourcebreakdown is 16.5V and onresistance is better than 1.50 at 5Vand 300mA. Kudos Thame Ltd, 0734351010.

Adjustable zener. Two externalresistors program the Zetex ZR431surface -mounted shunt regulator inthe range 2.5-20V. No-load current

consumption is 35uA and the devicehandles 2W maximum. Maximumoutput current is 100mA andtemperature stability is 50ppm/.C.Zetex plc, 061-627 5105.

Digital signal processor16 -bit 52Msample/s digital filter.Harris's HSP43216 is a digital half -band filter with 16 -bit precision. Itincorporates a 67 -tap filter processing16 -bit data with 20 -bit coefficients andgives better than 90dB stop -bandattenuation and 0.0005dB pass -bandripple, with 1.24-1 filter shape factor.Decimation or interpolation by 2 andquadrature up or down conversion areon -chip, as is coefficient generation.Harris Semiconductor (UK), 0276686886.

16 -bit DSP. TI's newest additon to itsTEC320C DSP family is theTEC320C52, which has a 16 -bit,fixed-point DSP and an array from the0.8micron TGC1000 series to provide10K usable gates, 3V or 5V operationand 25ns or 35ns processing speed.The core executes up to 40Mips, has4Kword of rom and 1Kword of dual -access ram. Texas Instruments, 0234223252.

Linear integratedcircuitsLow -noise amplifier. With a noisefigure of 2.5dB, bandwidth of 1.8-3GHz, gain of 17dB and 10dBmoutput power, Harris's HMP-130203 isa microwave monolithic galliumarsenide cascadable amplifier,designed for the 1.8/1.9 and 2.4GHzindustrial, scientific and medicalbands. Anglia Microwaves Ltd, 0277630000.

Digital volume control. With adynamic range of 110dB and THD ofbetter than 0.001%, C -ystal's CS3310stereo digital volume control isclaimed to be the industry's bestperformer and is on a single chip,needing no extras. Zero crossingvolume changes avoid noisytransitions and the log -lawcharacteristic gives good control atlow levels. The three -wire interfacecontrols two independent channelsand allows daisy -chaining of multipleunits. Crystal Semiconductor Corp.,(512) 445 7222 (US).

Pager receiver. Sensitivity of-130dBm is claimed for GECPlessey's SL6609 pager reciver IC,which offers better integration, lowerpower consumption and smalleroutline than its predecessor, the

SL6649-1. SL6609 uses directconversion and needs no externalceramic filters, operating up to350MHz at 512, 1200 or 2400baudwith 70dB adjacent -channel rejection.A 1V, 5mA regulator is included. GECPlessey Semiconductors, 0793518582

One -chip car radio. ITT's car audioprocessor (CAP) integrates stereodecoder, baseband processing, fast -tuning synthesiser, AM tuning for455kHz or 10.7MHz IF, AM IFprocessing and AM stereodemodulation. The CAP will handleboth analogue and digital audio inputand has a programmab e digital audiointerface. Flexibility in conferred bythe DSP core which, with standardsoftware, provides a completesolution but which can be easilyadapted to requirements. S:N ratio is85dB and THD less than 0.01%. ITTSemiconductors, 0932 336116.

SVGA video ICs. National's LM1205130MHz RGB video preamplifier,together with the LM2419 CRT driver,forms a complete video channel in1024 by 768 SVGA non -interlacedmonitors, inluding VESA formats.Video adjustment is DC to allowdigital drive from a microcontroller toadjust contrast, channel gain forcolour temperature setting and cut-off.LM2419 amplifies the 4V LM1205output to 50V with a bandwidth of65MHz. National Semiconductor,0793 697415.

Switched -mode controller. S liconixhas designed its Si9114 switched -mode control chip for use incommunications equipment. It has theelements of the standard Si9100series and increased functions andperformance, including a 500kHzswitching frequency. Soft start.internal start-up and latched shut-down are included and, usingtelephone -line voltage, flyback orforward converters can be built toswitch at up to 1MHz. Siliconix/Temic,0344 485757.

Charge pump/dual op -amp.Replacing two separate devices inless board space, TI's TLE2662consists of a negative -rail chargepump and a pair of op -amps it one16 -pin wide -body SM package. Theinverting charge pump supplies100mA, used to power the op -ampnegative rail and other sub systems,and each op -amp gives over 25mAwith micropower requirements of lessthan 600µA. When the negative rail isnot needed, it can be shut down.Texas Instruments, 0234 223252.

Fast cmos. The first 20members of Toshiba's 150MHzcmos logic WEN/ are nowbeing samplec. 3ropagationdelay is 3.5ns and switchingnoise 0.8V, and the devices willinterface betwaen 3V and 5Vsystems, by means of a signal -voltage shift. OLtput drive is8mA. Toshiba Eectronics (UK)Ltd, 0276 6946C0.

Logic building blocksDisk -drive chip. Allegro's A8980CJTSuperservo provides drive,management and control of the voicecoil and spindle -motor poweractuation subsystems for hard -diskdrives. Internal circuitry gives start-upand microcomputer -assisted runmodes with no reed for externalcomponents; all current -sensing anddiode protection is internal. AllegroMicroSystems, 0932 253355.

Video clock synthesiser. Amega'sAMCC S4503 b.cmos video clocksynthesiser is designed for clockdistribution, providing multiple clockfrequencies up to 300MHz from onecrystal, producing independentlyselected outputs in the 10-300MHzrange. A pair of positive -referencedECL outputs with only 250ps jitteroperate to 300MHz and a second pairprovide complementary 24mA outputsat up to 80MHz. Amega Electronics,0256 843166.

Microprocessor supervisors.Maxim's MAX805L and MAX813L



Please quote "Electronics World + Wireless World" when seeking further information

generate active -high resets when amicroprocessor's supply voltagedrops below 4.65V, in any phase ofoperation, this type of reset beingneeded by Intel devices, as opposedto active -low resets. A watchdog timermonitoring software operation issuesa reset whenever activity on aselected i/o line lapses for over 1.6s.There is battery back-up for othercircuitry in the system. MaximIntegrated Products Ltd, 0734845255.

Memory chipsPCMCIA memory. Atmel announcesthe AT28C16-T, a low -power eepromfor the attribute memory of PCMCIAcards in a TSOP package measuringonly 0.045in in the Z dimension andneeding only 0.165 square inches ofboard. The IC needs a 5V supply at30mA (10pA in standby) and it isreprogrammable in byte -sizedincrements. Write cycle occupies1ms. Atmel (UK) Ltd, 0276 686677.

PCMCIA memory development.Highland has put together adevelopment kit to allow MitsubishiPCMCIA memory cards to be

Woofers. Low and mid -rangeloudspeaker drive units fromMorel use shieldedneodymium magnets for highflux density and techniques tolinearise impedance andreduce distortion. A coppershorting device cancels voice -coil modulation, preventsimpedance increase withfrequency and eliminatesposition modulation. Units inthe range 5in to 12in aremade. 0284 828926

programmed from a PC. It includes aMitsubishi 1Mbyte sram card, ElanJ101 card reader/writer, applicationsoftware and all documentation andaccessories. Highland Technology,0444 236000.

Mixed -signal ICs.Television chip -set. Philips has acomplete chip -set for imageenhancement and flicker reduction inmulti -standard, improved -definitiontelevision applications. It improves thequality of pictures on standard50/60Hz transmissions and allows thedesign of a single, alignment -freePal/Secam/NTSC board for useanywhere in the world. The setconsists of the TDA9141 colourdecoder/sync. processor, theTDA9150B or TDA9151B deflectioncontroller, TDA8755 video A -to -Dconverter, SAA4950WP memorycontroller, SAA4940H noise reducerand SAA159WP back -end chip.Philips Semiconductors, 8071 5806633

Wave -table synthesis. CS8905 andCS9203 by Sequoia are wave -tablesynthesiser chips offering theperformance needed for professionalkeyboards and electric pianos. Theyare compatible with Roland GSenhancements to the General MIDIspec and with the MPC Level 2Extended Multitimbral spec definingperformance in Windows. SequoiaTechnology Ltd, 0734 311822.

Power semiconductors3A regulators. Semtech'sLM1576/2576 3A switching regulatorsare interchangeable with NationalSemiconductor chips. They come in arange of versions including 3V and3.3V types with fixed outputs from 3Vto 15V and variable outputs from1.23V to 37V, from inputs of 4-40V.Semtech Ltd. 0592 773520.

C -band power fets. 30W GaAs fetsby Toshiba are designed to replaceseveral lower -power transistors,giving 45dBm 1dB point total powerand gains of between 10dB and 6dB,depending on frequency. Bandwidthis up to 800MHz, the six devicescovering the 3.7-8.5GHz range. As anexample, the T1M7785-30L operatesat 7.7-8.5GHz, with intermodulationdistortion of -43dBc. ToshibaElectronics (UK) Ltd, 0276 694600.

Current -mode PWM controllers.Unitrode's UCC1/2/3806 BicMOSPWM controllers have dual, 1A fet-driving outputs, a true differentialinput current sense amplifier and awell defined voltage threshold forturn -on. Maximum operating current is1.4mA and delay from current -senseinputs to outputs is 125ns. Start-upcurrent is 50µA. Unitrode UK Ltd, 081318 1431.

PASSIVE

Passive componentsEMI suppression inductor. In a1.6mm by 0.8mm by 0.8mm package,Murata's BLM11Al2 chip inductor forEMI suppression has a current ratingof 200mA DC and 0.50 maximumresistance. Impedance at 100MHz is2200. Other models in the BLMseries have 5-20005 impedances.Murata Electronics (UK) Ltd, 0252811666.

Tantalum chips. Surface -mountedtantalum chip capacitors inPanasonic's KE series have no leadframe and are therefore only abouthalf the size of the previous TE type,measuring 2 by 1.25mm. Values inthe first to be made are 4.7, 6.8 and10pF in ratings of 10, 6.3 and 4V.More in the series are due in April1994. Panasonic Industrial Ltd, 0344853827.

EMI/ESD protection. Murata'sVFR303 combines electromagneticinterference suppression withprotection against electrostaticdischarges and is meant to protectcmos and TTL circuitry. It will handleESD surges of up to 30kV andattenuates radiated interference by30dB at 250MHz. SurtechInterconnection Ltd, 0256 51221.

SM inductors. Vishay's LPC range ofinductors, which cover the 47-6800pHrange, have wrap -round terminalsprinted on the ceramic base forincreased reliability, solderlesswire/pad bonding being used forinvulnerability to reflow soldertemperatures. The surface -mounteddevices are rated at 7-10mA. VishayComponents (UK) Ltd, 0915 144155.

Connectors and cablingMicrowave cable assemblies.Flexible 18GHz cable assemblies byITT Cannon can be cut to any sizeand terminated by the company withany current type of connector. Theycan be formed into the desired shapeby the user. Diameter is the same asin the RG-405/402 semi -rigid cables,but losses are lower. An FEP outer isfitted. ITT Cannon/Sealectro, 0256473171.

Data -network connectors. M/A-COM Greenpar connectors areavailable for data networks includingEthernet and PC networks.Connectors are made in nickel -platedbrass, the internal PC types being ofdie-cast material. They fit all commoncables, come in BNC, N and Twinax

types, can be assembled with a low-cost tool and the N and BNC versionshave an earth tagged terminal. M/A-COM Sales Ltd, 0344 869595.

Smart -card connectors. Connectorsaccepting ISO 7816 smart cards aremade by ITT Cannon. They have 16contacts for up to eight pads on thecard, the contacts being gold overnickel -plated copper alloy to give100m52 contact resistance.Connectors are either in the lower -cost friction version or in the landingvariation. RS Components Ltd, 0536201234.

Card -edge connectors. Palladium -nickel edge connectors in Thomasand Betts's Holmberg range arecapable of over 5000 mating cycles.The design accommodates a fullrange of board thicknesses and thecontoured mating surfaceconcentrates the force in the correctarea. Individual contacts arereplaceable. Operating conditions are600-1500V DC and 3-5A. Thomas &Betts Ltd, 0582 608816.

Audio connectors. A range ofprofessional audio connectors fromNeutrik, distributed here byVerospeed, now includes right-angledversions of the XLR and XLR-compatible mains connectors, audiojack plugs and sockets. Verospeed,0703 644555.

FiltersBand-pass filters. Covering most ofthe IFs currently in use, Chronoshigh-performance elliptic band-passfilters offer out -of -band rejection of45dB, insertion loss of 1.5dBmaximum and 1.2dB VSWR in thepass -band. Mounting is by 8 -pin relayheader or in leaded or non-leadedsurface mounting. ChronosTechnology Ltd, 0989 85471.

HardwareKeyboard components. Keys andindicators by Rafi are for use in low -profile, membrane keyboards and flatdata -entry equipment. The RF15 andRF19 series of board -mounteddevices includes non -illuminated,spot -illuminated and fully illuminatedkeyswitches with several indicatoroptions with standard or multi-coloured leds. Rafi (GB) Ltd, 0737778660.

InstrumentationPulse -response measurement. IMPis short for Impulse responseMeasurement and Processing. Itconsists of a software/hardwarepackage to be used with a PC toperform measurements onloudspeakers or associatedequipment. Its output pulse drives thespeaker, whose acoustic output ispicked up by a microphone, the



output of this being fed back to theIMP board, digitised and taken to thePC by way of its printer port. The IMPsoftware then analyses the data .Falcon Acoustics Ltd, 0508 78272.

Oscilloscopes. New Tektronixoscilloscopes include the TDS320, a100MHz digital real-time instrumentthat allows sampling at five times itsanalogue bandwidth, 500Msample/son both channels without aliasing. Ithas the TDS user interface a 1Krecord length and auto measurement.The TAS400 series comprises fouranalogue units with bandwidths from60MHz to 200MHz FeedbackInstruments Ltd, 0892 653322.

TV signal generators. Three newinstrument families from Fluke covermost requirements in television andvideo testing. Features include 16:9test patterns for wide-screenequipment; Y/C outputs for Super -VHS and Hi -8 recorders and satellitereceivers; and video program systemand program delivery control fortesting automated video recorderoperation. PM5414V offers basic tvand video test for Pal and NTSC;PM5415 versions cover moreextensive testing; and PM5418models offer the widest selection offunctions and will test Secamequipment. Fluke (UK) Ltd, 0923240511.

Laser analyser. Metes Griot/PhotonControl offers the 13 SKP 001BeamAlyzer, which measures width,3D intensity profile, power andposition of a CW laser beam in realtime, using a tomographic technique.Working with a PC, it will handlelasers in the 400-1050nm range withbeam widths between 3um and 5itm.The system consists of a plug-in cardand software. Melles Griot Ltd, 0223420071.

26.5GHz signal analyser. Rohde &Schwarz's FSMS is a spectrum andnetwork analyser working in the100Hz-26.5GHz range, findingapplication in the digital techniquesused in mobile and directional radio,satcoms and microwave module andcomponent test. Features include-142dBm inherent noise, -103dBcphase noise at 1kHz from carrier andsome flexible software. Rohde &Schwarz UK Ltd, 0252 811377.

2MHz function generator. Variable -symmetry sine, square and triangularwaveforms from 0.002Hz to 2MHzfrom Thurlby Thandar's TG215 aredigitally indicated in frequency,amplitude and DC offset. At lowfrequencies, resolution and speed ofdisplay up -date are preserved byarranging for the counter to read theVCO control voltage rather thansignal period. Output is 20V peakfrom 500 or 60012 and there is aTTL/cmos output. An externalvoltage -control input is provided.


Thurlby Thandar Instruments, 0480412451.

Interfaces Optical Tx/Rx modules.Claimed by Toshiba to the world'ssmallest and fastest, optical datatransmitter and receiver modules areless than one -sixtieth the s ze ofconventional systems bit, with atransmission speed of 10Gbit/s, willhandle the equivalent of 1C0 HDtelevision channels or 150,300telephone lines simultanewsly. FiveGaAs mesfet chips in 0.5microntechnology comprise the set, thetransmitter including multiplexer, laserdiode driver and laser diode and thereceiver a demultiplexer, pre -amp,decision IC and photodiode. ToshibaCorporation, fax (03)3456-4776.

LiteratureVideo/imaging ICs. Harris's videoand imaging product guide describes850MHz amplifiers, 8GHz transistorarrays, signal converters andprocessing chips such as FIR filters,convolvers, histogrammers,multipliers and buffers. -here are alsovideo switches, sync generators,PLLs and chroma processors. HarrisSemiconductor (UK), 0276 686886.

T & M catalogue. Among the 29oscilloscopes in the Hitachi Denshi1993/4 catalogue is the VC -704 four -channel, 100Msample/s. 150MHzdigitising instrument, which has itsown printer, 64Kbyte to 2Mbyte sram,auto set-up, go/no-go comparison andwindow trigger. Other equipmentdescribed includes signal processorand analysis software, televisionmeasuring instruments, counters,plotters and function generators.Hitachi Denshi (UK) Ltd. 081-2024311.

Data analysis tutorial. A freeinteractive software tutorial fromNational Instruments, AnalysisAdvisor covers data analysistechniques for use with LabVIEWgraphical programming software andLabWindows automatic code -generation. The package deals withDSP, statistics, simulation and time -domain analysis, with demonstrationsin each session. Requirements are a386/33 or better, Windcws 3.1, 8Mbmemory and a VGA or SVGA.National Instruments U<, J635523545.

Emulator tutorial. In-crcjitemulators in Pentica's dime seriesare the subject of a free tutorial disk.It shows screen displays concernedwith high-level debug and tracequalification and indica:es how theyare used. Typical problems arecovered in detail in a sirnilatedemulation session. Pertice SystemsLtd, 0734 792101.

IGBTs. Toshiba's range of second -generation insulated -gate bipolar

transistors is the subject of a newbrochure, which covers all thecompan is devices, including a 1300A,1200V module and a nu-nber ofdevices protected againstovercurrent, over tempe-ature aiddrive uniervoltage. ToshibaElectrorics (UK) Ltd, 0276 694500.

Power supplies55W SMPS. A new series of casedswitched -mode power supplies, thePUP from Amplicon, give 55Wcontinuous power from single, dual ortriple outputs. Input voltages are 85-264V , efficiency 65%, I -old -up t me10ms and line regulation at full bad±0.5%. Amplicon Liveline Ltd,(Free)0500 525335.

Batteries. NiCad and nickel metalhydride cells made by CP Batteriesuse foam or sponge type electrodesto allow a maximum of active

Shielding tape idt Anengineering kit -rom 3M consissof eight foil shelling tapes in adispenser and is ntended fordesign, prototype andmanufacture of small quantitieswhere a few Indies are needed.Each roll is 1.9cm wide and3.66m long, the kit being pricedto allow one for each engineer3M United Kingdom plc, 0344858000.

1.3GHz counter. Although ahand-held instrunent, ThurlbyThandar's PFM1300 digitalfrequency meter covers the 5I-z-1.3GHz range and usesreciprocal counting to give0.001mHz resakdion at lowfrequencies, the reciprocal bengcomputed for d solay. A low-passfilter can be sebcted. ThurItyThandar Instruments, 0480412451.

November1993 ELECTRONICS WORLD + WIRELESS WORLD 953



material. NiCad 1/3 AA cells have180mAh capacity, AA cells 850mAhand 7/5AF cells 2Ah, while the nickelmetal hydride types in 2/3AA give550mAh, AA 1.2Ah and 7/5AF 2.3Ah.The company now has ISO 9002approval. GP Batteries (UK) Ltd, 0278445995.

In -cable DC -DC converter.Development of Microspire's SCseries of 15W DC -DC smartconverters has produced the latest55mm by 18mm by 28mm diameterversion, which is designed to bemounted inside a cable for use intowed arrays and similar marine anddefence applications. Outputs arefrom ±5V to ±15V from inputs of 28Vor 170V. Microspire UK Ltd, 0227740368.

EMI suppressors. Surface -mountedEMI suppressors in the ACC range byTDK have current ratings between1.5A and 3A and use a ferrite chip toallow wide -band operation with thecorrect conductor thickness for lowresistance. Eleven versions haveimpedances from 600 to mon andwith resistance of 0.050 and 0.040 inthe 1.5A and 3A types. TDK UK Ltd,0737 772323.

Radio communicationsproductsDirectional coupler. Working in thefrequency ranges 400-1500MHz and1600-2000MHz, Murata's LDC seriesof surface -mounted directionalcouplers are claimed to be the world'ssmallest. They are meant forcellphone application, are shieldedagainst interference and offer -3dB to-17dB coupling. Nominal impedanceis 500, insertion loss 0.2dB andemissible power 3W. MurataElectronics (UK) Ltd, 0252 811666.

GPS receiver. Navcore MicroTrackeris Rockwell's new credit -card -sizedfive -channel global positioning systemreceiver, which has an average powerusage of 670mW. One optionavailable with the new design isRTCM SC -104 compatible differentialGPS, which improves error from100m to 5m most of the time. It isdesigner to work with a passiveantenna. Time to first fix is 20-30sfrom a warm start and dynamictracking avoids the effects of foliage,buildings and vibration. RockwellInternational, 010 33 93 00 33 01.

Mobile data terminal. Solo has arange of mobile data terminals for useby transport and distributionorganisations and field workersneeding access to a central database.The MDU800 series operates on theCognito communications network,being easily configurable and taking avariety of input and output devices,particularly for use in vehicles. It isdesigned for use by unskilled people.Solo Electronic Systems Ltd, 0202676859.

Switches and relaysSolid-state relays. High -voltageForm C relays are introduced by theAmerican company Coto Wabash.

They provide 3750V RMS isolation,linear AC/DC operation and lowthermal EMF characteristics withbreak -before -make operation. 200V,200mA and 400V, 150mA versionsare available. Coto Europe, +31-45-320838.

Reed relay. The Coto Wabash model2342 changeover reed relay in 2Cform occupies a board space of 5.3by 20.6mm and is encapsulated in asteel shell. The switches come in 3Vand 5V versions, are rated at 3W atup to 100V DC and peak AC, andmaximum switched current is 0.25-0.5A continuous. RhopointComponents, 0883 717988.

Transducers andsensorsLinear displacement sensors. Fastlinear displacement sensors fromControl Transducers are now reducedin length to give a length to measuringrange of 1:1 and a 15kHz frequencyresponse. No RFI shielding isneeded, accuracy is within 0.15% andthere is a range of signal processors.FS5000 operates over the -50 to125°C temperature range. ControlTransducers, 0234 217704.

Digital potentiometer. Based on anoptical encoder, ControlTransducers's DP10013T digipotproduces 10, 20, 50 or 100 two-phasesquare -wave counts per revolution toprovide a maximum of 400 binary 2bitcode changes per rev. A free designguide is on offer, which advises oninterfacing. Control Transducers,0234 217704.

COMPUTER

Computer board levelproductsVideo card. TI's TIGAVIDEO cardcaptures and displays high-res.images in Windows 3.1 in real time. Itis supplied with free AdobePhotoshop Light software for imagemanipulation, capturing images fromRGB, Pal, Y/C(SVHS,HI-8mm) inputs,still images being captured in .TIFFand .BMP format. The card providesscreen resolutions from 160 by 160,360 by 288 and 768 by 576 in 16 -bitform. Texas Instruments, 0234223252.

Development andevaluationDSP Eurocard. MPE's TMS320C31CPU board has 33Mflop capability intransient analysis, spectrum analysis,filtering and waveform generation. Ona 3u high, 160mm deep card, theboard includes up to 512K zero -wait -state static ram, two serial ports withRS232 or 2/4 -wire RS485, 24 TTL i/olines, a 1511s, 12 -bit A -to -D converterand a socket for a 1MByte eprom. It

le Set ps Be 119 ource race lodou

2031 Microilatcb 1

PC 1.1 ACC M RO Frl 82 R3

ornt NM 9 109 !BOO

EROS u

Source Rieu --

(1)couat>4;

08012 08 00

MI matt .1

u

NOE RAIL

BB RAMBMW

Stack -Use

C p I

i Skit i 4 to le loo/St

has access to all the MPEPowerboard i/o family and is suited tohigh-level languages such as Forth orC. MicroProcessor Engir eering Ltd0703 631441.

Fast firmware up -grades. Flashmemory in PEP's VM30 :...omputerallows complete firmware codechange in situ with no hadwarehandling. 1Mbyte of 5V flash epromon the VMEbus unit takes new codefrom disk or modem in a few minuteswith little technical effort Deingneeded. VM30 now operates atalmost 12Mips and, with a 68882 co-processor, at 4.5Mflops. EP ModularComputers (UK)Ltd, 0273 441188.

DSP starter kit. Texas Instrumentshas a kit which includes everythingneeded to make a start ir, DSP,including a PC -linkable board,assembler and debugger softwareand documentation. Two versions arebased on TMS320C26 orTMS320C51 DSPs. Polar ElectronicsLtd, 0525 377093.

SoftwarePC signal analysis. InteligentInstrumentation has the Signalyzer onoffer -a data -acquisition, analysisand display software package runningunder Windows. From 1 b 32channels of data at samp e rates upto 10MHz are acquired in bursts tothe PC ram or streamed b disk, thesoftware then supporting Doth timeand frequency -domain analysis, withFIR and IIR filter analysis being anextra. The software supports theexisting range of PCI dats acquisitionboards. Intelligent Instrumentation,0923 896989.

Emulator: The PC card-basecUniversal Emulator from FlashDesigns offers a fast way ofdeveloping embedded C orAssembler code for all 4/8/16 -bit microprocessors. Using theFlash DMA technique foraccessing all registers andsymbols allows very rapidprogram development anddebugging, No monitor isrequired. The software willwork with all popularassemblers and IAR/Keil Ccross -compilers. It can also beused within Windows to allowcomprehensive integrateddebugging. Animate, continueto next break and snapshot areall include. Turbo -trace giveslogic analyser functions suchas tracing memory reads andwrites in real time.

32 -channel A -to -D card. Anaddition to IMS's PC -Labrange is the PCL-813 32 -channel, 12 -bit A -to -D on a 2/3length card. Opto-isolators giveover 500V DC protection andinput range, A -to -D triggeringand data transfer are allsoftware -controlled. Analogueinput ranges supported are±5V, ±2.5V, ±1.25V and1-0.625V, gain being setindividually. IntegratedMeasurement Systems , 0703771143.


BENCH POWER SUPPLIESfrom DIAWA INDUSTRY CO

awasu REGULATED OC OOMA SUOMI 1.401

rr.--

..

I's I 20M1dIA PS140MkIIA PS304 RS4OX

UP VOLTAGE 230/117 230/117 230/117 210/117

0/P VOLTAGE 3-15 13.8 1-15 1-15

0/P CURRENT 12 14 30 40

MAX RATED 9.2 12 24 32

RIPPLE 3MV 3MV 3MV 3MV

SIZE (WHD) I 28x 104x225 I28x I 04x225 I 75x150x225 280x140x225

WEIGHT 5KG 5KG 8KG I OKG

PRICE INC VAT* 79.95 79.95 129.95 189.00

*Carriage extra

II Compact and lightweight Cost efficient Rapid delivery SMC

SOUTH MIDLANDS COMMUNICATIONS LIMITEDS M House, School Close, Chandlers Ford Ind Est.

Eastleigh, Hampshire, SO5 3BYTel: (0703) 255111 Fax: (0703) 263507


1111111111.01MMLow cost data acquisition for IBM PCs & compatibles

Al oar proihrets era easy to Antall -ether the printer or serial golf mgnay sag sapplied with easy 's woefee either agility or print -act.

8 - bit resolution

one channel

10-25K samples per second

Oscilloscope/Voltmeter software

0-5V input range

Connects to printer portf49 10 - bit resolution

II channel 5.10K samples per second

Data logger software

0-2.5V input range

Connects to printer port

8,17 I6 -bit resolution - sign 8 s/e or4 differential inputs

216 or 300 8 -bit samples per secant]

2.5V input range

Data logger software

Connects to serial port

PICO TECHNOLOGY LTD?roadway House, 149 151 St Heats bead, Hardwick, Cambridge CB3 70.1

A VISA TEL: 0954 211716 FAX: 0954 211880


LOW COST RANGER1 PCBDESIGN FROM SEETRAX

Circuit SchematicCircuit CapturePCB DesignHost Of Outputs

All -In -One Design System£100

Fully Integrated Auto Router£50

Ask Us About Trade -In DealsCall Now For Demo Disk on 0705 59103'7

Seetrax CAE Hinton Daubnay HouseBroadway Lane Lovedean Hants P08 OSG

Tel: 0705 591037 Fax: 0705 599036

REDUCED

PRICE!

What The PressSaid

For most small users,Seetrax

Ranger]provides

systemat an

affordab/eprice.

It is betterthan

EasyPCor Tsien'sthan

since it providesa lot more automationand

takesthe design

all the wayfrom schematic

to PCB - otherpackages

separatedesigns

for both,that is,capture/t is more expensivebut the ability

to drawin the

circuitdiagram

andturn it intoa board

designeasi/y rrakes

up for thisPractical

Electronics

AboutRANGER j

SourceJUNE

1991

Pay by Visa or Access



DESIGN BRIEF

Fig. la. Simplified circuitdiagram of a wideband rfnoise generator employinga temperature limiteddiode.

Fig. 1b. Suggested rf noisegenerator using a Schottkydiode.

WHITE NOISEWHITE KNIGHT?tan Hickman shows how to make noise work for you and looksat the principles behind an economical semiconductor noisesource operating up to 1000MHz.

Noise is an unwanted guest in all analoguecircuits, so it seems perverse to want to makeyet more noise; but the reason is simply

summed up in the old adage "Know thine enemy".A calibrated noise source is a great convenience

when developing a low noise circuit, and - althoughother methods do exist - is almost essential for theaccurate determination of the noise figure of a lownoise amplifier or receiver.

HT(anode)supply

D1 Schottky diodeE.G. HP5082-2301

For heater

(a)

(b)

50 RNoiseoutput

zsource = 50 t

Addmagichere

(see text)

Heater resistor RHthermally coupled

to D1

Output

The classical approach to the design of a widebandnoise generator is to use a temperature limitedthermionic diode. This is one where all the electronsemitted from the cathode are attracted directly to theanode: there is no cloud of electrons forming a spacecharge surrounding the cathode. The effect is usuallyachieved with a pure tungsten filament cathode, fedwith a smooth dc current which can be adjusted to setthe anode current to the desired value.

The resultant noise is described as shot noise sincethe electrons forming the anode current fall onto theanode like lead shot onto a corrugated iron roof. Ifthere is no residual gas in the valve to be ionised, andthe anode voltage is not so high that secondaryemission results, the rms fluctuation (noise) current iis related to the dc anode current /, according to theformula:

i2 = 3.18 x 10-19 x I x df

where I is in amperes and df is the bandwidth ofinterest. By contrast, the noise current i flowing in ashort-circuit across a resistor R, is given by:

i2 = (1.59 x 10-20 x df)IR

so that a noise diode passing an anode current of Igives as much rms noise current as an equivalentresistor Rey = 0.05//Q

Noise current available from a noise diode permitsconstruction of a noise source whose output forms aknown, absolute standard. Figure la shows thearrangement, where the anode current is passedthrough a 5052 resistor. This forms a source of noisematched to the circuit under test, the magnitude of thenoise power relative to that of a 500 resistor beingprecisely known.

In theory, df can extend from 0Hz up to anyfrequency, although in practice an upper limit is set bythe shunt capacitance to ground of the noise diodeanode, as well as other factors. Rhode and Schwarzare probably the best known European manufacturer


DESIGN BRIEF

of noise sources of this kind, with a specifiedoperating range up to 1000MHz.

MeasurementMeasurement of receiver noise is simple. With thenoise generator connected to the receiver under testand the diode anode current zero, the noise outputfrom the receiver is noted, using a suitable measuringinstrument. Then 3dB of attenuation is insertedbetween the receiver output and the measuringinstrument, and the output from the noise generatorincreased to restore the previous level.

Noise supplied by the noise generator is equal to thereceiver's own front end noise. A meter in the noisegenerator monitors the anode current and is directlycalibrated in dB above thermal, with correspondingvalues of kTB also given.

Practical considerations in manufacture of the noisediode limit the maximum output that can be achievedto around 15dB above thermal. If the aim is tomeasure the noise figure of a receiver higher than this,the output of the noise generator must be amplifiedfirst. Clearly the amplifier used for this purpose willneed to have a good signal-to-noise ratio.

A solid state alternative to the thermionic diodenoise generator was described by TH O'Dell'. Here.the source of noise was the flow of reverse leakagecurrent induced by the creation of hole - electronpairs in a photodiode, by photons illuminating thesame.

It was stated that the reverse photodiode current issubject to the same relation between dc and its shotnoise component as the saturated thermionic diode.But, as the practical limit to the available current, at1001.1A, is only about 1% of the maximum currentpossible with the thermionic diode, we must work atan impedance level of around 5K and provide a 10:1turns ratio transformation to 5052. As just 1pF of straycapacitance across a 5K source would give a -3dBpoint of 32MHz, a tuned transformer was used, thishaving the additional advantage of absorbing the selfcapacitance of the diode as well as that of thetransformer.

Subsitute diodeNot having a sample of the HP5082-4220 photodiodeto play with, I wondered whether an HP5082-2301(1N5165) Schottky diode could be used. The paintwas scraped off and the diode's reverse leakagecurrent at Vr = 15V found to be totally unaffected byany practical level of illumination.

But, there is another mechanism for inducing hole -electron pairs in a semiconductor - heat. The leakageof the sample diode at Vr= 15V and 25°C was0.056µA, against the manufacturer's quotedmaximum of 0.30011A. Raising the temperature of thedevice by holding it close to, but not touching, asoldering iron, produced a leakage current of morethan 100µA, at an estimated temperature of between200 and 250°C. This is beyond the device's top ratedtemperature of 150°C, but on being left to cool, thecurrent fell to less than a microamp in seconds andright back to 0.056µA within a few minutes.

Thus this scheme might form the basis of a practicalnoise generator, the utility of which would clearly bemuch increased if it were broadband, rather than

limited to a spot frequency'. Figure 1possible scheme.

In addition to the diode's self capacitance of under0.3pF at 15V reverse bias, there is the inputcapacitance of the amplifier to consider, typicallyseveral pF, limiting the useful top frequency to less

shows such a

(a)

(b)

Fig. 2a. Output spectrum ofNational SemiconductorsMM5437 digital noisegenerator (output 2, pin 5),with top -of -screen referencelevel -20d8m, resolutionbandwidth 3kHz, video filtermaximum, 10d8/div vertical,20kHz/div horizontal, andcentre frequency 100kHz. Theoutput of the MM5437 was notlow pass filtered, so some180kHz clock breakthrough isvisible in the first zero of thespectrum.

Fig. 2b. As Fig. 2a exceptresolution bandwidth 10kHz,100kHz/div horizontal, andcentre frequency 500kHz.

Fig. 3a. Circuit used totest the base -emitterjunction of a 2N918 as anrf noise source.Fig. 3b. Circuit of a noisesource using the base -emitter /unction of aBFR90A in reversebreakdown.

RF noiseoutput

+9 V

RF noiseoutput


DESIGN BRIEF

Fig. 4a. Output of the noisesource of Fig. 3a: lower

trace, diode current zero;middle trace, diode current

1560; and upper trace,diode current 3100

(10dB/div vertical,reference level -33dBm,

centre frequency 500MHz,span 1000MHz, IF

resolution bandwidth1MHz, video filter

maximum).

Fig. 4b. As Fig. 4a, but a51S1 load resistor added to

the source.

Fig. 4c. Output of anamplified BFR90 zener

source: lower trace, diodecurrent zero; upper trace,

diode current 1.3mA(10dB/div vertical,

reference level -33dBm,centre frequency 500MHz,

span 1000MHz, IFresolution bandwidth

1MHz, video filtermaximum).

than 10MHz. But, given a modern low noise currentfeedback op -amp with a bandwidth at a non -invertinggain of two approaching 1GHz, the high frequencyattenuation of the diode noise due to the total shuntcapacitance could be avoided by cancelling it with anequal shunt negative capacitance to ground. Here, itjust involves connecting the equal capacitancebetween points A and B in Fig. lb.

Noise measurements are also necessary in audiocircuits, and Fig. I of reference 3 shows threedifferent audio frequency noise generators, whilepointing out that they can conveniently be replaced bya simple digital noise generator, the NationalSemiconductors MM5437, shown in Fig. 3 of thatarticle. This also shows the typical output noise in thetime domain, that is waveforms.

Figure 2a shows the output of the MM5437 in thefrequency domain, indicating that the noise level isvirtually flat to 60kHz and only 3dB down at about100kHz. Note, however, that this is with no low-passfiltering of the pseudo random digital output from thechip, so that the amplitude distribution is notGaussian.

The omission of any low-pass filtering also makesthe first zero of the output at 180kHz very obvious,with a spectral line due to clock breakthrough sitting

in its middle. The spectrum repeats, at diminishingamplitude, around multiples of twice the clockfrequency, so the device can be used as a noisesource, over limited bandwidths, at frequencies wellabove that of the clock, up to low radio frequencies(see Fig. 2b).

Higher frequenciesFor higher radio frequencies, while a noise sourcebased on a temperature limited noise diode source isconvenient for lab measurements, it is too large andexpensive for building into equipment. One based onthe shot noise in an illuminated photodiode or aheated Schottky diode is likely to be limited tooperation at frequencies in the lower VHF range.

A number of manufacturers specialise in producingcompact semiconductor noise sources for OEMs tobuild into equipment, probably the best known makerbeing an American company4.

Figure lb of reference 1 shows a zener diode usedas a semiconductor noise source, with the commentthat this can work up to vhf, given a suitable diode. A2N918, running the base emitter diode in reversebreakdown with the collector left disconnected, withsome qualifications, works well and has been used asa noise diode in the built-in test equipment of amilitary tactical radio system, as a go/no-go test of thefront-end and IF modules.

Figure 3a shows a circuit using a 2N9I 8 throwntogether to reproduce those results, the performancebeing as in Fig. 4a. The lower trace is with the diodecurrent at zero: it shows the noise floor of thespectrum analyser, with a local tv station just makingitself visible at around 510MHz.

The top -of -screen reference level is -33dBm so thetrace is at -93dBm, and (assuming the noisebandwidth of the analyser's 1MHz IF resolutionbandwidth filter is equivalent to a 1MHz widebrickwall filter) this corresponds to -153dBm/Hz.Thermal weighs in at -174dBm/Hz, equating to anoise figure of 21dB - rising to 22dB at 1GHz.

This is good for a spectrum analyser, since these arealways designed primarily for linearity rather thansensitivity; 25dB is a not untypical noise figure. Witha diode current of 156µA, the power delivered to theanalyser is about 12dB above the noise level, or about33dB above thermal -a lot more than one can getfrom a noise generator using a thermionic noise diode.If the current is increased to 310µA, the noise levelabove 300MHz is unchanged, but the level risesbelow that frequency. Further increases of current seethe picture alternating smoothly between the twoupper traces.

The noise is definitely falling off by 1500MHz, sothe total noise delivered to the 5052 load presented bythe spectrum analyser's input is roughly -60dBm or abit less, around 0.001µW.

With the base emitter breakdown voltage of 4.5V,156µA represents a power input to the diode of700µW, giving a fairly low efficiency as a noisegenerator, but still much higher than a thermionic


DESIGN BRIEF

noise diode. The variations of around ±1dB in noiseoutput were a mystery at this stage. Their periodicityis around 150MHz, corresponding to a round journeyin co -ax of around 65cm, but the circuit wasconnected to the analyser by a lead of no more than6cm, including the BNC plug.

Figure 4b shows the effect of connecting a 510resistor in parallel with the noise output; the variationsin level have been largely damped out, especially upto 300 or 400MHz. The level has apparently fallen by4 or 5dB, but is so close to the analyser noise that thelatter is contributing to the indicated level. The truefall is probably nearer 6dB, which is what one wouldexpect if the diode acted as a perfect constant noise -current generator.

So we have a matched 5012 noise source, albeit atlower power. Where the noise power was i2 x 50, withthe extra resistor in parallel it becomes i2 x 25, the rmsnoise current i being constant. Not only is noise powerhalved, but half of what there is, is dissipated in theadditional 5052 resistor, hence the 6dB drop in output.

Another 2N918 was tried in this circuit withgenerally similar results, except that there was novalue of operating current that would avoid some risein output below 300MHz. As the 2N918 is a veryancient device, an obvious next step was to try a moremodern transistor. A BFR90A was thereforeconnected in circuit, but found to give a much loweroutput than the 2N918, barely above the analyser'sinput noise. A 20dB broadband amplifier stage, usinga Mini Circuits5 Mar 6 type amplifier was thereforeadded, as in Fig. 3b, the resulting output then beingabout 13dB above analyser noise (Fig. 4c).

Variations in output levelThe variations of output level with frequency are quitelow right up to 1000MHz. This is not due to thedifferent device but to certain other circuit changes.The lk resistor in Fig. 3a was an 1/8W miniaturecarbon film axial lead type. Such resistors are madewith a film of about 1% of the nominal value, requiredfinal value being achieved by making a spiral cut inthe film.

Such resistors thus have an appreciable inductance,though it is often possible to ignore this due to its lowQ. The output shown in Fig. 4c was achieved with adifferent feed resistor, Fig. 3b, namely a 6k8 sub-miniature solid carbon type, with a further substantialimprovement by selecting the optimum supply voltageto the amplifier. With the aid of a heater, the wholenoise generator circuit was raised to +75°C, with nomeasurable change in output noise at any part of the 0to 1000MHz range.

While the circuit of Fig. 3b offers the basis of apotentially useful noise source, its output level isfixed, not readily adjustable from thermal upwards asin the case of a thermionic diode noise source.

However, this limitation is easily circumvented bythe addition of a step attenuator. As the attenuation isincreased from zero, the noise delivered to the circuitunder test is reduced, in principle only reaching

20 Nose sourcezo = 50 R

Level +25 dBrel. thermal

15

10

5

\

0 \0 10 15 20

littenuater setting dB

Attenuator

Noiseoutput

-25 30 35

flermal when the added attenuation is infinite. Inpractice, as Fig. 5 shows, 31dB is sufficient to reducea noise level of 25dB above thermal to a mere 1dBabove thermal, low enough to test any amplifier orreceiver operating at room temperature, with thepossible exception of a parametric amplifier.

A noise output of 25dB above thermal was mooted,as it is sufficient for most applications (and certainlymuch more than obtainable from most thermionicdiode noise sources), but well below the levelavailable from the circuit of Fig. 3b. This allows forthe fitting of a fixed 9dB pad at the output of the Mar6 amplifier, which would be enough to provide asource with a return loss of 18dB even if the outputvswr of the amplifier were infinity. In fact, the outputvswr of the Mar 6 is 1.8:1 maximum up to 2GHz,corresponding to a return loss of 11dB, so the additionof a 9dB pad at the output would provide a noisesource with an output vswr of less than 1.08:1 -areturn loss of around 30dB.

It seems clear that a very economical semiconductornoise source operating up to 1000MHz, with acalibrated adjustable output flat to within ±1dB andsuitable for the laboratory measurement of receivernoise figures and other purposes, could be constructedfor little more than the cost of the variable attenuator:or no more than a few pounds if an attenuator isalready to hand.

References1. "Self -calibrating noise source using silicon," THO'Dell, EW + WW, February 1993, pp 170-172.2.'Negative approach to positive thinking," IanHickman, EW + WW, March 1993, pp 258-261.3. "Making a right white noise," Ian Hickman, EW+ WW, March 1992, pp 256-257.4. Noise/Com, E.49 Midland Avenue, Paramus,New Jersey, 07652, USA. UK agent DensitronMicrowave, 4 Vanguard Way, Shoeburyness,Essex, SS3 9SH. Tel: 0702-294255, fax: 0702-2939795. Mini Circuits, a division of ScientificComponents Corporation, PO Box 350166,Brooklyn, New York, 11235-0003, USA. UK agentBFI Electronics, BFI Ibexsa House, Burnt AshRoad, Quarry Wood Estate, Aylesford, Kent, ME207NA. Tel: 0622-882467, fax: 0622-882469.

Fig. 5. Showing the outputfrom a noise source 25dBabove thermal via anadjustable variableattenuator, against thesetting of the attenuator.

November 1993 ELECTRONICS WORLD + WIRELESS 959

APPLICATIONS

Low-cost 198 kHz radio data receiverPhase-modulated data from BBC Radio 4transmissions can be received via a

single IC from GEC Plessey and a common,low cost op -amp.

As described in note AN86, the SL6659 isa general-purpose FM radio IC. It containsa limiting IF strip and FM detector, both ofwhich are used in this application. Further,the device contains a signal -strengthindicator and a mixer stage. It needs asupply of between 2.5 and 7.5V at less than2mA.

Within the note are equations detailinghow a 1.8V peak -to -peak phase signal isobtained from the ±22.5° phase modulationusing integration.

Carrier at 198kHz received on the tunedantenna should be adjusted for maximum attest point TP1 via the trimmer capacitor, Fig.1. Because of the frequency of thebroadcast, the rf signal is affected byinterference from switch -mode supplies intelevisions and monitors. Without thecrystal filter following the fet buffer, the

Radio 4 198kHz Phase modulation

Aerial 275T ON

2 3" 0 4" DIAFERRITE ROD

36(SWG)

COVERS 2 1"

FLAT WOUND

receiver fails to work consistently at a metreaway from a switch -mode supply. With thefilter however, the distance at whichproblems start falls to a few centimetres.

To reduce Q, a resistor is placed in serieswith the crystal. Sourcing this seriesresonant 198kHz crystal may prove difficult;an address is given later.

Limiting within the SL6659 turns thesignal into a 198kHz square wave, availableat pin 1. Phase shifting takes place in thequadrature tuned circuit and the resultingsignal is fed to the demodulator. At thisstage, the signal is compared with the in -phase signal to produce a demodulatedoutput at pin 3.

Amplitude and source impedance of thissignal are 10mV pk-pk and 40k0respectively. Buffering via the transistor isneeded in order to drive the Sallen and Keyfilter.

Tuning of the quadrature circuit is set byDC voltage at the collector of the transistor.When adjusted for resonance at 198kHz,

output at 198kHz jumps from 1.2 to 4V.The inductor slug is then tuned to set outputvoltage at TP2 to 3V DC.

A critical component is the quadraturecoil. Since the inductor has a high Q of 200,temperature drift, winding settling and otherageing effects become significant. As aresult, careful design is needed. AnRM6/160 was used in the prototype.

Sallen and Key filterInitial low-pass filtering removesinterference, which could cause distortionand rapid DC shifts on the output, Fig. 2.Next the signal is amplified 47 times. Gainis adjustable by altering the 471(0 resistor,which may be necessary to compensate forthe quadrature-coil Q factor.

A clean signal, as in the upper part of Fig.3, should now be present at TP4. If thesignal is distorted, check the Sallen and Keyfilter bandwidth, the crystal series resistor orthe 330µF capacitor.

Output from the integrator will be between

Fig. 1. This low-cost radio -data receiver consumes only a few milliamps. Potential applications for radio -datainformation are numerous, among them high -accuracy clock/timer/calendars that never need adjusting.

Buffer FM detector

1p

1310

p sly150p

p.sty

150P

T1

4.7p

7p1

198k Hz

0

2-22p

TRIM

3k

1 1

10k

198kHz

El

-4 f -

680n

=820p

1000p

p.sty

2 7p

3k 680n

2 2 n

16

SL66599

TL. -J U U U 1_, U 1-J

640pH

607Q2:0

/7f77

T3

RS 228-214

RM6/160

470n 100n

I

4.5v

3k

Tp2

NOTES -All active components from PlesseyAerial on wide ferrite former

3 OV

DC

1k

OV; 0


APPLICATIONS

I and 3V pk-pk with a DC component thatcan drift between 1.5 and 4V. This drift isremoved by a comparator which producesthe final rectangular wave signal. A smallpiezo-electric sounder over the output helpsalignment.

Output data comprises two frequencies of12.5 and 25Hz. From these, both data andclock signals can be recovered.

Clock recovery is best carried out using amicroprocessor to detect edges within thephase waveforms. When the clock is

recovered, the data is sampled to see if thereis a falling or rising edge within the middleof each 40ns clock period. A falling edgerepresents logic one and a rising edge logiczero.

Crystals can be obtained from AELCrystals Ltd, Worth Corner, Turners HillRoad, Crawley, West Sussex, RHIO 7SL.Tel: 0293 882299.GEC Plessey Semiconductors, CheneyManor, Swindon, Wiltshire SN2 2QW.Tel: 0793 518000.

Fig. 3. Radio Data output at TP4 should beundistorted as in the top trace. If not,remedies are suggested in the text.

Radio DataFrom February 1988, BBC Radio 4 onlong wave shifted in frequency from2001..Hz down to 198kHz. This carriernow also contains phase -modulatedRadio Data as shown here. To avoid

the data Effecting the audioinformation, it is slotted into the 0 to50Hz band below the audio range at25bit/s.

One DIOCk is transmitted every twoseconds, with block zero staling at the

top of the minute. Block 29, the lastblock, contains time of day. -month,year, leap year and local offsetinformation. Each block also containsa cyclic redundancy check word.

1

+ 22 5°---1-

-22 5*40ms

0 0 0 1 1 1

Phase modelatedRadio Data signalson the Radi) 4 longwave carrier areinserted in al? sub -audio band o' 0 to50Hz and ran at25bit/s.

Radio 4198KHz Phase modulation

Filter

Fig. 2. Raw information from the Radio Data receiver is converted to a rectangular waveform ready for clock and datarecovery by this filter, amplifier, integrator and comparator.

Am phi er Integrator Comparator +5V

Tp2

016k

27k

220n 1

p Garb,

58K

lc., 25Hz

470n

p.carb

II

LM324

10k

330p

I LM324

1k

Tpt.

47k

56k

T

M 330p

dt

LM324

1p

40

Tp5

1M

1

27k

6.8p

LM324

1k

OPTIONAL

LED

4)

Tp6

0Output

OV


APPLICATIONS

Current conveyor circuitsUnlike op -amps, current conveyors donot have their bandwidth restricted by

feedback. According to LTP Electronics'data sheet on the CC//0/, they extendfamiliar op -amp functions to 100MHzbandwidths. Additionally, they remainstable with both inductive and capacitiveloads.

These circuits illustrate that currentconveyors need few additional passivecomponents. Many circuits can beimplemented by adding just one or tworesistors so the problems of resistormatching are reduced too.

Bandwidth of the CC//0/ dual conveyor is100MHz and its slew rate is 2000V/ps.Each element comprises three terminals.The one marked X is a virtual -groundcurrent-input/voltage-output. This i/o lineexhibits low impedance. Terminal Y is ahigh -impedance voltage input while terminalZ provides the current output.

From Fig. 1 you can see that currentmirrors replicate X -node current at the Zoutput, which has a high impedance. Portrelationships of the conveyor are simplyVx=Vy, /y=0 and /z=/x

Ideally, voltage at the Y input followsvoltage at the X node and input current atnode X is copied exactly by current at nodeZ. In practice though, the buffer between Xand Y has an output impedance of about

'OUT A

VOUT A, IIN A

VIM A Cv-

ly.0, Vy

Vx .Vy

VA

Xe

4yo

1.2.1 v+

'OUT B

11 VOUT B, IIN B

VIN B

Fig. 1. Current conveyors are a combination ofvoltage and current -mode devices offering lowcomponent count and high bandwidth. Voltageat Y is followed by voltage at X and inputcurrent at X is copied by current at Z.

I 0S1 up to 10MHz. Above this frequency,the impedance starts to rise, reaching 2552 at100MHz. This reduces accuracy of the Vyto Vx transfer, and hence the accuracy of 1xto 1z, as frequency rises.

The data sheet discusses voltagecompliance and maximum currentconsiderations. It also describes using two

conveyors as a single conveyor. Thisimproves the voltage buffer by more thantwo orders of magnitude and the currentbuffer by one order of magnitude.

LTP Electronics, 2 Quarry Road,Headington, Oxford OX3 8NU.Telephone 0865 200767.

Fig. 2. As current conveyors work without feedback, they do not suffer from the same bandwidthlimitations as op -amps. These circuits illustrate that they can reduce component count too, relativeto conventional op -amps.

Voltage controlled negative impedance converter

VIN

ZINZIN

e Composite current -conveyor as animpedance converter, ideal for filterapplications.

Filter example

A single CCI101 can be usedas a biquad filter to realiselowpass, highpass, andbandpass functions.

Low-pass and bandpass filterYl is an open circuitY2 and Y5 are resistorsY3 and Y4 are capacitors

High-pass fitterY1 is an open circuitY2 and Y5 are capacitorsY3 and Y4 are resistors

VLPF and HPF

VIN

"Y2Y5

Y5( Y2+Y3+Y4) +Y3Y4

12

c 9

co 6

0)

6> 3

0

Bandpass fitter

VBPF

VLPF, HPF

VBPF .Y2Y3

VIN Y5( Y2+Y3+Y4) +Y3Y4

BW.1.5MHz.

f0-5MHz

Q . 3.3

H.11.8.

+.

o-SMI-lz

. .

i

.

0 2 4 6Frequency MHz

8


APPLICATIONS

Fully balanced differential amplifier

Differential inputs

Ix=VIN

RI Common -mode inputs

Ix= 0

No matched components

Thoically CMRR=53dBat 1MHz

OA FET input op -amp forgood hold performance

Simulated grounded Inductance

ZIN j(01 -

L -C. RI R2

High -a simulated inductor, suitable forgrounded inductor applications in fitterdesign.

o31:3

cc

so

eo

70

so

50

40

303

4.

10 104 5 6

1 0 toFrequency Hz

' I

07

Lowpass/notch filterhis circuits a sample from the LinearT

I Technology Chronicle, Vol 4, No 4.Some applications require two transfer

functions superimposed. An A -to -Dconverter for example may need low-passfiltering at its input to remove LF noisetogether with notch filtering to reduce theeffects of mains hum. Normally thiswould involve two circuits but the solutionshown uses only one IC followed by abuffer.

The LTC1063 is a fifth -orderButterworth filter tuned via a signal froman built-in RC controlled oscillator orexternal clock. It remains accurate downto DC, where it exhibits less than ImVoffset, and can be tuned continuously up to50kHz.

To provide the notch, the upper tworesistors are chosen to cancel exactly atthe frequency where phase shift is 180°.This is at 1.19 times the corner frequencyof the low-pass filter and is not adjustable.It is set by the internal transfer function ofthe filter. A 50.42Hz low-pass frequencyfor example sets the notch at exactly 60Hz(this circuit was designed for Americanmains hum of course).

R

10k

01'.

NIN

200r F

I-

9 53k0

1.1KhaorcH=f1904

Normaly, providing low-pass filtering withadditional notch filtering for removing mainshum needs two circuits. This IC combines thetwo functions using very few additionalcomponents.

Linear Technology, 111 WindmillRoad, Sunbury -on -Thames. MiddlesexTW16 7EF. Telephone 0932 765688.

-60

70

V0111

61Hz

15 24 33 42 51 60 69 73 87 96 10`

INPUT FRE:WEND. 11-1)


RF MODULES UP TO 2GHzTELEVISION TRANSMISSION EQUIPMENTTYPE 9169 Tunable television modulator. Bands I or III or IV or V. Output50mW. With audio channel £375TYPE 9169A As above but video channel only £350TYPE 9269 Phase locked loop vestigial sideband television modulator withsound channel. RF o/p 10mW on your specified chs in bands I, III, IV or V.

£650TYPE 9115 Transposer. Converts your specified i/p chs in bands I, Ill, IV, orV to your specified o/p chs in bands I, Ill, IV or V. Minium i/p to o/p separation10 chs. ImV i/p, 10mW +10dBm o/p. Low noise Gasfet front end. NF 0.7dB.AGC. £650Linear channelised power amplifiers: -TYPE 9252 10mW input, 500mW output £353TYPE 9254 50mW input, 2 watts output £395TYPE 9259 500mW input, 3 watts output £378TYPE 9263 2-3 watts input, 12 watts output £638TYPE 9364 3 watts input, 22-25 watts output £1245TYPE 9266 13 watts input, 50 watts output £1919TYPE 9367 50 watts input, 150 watts output. £3950

TELEVISION RECEPTION EQUIPMENTTwo -stage Gasfet preamplifiers. High 0 filters. Masthead or local use.TYPE 9006TV Bands I or III. NF 0.6dB. Gain 10-40dB variable £105TYPE 9002 B/W up to 10 adjacent chs in bands IV or V. NF 0.7dB Gain25dB £135

LOW NOISE GASFET PREAMPLIFIERS 5MHz - 2GHzTYPE 9006 Freq: 5-250MHz. B/W up to 40% of CF. NF 0.6dB. Gain 10-40dBvariable £105TYPE 9004 Freq: 250-1000MHz. B/W up to 10% of CF. NF 0.7dB Gain25dB £135TYPE 9304 Freq: 1-2GHz. B/W up to 10% of CF. NF 0.4dB. Gain 20dB £185

WIDEBAND AMPLIFIERSTYPE 9301 100KHz-500MHz. NF 2dB at 500MHz. Gain 30dB. 0/p 12.5dBm,18mW £165TYPE 9302 10MHz-1GHz. NF 2d8 at 500MHz. Gain 30dB. 0/p 12.5dBm,18mW £165TYPE 9008 Gasfet. 10MHz-2GHz. NF 2.5dB at 1GHz. Gain 10dB. 0/p 18dBm,65mW £165TYPE 9009 Gasfet. 10MHz-2GHz. NF 3.8dB at 1GHz. Gain 20dB. 0/p 20dBm,100mW £185

UHF LINEAR POWER AMPLIFIERSTuned to your specified frequency in the range 250-470 MHzTYPE 9123 500mW imput, 5 watts output. £350TYPE 9124 2-3 watts input, 25 watts output. £510TYPE 9126 8 watts input, 50 watts output. £1495

PHASE LOCKED SIGNAL SOURCESTYPE 8034 Freq. as specified in the range 20-250MHz. 0/p 10mW. £194TYPE 9036 Freq. as specified in the range 250-1000MHz. 0/p 10mW £291TYPE 9038 Freq. as specified in the range 1-2GHz. 0/p 10mW. £350TYPE 9282 FM facility. Freq. as specified in the range 30-2000MHz. 0/p10mW £378

PHASE LOCKED LOOP FREQUENCY CONVERTERSTYPE 9315 Down converter. I/p frequencies 250MHz-2GHz. 0/p frequencies20MHz 1GHz. B/W up to 10MHz. NF 0.7 dB. Gain 30dB variable. £350TYPE 9316 Up/down converter. I/p & o/p frequencies 20MHz to 2GHz. B/Wup to 100MHz. NF 0.7dB. Gain 40dB variable. £550TYPE 9115 Up/down converter. I/p & o/p frequencies 20MHz to 1GHz. B/Wup to 100MHz. NF 0.7dB. Gain 60dB variable. 0/p up to 10mW + 10dBm.AGC. £650TYPE 9317 Tunable down converter. I/p will tune 30% of CF specified in therange 300MHz-2GHz. 0/p 70MHz. NF 0.6dB. Gain 60dB. 0/p up to 10mW +10dBm. AGO £950

Prices exclude p&p charges and VAT

RESEARCH COMMUNICATIONS LTDUnit 1, Aerodrome Industrial Complex, Aerodrome Road, Hawkinge, Folkestone, Kent CT18 7AG

Tel: 0303 893631 Fax: 0303 893838


Electronics World offers you the chance to advertise

ABSOLUTELY FREE OF CHARGE!Simply write your ad in the form below, using one word per box, up to a maximum of twenty

words (remember to include your telephone number as one word). You must include your latestmailing label with your form, as this free offer applies to private subscribers only. Your ad will

be placed in the first available issue.This offer applies to private sales of electrical and electronic equipment only.

Trade advertisers should call Pat Bunce on 081-652 8339All adverts will be placed as soon as possible. However, we are unable to guarantee insertion dates. We regret that we are unable to enter into correspondence

with readers using this service, we also reserve the right to reject adverts which do not fulfil the terms of this offer.

Please send your completed forms to:Free Classified Offer: Electronics World, 11th Floor, Quadrant House, The Quadrant, Sutton,Surrey SM2 5AS

964 ELECTRONICS WORLD+WIRELESS WORLD November 1993

CLASSIFIEDTEL 081 652 8339 FAX 081 652 8931

ARTICLES FOR SALE

Access

Atigk VISA

Cooke InternationalSUPPLIER OF QUALITY USED

TEST INSTRUMENTSANALYSERS, BRIDGES, CALIBRATORS,

VOLTMETERS, GENERATORS, OSCILLOSCOPES,POWER METERS, ETC. ALWAYS AVAILABLE

SPECIALIST REPAIR WORK & CALIBRATIONUNDERTAKEN

ORIGINAL SERVICE MANUALS FOR SALECOPY SERVICE ALSO AVAILABLE

EXPORT, TRADE AND U.,K. ENQUIRIES WELCOME,SEND S.A.E. FOR LISTS OF EQUIPMENT AND MANUALS.

ALL PRICES EXCLUDE VAT AND CARRIAGEDISCOUNT FOR BULK ORDERS SHIPPING ARRANGED

OPEN MONDAY -FRIDAY 9AM-5PM

Cooke InternationalELECTRONIC TEST & MEASURING INSTRUMENTSUnit Four, Fordingbridge Site, Main Road, Barnham,

Bognor Regis, West Sussex, P022 OEB

Tel: (+44) 0243 545111/2 Fax( (+44) 0243 542457

HIGH END TEST & COMMUNICATIONSEQUIPMENT PURCHASED

ARTICLES WANTED

WANTEDHigh -end Test Equipment, only brand

names as Hewlett-Packard,Tektronix, Rhode & Schwarz, Marconi

etc. Top prices paid.Please send or fax your offer to:

HTB ELEICTRONDEAlter Apeler Weg 5, 2858 Schiffdort,

West GermanyTEL: 01049 4706 7044FAX: 01049 4706 7049

WANTEDReceivers, Transmitters, Test

Equipment, Components, Cableand Electronic, Scrap. Boxes,

PCB's, Plugs and Sockets,Computers, Edge Connectors.

TOP PRICES PAID FOR ALL TYPES OFELECTRONICS EQUIPMENT

A.R. Sinclair, Electronics, Stockholders,2 Normans Lane, Rabley Heath, Welwyn,Herts AL6 9T0. Telephone: 0438 812 193.Mobile: 0860 214302. Fax: 0438 812 387

780

WANTEDTest equipment, recovers, valves,transmitters, components, cable

and electronic scrap and quantity.Prompt service and cash.

M & B RADIO86 Bishopgate Street,

Leeds LS1 4BBTel: 0532 435649Fax: 0532 426881 9956

STEWART OF READING110 WYKEHAiVI ROAD,

READING, RG6 1 PL.TEL. 0734 268041FAX: 0734 351696

TOP PRICES PAID FOR ALLTYPES OF SURPLUS TESTEQUIPMENT, COMPUTER

EQUIPMIENT,COMPONENTS, etc.

ANY QUA NITYT103

Illatmos computers

complete systems486-33 386-40

N eta local hut. 170 Mbid 411\11)1,1rd drily

2 Nth) le R 1.4 Rupp. [toad port.. 14 inch 11.28 dot 'Mull SN colourmot Mir am full ss arrant included in prkT

£749 A- £547 plus V,XQuota(' and upgrades tot our specification. Sharp sirs ire aml prices from

con- pal ss it h ears of stirs jut. to imisersities. companies and lois ate htiers.motherboards:

cards: AT multi I/O card with 1 parallel, 2 serial, 1 game, 2 fdd, 2 x IDE £14SVGA 512K £37

multimedia:

48ESX-33MHz VESA Local Bus, 256K cache41WDX-33Iv1-1. VESA Local Bus, 256K cache48EDX 66M -IL VESA Local Bus, 256K cache

38ESX-40 0 5£159£299£419

SVGA 1 Mbyte Trident or similar £48Local bus video accelerator 1 Meg (exp. 2 Meg), Hi -Colour I:79AT SCSI controller £38AT ESDI controller (caching) £49Ackiptec SCSI S bus master controller for all SCSI devices £99Local bus IDE controller £49Fax/modem 9600bps £99Novell NE2(100 compatible 16 bit card £49Mitsumi internal CDROM, Photo CD compatible, includes card i 1 49Panasonic CR562 Double Speed/Multi Session CDROM £199Soundblaster 11 compatible £59

floppy disc drives: 1.44 Mbyte 3.5 £351.2 Mbyte 525 inch £39

hard disc drives: 10 Mbyte NEC MFM 5.25 inch £1940 Mbyte Seagate IDE £87170 Mbyte Conner IDE £159250 Mbyte Conner IDE £199340 Mbyte Comier IDE £269640 Mbyte Seagate ESDI with caching controller £479

387 co -processors: Intel 387-16, 20, 25 and 33 price range £19 to 39monitors: Colour SVGA 14 inch 1024 by 768, 0.28 dot pitch £189

Colour SVGA Low Rad, 1024 by 768 NI, MultiSync £214IBM 8514 I6 inch non -interlaced £359Hitachi CAD 1280 by 1024 15 inch non -interlaced,with CAD card £179

printers: Dot Matrix -9 Pin with 1 year's on -site warranty 1:109Dot Matrix - 24 pin, 80 column, with 1 year's on -site warranty £159Canon bubblejet BJ10, near laser quality UV)

parts and peripherals: Mouse, Microsoft compatible, serial with all software £9Keyboard 142 key UK, top quality £24Internal 250 MB rape Drive £149Full range of attractive cases with psu 12.59499Hitachi Colour Video Printer with print pack £199psu Astec BM140 150W, 12v, + and -5v, fan cooled, rear switch ...04

Stock andprices continually changing -'phone for update

Matmos Ltd., Unit 11, The Enterprise Park, Lewes Road, Lindfield,West Sussex RH16 ITN

Tel: 0444-482091/483830, Fax: 484258

PURCHASE FOR CASHSURPLUS - OBSOLETE - REDUNDANT

EXCESS Stocks of electronic, electrical components/accessories,parr processed and/or finished products. Please submit preliminary

information or lists for immediate response to:K.B. COMPONENTS

21 Playle Chase, Gt. Totham, Maldon, Essex CM9 8UTTelephone: 0621 893204 Facsimile: 0621 893180

TURN YOUR SURPLUSTRANSISTORS, ICS ETC, INTO CASH

Immediate settlement.We also welcome the opportunity to quote for

complete factory clearance.Contslal:

COLES-HARDING & CO. 103 Scmth BrinkWisbech, Cambs PE14 ORJ.

ESTABLISHED OVER 15 YEARSBuyers of Surplus Inventory

Tel: 0945 584188 Fee: 0945 475216

PRODUCTION CAPACITYA BS5750 registered manufacturingcompany located in Hertfordshire.

We currently have spare capacity and ourhighly skilled team can offer high qualify

assembly, hand soldering,visual inspection.

We also have a surface mount capability.Please contact us for a competitive price.

BOX NO. A3223

ADVERTISERS PLEASE NOTEFor all your future enquiries

on advertising rates,please contact Pat Bunce on:

Tel: 081-652 8339 Fax: 081-652 8931


ARTICLES WANTED ARTICLES FOR SALE

WE WANT TO BUY !!

IN VIEW OF THE EXREMELYRAPID CHANGE TAKING PLACE

IN THE ELECTRONICSINDUSTRY, LARGE QUANTITIES

OF COMPONENTS BECOMEREDUNDANT. WE ARE CASH

PURCHASERS OF SUCHMATERIALS AND WOULD

APPRECIATE A TELEPHONECALL OR A LIST IF AVAILABLE.

WE PAY TOP PRICES ANDCOLLECT.

R.HENSON LTD.21 Lodge Lane, N.Finchley,

London N12 8JG.5 Mins, from Tally Ho Corner.

TELEPHONE081-445-2713/0749FAX 081-445-5702.

REPRINTSa ready madesales aidIf you are interested in a particulararticle or advertisement, you shouldtake advantage of our reprint service.We offer an excellent, reasonablypriced service. For further detailsand a quotation (minimum no. 250),contact:

Jan CrowtherRoom 1006Quadrant HouseThe QuadrantSutton, Surrey SM2 5AS, UKTelephone: 081-652 8229Fax: 081-652 4728

VALVES AND C.R.T.s(also Magnetrons, Klystrons, 4CX250/350)

Minimum order charge of £50 VATOne million valves in stock. Obsolete types a speciality! Fax or phonefor quote.Special prices for wholesale quantities.Orders from government departments, overseas etc. most welcome.Many other types in stock. Please enquire re any type not listed.CATHODE RAY TUBES 400 different types in stock.Please enquire if your requirements are not listed below.3JP1 £18.00 013.630011 £53.00 F-28-13OLDS £41.00 M31 182G V £41.0012CSP4 £27.00 D 14 200GM £79.50 F31.12LD C132.00 M31.184W £41.001074H £43.50 D.16.100GH97 079.50 LD708 £61.50 M31.1900R £61.501396P £43.50 0G7-5 f53.00 M7.120W £15.75 M31.191W £61.50cmEtsaw £27.00 DG7-6 £61.50 MI4.1000M £18.00 M31.325GHf29.00CRE1400 £27.00 007-32 £28.80 M17.151GVR £112.00 M38.100W £135.00D9.110GH ... ..... C61.50 DG7-36 £12.00 M23 I12GV £61.50 M40.120W ... ..... £61.50CMEI431W ...... £21.00 DH3-91 £97.50 M24.12I GH £61.50 MV6-5 (Mul) ...... £47.00D.13.6I IGH ..... £53.00 F21-12LC ... £125.00 M24.122WA £81.50 SE5FP3I £41.0040X2508 ITT. used but fully tested £27.00 M28.13LG 061.50 VLS429AG C25.004CX350A Eimac. used but fully tested .. £29.00 Discounts for 10 or more pcs

VALVES Prices on application. Please enquire re any type not listed below.A2426 EC158 M8162 Mul 2803U 6133A2521 ECC81 M5138 Y644 6L6GCC1149-1 ECC81 Spec Q Magnetrons 1835A 6SL7GTC1166 ECC82 PC900 2K25 6SN7GTCCSI ECC82 Spec 0 PCC89 3828 12BH7CT TYPES: Many ECC83 PD500 3J -160E 12E1in stock. Not all ECC-81 Spec 0 PL509 4-65A 13E1listed below. ECC88 00V03-10 4-125A Eimac 19AQ5Please ECC88 Spec 0 00V03-10 Mul 4-400A 211inquire. EF39 00V03 -20A 4C28 805CV488 EF73 Q0V03-20A EEV 4CX2508 807CV1881 EF91 O0V06-40A 4CX250BC 811ACV2355 EF92 00V06 -40A Mul 4CX350A 813CV4014 EF93 0Y3-125 4CX1000A 4635CV4024 EF95 0Y4-250 4CX5000A 5763CV6087 EL34 OVO4-7 5B -254M 6336ACV7180 EL38 RIO 5B -255M 6973CX1140 EL81 SU2150 5B -257M 8056DA42 EL81 Mul TT21 5B -258M 8122DET22 EL84 S11E12 5U4G Sockets:DET23 EL5070 TD03-10E 6AK5W B9A PCBDF91 GY50 / U19 6A56 B9A chassisE8OLE F Mt1r°r's

UBC41UCL82

6BH66BJ6

Octal chassisMany others

E88CC 1061 UY85 6BM6Et 8OF 1088/6550 VL5631 6CH658101 M8136 Mul 2759 6CJ6

Testing to special quality - Military/CV, low microphony etc available on request

BILLINGTON EXPORT LtdUnit 1E. Gillmans Industrial Estate. Billingshurst. Sussex RH14 9EZ.

Callers by appointment only.Telephone: 0403 784961 Fax: 0403 783519

Mm. UK order E50 VAT. Min. Export order £50 Carriage.

BOOKS & MANUALS

CELLULAR TELEPHONE MODIFICATION HANDBOOK

How are hackers making cellular phone calls for free? How to have two phones with the same number Techniques for decoding & changing cellular phones' NAMS

Descriptions of cellular phones's vulnerabilities'Cellular phone manufacturers ESN codes

Complete Manual only £ 50SPY Supply, 108 New Bond Street

London W1Y 9AA(US) 617-327-7272

Sold or educational ur oses onl

FREE CLASSIFIED8514 MONITOR (IBM) Service manualor Schematic needed urgently. Your costsreimbursed. R. Mueller, Germany (49)246 161 4259.

EPROM PROGRAMMER MOP model18 £65 ono, telequipment D75 scope par-tially working for spares or repair inc.manual £50. Colchester 0206 48571.

FOR SALE HP 8556A L.H. section H.P.553B 110 MHz plug-in units for 141Tanalyzer. Excellent condition O.1.R.O.£550 or exchange/noise source. Tel: 0442842457.

MULTI -TALENTED BROADCASTENGINEER (EX -BBC) with strong prac-tical bias seeks challenging new position.Morgan Jones makes things work! 0703-789805.

WANTED W.W.2 German ex -servicesgear resistance sets SOE/SAS/SSTR-sets.Parts s -phone etc OZSRO Rae Otterstad,Hosterkobvej 10, DK 3460 Birkerdd,Denmark, Tel: 011-45-4281-5205.

966 ELECTRONICS WORLD+WIRELESS WORLD November 1993

ELECTRONIC UPDATEContact Pat Bunce on

081-652 8339

Models S2200 and S2400

Gan4 and Set Programmers for24, 28 8 32 pin EPROMs, EEPROM,

FLASH, Emulators and OTPs up to 8kt

The system 2000 is an idealprogrammer for the produc-tion environment. Fast prog-ramming results in highthroughput and rigorous veri-fication leads to improvedquality control. Single keyfunctions and checks againstmisoperation facilitates itsuse by unskilled staff.

MQP ELECTRONICS LTD.Tel: 0666 825146Fax: 0666 825141


FUSED SUPER SLIMSues ors rareuriolv

DOUBLE POLEED SOCKETS

OLSON ELECTRONICS LIMITED isa leading manufacturer in the field ofmains distribution panels of everyshape and size to suit a variety ofneeds. For use in Broadcasting,Computing, Data Communications,Defence, Education, Finance,Health etc. All panels aremanufactured to BS5733. BRITISHAMERICAN, FRENCH, GERMANCEE22/IEC and many othersockets. Most countries catered for.

All panels are available ex -stock andcan be bought direct from OLSON.

Olson Electronics LimitedTel: 081 885 2884


IR Group, Europe's leadingsupplier of used

instrumentation, haspublished the latest updateof models available. With arange from power suppliesto network analysers, mostitems are available on short

delivery and come with a12 month parts and labourwarranty. For a detailed

quotation call0753 670000.


ELECTRONICSWORLD+ WIRELESS WORLD

1 re nes no

barnimo radio

1=13:Workim withswitchedcapacitor fillers

C:123:ZEGermany'simperial

rand

wireless system

LriX2F=t:31

rrs7"CFA

parasiticoscillations

SPECIAL FEATURE: :411:".:;!:=

ELECTRONIC UPDATE isElectronic World andWireless World's section foradvertisers to market theirproduct information. Fromcatalogues to newsletters,Data Update is designed topresent your productinformation in a clear andattractive manner while our"CIRCLE NUMBERS"help readers to obtain theinformation they need fast.


A regular advertising feature enablingreaders to obtain more informationon companies' products or services.

FREE VXI BROCHURE

The National InstrumentsVXI brochure describes thecompany's embedded PC andGPIB controllers, MXIbusinterface kits for multipleplatforms, and NI-VXI,LabWindows, and LabVIEWsoftware for developing andcontrolling VXI instrumen-tation systems.

NATIONAL INSTRUMENTS

Tel: 0800 289877CIRCLE NO. 146 ON REPLY CARD

eeee.

Ailmar

..... ...... .

DATAUPDATE isElectronics Weekly'ssection for advertisers tomarket their productinformation. Fromcatalogues to newslettersData Update is designed topresent your productinformation in a clear andattractive manner, whilstour colour coded enquirynumbers help readers toobtain the information theyneed fast.


2nd EDITION TOKO RFCATALOGUE

Cirkit have just published the 2ndEdition of the Toko RF Catalogue,featuring details of Tokos' extensiverange of RF coils, inductors, filtersand comms ICs.

The 128 page catalogue includesmany new products such as;Surface mount high currentinductors, surface mount multilayerinductors, helical filters at 2.5GHzand a new section of push buttonand tact switches.Cirkit Distribution Ltd, Park Lane,Broxbourne, Herts, EN107N0Tel: (0992) 441306Fax: (0992) 441306


High Speed EPROM & FLASHProgramming from your PCO Programs EPROMs to 4 Mblts/

32 -pins Superfast 8, 16 & 32 -bit

programming Approved algorithmsO Menu driven software includedO Sophisticated editor functionsO Easy file managementCI FREE demo disk available

Stag Programmers LimitedMartinfield Welwyn Garden City,Herfordshire, AL7 1 JT UKTel: (0707) 3321 48Fax: (0707) 371 503


SPECTRUM ANALYSERS

TEKTRONIX 492P PORTABLE 21 GHz

50 kHz-21GHz (ext. mixing to 220G Hz). GPIB.

60dB dynamic range. Lowest ever price. £5000

HP85688100Hz-1503MHz.

High performance. £9500

HP8569B 10MHz-22GHz (ext. to 115 G Hz).

Internal pre -selector. £6000

RALFE ELECTRONICS36 EASTCOTE LANE. S HARROW MIDDLESEX HA2 8DB

TEL: 081-422 3593. FAX: 081-423 4009

NOWIN

40thYEAR

TEKTRONIX 496P as above with tracking generator TR503 8 frequency counterinstalled in GPIB-main frame TM5006 £6000

MARCONI INSTRUMENTS

2019 SYNTHESIZED SIGNAL GENERATORS

80kHz-1040 MHz. AM/FM. £1950

DISTRIBUZIONEE ASSISTENZA, ITALY: TCL RADIO, ROMA, (06)890763

TEST EQUIPMENTBRUEL & KJAER 3534 sound & vibration field measuring set

;4"Nti&I<J2E1RS2L5k11/14,;intlio612-1,1:::=123°12BRUEL & KJAER 2610 measuring amplifierBRUEL & KJAER 2307 level recorderBRUEL & KJAER 2317 portable level recorderBRUEL & KJAER 1618 band bass filterBRUEL & KJAER 3204 tapping machine

£3500£2250£1000£1000£1650

£750£1000

* MUCH MORE. ASK FOR FU LL B&K STOCK LIS *AVO RM215L-2 insulation & breakdown testerDATRON 1065 digital multimeterDRANETZ 626 mains disturbance analyser/2 x PA -6001DRANETZ 606-3 line disturbance analyserFLANN MICROWAVE 27072 frequency meter 73-113GHzFLUKE 8050A 41/2 -digit bench DMMKEITHLEY 192 programmable dmmMAURY MICROWAVE 8650E TNC-calibration kitNAGRA IV - SJ tape recorderPHILIPS PM5193 synthesized function generatorPHILIPS PM2534 digital multimeterRACAL 9008 automatic modulation meter £325.9009RACAL 9081 synthesized AM/FM sig' gen' 5-520mHzRACAL 9300 RMS voltmeter -8048 to 50dBRACAL 9341 LCR databridge component testerRACAL -DANA 930'2 RF mill -voltmeter 1.5GHz

C650£750

£1250£275£275E200£400

£1500£2000£1500

£450£300£650£325£350£450

MANY MORE FULLY RE -FURBISHED, FULLY GUARANTEED TESTINSTRUMENTS AVAILABLE FROM STOCK. PLEASE ASK FOR OUR

CURRENT LISTING. WE CAN FAX LISTS & SHIP GOODSWORLDWIDE. HIGH -END EQUIPMENT ALWAYS WANTED FOR

STOCK. "CALL US NOW"6460/6420 power meter 10MHz-12.4GHz 0.3uW-10mW6460/6423 power meter 10MHz-12.4GHz 0.3mW-3W6600A sweep generator 26.5-40GHz67008 sweep ossillator 8-12.4GHz 12.4-18GHz6960/6910 digital RF power meter 10MHz-20GHz GPIB6912 power sensor 30kHz-4.2GHz for above series8938 audio power meterOA2805A PCM regenerator test setTF2015/2171 signal generator AM/FM 10-520MHzTF2304 automatic modulation meterTF2370 110MHz spectrum analyserTF2910/4 non-linear distortion (video) analyserTF2914A TV insertion signal analyserTF2910 TV interval timer

£350

£400£1000

£1000£1000

£150

£350£750£400£350

£1750£1000£1250£500

WILTRON 6647A SWEEP GENERATORS

TO 18GHz. £4000

WILT RON 560A SCALAR NETWORK ANALYSERS

complete with detectors. £750

HEWLETT PACK AR D

331A distortion meter339A distortion meter (option 01)3406A sampling voltmeter355C attenuator DC-16Hz 0-11db 8 355D 0-120db

3325A synthesizer/function generator33256 synthesizer/function generator3335A synthesizer/level generator with option 013552A transmission test set £12503575A gain/phase meter 1Hz-13MHz dbV ratio & o opt 01 £12503711N3712A microwave link analyser (MLA) with 379388 37308/37366 RFdown -converter (1.7-4.2GHz) £40003781A pattern generator £12503782A error detector E1250

HP8673M SYNTHESIZED SIGNAL GENERATORS

2-18GHz frequency range. AM/FM/Pulse mod.

# Calibrated o/p from -120 to + 8dbm. £7500.

HP8901A MODULATION ANALYSERS 150kHz-1300MHz

Measures AM/FM to 1% accuracy. Also measures

RF frequency & power. Automatic. £3000

HP8559A 10MHz-21GHz SPECTRUM ANALYSERS

Installed in 182T main-frame. £4000

HP5344S MICROWAVE SOURCE SYNCHRONIZER -

phase locks p wave signal to give synthesizer asccuracy.

Includes 5342A/01 18GHz counter.

£1500

8601A 1 I OMHz sweep generator

86200 sweep generator, many plug-in units available867IA synthesized signal generator 2-6.2GHz

£200£1500

£250£125

£1500£2700£1500

E500

Ecall

12500

PLEASE NOTE: AMOUR EQUIPMENT IS NOW OPERATION -VERIFICATIONTESTED BEFORE DESPATCH BY INDEPENDEIVT LABORATORY

We would be pleased to handle all grades of calibration or NAMAS certificationby same laboratory at cost price. All items covered by our 90 -day parts and labourguarantee and 7 -day 'Right to Refuse' (money back) warranty.

ALL PRICES SUBJECT TO ADDMONAL VAT AND CARRIAGE


INDEX TO ADVERTISERS

Alternative Distribution (UK) LtdAntex ElectronicsBull Electrical

Citadel Products LtdDataman Programmers Ltd

919943

887

IFCOBC

Display Electronics Ltd 882

Electrovalue Ltd 950Ellmax Electronics Ltd 935Ericsson 889

Halcyon Electronics Ltd 968

IPK Broadcast Systems Ltd 950

Johns Radio 882JPG Electronics 889Keytronics 916

Labcentre 901Langrex Supplies Ltd 949

M&B Electrical Supplies Ltd 926M&B Radio (Leeds) 935MQP Electronics 943

Number One Systems Ltd 949

Pico Technology Ltd 955Powerware 943Ralfe Electronics 968Research Communications 964SAJE Electronics IBCSeetrax Ltd 955Smart Communications 889, 919SMC Ltd 955Stewart of Reading 949Surrey Electronics Ltd 935

Telnet 919Tsien Ltd 950

Only

E1 95.+VATcarriage extra

Output frequencies -10MHz, 5MHz, 1MHzShort term stability - betterthan 1010-0 (1 sectTypical - ±4x10-9(1 sec)Long term-tends toat o-1, (1000 sec)

NEW THE DEFINITIVE `OFF -AIR'FREQUENCY STANDARD

.......---------'--_------7CYONHALCYON rLE,-,Tpc ,r.s lin

r( 16\ 1 - 't.j

i II__ _ _ _ __- - ._ ___

* Provides 10MHz, 5MHz 8 1MHz* Use it for calibrating equipment that relies on quartz crystals, TCX0s,

VXCO5. oven crystals* Phase locks to DROITWICH (rubidium controlled and traceable to NPL)* For ADDED VALUE also phase locks to ALLOUIS (cesium controlled

and traceable to OP- French eq to NPL)* British designed and Britishi manufactured* Now with Sine Wave Option, output 1 volt into 500

TELEOUIPMENT D1011 10MHZ DUAL TRACE £165 BACHARACH MV2 MERCURY SNIFFERS £79IWATSU SS -5802 DIGITAL STORAGE POA FISONS FI-MONITORS LIO LEVEL SENSORS £85SCOPE% 4S6 6MHZ SINGLE TRACE £95 JANKE 8 KUNKEL HI SPEED MIXERS 2OKRPM C29TEKTRONIX 2215 60MHZ 2 TRACE DEL T/B 0450 JAQUET TIMER 1110SECS. RES'N .01SEC £59TEKTRONIX 453A 50MHZ 2 TRACE DEL T/B £249 COMMODORE PETS, D/DRIVES, PRINTERS £29eaTELEQUIPMENT S62 SINGLE TRACE 5MHZ SCOPE £95 COMARC 2303 MV SOURCES, DUAL RANGE C49H.P. 84058 VECTOR V/METER 161-IZ £595 INTRON IFG422 FUNC GEN 0 1HZ-2MHZ £125PLESSEY TCT10 SIG GEN/ANAL 50-300 BDS £95 ECG MONITOR SEM430 WITH SEM420/2 £75TELEOUIPMENT D61A 10M HZ DUAL TRACE from f99 CARDIAC RECORDERS LTD MINIGRAPH TYPE 123 POASE LABS SM111 18MHZ DUAL TF ACE £129 GF PALMER CARDETTE 4 ELECTROCARDIOGRAPH POATEK 46513 100MHZ DUAL TRACE DEL T/B £475 GOULD 24004 -PEN CHART RECORDER £195TELEQUIPMENT D67A 25MHZ, 2T, DEL VS £215 X -Y PLOTTERS A3 & A4 from f35 to £139H.P. 1700A 35MHZ DUAL TRACE £249 PHILIPS PM6456 FM STEREO GENERATOR f195HITACHI VC 6015 10MHZ DIGITA_ STORAGE £345 7SEG 17 & 9" DISPLAYS DIGITEYJSIGNALE X £15 & CIOH.P. 1340 X -Y DISPLAYS £149 VALVE TESTERS AVO MK1, 2, 3 from £49 to £89OERTLING V20 SINGLE PAN BALANCES 200GM £69 MARCONI TF2300 FM/AM MODULATION METER £195ANALYTICAL BALANCES WITH WEIGHTS 250GM £59 CASELLA TEMP RECORDER 7 DAY C89VACUUM PUMPS 1.5 & 2.8cu. M/HR £125 & C149 McKENZIE 7 DAY TEMP/HUMIDITY RECORDER £95KINGSHILL NS1540 15V 40A PSL's CASED, AS NEW £195 FEEDBACK SS0603 1MHZ SINE/SO OSC £125ACRON 402P SYNCHRONISING 'ULSE GEN & 605P FARNELL E3500 -350v 100mA, 2 0 6.3V £49 to £69ENCODER C375ea £695/pr FARNELL FG1 FUNC GEN .2-2.2MHZ £129RADIOMETER BKF6 DIST. METER 20HZ-20KHZ POA COMMUNICATIONS RECEIVERS, HF, L F, VHF POARADIOMETER AFM2 MOD METER 7MHZ-1GHZ POA LCR MARCONI TF1313 025% £95MARCONI TF2304 AM/FM MOD NETER PRTBLE £249 LCR COMPONENT COMPARATOR AVO CZ457/S £95MARCONI TF2330 WAVE ANALY.3ER 20HZ.50KHZ £149 LEVELL TM6B MICRO V -METER 450M HZ C95H.P. 5315A 1GHZ F/CTR, OPTS t, 2 8 3 C750 LEVELL TM3I3 MICRO V -METER 3MHZ £85

UST AVAILABLE BUT 1000's OF UNLISTED BARGAINS FOR CALLERS. ALL PRICES EXC. OF POP AND VAT

QUALITY ELECTRONIC EQUIPMENT ALWAYS WANTED

HALCYON ELECTRONICS423, KINGSTON ROAD, WIMBLEDON CHASE, LONDON SW20 8JRSHOP HOURS 9-5.30 MON-SAT. TEL 081-542 6383. FAX 081-542 0340

968



INSTRUMENTS TO BUYFROM SAJE ELECTRONICS TEL: (0223) 425440 FAX: (0223) 424711

700 - 14111b-20OPIPOT.to

MULTIMETERS - Tie 180 series of multimeters prand are supplied complete with pr

r holsters. 183: 3.5 digit LCD, ACV,ACA, DCA, resistarce, continuity buzzer, diode test,basic accuracy 0.5%. 185: As 183 plus bar graph, tern40°C to 1370°C), capacitance (lpF to 40uF), frequto 200kHz), max/rain, edit, %, compare, basic,0.3%. 187: As 185 plus Auto ranging. 285: As 18

EPROM PROGRAMMER EMULATOR - The SP1000 is aeprom program

PC remote link.

toms up to 1M Bit (expandable to 4M Bit) cardgrammed,

empty checked, listed, edited, verifie

COUNTERS SC series are high performafrequency counters with advanced feat

to 400MHz, hand held, battery powered, 8D, sensitivity topically 10mV, hold, min, max, aye,iable gate and filter. SC130: as SC40 but 5Hz to 1.230: Bench ve-sion of SC130, backlit LCD, RS23

RF GENERATORS -

OSCILLOSCOPES -

160B, 100kHz to 150MHz (45modulation. SG4162AD: As SG4

y counter.

fessional range of high qual20MHz dual trace, full feat

bes). CS5110: 100MHz dual trace, cursor reado

bes). C01305: 5MHz single trace.

FUNCTION GENERATORS - X2020: 0.02MHz to 2MHz squency readout, output wa

ms include sire, square, triangle, skewed sine, pulse ant

L, lin & log sweep, DC offset and symmetry. FG2020B0.5Hz to 500kHz function generator providing sine, square

ms.

POWER SUPPLIES -

MULTI INSTRUMENT

e PS series of low cost benchdual output with output prot

er supply, 0-30V 3A. PS3

combines four instrumentsTriple output )ower supply with LCD offering 0-V 1A, 5V 2A, with full overcurrent protection. 2. A

1Hz-100Mfr2 frequency counter with gating rateHz, 1Hz, 10He, 100Hz providing resolution to 0.1Hzenuation inpits and data hold. 3. A 0.02Hz to 2MHtured sweerfunction generator producing sine, squat,ngle, skewed sine, pulse and a TTL output and lin or lot.

eep. Outputs of 500 and 6000 impedance are standaadtures. 4. Aub/manual 3.5 digit LCD multimeter readirgV, DCA, ACV, ACA, resistance and rel

measurement wth data hold functions.

LCR METER - e MIC4070D LCD digital LCRcapacitance, inductance, resist-

ce and dissipation measurement. Capacitanceranges are fron 0.1pf to 20,000uf plus dissipa-

IIIn. Inductance ranges from 0.1µH to 200H plusdigital readout of dissipation. Resistance

nges from 110 to 20M0. Housed in ruggedABS case wits integral stand complete withbattery and probes.

CLAMP METER - he clamp meter provides digitalfollowing ranges, ACA to 600A,

ACV to 750V, DCV to 1000V. Resistance to 2110.Peak detector holds the max rms value. Audiocontinuity for short circuits.


MX2020 - £233.83, F62020B - £159.11

CREDIT CARD ORDERS BY PHONE/FAXTo order any of the above items please send this form with yourdieque/credi card details to: B&W Electronics, 117 Lovell Road,Cambridge, C84 2QW. Please send me the following instruments:-

I enclose a cheque to the value of £

redit call soIle sum of f. (NB: All prices quoted above include VATI.

OR please debit my

expiry date

*lame:

Iddress

Please Allow 28 Days Delivery

Telephone:

The smallest, most powerfulpersonal programmer youcan buy!Owning the worlds bestselling portableprogrammer/emulator is just aphone call away.From enginemanagement toAntarctic surveyteams, the powerfuland versatile S4 goeswhere others get leftbehind.

A 32 pin ZIF socket programs a huge library of

EPROMs, EEPROMs and FLASH devices up to

8Mbit. And our unique user loadable Library

means that new parts can be added quickly, and

at no cost. All software upgrades are free and

available for 24hr download from our high speedbulletin boards.

See your code running before committing yourself to

an EPROM. With S4's powerful and easy -to -use

internal emulation system, download your code to

S4, press EMULATE, and your target system runs

in real time as if an EPROM was plugged in to the

socket. Use S4's 'EDIT command to make minor

alterations to your code and see the changes

happen immediately- just one reason why S4 is

used by the world's car manufacturers to develop

advanced engine management systems in real time!

With S4 emulation there's no need for trailing cables

or external power sources; earth loop problems are a

thing of the past. S4 even emulates RAM.

As well as being totally stand alone and self

contained, S4 can be operated remotely via it's serial

port at speeds up to 115,200 Baud. We supply you

with a FREE disk containing custom terminal

software and a pop-up TSR communications utility.

If you are looking for a supplier with longevity and

stability, then you'll be pleased to learn that

Dataman has been

designing and selling

innovative programmers

world-wide for over 15 years.

As well as having sales and

support offices in both the UK and

the USA, we supply the world

demand for our products via a network

of approved dealers stretching from

Norway to Australia.

S4 comes fully charged and configured for

immediate use. You get a mains charger,

emulation lead, write lead, personal organiser

instruction manual, MS-DOS communications

software, spare Library ROM and a 3 year

guarantee. Optional modules available for serial

EPROMs, 40 pin EPROMs and microcontrollers.

S4 is always in stock. Phone through your credit card

details to ensure next working daydelivery. Full 30

day no -risk refund.

Size:

186 x III 46mntWeight: 515g

Dataman Programmers Ltd

Credit card hotline:0300 320719for same -day dispatch

Station Road, Maiden Newton, Dorset DT2 OAE, UK. Telephone: 0300 320719; Fax: 0300 321012; Telex: 418442; BBS: 0300 321095 24hr; Modem: N 32bis/16.8K HST22 Lake Beauty Drive, Suite 101, Orlando, FL 32806, U.S.A. Telephone: (407) 649-3335; Fax: (407) 649-3310; BBS: (407) 649-3159 24hr; Modem V32bis/16.8K HST


electronics world · frame giving +5v 35a, -5v 1.5a, +12v 4a (8a peak), -12v 1.5a, massive...

Documents