1

CambridgeshireRepeater Group

Newsletter Number 41Autumn 2000

The One-Transistor Challenge 6GB3CI And GB3CO Without Tears 8Answers To Puzzle 40 12Home Construction Tips 13Let There Be Light pt III 14The Keyfob Issue 15Sound-In-Sync 28Mono-Alphabetic Code 31

2

2000 Committee Members

CHAIRMANGerald Gardner G0HEM 01799 500543New House, Birdbush Avenue gerald@gardner.enta.netSaffron WaldenEssex CB I I 4DJ

SECRETARYDavid Leech G7DIU 01480 4313334 Rydal Close david.leech@lineone.netHuntingdonCambs PEI8 6IJF

TREASURERRoger Carder G7SRK 01223 89166845 Chalklands rcarder@virgin.netLintonCambs CBl 6HQ

REPEATER KEEPERTony Collett G4NBS 01954 21152110 Quince Road 0468 0224992HardwickCambs CB3 7XJ

TECHNICAL COORDINATOREddy Boyd G8CRN 01223 89478820 Dolphin Close 07909 535029Linton eddy.boyd@ntl.comCambs CB1 6XA

RALLY ORGANISERPaul Dyke G0LUC 01462 68357476 Gaunts Way 07050 1261692Letchworth g0luc@btinternet.comHerts SG6 4PN

NEWSLETTER EDITORTerry Bickell G0UIO 01223 572226161 High Street g0uio@ukonline.co.ukChestertonCambridge CB4 INL

COMMITTEE MEMBERIan Waters G3KKD 01223 81147739 Stow Road ian.waters@freenet.co.ukStow-cum-QuyCambridge CBS 9AD

3

Editorial

First let me thank all those who told me how much they enjoyed the lastedition of the newsletter. It does take a long time to produce, and I’mglad the effort is appreciated. Not to mention those few people who makethe newsletter what it is by sending in articles for publication.

Once again this issue has more content than has been the case, and I hopeI’ll be able to continue this trend. We should be proud of the group, andgive it all the good publicity we can. This is despite the fact that therepeater(s) featured in the main article are not run by the CRG!

Don’t forget the AGM is coming up on the 17th November, at Stow-cum-Quy Village Hall. Members should try and come along if they can, tomake their views known. It’s really no good complaining on air if youdisagree with something that has changed – make an effort and get to themeeting. I’ve been in the group for ten years, in all that time there’s neverbeen a quorum! Also, just a reminder that if you can’t make it to theAGM, membership subs can be paid direct to the treasurer G7SRK at theaddress shown opposite. Please make cheques out to ‘CambridgeshireRepeater Group’.

I hope you like this issue as much as the last one. As usual I have to keepnagging the same people for articles, so please surprise me by sendingone in. Letters and Items for sale are also welcomed.

I look forward to seeing as many of you as possible at the AGM.

73 de Terry Bickell G0UIO

4

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5

Notice Of Annual General Meeting 2000

Notice is hereby given of the Annual General Meeting of theCambridgeshire Repeater Group.

Date Friday, 17 November 2000Time 7:30pm for 8:00pm startPlace Stow-cum-Quy Village Hall

Agenda

1. Chairman’s Introduction

2. Minutes of 1999 AGM

3. Matters arising

4. Secretary’s Report

5. Treasurers Report

6. Technical Report

7. Competition Prize(s)

8. Nomination and Election of Committee

9. A.O.B.

10. Adjourn To The White Swan

[Please Note: The committee should receive items for inclusion onthe agenda no later than 14 days before the date of the meeting.]

6

The One Transistor Challenge.John Smith G4KJJ

This little rig can literally be built in a few minutes. The ‘challenge’is to complete the rig, put it on the air and have the first contactwithin 15 minutes! If you prefer a more pedestrian approach andhave never constructed a transmitter before then enjoy justbuilding your first H.F. transmitter. I have worked stations aroundthe UK and into PA/F/ON so don’t be too critical about thepower output before you try it Choose your operating timecarefully, late afternoon just as the Band is picking up and ‘early-home’ ops are relaxing before their evening meal J. The Bandis noisy at the moment of writing and the indicated frequency isnot ideal because of the DKO Beacon, but alternative cheapcrystals can of course be used.

BFY51

Xtal

RFC1R1

C1

C2 Key

C3

C4

L 2

C5

AN

1

-

Circuit Dia g ram

7

C2

C1

R1

(X)

RF

C1

Xtal C3

L2

C4

C5

b

c

e

Key Ant -ve

9-12V +ve

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19

(X)Solder totrack

Link wire Cut track

Proposed future projects include simple: 80m Rx, SWR Bridge, R.F. ant.switch, ATU. The component count in all cases should not exceed 12 andlow cost. The satisfaction level is of course extremely high!

73 de John G4KJJ

Parts List

C1

10nF ceramic RFC1220mH

C2

10nF ceramic L2

T-50-2 ToroidC

3100nF ceramic 21T 24SWG

C4

1000pF polystyreneR1

22kC

51000pF polystyrene Xtal 3.57954MHz

3.5mm jack socket 2 phono sockets10x20 matrix board BFY51

Key down current » 115mA @ 12V

8

CRG Members 2000

G0: ANV, DKE, EVZ, GKP, HEM, KRB, LUC, NDY, NQN, OKL,OQD, OQE, PYS, SFQ, TLQ, UBX, UEU, UIO, UPY, WVE

G1: DRM, JZN, LTL, MHU, RVF, UAF, WSF, XAA, XAM, YFE,YFF, ZPU

G3: EDD, FCM, GGK, KKD, KZE, LAZ, MUI, NUL, PTQ, PWK,XDA

G4: AKD, BAO, BIK, ETG, FDF, HXH, JRC, KJJ, NBS, WIA, YFV,YHN, ZZM

G6: DFR, DGT, FKS, FNB, GZH, HBQ, HKQ, KJR, RNN, TQM,XRX, YMU

G7: ASH, DIU, JJP, JSB, JUC, SRK, RVS, VCE

G8: CRN, DJK, IDL, INI, JHE, JSL, KMM, UGR, VJF, XLH

M0: ASH, BWH

M1: ADV, AQP, CKO, DDZ, DFR, DJY, DTX, DZF, EEO, EOI, GRT

M5: AAX, AGX

2E1: CRK, HLF, HLH, HVP

2E0: ASU, AUY

KC2BWZ AND 3 SWL. 111 Members.

9

GB3CI AND GB3CO WITHOUT TEARS 1

Phil Richardson G8MLA

1. Introduction2. The aims and objectives of the project3. A brief description of operation4. Specifications5. Things to look for6. Future developments

Introduction

This document is a guide to the make up of GB3CI and GB3CO, theideas behind them, what the repeaters can do, and the ins and outs of theiroperation.There are also some ideas for the future enhancement, improvement ofperformance and operational ease.

The Aims And Objectives Of The Project

There are a number of aims for this project and I will list them, notnecessarily in order of importance

· To provide a 70cm repeater with a performance that is as near aspossible to, if not better than the coverage of the old repeater fromthe old site.

· To have on the same site a 23cms repeater which will be linked togetherwith the 70cms unit. The thinking behind this is to give added interestto the 23cms band, To explore and enhance the understanding of thebehaviour and propagation of 23cms signals for every day use (thereis precious little understanding of this in the professional field let alonethe amateur world!)

10

· Doing it like this will allow stations to use possibly simple equipmentlike receive converters, scanners and TX frequency triplers and makechanges to aerial arrays and easily monitor any performance changes.Also a very small amount, even only one 23cms user can get good useout of talking cross band to 70cms.

Operation On GB3CI And GB3CO

The two repeaters can be visualised as separate units that have been joinedat their inputs, so they can both see each others input and interpret thesignals in their own separate ways.

So a signal accessing from 70cms will be relayed on both 70 and 23 cmsand the same can be said for a signal incoming from 23cms.

70cm Input

70cms

23cms

11

With an input on both bands the audio signals are mixed, so bothtransmissions are heard on both repeaters together (could be called fullduplex)

23cms Input

70cms

23cms

Input onboth bands

12

Specifications

70cmsTX power is 9.3w output from filters and duplexer to base of feeder, withabout 3.5db loss in feeder and 6dbi aerial gain. Giving about 10w ERP.

Rx gives 12db sinad is at approx. 0.17mV at input to duplexer and filters,and squelch opens at about 0.15mV

23cmsTX power is 3w output from filters and duplexer to base of feeder, withabout 6db loss in feeder and 9dbi aerial gain. Giving about 3.5w ERP.

Rx gives 12db sinad at approx. 0.24mV at input to duplexer and filters,and squelch opens at about 0.24mV.

Things To Look For

Always be ready to be surprised and disappointed, 23cms is closer to lineof sight propagation than 70cms, but seems to be more efficient when itis. 23 cms also reflects better. Results can be astounding both good andbad.You will find out that near line of site paths to the repeater site happen inmany places near and far (I can get signals into Corby using my 1W 23cmmobile from the Chatters Bypass)

On 23 cms especially close attention must be paid to things like coaxquality, connector type and quality and aerial location. All these have abig affect.

Future Developments

A list of jobs is being compiled for future site visits. This includes

13

· Setting the talk through audio level on GB3CI it is a little low· Maybe resetting the 70cm receive squelch level· A 23cms-power amplifier that will give about 20W output instead of

3W.· An indication of which band input signals are coming from· A way of separating the two repeaters when needed, a more

sophisticated linking logic giving DTMF control for users· Adjusting the aerials on site to help signals in the Kettering area· Maybe changing feeder to give less feeder loss (this would maybe

double the erp figures and half receiver losses) a well worth whileexercise.

Some of these things may take time and good scrounging power but areon the wish list of things to do.

Corby Amateur Repeater Group TrusteesG8MLA

1[ Please note that the ‘Key Fob’ issue is dealt with an a separate article, elsewhere in

this issue. ED]

Answers to 20th Century Dates Puzzle

1) 1968 2) 1957 3) 1937 4) 1903 5) 19006) 1972 7) 1989 8) 1996 9) 1962 10) 190911) 1940 12) 1925 13) 1914 14) 1983 15) 195216) 1977 17) 1999 18) 1949 19) 1929 20) 193321) 1901 22) 1923

Many thanks if you could be bothered to enter, just so I know I’m notwasting my time putting a quiz in. Or am I?

14

Home Construction TipsSid Robinson G6FKS

To make home-brew constructions look professional, sparay the panelswith AUTO SPRAY. Apply the lettering with DECADRY press-on letters(obtainable from Heffers of King Street – they are still there). This ismuch cheaper than Letraset and more manageable in quantity.

Protect the lettering with your wife’s hair spray (or your boyfriends), butmake sure the panel is well and truly dry as some paint is water-based andthe hair spray can lift it.

New resistors and capacitors have long leads which have to be trimmed.Retain these short pieces of wire, as it’s surprising how often short bits ofwire are required for links and breadboarding, etc.

When winding small multilayer coils using for example a hand brace, puta spot of polystyrene cement (Airfix kit cement) on the former first. Whenwinding the coil the cement oozes between the layers setting fast after anhour, thus making a solid winding. Always put more turns on than youthink you require as it’s easier to take turns off than to add them.

To check the resonance of a coil, use the set-up shown:

Coi l Under Test

Signal Generator

Osci l loscope

2.2pF

10-1 Probe

15

Adjust the signal generator until an increase in trace is observed; this isvery noticeable. Adjust the turns on the coil until the required resonanceis obtained. It is suggested that the core, if used, should be half-way induring this operation.

The 2.2pF capacitor plus the probe (10pF?) take the place of the externalcapacity in the circuit used. I have used the method up to 40MHz withcomplete success over the years.

Let There Be Light IIIJohn Bonner G0GKP

In the HF transmitter hall the C.O. said one day; “what we need is adummy load.” Good idea,” we all agreed. “I’ll get started right away,” hesaid and went to the workshop. Some days later he showed off his newproject and jolly fine it looked. He had used our stock of Robertson lamps(which are about a foot long with brass endcaps and some 3 inchesdiameter) and are designed for RF use as they are non-inductive andbetween 400 and 600 ohms impedance with a rating of 200 W or moreand were used as terminating loads on rhombic aerials. They had beenarranged in a framework with some links to select either co-ax or openwire input, load impedance of 50 or 500 ohms, and correct power ratingsfor the various types of transmitters, up to 5kW.The assembly was movable on its wheels and even had a mesh cover tokeep fingers away from the hot bits.It was connected to a spare transmitter, its links set and low power appliedand we had light. As maximum power was reached there was more lightthan expected because the mesh, being some kind of plastic, and theframework which was wooden, had both caught fire!

16

THE KEYFOB ISSUEPhil Richardson G8MLA

In my capacity as repeater keeper of the Corby UHF repeater I am writingto you about GB3CI, a repeater very close to my heart. It was licensedsometime in the 76/77 era as was I. The original repeater (which is still inmy loft) was built by the Corby Repeater Group involving Mike FosterG8AMG and others, with lessons that must have been very well learnedfrom the GB3LO experience as he was very closely involved with thatmachine (designed and built the first 2m repeater for London). This, themark one repeater had at least ten or more years very good service. Thedesign and logic operation formed a template, which I could not reallyimprove upon, but only hope to emulate with the odd little improvement.The main rules of CI’s format was

· Simple to use no frills (perceivable by the user) and snappy logic.· Good quality through audio· No holds barred striving for absolutely every last nanovolt of rf

performance

The rf spec of the latest version of this machine is I believe worth noting,the thinking behind it being that every dB or two gained at the repeater isa gain for all of its users, the cumulative gain then is enormous.This particular mk3 repeater has been in service since about 1988ish andis off site for refurbishment.The general spec for the anoraks amongst us (that includes me) is asfollows

· TX erp 25w which is about 9w into to the base of the feeder to set offour stacked dipoles

· The receiver sensitivity measured through the cavities not straightinto the receiver is about 0.12mV for 12db sinad fed from a set ofstacked dipoles mounted above the TX aerials

17

This set up allowed the repeater to be reciprocal to most portables letalone mobiles and the performance, which will be the target for the machineon the new site.

That is the story up until about august last year (1998). Sometime aboutthen we had a call from the site people to say that they thought theremight be a problem with the repeater as some people could not open theircars with their remote key fob when the repeater was on air. This I believetook them some considerable time to realise but it was discovered tocoincide with repeater activity by one of the staff who was an amateur.

The car park at the problem area is located directly below the repeaterabout five floors down. Tests were carried out with the help of some ofthe people suffering with this problem and then some trial changes weremade to the repeater TX configuration as follows:

· Adjustment to power down in steps which ended up at 1w yes 1w erpabout 300mW into the feeder.

· Fitting a temporary aerial at the same height as the flat roof of thebuilding the repeater was on

· Test transmissions from a TX into these same aerial but on 438MHzalso on power levels down to about 1w

The effects of these trials were to show that there was no or very littleimprovement in the situation.

Whilst this was happening I was also carrying out tests on some vehiclesthat I could use to attempt to find out the bandwidth of the in car receivers.The results of these tests are in the following charts. The method used inthese tests was to use a low power hand held 100mW at a range of 25metres from the car and to key the TX in one megahertz steps whilstobserving the effects on the operation of the remote key fob. The resultantcharts give an indication of range that the key fob would work from inmetres whilst the handheld was keyed.

18

Two year old Vectra

Two year old Mondeo

Brand new Mondeo

key fob range

0

2

4

6

8

10

12

432 433 434 435 436 437 438 439

Tx Freq

Ran

ge

m key fob range

key fob range

0

2

4

6

8

10

12

432 433 434 435 436 437 438 439

Tx Freq

Ran

ge

m key fob range

key fob range

-5

0

5

10

15

20

432 433 434 435 436 437 438 439

Tx Freq

Ran

ge

m key fob range

19

As you can see the results are bad. The new car has an improved responsebut is still is wide enough for any repeater to be well within its bandwidth.There must be tens of thousands of these remote key fobs around and willbe for some time. With this and the bad press that the repeater could getif somebody was kept out of their car late at night in Corby the repeaterwas turned off.

This raises all sorts of questions, some of which have answers:

· Was this known of before? Answer yes the RAKE committee wasformed

· Is this problem happening else ware? Answer yes all over.· Is this realised? Not fully either by amateurs or the RSGB or radio

agency!· Will the problem go away? Definitely not!· Will the problem get worse? Yes lots especially as more people discover

what is happening· Are the repeaters to blame? No they have to conform to a tightly

controlled specification!· Are the repeaters perceived to be at fault? Yes I am afraid so!· What about other users of this piece of spectrum? —

The hoped answer for CI is to move site to where there is no car park inthe vicinity and if there are still problems, apply for a European style7.6MHz split allocation

The good news is that gb3ci now has a new site with no car parks thatclose, and much higher aerials to improve isolation to the ground, there isa challenge to be met in the installation of this new machine as the repeaterwill have to be weather proof, but that is a small price to pay for thechance of going back on the air and from a higher site. The intention is tokeep to the same channel RB2 and to closely monitor for any problems .

20

The Closedown

The repeater continued in this fashion until mid 1998 when reports fromthe college led me to look into the fact that when GB3CI was on keythere was a number of cars in the car park that had alarm, central lockingand immobiliser problems. With some horror I investigated with help andassistance of a local Ford dealer and other volunteer car owners, theresponse of the remote radio key fobs in modern cars.The results of these tests and the method in the charts on page 18.

Many things were tried, trialing another TX in case of sprogs on the oldone, temporary screening the aerial, low power (one watt RF) and testtransmissions on 438Mhz as described earlier.But to no avail and with the fault not being with the repeater I pulled theswitch (the bad press that would result in somebody being locked out ofhis or her car at night in Corby does not bear thinking about)

You will have to imagine the correspondence that then was carried outwith other interested parties, RSGB, the RA, and the RAC, the EMCpeople

It was allowed to happen and I was not happy, but this is now old news. Idid have good support from the Radio Agency and was offered the chanceto apply for a 7.6 MHz shift Repeater.

With more testing it was seen that there would still be some problems andwith the repeater off air a search for a new site was started.

The new site

Now good sites are very hard to find so the search was on it now beinglate 1998. A fair bit of driving round with radios and aerials, looking atmaps and drinking beer Lots of help was given, I will name all I can. PaulG4AJE, Chris G4DCD, Paul G1DIW, Dave G4NAC; in fact it felt likemost of north Northants was involved in some way or other J

21

Paul G1DIW was able to come up trumps with Corby power station. Thisincluded written permission to use the site and the works - WOW

The New SpecThe build was on.Technical andm e c h a n i c a lchallenges were notsmall.- to give someidea of these:

The repeater wouldbe about 35 m upwith no shelter(power wasavailable, there beingseveral hundredmegawatts lyingabout)

A complete rebuild for tworepeaters , two sets of filters andcombining, also a new logic basedon a pic processor for the linked23cms bitThe aerials to be mounted on a highchimney, lets just say 70 metres ofcable for each run was used.The repeater has 23cms input andoutput as GB3CO (this is totallyunique!)A complete new application had tobe processed for a move of morethan two kilometres

22

The BuildThe build took some time but I was just about able to keep pace with theapplication. Absolutely loads of stuff was donated right from things likewaterproof boxes, coax cable, the aerial rigging even down to coverageprediction plots. I cannot mention names!The original sense of purpose, no compromise on RF performance andaudio quality as first laid down many years ago was followed

The New Installation

On April the first 2000 a team assembled at the power station and theinstallation proceeded. I think the pictures say most.

Team members for the site installation were as follows.

Paul G1DIWChris G4DCDPhil G8MLAJake G1YFFDave G4NACMalcolm G7HPE

This is the smalltin shed at thebottom of thechimney!!!

23

The Long Lift

I cannot hope to give a full idea of the scaleAll my precious bits being flown!

24

A Delicate Moment

25

Now If I Just Push This!!

Please observe roof and cars below.Again get the scale!

26

More Delicate Fixing

Just A Little Tweak And We Are On!

27

That Bit Done

28

Pictures From The Riggers

The Aerials

the aerials are now moved to a bithigher to clear the chimney - theplanning and team work and thefeeling of success of this project canonly be imagined The repeater wasput back in service from about 14:00The 23cms section was licensed andactivated two weeks later Abouttwo months later the aerial positionswhere adjusted and this is now as itstands

There is a web page being built and as soon as it is in a useable statethe URL will be published

29

Sound-In-SyncIan Waters G3KKD

I note with interest the recent proposal from the Netherlands to removethe Sound sub-carriers from our 23cm and SHF ATY channels and toemploy some sort of sound-in-sync system. I do not propose, at this stage,to comment on the merits or otherwise of this idea but to recall some ofthe background to S-I-S.

The roots of S-I-S probably go back to the latter part of the war, whenPye Ltd. Cambridge developed and manufactured Wireless Set (WS) 10for the British army. This provided a fairly secure 10-channel telephone/teleprinter link for trunk communications behind the advancing invasionof Europe. From memory it worked by generating a 100 kHz train ofpulses each nominally about 5 microseconds wide. Time division multiplexwas used with every tenth pulse width modulated by one of the audiochannels. The signal was carried on a microwave bearer I believe in theregion of 2GHz. At the receiving end every tenth pulse was selected by agate and integrated by a low pass filter to recover the modulation. Thewhole equipment was accommodated in a large 4-wheeled trailer withdishes on the roof.

As soon as the war was over Pye switched its research effort to televisionbroadcasting. Before the BBC service from Alexandra Palace had restartedin 1946, Pye had built an experimental/demonstration studio withIconoscope cameras. It then went on to develop VIDEOSONIC. In thissystem the broadcast television sound was carried by a width modulatednominally 5 microseconds pulse inserted into the line sync interval. Thesystem offered several potential advantages. The cost of the TV soundtransmitter, with its (in those days) separate aerial and feeder could havebeen rendered unnecessary. There would also be some saving in occupiedbandwidth. Receivers could have been made less expensive with the soundrf/if circuits replaced by a gating circuit. Although probably not foreseen,because transposers were then a long way in the future, its use would

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have been beneficial when gap filling became necessary. Combined visionand sound power amplification, used in transposers and in some types ofmain transmitters, always suffers from amplifier non-linearity giving riseto intermodulation products between the vision, colour and sound carriers.Life would have been easier without the sound carrier. The down side ofVIDEOSONIC was that with a 405 line TV system, a 10 kHz line scanand only one audio sample per line the maximum audio bandwidth wasless than 5 kHz. In those days the BBC was proud of its hi-fi TV sound.so much better than old MF/LF radio. Pye did a demonstration to topindustry executives. A VIDEOSONIC transmission from thedemonstration studio was linked to some receivers at a Cambridge hotel.All went well until, Just as a senior Pye executive was making a speech,one of the receivers went out of line hold. They often did in those days.The sound gate swept over the video signal and a loud raspberry camefrom the loudspeaker. The system was not adopted!

The system surfaced again in the early 1960s, when It vas used by ATVoperators in the Cambridge area on 70 cm. A width-modulated pulse wasinserted into the sync interval. A modification kit was produced forreceivers/monitors. This extracted the video signal and fed it to a boxwhere it gated, integrated, amplified and fed to a loudspeaker. A signalwas also fed back to the monitor CRT to suppress spurious modulationthat appeared on the line fly back. Although the system worked well and5 kHz audio was adequate for amateur purposes, it failed to catch onbecause people were unwilling to modify their, in those days very valuable,TV sets and transmitting sound on 2 m was much easier.

The sound channel was secure because anyone listening on the band couldnot pick out the sound from all the video ‘buckshot”. However if videowas faded to black then sound signals could be heard, using acommunications receiver, every 10 kHz over some 4-5 MHz of the 70 cmband! This did not impress other band users and I am glad we never foundout what the Post Office (now the RA would have said.

The story now moves to the BBC Research Laboratories at Kingswood

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Warren who in the late 1960s developed the sound-in sync system weknow today. This was not for public broadcasting but to carry the soundwith the video on programme contribution and studio to transmitter linksetc. Up to then sound and vision had been conveyed separately, oftenusing different routes and a combination of microwave links and GPOlandlines. It resulted in valuable network simplification and removed thepossibility of the sound getting lost or the wrong sound being broadcast.

By now television was on 625 lines with a 15 kHz line scan. The originalS-I-S carried a single sound channel. Briefly the sound signal was sampledtwice every line thus permitting an audio bandwidth of 14 kHz. The twosamples were converted to pulse code modulation, using a 10 digit binarycode, delayed, compressed in time and the sound information lasting 4.0microseconds was inserted into the next line sync interval. Large amplitudepulses with a 2T form are used to make the system immune to interferenceand distortion and the order of the binary digits are reversed so that theleast significant digits are transmitted first.

Subsequently with the advent of stereo television sound using NICAM itbecame necessary to develop a two-channel/stereo version of thisequipment. Considerable quantities of S-I-S, both mono and stereo weremanufactured by Pye TVT Ltd to the BBC designs over many years. Ithas been used extensively on terrestrial and satellite links within the UKand worldwide. One wonders if some new variant optimised for amateurneeds will now emerge.

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MonoAlphabetic CodeJohn Smith G4KJJ

Some of you may be familiar with the recent news stories concerningBletchley Park, the Enigma coding machine and the recent film release‘U571’. If you’re interested in ‘communications’ and problems of secrecyyou may like to try your hand at solving the monoalphabetic ciphershown below.

Unlike the Enigma the original text has been matched to a randomlyshuffled alphabet, which requires a little knowledge and care to teaseout the original text message. You will need some information beforeyou begin:

Most frequent letters in EnglishE=12.51%T=9.25% A=8.04% O=7.6%I=7.26% N=7.09%

Most frequently paired lettersTH HE AN IN ER

Most frequent short wordsTHE OF AND TO A IN THAT IS I

Letter that follows ‘E’ most frequentlyR S N D

Now try to decode the following:

PENW LSYBKNI OYSBSNF UYM KYI UEND EN MYBI PENNYJPE FJZBPNI PEN MQD, ZQP EN UYM JBOEP; PENW MYBIPEN UJBOEP ZJFPENJM UNJN LJYXW UEND PENW PJBNI PFCSW, ZQP PENW IBI; PENW MYBI KW QDLSN UBSZQJ UYMKYI YM Y EYPPNJ – YDI EN UYM. OJYQLEF KYJV

As usual, answers to Roger, G7SRK at his home address.

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The next two pages could contain read-ers letters or items to trade. It�s up to

you to fill them...

34

35

This �White Van Man� is known to fre-quent the fringes of the GB3PI coverage

area, attempting to �mug� the gulliblenewly licenced for the price of a cup of

tea.

Can be recognised by the mating call��Ere, who�s buying the teas, then�.

W A R N I N G

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