JULYAUGU

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Police RadiCombating

Crime

Multivibrato

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VOLUME IV N( ')

JAMES J. DELANEY,Editor

BERNARD EPHRAIMTechnical Editor

L. D. McGEADY,Business Manager

Associate Editors:BALTIMORE, MD.

Wm. D. Kelly, WFBRBOSTON, MASS.

Harry R. ChethamSomerville, Mass., Police RadioST. LOUIS, MO.

C. H. Stoup, WIL

IN the following pages your attentionis called to the invitation of the Tech-

nical Editor to discuss technical sub-jects in which sufficient interest appearsto be present.

Early in the month the so-called Wag-ner bill was signed by the President. Itis rather surprising to find criticism ofthe bill in certain labor circles, but nomore so than to find certain loyal paidup members of labor organizations cometo meetings with the usual shout, "Wepay our dues and get nothing for them."What both mean is, "We want morel "A perfectly human, if not excusable,trait.

The old expression, "The rich getricher, the poor get - troubles," seemsto hold good with the broadcast stationsof the country. The big stations get big-ger, and the little fellow certainly getshis share of troubles. It is probably forthe same reason; the big fellow spendshis energy figuring out how to get big-ger, and the little fellow spends his try-ing to bite off more than he can chew.

Your assistance is asked in our per-sonals. No more interesting reading ispossible than the little goings on aroundyou. Not only is the man close to theselittle personals interested, but others aswell find them worth while. We will ap-preciate the favor if you will tell usmore of what is going on in your ownstation as others have been doing sowell for you in our pages.

(FORMERLY "C -Q")The Only Magazine in America Devoted Entirely to the Commercial Radio Man

Contents for July - August, /935

Wireless Operators Doing Picket Work During Strike onS. S. Manhattan, New York, June 19, 1935 Front

Police Radio Comba-ing Crime,By Matt Sloan

Multivibrators,By Bernard Ephraim

Automatic Receiver for Distress Signals,By 0. Bracke and P. Giroud

Short Wave Program for Waldorf Guests,By H. T. Budenbom

"In Baltimore", - -By Wm. D. Kelly

With the Technical EditorA 13.5 to 550 Meter Receiver

Total Operating Revenues of Radio -Telegraph

Airway NewsRadio Operators Win a Rise in PayExperimental Visual Broadcast Stations in theRelay Broadcast Stations in the United States

Assignments

An Efficient Marine Transmitter

Nikola Tesla Now 79

Page

Cover

5

7

10

11

13

13

14

Concerns 17

17

- - - 18

United States 18

- 18

19

20

20

New Orleans Airway Radio Station on Ancient Graveyard 20

New ApparatusFederal Communications Commission Memorandum

Can Serve Only OneWhere You Will Find It

21

21

21

22

Published Monthly by CQ Magazine Company, 7 West 44th Street, New York.N. Y.. Phone VAnderbilt 8-9461. Yearly subscription rate $2.00 in U. S. and Canada;22.60 foreign. Make all checks, drafts and money orderr payable to the Company.Single Copies, 20 cents. Text and illustrations of this Magazine are copyrighted, andmust not be reproduced without permieaion.

Ghirardi'sRADIOPHYSICS COURSE

The most popular basic text on radio in existence, used by students,schools, technicians and experimen-ters the world over. Everythingfrom fundamental ere:Heal theoryright up to The latest applicationsand developments. Clear, concise,complete, uptodate, written in lan-guage easy to understand, withover 500 diagrams and illustrations.Invaluable for broadcast techniciansfor rounding out their radio background. You need this great bookIn your work. (972 pages, $4.00 postpaid.)

RADIO OPERATINGQUESTIONS AND

ANSWERS

Nilson & HornungThis book gives over 600 questionsand answers covering all radio op-erator license examinations. Ques-tions are typical of those used onexaminations; answers are fulland well illustrated. This editionhas been enlarged to include infor-mation on broadcasting, marine,aeronautical, police and amateur ra-dio operating and contains manynew questions and answers on newtransmitters, new radio laws andlicense regulations, etc.

5th edition388 pages, 51/2x8, 96 illustrations

$2.50

RADIOTRANSMISSION

Practical Radio Communication, Nilson & Hornung 65.00How to Pass U. S. Govt. License Examinations,

Duncan & Drew (1032) LOCRadio Traffic Manual and Operating Regulations

(1929) 2.00Radio Operating Questions and Answers, Nilson &

Hornung 0.50Practical Radio Telegraphy, Nilson a Hornung 8.00Principles of Wireless Telegraphy, George W. Pierce 3.00Principles of Radio Communication, J. H. Morecroft 740

GENERAL

Principles of Radio, Keith Henney $3.50Elements of Radio Communication, .1. H. Morecroft 3.00Radio Engineering Handbook, Keith Henney 6.00Radio Engineering, F, E. Terman 6.00Radio Engineering Principles, Lauer & Brown 3.50Radio Handbook, Moyer & Wostrel 6.00Radio Telegraphy and Telephony, Duncan & Drew 7.50

SERVICE

Perpetual Trouble Shooters Manual, J. E. Rider, Vole.I, II, III, IV V, each $7.50Radio Construction and Repairing, Moyer al Wostrel 2.60

ELECGENERAL

Standard Handbook for Electrical Engineers $7.00Handbook for Electrical Engineers (Panders) 7.410Ready Ref Tables, C. Hering 2.50Elements of Electricity for Tech, Students, W. H.Timbie 8.110The CEIments of Electricity, W. Robinson 4.00

ADVANCED THEORY

Lectures on Electrical Engineering, C. P.Steinmetz

Theory and Calculation of Electric Circa:to, C. P.Steinmetz

Theory Elements of Electric Engineering. C. P.Steinmetz 4.82

THEORY

Radio Frequency Electrical Measurements, H. A.Brown $4.00Electric Oscillations and Electric Waves, G. W.Pierce 6.00

VACUUM TUBES

Electron Tubes and Their Application, J. H.Morecroft $4.50

Theory of Thermionic Vacuum Tubes, E. L. Chaffee 6.00Theory of Thermionic Vacuum Tube Circuits, L. J.

Peters 8.00Radio Receiving Tubes, Moyer & Wostrel 2.60

TELEVISION

Photocells & Their Application, Zworykin & WilsonPractical Radio -Including Television, Moyer &

1VostrelTelevision -Its Methods and Uses, E. J, Felix

Recording sound forL. Cowan

Projecting Sound Pictures, A. Nadel!

TRICAL

TELEPHONY andCommunication Engineering, W. L. Everitt 01.00Handbook of Telephone Circuit Diagrams, J. M. Heath SAOPrinciples of the Telephone, 'spiky & Faier 1.60

RECTIFICATION

SOUND

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Mercury A:c Rectifiers, Marti & Winograd $6.00Electric Re !tillers & Valves, I. R. Onntherschulze 46..11100

TESTING

Elementary Electrical Testing, V. Karapetoff 1.50Electrical Measurements and Testing, C. L. Dawes .75

MOTORS

Armature Winding and Motor Repair, D. H. Braymer $5.00Rewinding Small Motors, Braymer & Roe 2.50Alternating Current Armature Winding, T. Croft 3.90Commercial Dynamo Design, W. L. Waters 2.00

TELEGRAPHYAutomatic reiephony, Smith and CampbellAmerican Telegraph Practice, D. McNicol $5.00

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Page Four

7 West 44th StreetNEW YORK, N. Y.

Mention Commercial Radio when answering Advertisements

S -7S60POWER

UNi T

A3-7570POWERAjNIT

have been added in the last year. Dueto the speed with which intelligence maybe transmitted to all points within theworking range, there is nothing to com-pete with the radio system in policework.

The early systems called for a centraltransmitting point, generally policeheadquarters, for the transmitting. Morerecent developments of the two-waycommunication is fast gaining populari-ty, and the police cruising cars are car-rying their own means of reportingback to headquarters their positions,and acknowledgements of messages re-ceived. This also affords a means ofimmediately advising headquarters ofinstructions followed and results ob-

tained.Transmitters are sometimes remotely

located from police headquarters. Thisis often advisable in the case of ultrashort wave transmission, to give a better aerial facility for sending.

It is always possible for cities atpresent using the medium high frequencypolice transmitter to inst41 two-waycommunication by providing ultra highfrequency "report back" transmittersin police cars, by providing a suitableheadquarters receiver and antenna point.

Cost of SystemsA 50 to 200 watt transmitter with

from .5 to 1 KW power output may bepurchased and completely installed forless than $5,000 and often will more thanpay for itself in economies made possi-ble elsewhere in less than one year. A500 watt transmitter with approximate-ly 4 KW antenna power completely in -

Police Radio Combating Crime

THE number of municipalities in theUnited States using police radio

systems is rapidly increasing, and whatwas first looked upon as just a newbranch of radio work is now a matter ofserious intent.

Today, there are close to two hun-dred cities, and almost a dozen statesusing this type of radio. About fifty

CARGENERATOR

By MATT SLOAN

stalled can be had for about $7,500.Larger equipments of 1,000 watts

with 6.5 KW power output may be hadcompletely installed for about $12,800.Of course these are round figures, and inmany cases the cost will run a littleunder or over this figure. It takes intoconsideration the installation, the com-plete equipment, antenna and mast, set

teE tiny 71 ,1(A FIF.OUtt,E.A,

?A A CONTROLUNIT

ie A RADIORECEIVER

ETAHANDSET

CAN BATTERY

23 A CONTROL UNIT(mow(IPNCISCT POSITIONNOT NI usc)

ter installed. In some cities a largenumber of cars are equipped with re-ceivers, and a fewer number with two-way communication. This allows imme-diate contact with all cars, and reportback facilities from a selected few.

At headquarters, where two-way com-munication is used, the cost of receiverswill run a little higher than ordinary

ANTENNA

le ARADIO

ERA N3miTTER

Western ElectricSchematic drawing of a police car completely equipped with Two -Way Ultra -High Frequency

Radio Telephone Equipment

of tubes for the transmitter, and suchother incidentals as may be expected.

There is then the additional cost ofthe receivers, depending upon the num-ber and type. These will run for earreceivers with tubes, and installation,about $125 each. Where installations aremade at fixed points, such as precincthouses, or fixed posts where police arestationed at roads leading to or out ofthe city, the cost of the receivers isabout $75 each.

Two -Way Communication

On ultra high frequency for citieswhere two-way communication is per-mitted, the cost of the installations willrun about $750 per car with transmit -

Photo

fixed receivers, as a better type of re-ceiver, and of a more permanent and re-liable nature, is used. Also, a suitablelocation of the antenna which must behigh is a matter that may lend additional cost to this item bringing it inmost cases to about $350 for a firstclass installation.

Where line amplifiers are required forremote control as have been adopted inmany points where police headquartersdo not afford the best location for trans-mitters, an additional cost factor entersinto the picture to the sum of about$250 additional cost.

Two -Way Is More Costly

The ultra high frequency two-way

Western Electric Photo('orrect design and rugged construction enable thetransmitter to withstand all the shocks and jars of

constant mobile use

JULY -AUGUST, 1935 Page Five

=". Itttrfer..7-.""4":11.-'9,..W 2, r; 7

communication while affording the bet-ter means and more satisfactory in ma-ny cases, increases the cost. The re-sults more than warrant the additionalcost of such installations.

In two-way communication it is some-times possible to use the car batterycharger with the standard generator sup-plied with the car. However, it is con-sidered better practice to replace thischarger, never intended for such heavy

r--

ments by the Commission. Two-waycommunication is in use on the ultrahigh frequency in many of the largercities of the country, and is provingvery satisfactory. The Boston (Gener-al Electric), Newark, N. J. (WesternElectric), and the uncompleted Erie,Pa. (Westinghouse), police radio instal-lations are considered models of whatmay be accomplished as they are theproducts of three of the largest manu-

NO. K5-7569 AND NO. KS -7570POWER UNITS WITH

NO. KS -7572 MOUNTING PLATE

NO.188 RADIO RECEIVERWITH NO. 6A RADIO

. RECEIVER MOUNTING '

NO. 23A CONTROL UNITWITH NO. E3A HANDSET

Layout of complete equipment for two-way communication as installed in a

duty, with a more suitable type of char-ger. The special charging generatorsinstalled in cars cost about $50 addi-tional completely installed.

License RequiredThe usual formality preceding any in-

stallation is to first submit plans and out-lines of the radio equipment to the Fed-eral Communications Commission and re-ceive a "license to construct" beforeany actual installation work is attempt-ed. This point is entirely covered in aprinted pamphlet which may be hadfrom the Superintendent of Documents,Government Printing Office, Washington,D. C. at a cost of 30 cents.

When construction permit has beenissued, it is entirely satisfactory to goahead with installation work, as it issanctioned by the Federal Communica-tions Commission. When constructionhas been completed along the lines givenin the original plans submitted to theCommission an operating license willreadily be granted.

Those actually engaged in operatingthe transmitter itself must of coursehave a commercial radio operating li-cense. No one else is at any time totake charge of the transmitter while itis on the air. Where commercial radiomen are not engaged for this work ithas been the practice to have certainmen trained and licensed for this work.

Frequencies AvailableFrequency allotments in the band be-

tween 1712 and 2490 kilocycles havebeen given municipal police. Between1610 and 1706 kilocycles is reserved forState police work, in the medium highfrequency band.

The ultra high frequency channel ofbetween 30,000 and 42,000 kilocycles (10to 7.14 meters) is considered experimen-tal, but two-way communication has beenfound best on these bands, and they arethe ones being licensed to police depart -

Page Six

facturers, working with the best avail-able engineering staffs, on two-way ul-tra high frequency installations.

About two-thirds of the police radioinstallations of the country today arein the medium high frequency band, andone-third in the ultra high frequencyband. The trend is toward the ultrahigh frequency band.

Power AllotmentIn the matter of State Police Trans-

mitters a slightly different problem of-fers itself than in the case of munici-palities. The distance covered does notlend itelf to the ultra high frequencytransmission, and it then becomes aproblem of power for coverage. Au-thorizations have been made front 400watts to 5 KW, but the Commission'sattitude is to not allow anything above5 KW, and to encourage the construc-tion of several transmitters at differentpoints within one state rather titan totry to cover the entire territory withone transmitter. With one transmitterthe power required may be above the 5KW limit already set. Ultra high fre-quency is not adaptable to State Policework.

Municipalities offer a much simplerproblem in regard to power. On medi-um high frequency transmitters the an-tenna power is set by, population of areacovered, by the Federal CommunicationsCommission, as follows:

100,000 population -50 watts100,000 to 200,000-100 watts200,000 to 300,000-150 watts300,000 to 400,000-200 watts400,000 to 500,000-250 watts500,000 to 600,000-300 watts600,000 to 700,000-400 wattsover 700,000 -500 wattsWhere particular problems present

themselves, the Commission will studythe individual case and make recommen- Western Electric Photo

dations to the municipality concerned, View of 500 -watt Headquarters

or allow a larger output than is ordi-narily allowed for the size of the cityhaving trouble in transmission.

Ultra high frequency lends itself wellto city police %cork. The range is lim-ited depending on the elevation of thetransmitter, and earth curvature. Wherethe ground is fairly flat it is most sat-isfactory. Where mountains or hills, orlarge metal structures such as buildings,etc., are between the receiver and the

NO. IBA RADIO TRANSMITTERWITH NO.10IA RADIO '

TRANSMITTER MOUNTING -1

police car Western Electric Photo

transmitter it will give "dead spots"(Continued on Page 23)

Radio Transmitter

COMMERCIAL RADIO

IIIERNARDAn Analysis and Discii,..,on Replete With Practical Notes and Technical Information

IN FOUR PARTS-PART IN foreign and domestic engineeringIjournals, there have appeared a num-

ber of general discussions treating thetheory, design or technique of the mul-tivibrator. To the technician, laborator-ian, and practical radio engineer, it isregrettable that most of the featuredmaterial has been either intensely objec-tive, highly academic or too technical, orthe papers have been cast in foreign lan-guages which necessitates costly trans-lation. In this series of papers thesecomplexities have been largely overcome;and herein will be found the essence ofmany authoritative papers published inscattered journals throughout the world.In preparing these articles, the technicaltheme has been interwoven wheneverpossible, yet at all times it has been theendeavor to keep within the practical as-pects of the subject; hence, for the firsttime, a practical presentation of the the-ory, design, and technique appears un-der one general heading.

Definition

The multivibrator, an invention of H.Abraham and E. Bloch' k.'rance), is atype of harmonic oscillator consisting ofa two -stage capacity -resistance coupledamplifier in which the output is connectedback to the input in order to produce adistorted wave -form containing a power-ful high -harmonic output.

The basic principle underlying the ac-tion in a multivibrator is dependent up-on the phenomenon known as a ''relaxa-tion oscillation." A complete survey ofthe electrical phenomena leading up toa relaxation oscillation' is so vast andthe ramifications are so far reaching,that it would be practically impossibleto be content with the briefness of thesubsequent exposition. However, forthose who desire greater detail than thatwhich is encompassed herein, referenceshould be made to the footnotes and tothe appended bibliography.

Relaxation OscillationsAny type of oscillatory phenomena

that wholly or partially comes to rest,or is appreciably retarded during anypart of its harmonic motion is called arelaxation -oscillation This specie of os-cillation can be electrically produced byautomatically allowing a condenser tobe quickly charged at regular intervals,then allowed to gradually discharge overa high resistance; or by permitting thecondenser to slowly charge, then rap-idly discharge over a comparatively lowresistance.

Relaxation oscillations produced bythe slow -charge fast -discharge methodare commonly generated by oscillatorsemploying neon' or grid -glow (thyra-tron type) tubes. The shape of the vol-tage wave -form produced by the gas

JULY -AUGUST, 1935

tube relaxation oscillator during con-denser charge and discharge cycles isshown in Figure 1. By closely examin-ing the curve, it will be seen that thecondenser charging voltage rises slowlyand linearly to sonic fixed and finiteamplitude. The linearity of the charg-ing time is due to the charging epochoccurring over a limiting device, suchas a pure resistor or saturated pentode -type vacuum tube. The finite ampli-tude attained by the accelerating vol-tage is governed by the ignition level ofthe gas in the tube. When the criticalignition point is reached, the gas in thetube ionizes which provides a low resis-tance path over which the condenserquickly discharges. The curve showsthis speedy discharge by almost drop-ping vertically from the critical igni-tion level down to where the voltageacross the tube can no longer maintainionization. As soon as this extinguish-ing point has been reached, the chargeagain begins to build up as shown by therising charaeterictic in the second partof the curve. It should be observed thatthe relaxation period in, the oscillatoroccurs to suddenly relieve the charge onthe condenser; this is depicted in theFigure by the abrupt drops in the saw -shaped sinusoid. This same period al-so occurs in. certain types of multivibra-tors, although the rapidity of relaxationis often lengthened into a more gradu-al discharge.Relaxation Characteristics in the Multi -

vibratorIn the multivibrator the principle re-

laxation -oscillations are produced by uti-lizing two separate condenser chargeand discharge paths. Here, the con-densers are alternately allowed to ei-ther charge or discharge slowly or rap-idly in their respective circuits, whilethe reversals or periods of each alter-nation are being governed by the valuesgiven to the resistance in the various cir-cuit branches. A simple circuit by whichit is possible to trace the aforementionedelectrical paths is shown in Figure 2.

A typical relaxation -oscillation curve,produced in the grid circuit of any oneof the vacuum tubes referred to in theabove diagram, is shown in Figure 3. Aninspection of the curve will show how therelaxation characteristic is developed.Note that the curve " jumps" frompoint "a" to "b". Next the curveslowly decreases from "b" to "c"whence then it suddenly drops thru zeroaxis to point "d." Here the curve grad-ually increases to "e," then suddenlyjumps to " f " or "a" as above, thusstarting another relaxation -oscillation.

By closely examining the wave -form, itwill be seen that each relaxation -oscilla-tion has a form that reaches a finiteamplitude after one relaxatory period.

(In any other oscillator, save the relaxa-tion type, the wave -form is built up slow-ly and exponentially from a zero stateto a finite stationary amplitude after aseries of sinusoidal oscillations.) Thefinite amplitude attained during any oneperiod of relaxation is governed by theamount of negative resistance in the cir-cuit and upon the characteristic curva-ture of the tubes' operating resistance.The stability of amplitude (meaning thecondition necessary for maintenance ofa steady state of oscillation for an un-controlled multivibrator) is maintained,claims B. van der Pol' (Holland), bythe inherent residual inductance in thegrid circuit leads, there being no'lumped' inductance in the circuit. Onthe other hand, K. .Heegner" (Germany),states that the steady state is main-tained by the "falling characteristic"of the system (a property inherent in

Limitingbolster

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-II

Mina tuts

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Condenser Cherge end DischargeTias

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any regenerative amplifier. Of late, Y.Watannabe (Japan), building uponHeegner's theory, claims that the stea-dy state can be maintained by bothfalling and non -falling characteristics.Whether the theories of these able in-vestigators can be melded into a singlegeneralization is without the scope of

1 Abraham and Bloch, "Mesure en val-our absolve des. periodes des oscillations elec-triques haute frequence," Ann. der Phys.,Vol. 12. pp. 287. 1919.

2 B. Van der Pol. "Relaxation oscillations:"Phil. Mag. pp. 978-92. Nov. 1926; also Zeits. f.Hochfr. Vol. 29; pp. 14. 1927.

8 D. Pollack. "Neon tube oscillators,"Radio News, Two Parts. Dec. 1932. and Jan.1933; with seven references.

4 B. van der Pol. Loc. oh. No. 2.5 K. Heegner. Zeits. f Phys., Vol. 42; pp.

173, 1927, also Jahr. der Draht Tel and Tel..Vol. 29. pp. 151, 1927.

6 Y. Watannabe, "Some remarks on the. IRE Vol. 18. No. 2

op. 327, 1929.

Page Seven

".. -1 :W.A... sis.z..",--ra's ArZe

this discussion. However, a study ex-ploring the salient details of the aboveauthors' published works would, nodoubt, be an interesting investigation.

Unfortunately no discussion can hegiven in these articles investigating oranalyzing the harmonic content of themultivibrator by the use of the FourierSeries. The reason for excluding thisformal topic is because the multivibratorsystem cannot be exactly analyzed or

R.

1`.

"A" - C1 Dioelarring

C2 Clwrcinc

4

on" - C1 Charging

C2 Discharging

riatre 4

S

4

investigated by the Fourier method. Thewave patterns may, never -the -less, hequalitatively studied through the me-dium of the cathode-ray or string oseil-lograph device.

Since the control function in most alltypes of vacuum tubes depends upon thegrid bias, it is obvious that if this biaswere of a simulated alternating voltage,and each alternation had sufficient ampli-tude, the tube could be swept over itsentire characteristic. Through such con-trol, and by proper selection of the cir-cuit constants, the condensers in themultivibrator can be made to quicklycharge and slowly discharge or vice ver-sa in practically any sequence with re-spect to time. Thus, a wave -shape of thefamiliar saw -tooth configuration can bedeveloped in the system. This wave-form is similar to that produced by aneon -tube oscillator with the exceptionthat the progression of the wave devel-opment+ is reversed in the multivibrator.For comparison, see Figures 1 and 3.

The general outline of the wave -formdepends upon the time periods allowedto the alternate condenser charge anddischarge transitions. If these periodsbe equal, that is, if the charging timesbe of one value and the discharge timesanother, the contour of the voltagecurves described by the alternate con-denser charge and discharges will havepractically the same shape. When such

Page Eight

a symmetry exists, the multivibrator hasSYMMETRICAL CHARACTERISTICS.On the other hand, if the charging anddischarging alternations have differenttime periods, such as charging times un-equal, the shape of the wave -forms inone circuit will be somewhat modifiedfrom that of the other, the degree of dis-similarity depending upon the differenceexisting between the two circuits; hence,if the multivibrator develops dissimilarwave shapes in each circuit, the systemhas UNSYMMETRICAL CHARACTER-ISTICS. Any multivibrator circuit canbe instantly classified by simple inspec-tion of the values of the grid and plateresistors in the two circuits forming theoscillatory system. In addition, in asymmetrical system each time the gridchanges potential, the change is greaterthan the straight line part of the tubecharacteristic. In an unsymmetricalsystem one of the tubes usually operatesas a straight amplifier, while the otherfunctions over the complete tube charac-teristic from saturation to cut-off.

Function of a Symmetrical Multivibrator

In Figure 4 are two simplified wiringdiagrams which, with the subsequent ex-planation, illustrate the electrical actionin the multivibrator. In the Figure,open and closed arrows indicate the di-rection in which the current flows dur-ing alternate condenser charge and dis-charge periods. Plus and minus signsshow the grid voltage biases on the re-spective tubes during inter -circuit rever-sals.

GENERAL EXPLANATION: Referto either drawing a" or "b" in Fig-ure 4, then assume that the plate sup-ply voltage has suddenly been applied tothe plate circuits. Now, from a brief ex-amination of either diagram, it wouldseem that if resistors r, and r, were ofan equal value, an equal charge would beplaced upon condensers C, and C, there-by stabilizing the system. But, in a sym-metrical or unsymmetrical combination,experiment and theory prove that an un-balanced condition exists in the intra-cir-cuit of some one tube causing an un-symmetrical current equilibrium to beestablished between one tube and theother. This instability causes the cir-cuits to feed back upon each other pro-ducing self-excited oscillations.

CIRCUIT ACTION: To properly de-pict the circuit action together with thebuilding up of the relaxation character-istic, reference will be made to the dia-grams in Figure 4 together with thegraphical representations shown in Fig-ure 5. As regards the graphs, these de-scribe excursions of the plate voltageE, E,,,; plate currents I,, I,; grid vol-tages E.,, E; and condenser voltagesC,, C,.

In drawing "a" suppose that the po-tential applied to plates Ej1, E0, and tocondensers C,, C, were of one value.(This is strictly a supposition as suchconditions do not exist for even the du-ration of a moment. In experiments ithas been repeatedly demonstrated thatin order for self excited oscillations tobe produced it is a necessary conditionthat there be no point of equilibriumwith respect to the direct current.) Now,if the plate current i, flowing throughr, should slightly increase (1) (thesenumbers refer to portions of the curves

shown in Figure 5) a small voltage drop(2) would occur at Erj due to the IRdrop in r,. The reduction of voltage atE,,, permits condenser C, to slightly dis-charge (3) through the elements of tubenumber 2, thence through resistor R,back to the negative side of C,. Duringthis slight discharge, the voltage acrossR, increases the negative bias E (4)which decreases the plate current I, (5)more times (amount governed by the muof the tube) than the initial currentchange through r,. The decreasing platecurrent at I, increases the voltage atE,,, (6) which starts to increase thecharge on C,. The charge acting throughC, decreases the negative bias (7)which, when multiplied by the mu of thetube, is great enough when carried backto E,, to drive the grid so negative (8)that the plate current Ij (9) is suddenlycut off. This, of course, increases thevoltage at E0, (10) which charges con-denser C, (11). The charge actingthrough the condenser drives grid E,2positive (12), which increases the platecurrent I, (13) and decreases the vol-tage at E, (14) causing condenser C,

r2 2 12

ea

,I Ix,

pl.

0

te.x.

Ave.3S

0

as

in

a

10

18

Mex.

Ave.'

Min.

Mx.

Ave.

Curves X,. and C nre similar to thoseprodacen by oscillographic devices. Theremaining curves are only relative.

Figure 5

to discharge (15). The condenser willcontinue to discharge until the grid vol-tage on E,, has reached such a value(16) that the plate current begins toflow (17). At this instant, refer now todiagram "b", the voltage E,, across r,begins to drop (18) causing condenserC, to slightly discharge (19) across R,which, due to the IR drop therein, causesE,, to be driven slightly negative (20).This change decreases I, (21) and in -

COMMERCIAL RADIO

creases E" (22) more than the initialchange across r, due to the mu of thetube. The increasing voltage at E,2starts to charge condenser C, (23). Thecharge acting through the condenserdrives E positive (24). This causesC, to suddenly discharge (25) across R,which due to the IR drop therein, drivesE negative (26). This cuts off theplate current (27) at I2, raises the voltage at E" (28) and so charges con-denser C, (29). While E is positive, theplate current I, is at maximum (30)and the plate voltage EN is at minimum(31). When the bias E reaches a lowvalue (32) the plate current I, (33) be-gins to flow and the plate voltage E"(34) begins to drop, which brings thisexplanation back to the conditions firstassumed in (1) and (2).

The above cyclic relaxation oscillationcontinues; the period or frequency ofeach oscillation depends EXACTLY up-on the "initial time of condensercharge" PLUS "the initial time ofcondenser discharge" or approximatelyupon the capacity resistance product(CR) of the grid oscillatory circuits. Amore thorough discussion regarding thefrequency of the system will be takenup later on.

PLATE CURRENTS

1,, = 0(E, E")= .0(Ey, E")

CONDENSER CHARGE AND DIS-CHARGE CURRENTS:

= C

ing

dEgl 4E61

dt dt

4Egl=

Iq,= C

ing

=

dt

,E

Condenser charg-

Condenser discharging

dE"Condenser charg-

dt dt

dE,Condenser discharging

dt

The condenser charge and discharge cur-rents must be determined by differenti-ating over the charge and discharge

Ectl

ICI

Voltage and Current Changes

The variations in current and voltage ENoccurring during any relaxation -oscilla-tion may be determined by inserting asimple vacuum -tube voltmeter in any ofthe branch circuits shown in Figure 6.

Eet

When using the meter, it is essential thatits damping constant be higher than theCR period of the multivibrator, in sec-onds. This limitation means that onlyquantitative readings can be obtained atonly very low relaxation frequencies.

R, -.J41

With the meter it is possible to deter-mine six voltage and six current varia-tions during each oscillation, a list ofthese appears below.

1Pi

(1) Two changes in grid E, Ey

charges(4) Two changes in grid cur-

rent(5) Two changes in plate

current

voltage(2) Two changes in Plate

voltage(3) Two changes in condenser Ey, E

(6) Two changes in condensercharge and discharge currentsEquations by which any of the above

variations may be determined are:

GRID VOLTAGES:

E1, = IiiR = Ri(I" Iy)Ey = I,,R, = R5(I,1 + Isr)PLATE VOLTAGES:

EMI E22

To, Igg

Tint Ip2

E61 = r,(Ir, - Iqz)

E" = r,(Ip, - I)CONDENSER CHARGES

Ey = C(Er, - E)Ey = C(E - Ey)GRID CURRENTS:

Ict = (p(Ey, E,)I, = (p(E22, E22)

JULY -AUGUST, 1935

TOP 152

Figure 6

times. In practice, it is seldom necessa-ry to determine these values

Frequency Determination

The fundamental frequency of themultivibrator cannot be determined fromformula employed in determining fre-quency in other types of oscillatory sys-tems. This is because the sustained os-cillations produced in the multivibratorare arc oscillations of the second type.In this category even the abridgedThomson formula is valueless becausethe circuits comprising each shuntbranch have no effective inductance dur-ing the times when the current remainssubstantially at one value over a certainpart of each relaxation -oscillation. How-ever, the fundamental frequency may beclosely approximated by computing therelaxation -oscillation time constant ofthe system. This constant may be de-termined from the following expression

T = RC log -V,

where C is the total capacity in the cir-cuit, R the total effective resistance inseries with the capacity, and V, and V,the initial and final voltages, respective.ly, across the condenser.

Another method fer calculating the fre-quency of the system, while not as accu-rate as the above, consists of simply tak-ing the CR product of the grid circuits.Expressions for calculating frequency bythis method are

r =

f

1

Cif-C,(R)1

R, (C)where f is the frequency in cycles; C, thecapacity in microfarads; and R, the ohm-age of one of the grid leak resistors.

Applying one of the above equations,take the following example:

If a multivibrator had grid leak re-sistors of 20,000 ohms each, condensersof 500 micro-microfarads each, the fre-

E92 EP2

19

- 'I a

IP2

I 1-1Pi Pa

Egquency could be determined by the fol-lowing solution:

SOLUTION:

_1

C1 + C, (R)1

500 + 500 (20,000)

1 1

(10-*) (2 x 104) 2 x 10-s

1- 50,000 or 50 KC/sec.

.00002

NOTE ON TECHNIQUE:

To find the value of the grid leaks forsome specific frequency when the valueof the condensers are known, use the fol-lowing method.

(1) Take the frequency in cycles and(Continued on Page 21)

Page Nine

Automatic Receiver For Distress SignalsBy 0. BRACKE and P. GIROUD

Introduction required that the auto -alarm equipment era have been developed by differentshall be capable of receiving signals firms, the signal time checking being

CCORDING to their classification andACCORDING all sea -going ships are

within certain limits. The duration ofeach dash may vary between 3.5 and

done by tuned relays,systems, or clutch or

pendulum clockmotor driven

compelled to have one, two or three wire-less operators on board, who, under theMerchant Shipping Act of 1927, are tokeep a wireless watch during certainhours imposed by the rules laid down inthe Act.

Outside these watch -keeping periods,the ships have been unable to receive dis-

tress signals. To obviate this inconven-ience and in order to reduce the numberof required wireless operators, the Wash-ington International Wireless Telegra-phy convention of 1927, instituted the

4.5 seconds, and the duration of the in-tervals between 0.2 and 1.2 seconds.

The automatic instruments used forreceiving the alarm signals must satisfythe following conditions:

(1) They must respond to the alarmsignal after three consecutive dashes,even when numerous transmitting sta-tions are working and when there isatmospheric interference;(2) They must not be started by at-mospheric or by powerful signals oth-er than the alarm signal;

switches. All of them are based on theprinciple of the direct measurement ofthe duration of each individual dash andinterval.

The duration of the dashes is a rela-tively stable element; atmospheric inter-ference or powerful signals other thanalarm signals can only add to their du-ration without changing their charac-teristics. The intervals which, accordingto the regulations, may be as short as0.2 second are, on the contrary, liableto be upset to a greater extent by the

I

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VS V4Cl

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Ar

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SI

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CHARGING PANEL

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3 82 BI.CAPTAIN'S BELL.

"automatic distress signal" which pre-cedes the ordinary distress signals.

The "automatic distress signal" istransmitted on a wavelength of 600 me-ters. It consists of a series of twelvedashes sent out in one minute. The du-ration of each dash is four seconds, witha one second interval between dashes.

The only purpose of this special sig-nal is to set in operation the automaticreceiving apparatus which gives warningof the receipt of a distress call whenwatch is not being kept by an operator.It is used solely to announce that the dis-tress call or message is about to follow.

The automatic distress signal may besent out either automatically or manu-ally. For the latter case, it is generally

Reproduced by courtesy "ElectricalCommunication," April, 1935.

Page Ten

Circuit schematic of A.A.2.B. type auto -alarm.

(3) They must4possess a sensitivityequal to that of a crystal detector re-ceiver connected with the same an-tenna;(4) They must give warning whentheir operation ceases to be normaLTo comply with the aforesaid regu-

lations, the laboratories have recentlydeveloped an automatic receiver for dis-tress signals of a new type. This equip-ment has been approved by the GeneralPost Office of Great Britain for instal-lation on board of compulsorily fittedships and it has been standardised bythe Interational Marine Radio Company,Ltd.

This article describes the equipmentknown as the A.A.2.B. Auto -Alarm.Signal Time Checking

Numerous types of automatic receiv-

interferences. Consequently, under nor-mal service conditions, two consecutivedashes are not separated by an intervalof the correct duration but by an in-terval containing a number of extrane-ous short signals.

By eliminating the measurement of theinterval separating two consecutive dash-es and substituting a cheek of the totaltime from the end of a first dash to theend of the following second consecutivedash, the new auto -alarm developed bythe Laboratories completely solves theproblem. The principal cause of failureof the other types of automatic distresssignal receivers is suppressed.Description

The equipment consists of:(1) A watertight box containing the

(Continued on Page 15)

COMMERCIAL RADIO

Short Wave

Programs forWaldorf Guests

By H. T. BUDENBOMMember of Technical Staff, Bell

Telephone Labs,

SINCE its opening some four yearsago, the new Waldorf-Astoria Ho-

tel has provided radio broadcast pro-grams for its guests in over two thou-sand rooms. A horizontal antenna, sus-pended between towers forty-seven stor-ies above the street, is connected to highquality Western Electric receivers on thesixth floor, from which point the pro-grams are distributed over a building -wide network developed by the Labora-tories. Since the Waldorf enjoys an in-ternational reputation, and attracts ma-ny foreign guests, the management feltit would be desirable to make availableto them radio programs broadcast onshort waves from their own countries,in addition to our local broadcasts. More-over, the increasing general interest inshort-wave reception would make theavailability of short-wave programs anattractive feature for American patrons.To receive such, programs the Waldorfhas now installed a Western Electricshort-wave receiver which can be con-nected to any of the circuits of the pres-ent distributing system.

Most of the short-wave programs arebroadcast :it frequencies from 6 to 25megacycles, corresponding to wavelengths from fifty down to twelve me-ters, and it was decided that the West-ern Electric 13A Radio Receiver wouldprovide the best quality of signal andmost general satisfaction over this range.this receiver was designed for variousapplications in the short-wave field, in-cluding aviation, point-to-point, andship -to -shore. It was first applied to theCaribbean radio telephone project. asalready described in our September, 1933issue, but has since been widely usedboth at home and abroad. As shown inFigure 1, all the apparatus is housed ina seven -foot cabinet about twenty incheswide. The cabinet itself forms the bark,sides, and top for a number of units.each of which has its own function andcarries its own front panel. The scopeof the receiver may he broadened, afterpurchase. by the addition of other unitsas desired.

Units available are three radio -fre-quency amplifiers, each with a differ-ent frequency range, an intermediatefrequency amplifier, and an audio -fre-quency amplifier and power supply un-it, as well as antenna tuning units, apatching panel, and an oscillator panel,which allows the set to he used for re-ceiving telegraph signals. There is alsoavailable a panel, used chiefly for point -to point communication, which may beemployed to disable the receiver eitherwhen no carrier is being received or whenthe transmitter associated with the re-ceiver is on the air. Of these variouspanels available, the installation at theWaldorf includes only the audio and in-termediate -frequency amplifiers and thethree radio -frequency amplifiers, which

JULY -AUGUST, 1935

are sufficient for broadcast reception ov-er the frequency range from 2.2 to 25megacycles. Such an arrangement willpermit them to receive not only all theshort-wave broadcasts, but many police,aviation, and amateur radio -telephonechannels as well.

The use of three separate radio -fre-

quency amplifiers makes it much easierto tune in on a given station promptly.Depending on the time of day, a broad-cast station may employ any of severalfrequencies. If it were desired to geta station which used either 6, 9, or 15megacycles, for example, one amplifiercould be tuned to 6 megacycles, one to 9,

Fig, 1-H. R. Martin, Superintendent of Communicationat the Waldorf, tunes the short-wave receiving unit

Page Eleven

:e..

,ci-_-_vi:;

":

2 --The radio -frequency amplifiers incorporate accurate gangtuning through a worm drive with a double scale dial

and one to 15, and all three would beconnected to the intermediate -frequencyamplifier. If the station were on the airit would be immediately heard, and thetwo unnecessary amplifiers turned off.If it had not yet come on the air theoperator would hear it the moment itdid and would not lose the station announcement by having to tune succes-sively to several frequencies.

The 13A Receiver is completely a -c.operated: the necessary transformers,rectifiers, and filters being incorporatedin the voice -frequency amplifier unit.The signal gathered by the antenna firstenters one of the radio -frequency ampli-fiers where it is amplified, passed througha series of selective circuits, and is thenbeat down to a frequency of 385 kc.-the frequency of the intermediate am-plifier.* Here undesired frequencies arefiltered out by sharply tuned circuits,further amplification is obtained, andthe signal is detected. The resulting au-dio -frequency signal, which covers theband from 40 to 5000 cycles, is then further amplified in a suitable audio am-plifier before distribution over the Wal-dorf system.

Outstanding features of this receiverare the high degree of selectivity, anelectrical and mechanical design thatinsures dependable operation as well ashigh quality reception, and a sensitivitythat permits good reception on signalsas low as one microvolt. In the radio -frequency amplifiers there are five tunedcircuits ahead of the modulator. These,together with the beating oscillator, aretutted by a six -gang condenser operatedthrough a carefully constructed wormdrive, shown in Figure 2, which givesvery accurate selection. Frequencies sep-arated less than one -tenth of one percent may be readily tuned in. In the in-termediate -frequency amplifier, Figure5, there are eight additional tuned cir-cuits. In this amplifier there is also aband -changing switch which, in theevent of bad noise conditions, can beused to decrease the width of the audi

*Suppressor gridployed.

Page Twelve

ble frequency band and thus reduce theinterference. Automatic gain control isprovided, which is particularly importantfor short-wave reception, where the vari-ation in signal strength with time maybe considerable.

No matter how efficient a radio recei-ver may be, it must depend on the an-tenna to extract the maximum amount ofenergy from the arriving signal withthe least amount of noise. Considerableattention was therefore given to the de-sign of an antenna that would best se-

would not mar the appearance of thebuilding with tall ungainly structures.The multiple -doublet arrangement pro-

vided serves admirably to receive sig-nals over a wide range of frequency anddirection of arrival with a maximum ofnoise elimination.

When a horizontal wire is exposed toa high -frequency eleetro-magnetic field,it acts somewhat as a tuned circuit, anda current -measuring device placed at themid -point would show maximum currentwhen the length of the wire was approx-imately half the length of the radiowave. Such a wire differs in action froma tuned circuit, however, in respondingnot only to the fundamental frequencybut to all odd multiples of this frequen-cy. Thus a wire equal in extent to ahalf wave -length of a 3000 kilocyclesignal, or 50 meters, would respond tofrequencies of 3,000, 9,000, 15,000, and21,000 kilocycles, and so on. If such awire is broken at its mid -point and atuned circuit or a transmission line lead-ing to a tuned circuit is inserted, the re-sulting arrangement is known as a doub-let. After the introduction of this as-sociated circuit the tuning of the wireis only moderately sharp, and as a re-sult it responds fairly well over a fre-quency range extending perhaps 20 percent above and below the various fre-quencies corresponding to the length ofthe wire. By using several of thesedoublets, therefore, it is possible to se-cure good reception over a wide rangeof frequencies.

EQUATOR--,,PANA

0 2000 4000 6000MILES ALONG ANY STRAIGHT LINE

MEASURED FROM NEW YORK

In the Waldorf installation, threesuch doublets are employed, having ap-

(Continued on Page 19)

I PRIME/MERIDIAN

modulation is em -fig. 4-A great -circle chart of the world centered at New York. The pathscoming to New York are straight lines on this chart.

of radio waves

COMMERCIAL RADIO

"In Baltimore" WITH THE TECHNICAL EDITORBy WM. D. KELLY

In Baltimore, vaca-tions are the order ofthe day.

At WFBR:Control Man Ruck-

ert and AnnouncerHickman have just re-turned from a trip toBermuda. Neither willadmit having felt theleast bit seasick.

Stewart Kennard, that demon of Me -nos, has journeyed to Ocean City, Md.We all expect to hear some fine fish stor-ies when Stewart gets home.

Eddie Stover has a nice mountain tourmapped out for his vacation.

Bill Kelly will journey down Norfolkand Virginia Beach way.

The Chief-Win. Ranft-has just re-turned from his vacation down on theMaryland Eastern Shore and Ocean Ci-ty, Md.

Carlton Nopper will celebrate his firstyear of married bliss down at AtlanticCity.

The studios and transmitter shack ofWFBR have been all fixed up with airconditioning equipment to keep the boyscooled off.

Clem Holloway promises himself atrip back home for his vacation. Norman0 'Hearn is the Relief Engineer atWFBR again this year.

At WBAL:W. J. Kelly spent his vacation down

at Ocean City, Md.Edward W. Shristhlif used his va-

cation days for a honeymoon. Good luck,fellow, and may the Sea of Matrimonybe as smooth as those local pgms ofWBAL.

Win. C. Barham spent hie vacationdown on the Chesapeake Bay.

John Match says he expects to spendhis vacation at Ocean City, Md., also.

Stafford Carson is a new man atWBAL, coming there in February.

Andrew Massy is the relief man onthe WBAL staff.

At WCAO:Martin Jones is going down Virginia

way in his new Ford.The Chief-James Schultz-whether

to start work on his ham station or takea trip to New York City is the ques-tion.

Lynch has left WCAO and has gonedown South to take a job with EAT.

Charlie Seibold made a trip to N. Y.C. to see the big time radio.

Sydney Basford is planning a veryquiet vacation at home.

At WDBM:Sammy Houston was married recently

and used his vacation for a belatedhoneymoon trip to Norfolk and Virgin-ia Beach. Happy landings, fellow, andmay your new job run very much moresmoothly than that Ford you used todrive.

August Eekles is planning a trip tothe Middle West.

Frank Snyder, they say, is gettingfat-maybe he'll spend his vacation re-ducing.

Ed Laker-a sound man-will jour-ney out to Akron, Ohio.

George Porter Houston-the Chief-says that he expects to go to Ocean City,Md., for hie time off.

JULY -AUGUST, 1935

Contributions to these columns areinvited from readers. They should beconcise and may deal with technicalarticles published in previous issues,or other subjects of some general in-terest and professional importance.

Statements made by writers do notnecessarily carry the endorsement of Ithis publication. Address all commu- Inications to the Technical Editor. 1

England's First Television Station

LONDON, England: The first televi-sion station in England, under the

new British Broadcasting Corporation'shigh -definition system, is to be built im-mediately. The transmitter will be lo-cated in the Alexander Palace; thisbuilding is in the London sector.

Bids for transmitters have been ten-dered to the Baird Television Company(240 line type) and to the Marconi EMITelevision Company (405 line type).

The British are now on the double to"beat" U. S. broadcasters to this tele-vision thing.

AT&T Television 12 Month (?) Away

By using a co -axial cable, see Elec-trical Engineering, October, 1934, theAT&T Company plan elabOrate testswith the new cable which is capable oftransmitting (according to the cablediameter) a frequency of 4000 kilocycles.The cable is useful for interlinkingtransmitters for chain visual broad-casts. At present, plans are being drawnand monies appropriated for construct-ing a line between New York City andPhiladelphia. According to New Yorkresearch experts, it is rumored that theproject will cost over a half -million dol-lars.

In this country the ultimate destina-tion of television will greatly dependupon the co-ordinated experiments ofboth the AT&T and RCA companies.

(Note: An article treating the morepractical phases of transmission over co-axial cables will be published in this pa-per, if sufficient requests are received.)Tech. Ed.

Frequency Modulation

Major E. H. Armstrong, famous forregeneration, the superheterodyne, andsuper -regeneration, now startles the pro-fessional world with his latest develop-ment-" frequency modulation.''

Briefly, the invention essentially con-sists of displacing the station frequencya certain number of cycles each side ofthe carrier. During frequency transi-tions the power output remains constant.(Compare this with amplitude modula-tion and note the differences requiredto obtain output.)

The practical utility of the Arm-strong invention will be principally onthe short waves, 10 meters and below.This is because the system requires awide channel for normal operation. Atotal band -width of 200 kilocycles beingrequired for 10 kilocycle high-fidelityfrequency modulation.

One of the salient features of the de-velopment, which is contradictory to allaccepted theory, is that the wider theband the better will be the signal to

noise ratio. Usually receivers are madehighly selective so as to admit only thedesired signal, here is a system wherejust the opposite is true!

Conventional receivers cannot receivethe frequency modulated signals, hence,an auxiliary device must be used to con-vert the received signal into an ampli-tude -modulated signal before demodu-lation is possible Push-pull radio frequency input stages operating each sideof resonance are required for receivingthe signal. The stages selectively ampli-fy frequencies above and below the car-rier; these are then combined in a circuithaving linear frequency response, theoutput being demodulated in the con-ventional manner.

Further details on the Armstrong in-vention will appear in this journal assoon as released by the IRE. Until suchtime, the reader is referred to U. S. Pat.No. 1,941,069 and to "A Treatise onFrequency Modulation" published in theJune issue of Communication and Broad-cast Engineering.

Wanted: A Silent Tuning AidAt present there is a trend toward

incorporating auxiliary beat -frequencyoscillators in broadcast receivers to ob-tain an audible beat -note signal for in-dicating and bringing to resonance strongor weak signals. While this method oftuning materially aide in resonating thereceiver to the signal frequency, it hasa number of disadvantages; some ofthese are enumerated below:

(1) Close manual adjustment and te-dious concentration are required by theuser who is generally unskilled in themanipulation of such devices.

(2) The beat -note whistle, which isa varying high -to -low pitched tone, isnot only irksome but is also disagreeableto the ear.

(3) Exact or near -resonance tuning islargely accidental; the users of broad -east receivers are not as accurate intheir tuning as many engineers wouldbelieve them to be. Witness, for exam-ple, that receivers equipped with tuningmeters usually are tuned 200 to 500 cy-cles off resonance.

(4) At present beat -oscillators areprovided with a cut-out switch to enablethe user to silence the beat -note tone.This switch becomes a nuisance in tun-ing distant stations.

(5) It is practically, impossible toleave the beat oscillator permanentlyconnected in the circuit due to varia-tions in the oscillator frequency causedby temperature, humidity, and supplyvoltage fluctuations.

To eliminate the disadvantages enu-merated above involves the design of acircuit in which the beat -oscillator re-mains operative only until the resonancecurve of the receiver is aligned or near-ly aligned with the signal frequency.When this point is reached, the oscillatormust automatically stop oscillating, andat the same time the amplifier channelin the receiver must be unblocked.

In designing the circuit, provisionmust be made for the operator to con-trol the beat -frequency "band width'so that the receiver may be adjusted totune; that is, to trigger the amplifierwithin 0 to 200 cycles off resonance. In

Page Thirteen

Irigetarlf.7.712CCNP,:.!5a-414WiMirgirP;k7M474- ft-:C-7"1"7:"11Fen-"°:77ef"::

la -4"

.

this manner the receiver may be adjust-ed at one's discretion to respond to eith-er narrow or broad resonance peaks. Inaddition to this refinement, the usershould be able to switch "in" or "out"the BF oscillator at will.

It is requested that some of our in-ventive readers will offer suggestionstoward the solution of this problem.Hints: See references in "Funkt. Mo-natsh (1934) No. 7, pp 259-63" and"Electronics, Feb. 1933, p-40."

* * *

"Mail Order" Education

Here is an excerpt from a letter thattells a complete story-the writer wish-es to remain anonymous:

"Has it ever occurred to you by whatmeans the purveyors of mind -trainingsystems, no matter how superficial andmetricious, achieve such a measure ofsuccess? It is simply owing to the factthat a man, when he has put down asubstantial sum, is possessed by subcon-scious determination to avoid at all costthe humiliation of feeling that he hasbeen such a nincompoop as to havethrown all that money down the drain.Accordingly, he applies himself for thefirst time in his life, and with grim de-termination, to the reform of his ownmind. Under such circumstances, the pur-suit of any system whatever is bound tomeet with a certain measure of suc-cess. "

* * *

Notes on Fixed Attenuation NetworksSince attenuation networks are com-

posed of resistances, it is important thateach resistive element employed in thevarious circuit branches be of certain de-sign; that is, if stability and perma-nence of calibration are desired. Themajor factors dealing with the designof the resistive elements are:

(1) Each resistive winding must havea low temperature co -efficient over am-bient room temperatures. This meansthat the resistance of each winding mustnot change appreciable over ordinaryroom heats.

(2) Each winding must he free ofreactance effects and have a low or zerophase angle. In other words, the wind-ings must be non -inductively wound.

(3) The resistance of each windingmust be free from frequency variationsbetween wide limits throughout the en-tire audio -frequency spectrum. If theelements have poor frequency character-istics, certain frequencies will be attenu-ated more than others. This effect isespecially noticeable in the zones of theupper register.

(4) The impedance of the circuit el-ements must not vary with frequencyelse there will be an over -emphasis orloss of certain audio components duringrandom levels of attenuation.

The above requirements have beenprincipally given to show that a greatdeal of care must be taken in designingor selecting resistors for use in looseror impedance -matching networks. It iswell to bear in mind, that it is almostimpossible to satisfactorily pattern afixed network with just "ordinary" or"cheap" resistors of inferior, design.

Page Fourteen

A 13.5 to 550

Meter ReceiverTHE R.M.10 Radio Receiver is a nine

valve superheterodyne general pur-pose receiver designed for telegraphy andtelephony. The range of 13.5 to 550 me-tres is covered by five sets of plug-incoils. The high frequency coils for eachband are ganged on a single triangularunit and changed simultaneously. Thelarge drum dial is calibrated directly inkilocycles for each of the five waveranges.

The appropriate calibration track isautomatically illuminated by insertionof a coil unit.

Rapid adjustment of tuning is doneby turning the knurled rim of the drumdial, and fine adjustment by means ofan anti -hack lash worm drive. The re-duction of the worm drive is sufficient tomake band spread coils unnecessary.

A local beat -oscillator is provided forreception of C.W. telegraphy and a con-trol for adjusting the pitch of the re-ceived note is also provided.

For conditions of extreme selectivity,an audio frequency filter panel passing aband of 900 to 1,100 p:s is available. Tomatch the receiver to all types of an-tenna systems, an antenna impedancematching panel is provided. This sup-plementary panel adds an extra balancedtuned circuit which improves secondchannel selectivity and assists in duplexoperation in addition to providing the

r,.

-tot

correct matching impedance for alltypes of antennae. This device also con-siderably attenuates noise pick-up on thetransmission line from a doublet an-tenna.

Further refinements are provided in atime lag control for the automatic vol-tage control permitting the choice of along time lag in low speed telegraphy,or a short time lag in telephony or highspeed telegraphy. The resonance meter isprovided with a switch and multiplierto check high tension voltages. A crashlimiting circuit is provided for head-phone or loudspeaker operation.

The receiver can he supplied eitherwith four sets of coils to cover 13.5-200metres or with five sets to cover 13.5-550 metres.

The receiver illustrated, the first mod-el of which was manufactured by Kol-ster-Brandes, Limited, Sidcup, covers thewave range of 13.5-200 metres. Theunits from top to bottom are:

(1) Combined spare coil rack andpower supply unit.

(2) Antenna matching panel.(3) Receiver unit.(4) 1,000 p:s note filter.

PX or position reporting kept the PopeField, Fort Bragg, N. C., commerce sta-tion pretty busy recently during the sev-enth annual All American Air Races atMiami. PX traffic was January 9, 117;January 10, 177; January 11, 296; Jan-uary 12, 135; January 13, 175; January14, 202. Pretty heavy traffic we think.

COMMERCIAL RADIO

Akkompal.....mm - . - *tr f.,J --t;Lt

romogoirr.,:n77-riMer.41,71714g.. ' .

Automatic Receiver forDistress Signals

(Continued from Page 10)wireless receiver(2) A similar box containing the sig-nal selector device;(3) Three alarm bells;(4) An antenna change -over switch;(5) Two individual power supply bat-teries and' charging panel.

Wireless Receiver

The wireless receiver responds without readjustment to signals on wave-lengths between 585 and 615 meters.

The circuit consists of a stage of highfrequency amplification, a detector stage,a stage of low frequency amplification,and a low frequency detector.

The valves are of the indirectly heat-ed type, the heater current being regu-lated by a ballast lamp which compen-sates a variation of battery between 22and 26 volts, the normal voltage being24 volts.

A relay connected in the plate circuitof the low frequency detector valve op-erates the selector device, whenever aradio signal of required frequency isreceived.

A safety relay is connected in theplate circuit of the second and thirdvalves and operates the alarm bell cir-cuit whenever the receiver ceases towork, either by reason of failure of avalve, or because of failure of the bat-teries. This relay otherwise has no di-rect action on the operation of the auto -alarm device.

A testing buzzer controlled by a pushbutton key located in front of the re-ceiver case is provided to test the work-ing of the complete installation by lo-cal excitation.

A special non -locking key is also pro-vided so that, when desired, the bridgealarm bell can be prevented from ring-ing when the alarm is being tested bylocal excitation. Release of this key au-tomatically reestablishes the circuit ofthe bridge alarm bell.

The complete unit is enclosed in a wa-tertight box which is so arranged as tobe bulkhead or table mounted. The frontof the box is hinged at the bottom.When it is open, the whole unit is read-ily accessible.

Signal Selector

The signal selector registers the gen-uine distress signals and rejects all oth-er signals produced by transmitting sta-tions or atmospheric interferences. Itchiefly consists of:

(1) A bank of relays;(2) A constant speed motor and re-duction gear;(3) A time measuring device.

The selector also contains a signal trans-mission device.

Relay Bank

The relay bank. composed of a mount-ing plate with an assembly of ten relays,is elastically mounted by means of rub-ber pads on another plate which in turnis hinged to a small support fastened tothe rear part of the containing box. Byswinging the hinged plate, easy access isobtained to the soldering lugs of the re-lays and to the cable form.

The ten relays are in three groups.The first is a group of counting relays

JULY -AUGUST, 1935

which register three consecutive dashesof the distress signal. The second groupof relays controls the resetting at zeroposition of the first time -measuringswitch when signals other than distresssignals are received. The third and lastgroup of relays controls and blocks thealarm bell circuit after a correct distresssignal has been registered. The alarmbell circuit can only be released by anon -locking push button key providedfor this purpose on the front of the se-lector box,

Driving MotorThe driving motor is of the series

wound type and is permanently rotatingwhen the equipment is in operation. Itis provided with a governor keepingthe speed constant at 1,617 R.P.M. -±and a reduction gear device which re-duces, the speed to 10.1 R.P.M. To givea signal when the motor speed falls be-low a given value, a special contact in-corporated in the automatic governorcontrols an alarm -bell circuit.Time Measuring Mechanism

The time measuring mechanism is com-posed of a small frame on which twospecial timing switches are mounted. Inline with the timing switches and onthe same frame, the signal transmissioncommutator is assembled. The two tim-ing switches and the signal transmissioncommutator are driven by means ofgears fixed on a driving shaft mountedon the frame by two self -aligning bear-ings. The whole unit is mounted in theselector box and coupled to the motorshaft by means of the reduction gear.

The first switch discriminates amongthe correct and incorrect received signaldashes and controls, by means of its dif-ferent contacts, either the counting re-lays or the releasing and resetting relays.

The second switch verifies the maxi-mum duration admissible for the correctconsecutive signal dashes and intervalsto be recorded.

For the transmission of alarm -signals,the permanently connected transmissioncommutator takes the place of the trans-mitting key and operates in conjunctionwith the ship's transmitting equipment.Alarm signals are automatically trans-mitted by the simple process of depress-ing a key mounted in front of the se-lector box. This operation can be exe-cuted whether the equipment is in theoperating position or at rest. The sim-plicity of starting the alarm transmis-sion is such that the ship is not en-tirely dependent on its operator in timeof distress. It provides means for auabandoned ship to continue to send outthe distress alarm signal, thereby in-creasing the chances of other ships lo-cating her and the lifeboats by meansof their direction finders.Timing Switch

The timing switch consists of a smallframe to which the following parts areassembled:

(a) A spindle on which are mounteda magnetic clutch with its driven gear,the contact brushes, the friction spring,and the main spiral resetting spring.

The driven gear attached to the clutchmagnet is permanently in gear withthe driving gear on the main shaftand consequently keeps the clutchmagnet in continuoun rotation.The clutch armature is freely mountedon the spindle and rotates when at-

tracted by the magnet. It drives, un-der the pressure of the friction spring,a plate to which the contact brushassembly is rivetted.The pressure of the friction spring isadjusted by means of a nut which inturn is securely locked in position onthe armature by means of three setscrews. The main spiral resettingspring is located in a small housinghooked to the armature by means of abayonet joint. One end of the springis fastened to the spring housing andthe other end to a hub fixed at theend of the spindle. When the clutcharmature is attracted and rotates itcarries the contact brush assemblywith it and winds up the resettingspring.(b) An insulated arc on which are as-

nembled the metallic sectors upon whichthe contact brushes driven by the mag-netic clutch make contact.

(c) A contact spring used as a feed-er brush for the magnetic clutch.

The operation of the timing switchesis as follows:

When the clutch magnet is energisedby the relay controlled by the low fre-quency) detector of the receiver, theclutch armature is attracted and startsrotating instantaneously with the con-stantly rotating magnet. The armaturedrives the contact brush assembly underthe pressure of the friction spring androtates it 90° or 185°, depending onwhether the first or the second switch isinvolved. At the end of the movement,a special lug on the brush member buttsagainst a stop provided on the frameand stops the rotation of the brush mem-ber. The contact brush assembly nowslips, although the armature still ro-tates as long as the magnet is energised.When the clutch magnet is deenergised,it releases the armatures and brushmember. These return to their initialposition under the action of the reset-ting spring which has been wound up bythe forward rotation of the brush mem-ber. The resetting movement of the ar-mature and brush member is stoppedwhen the lug on the brush member reach-es the home position back -stop on theframe. There is no rebound as the brushmember is kept against the back -stop bythe inertia of the armature which, slid-ing on the brush member, continues torotate for a short period. Due to thisprinciple adopted in the design of theswitch, the latter has the great advan-tage of starting rotation instantaneous-ly when the magnet is energised and ofreturning to its correct home positionwithout rebounding. The last point isparticularly important since it is abso-lutely essential that, if the switch has tostart almost instantaneously after hav-ing come back to its home position, itshould really start from its home posi-tion and not from any other position ofrebound, as in this case a wrong signalmight be registered or a correct one re-jected.Alarm Bells

Three alarm bells are required by thestatutory rules of the Merchant Ship-ping Act: One of these alarm bells isprovided in the wireless telegraph room,one in the wireless operator's cabin, andone in the captain's quarters on thebridge. The latter can be prevented fromringing when the complete outfit is beingtested by depressing the special key pro-vided for this purpose on the receiver.

Page Fifteen

Antenna Change -Over Switch

A three -pole change -over switch isprovided for changing over from normalreception to auto -alarm reception.

This switch is so connected that onepole transfers the ship's antenna fromthe normal receiver to the auto -alarmreceiver. The two other poles control,respectively, the power supply for thereceiver and relay circuit and the pow-er supply for the motor.

Power Supply and Charging Panel

The power supply consists of a lowtension battery of 24 volts, the currentdrain for the receiver and selector be-ing approximately 2.5 amperes, and ahigh tension battery of 120 volts, thecurrent drain for the receiver being ap-proximately 0.025 ampere.

A spare low and high tension batteryis furnished as a standby.

The charging panel is for operationfrom the ship's mains and includes allthe necessary fuses, switches, and met-ers.

Operation

Before explaining in detail the op-eration, it is necessary to consider thevarious possibilities which may arisewhile the equipment is in service andready to receive the distress signal.

The possibilities are as follows:(1) First dash of correct duration;(2) Second dash of correct duration;(3) Third dash of correct duration;(4) Dash of too short a duration;(5) Dash of too long a duration;(6) Spurious dashes of correct dura-tion;(7) Distress signals superimposed onother signals.Possibilities (1), (2), and (3) cor-

respond to the case of reception of a cor-rect distress alarm signal not marred byany interference.

Possibilities (4), (5), and (6) cor-respond to the case of reception of aspurious signal mixed with interferencesor atmospherics.

Possibility (7) corresponds to thecase of reception of a correct distressalarm signal on which are superimposedother signals or atmospherics.

The general schematic of the A.A.2.auto -alarm is shown in circuit sche-matic. It is assumed that the receiverand selector mechanism have beenswitched on by throwing the antennachangeover switch to the operating po-sition. The equipment is ready for op-eration after the short time necessaryfor the indirectly heated valves to bewarmed up.

(1) First Dash of Correct Duration.When the first dash of a distress signalis received, the rectified current cor-responding to this first dash energisesrelay Sr which pulls up and operates inturn the input relay Ar of the selector.The electromagnet of the first timingswitch MI is energised and the contactbrushes N1 and N'l start rotating. Con-tact brush NI connects negative poten-tial to the contact segment BC maintain-ing the contact on same during the timeof rotation of arm N1 either way. Theother brush N'l leaves the home contactsegment HC. After 3.5 seconds it reach-es segment C4 and energises relay Krlwhich operates and through its frontcontact is placed in series with the wind-ing of relay Lrl which is short-circuited

Page Sixteen

and therefore does not operate.As it is assumed that the received dash

is of the correct length, it will ceasewhile the brush N'l is still on segmentC4 and before it reaches segment C5.

Segment C5 is located on the arc insuch a position that the time brushreaches this contact after 4.5 seconds.

Relay Sr will release at the end ofthe dash, as will also relay Ar. The mag-netic clutch Ml being deenergised, thebrushes Ni and N'l will return to theirhome position under the influence ofthe resetting spring.

As soon as the brush N'l leaves thesegment C4, relay Lrl is no longershort-circuited. It becomes energised andcauses the following operations,

(a) By means of its contact 2, ittransfers segment C4 to the secondgroup of counting relays Kr2 and Lr2in order to allow the recording of thesecond dash, provided this dash be ofcorrect duration.(b) Through its contact 3, it ener-gises the magnetic clutch M2 and thetiming brush N2 starts rotating.(2) Second Dash of Correct Duration.

When a second dash of correct duration,succeeding a first correct signal, is re-ceived, the cycle of operations describedabove will again take place, but insteadof energising relay Krl, the brush N'lnow energises relay Kr2.

When the second signal ceases, thetime -arm N'l leaves the segment C4, andrelay Kr2 locks up in series with thewinding of Lr2 which operates.

By means of the front contact of re-lay Lr2, segment C4 is now connected tothe third group of counting relays Kr3and Lr3 and the circuit is ready for therecording of a third dash of correctduration.

(3) Third Dash of Correct Duration.When a third dash of correct durationis received, the same sequence of opera-tions will be repeated as previously de-scribed for the first and second dashesbut now the brush N'l will energise,through segment C4, relay Kr3 whichlocks up in series with the winding ofrelay Lr3 as soon as the signal hasceased, that is to say, when brush armN'l leaves segment C4. Relay Lr3 thenoperates, closing its front contact 2.

When the brush arm N'l has returnedto its home position, the alarm bell cir-cuit is established. At the same time re-lay HT operates and locks up over itsown contact, maintaining the alarm -bellsoperated.

It should be noticed that 12.4 secondsafter the recording of the first dash ofcorrect duration, the brush arm N2makes contact with segment C13, thusenergising relay Gr which operates. Theback contact 2 of relay Gr breaks. Thisopens the feeding circuit of counting re-lays Lrl to Lr3 and Krl to Kr3 and allthese relays come to rest. The magneticclutch M2 is no longer energised andthe brush arm N2 returns to its homeposition by means of the resetting spring.The selector is now ready to record oth-er alarm signals.

Should still another correct distresssignal be received, the circuit operatesas before, but the alarm bell circuit it-self remains independently closed. Tostop the alarm bells from ringing it isnecessary to depress key RK which op-ens the alarm bell circuit and the lock-ing circuit of Hr.

'(4) Dash of Too Short a Duration,.

Any signal having a wavelength between585 and 615 metres will energise relaysSr and Ar and consequently the magnet-ic clutch Ml.

As the duration of the signal is be-low 3.5 seconds, the brush -arm N'l can-not reach segment C4 before the ter-mination of the signal. When the signalceases, the brush arm N'l returns to itshome position.

As soon as the signal has ceased, relayAr is deenergised and closes its back con-tact 2, causing relay Er to energise andlock up through its front contact 1. Atthe same time, the back contact 2 of re-lay Er breaks and opens the feeding cir-cuit of magnetic clutch MI.

(5) Dash of Too Long a Duration.The rectified current generated by theincoming signal having energised relaysSr and Ar and the electromagnet Ml,the time brushes NI and N'l start ro-tating as if a correct signal had beenreceived.

After 3.5 seconds, contact arm N'lreaches segment C4 and energises relayKr (1, 2 or 3) which operates and thruits front contact is placed in series withthe winding of its associated relay Lr(1, 2 or 3). Relay Lr does not operateas its winding is short-circuited. As weassume the dash to be of a too long du-ration, the brush N'l will continue torotate, and will pass on to segment C5,causing relay Gr to be energised and thefollowing operation takes place:

(a) The opening of the back contact2 of relay Gr causes the feeding cir-cuit of the counting relays to be brok-en, and so annuls the signals whichmay already be recorded. Relay Lrlis deenergised and its contact 3 opens,thus deenergising the magnet -clutchM2. The timing brush N2 stops rotat-ing and returns to its home position.(b) By the closing of the front con-tact I of relay Gr the latter locks it-self.When the signal ceases, the magnet

clutch M1 is deenergised and the brush-es NI and N'l return to their home po-sition. As long as brush Ni is in con-tact with segment BC, the relay Er re-mains locked and prevents the recordingof the signal during the passage ofbrush NI over segment C4.

Relay Er will release and bring backthe magnetic clutch circuit to normalonly when brush arm NI has left seg-ment BC and has returned to its homeposition. In this way, if another signalis received during the return to its homeposition of timing switch Ml, this sig-nal will be without effect.

(6) Spurious Dashes of Correct Dura-tion. Due to the superimposing of sev-eral radio signals and also due to at-mospheric interference, it may happenthat relay Sr in the receiver remainsenergised during a duration of time cor-responding exactly to the duration of adash originated by a distress signal.

In this case, the selector will operatein a similar way as when a firsh dash ofcorrect duration is received. Counting re-lays KO and Lrl will lock up and thetime brush N2 will start rotatng.

If the signals following are of tooshort a duration, the operation of the se-lector will be the same as in the case ofa received signal of too short a dura-tion.

Here again it should be noted that 12.4seconds after the recording of the cor-rect signal, the time brush N2 will, come

COMMERCIAL RADIO

Total Operating Revenues ofDifferent Radio -Telegraph Concerns

Year, 1935 Jan. Mar. Apr.

Central Radio Telegraph Co. $43.11 $260.48Globe Wireless, Ltd. $25,296.49 $26,437.86 30,252.41 28,519.72Mackay Radio & Tel. (Cal.) 79,026.08 74,982.47 83,119.94 87,174.86Mackay Radio & Tel. (Del.) 65,006.73 59,227.59 65,862.15 66,857.78Magnolia Radio Corp. 209.10 251.30 212.40 191.68Mutual Tel. Co. (Wireless) 4,235.25 3,902.61 4,073.11 4,207.09Olympic Radio Co. 174.57 174.96 175.93Pere Marquett Radio Corp. 788.48 734.52 677.94 1,145.94RCA Communications, Inc. 353,398.11 310,271.41 345,986.89 333,605.09Radiomarine Corp. of Amer. 71,069.38 70,947.00 75,984.34 76,065.88Tidewater Wireless Tel. Co. 367.55 380.10 501.27 322.36Tropical Radio Telegraph Co. 71,776.53 45,717.31 58,048.63 57,433.14U. S. -Liberia Radio Corp. 4,925.94 5,762.33 5,406.50 5,006.11Wabash Radio Corp. 957.37 995.08 1,264.70 1,030.68

into contact with segment C13, annul-ling the previous' recording. If the sig-nals following are of too long a dura-tion, the selector will operate as in thecase of a received signal of too long aduration and the selector will be broughtback to its normal position.

If a second dash of correct durationtakes place during the time interval of12.4 seconds following a first correctdash, it will be recorded as a seconddash of correct duration.

In order that the selector may operatethe alarm bells, it is necessary that athird spurious dash of correct durationbe produced before the brush arm N2reaches segment C13. The probability ofsuch a happening is very remote indeed.

(7) Distress Signals Superimposed onOther Signals. Simultaneously with thedistress signal, other signals may be re-ceived with the following result:

(1) The duration of the dashes maybe lengthened in a proportion rather dif-ficult to determine exactly. Practice hasshown, however, that this lengthening inmost cases is of the order of 0.5 secondmaximum.

(2) The intervals between consecutivedashes may be filled by spurious signalsof short duration, even to the point ofcompletely disappearing, thus prevent-ing any accurate determination of theduration of intervals between the dash-es.

Under these conditions, the receivedsignal corresponds to:

(a) Three dashes having a durationnot exceeding 4.5 seconds each. In thiscase, the selector will work as ex-plained above for a correct sequence ofsignal dashes. If a signal due to in-terference is received during the in-terval of time separating two consecu-tive dashes, the selector will functionas for a dash of too short a duration.(b) Normal dashes mixed with dash-es of too long a duration. In this case,the normal dashes are recorded. Toolong a dash succeeding one or twocorrect dashes will annul the previousrecording and the selector will startagain to record new signals.As has been previously stated, the

"automatic distress signal" consists oftwelve dashes sent out in one minuteand, provided that the receiver can de-tect out of the twelve, three consecutivedashes of correct duration, the selectorwill record them and cause the alarmdevice to operate.

JULY -AUGUST, 1935

Results of Practical TestsThe type A.A.2.B. equipment as de-

scribed above was submitted for approval to the General Post Office of GreatBritain, which carried out the followingtrial tests:

(a) The complete outfit was installedin a small building along one of thequais at Ramsgate, situated at thenorthern entrance of the Dover Straits.At this particular spot, the interfer-ence from numerous ships and coastaltransmitting stations is exceedinglyheavy.(b) The receiver was locally excitedby an oscillator operating on a wave-length between 585 and 615 metres,and "distress signals" were keyed bya Weston transmitter. Eleven differ-ent combinations of signals, takinginto consideration the different toler-ances on the duration of the dashesand the intervals, were sent out. Eachcombination was repeated ten consec-utive times. Under these conditions,there were no failures in the operationof the auto -alarm.(c) According to the Board ofTrade's Statutory Rules and Orders,1932, No. 897, the equipment when in-stalled in an area of intense interfer-ence for a continuous period of sixweeks, must not give more than twofalse calls in any week, while on the.other hand, it must respond to 90per cent. of test calls.For these tests, the receiver was con-nected to an antenna and the "dis-tress signal" received /consisted oftwelve dashes of 4 seconds separatedby intervals of one second, the trans-mission of the signals being made atrandom intervals.During these tests, lasting for twomonths, there were only eight failuresto respond to the test calls out of atotal of 700, although the test condi-tion allowed 70 such failures.Although the "distress signal" wastransmitted only during certain per-iods, the equipment was permanentlyin service and was subjected to theaction of atmospherics and signalsother than alarm signals. Not morethan the prescribed two false calls inany one week were recorded duringthe testing period..(d) During the test, the equipmentwas placed in an oven as required bythe Board of Trade Rules, and raised

to a temperature of 113° F. for twohours on every third day for fourweeks. The efficiency of the equipmentwas maintained during the operationof this test.In addition to the foregoing, the equip-ment was also subjected to anothersevere test, which may be called the"bumping test." The apparatus wasmounted on a platform which wascapable of being rocked about, andof being dropped vertically througha distance of three inches every sevenseconds. This rough treatment, con-tinued for one hour a day for fourweeks, did not affect the efficiency ofthe apparatus, or its ability to func-tion satisfactorily during the actualperiods of "bumping.''As a result of the above mentioned

trial tests, the equipment was approvedby the General Post Office of GreatBritain for installation on board of allcompulsorily fitted ships.

AIRWAY NEWS

RUMORhas it that Tom Wollon is

looking for another place to live.-The operator in charge at Nashville Air-way Radio and Range Station has beenholding his ear to the ground and it isbelieved that he is expecting to be or-dered to Sky Harbor.-This will meanselling or renting his home and movinghis family (wife and two pretty girls).-The present indications are that theDonelson station will be remotely controlled from Sky Harbor and that someof the present personnel will be releasedto other stations.-Sky Harbor is 25miles from Nashville but is extremelyinconvenient to operate the Departmentof Commerce Weather Bureau at SkyHarbor and have the radio personnel alllocated some eighteen miles away atDonelson.-The Bureau has started sev-eral times to build better radio facili-ties at Sky Harbor but Nashville's lat-est action and sentiment in regard tobuilding herself an airport that wascloser in is probably the cause of theAir Commerce Bureau holding backwith its Combined Range and BroadcastStation for Sky Harbor.

* *

Charley Goldtrap, America Air Linesacting Flight Superintendent, is a firmbeliever in radio facilities and he knowshow to use them, too.-He is blind land-ing and beam flying instructor fortransport pilots and can land and takeoff with a covered cockpit.-Charley hasone of the finest note books giving com-prehensive sketches of each airport andthe radio facilities available there thatyour correspondent has ever seen com-piled.

* * *

The Second Air Navigation DivisionDistrict Headquarters, Atlanta, Ga., hashad a new assistant manager appointedto take the place of Mr. VanderWater,now in the First District. The new as-sistant for Mr. Irl H. Polk is Mr. R. C.Copeland, and he is said to be a nephewof Senator Copeland.

Only two other stations in the entirecountry use the same letters of the al-phabet as does KROW of Oakland andSan Francisco. They are WORK atYork, Penna., and WROK at Rockford,Dl.

Page Seventeen

RADIO OPERATORSExperimental Visual Broadcast

Stations in the United StatesWIN A RISE IN PAY

Arbitrator Sets Up a Scale Basedon $155 a Month for Chiefs

of Class A Ships

UNION IS RECOGNIZED

Working Day Is Reduced to 8Hours-Attitude of Both

Sides Is Praised

ANEW wage schedule providing $155a month for the chief operator on

Class A ships, an increase of $45 overprevious rates, and the reduction ofworking hours from 12 to 8 a day areincluded in the findings of Ben Golden,associate director for the Regional La-bor Board, who was recently named ar-bitrator in the controversy between theInternational Mercantile Marine Compa-ny and the American Radio TelegraphistsAssociation, Inc. In a decision handeddown yesterday afternoon Mr. Goldenfurther ordered the steamship companyto recognize the union.

The appointment of Mr. Golden as ar-bitrator followed the unexpected strikeof three radio operators which held theManhattan at her pier for five and a halfhours after her sailing time on June 19.At the end of that strike P. A. S.Franklin, president of the I. M. M.,made a tentative agreement on wagesand hours pending a final decision byMr. Golden, who was selected by bothsides as arbitrator.

The $155 -per -month salary for chiefoperators ordered by Mr. Golden is $30below the maximum wage schedule of$185 agreed to by Mr. Franklin in hisnegotiation with the strikers on the pierof the Manhattan. Likewise, Mr. Gol-den's order for a $140 monthly pay forthe first assistant is $45 above the pre-vious schedule but is $35 below the $175-a -month agreement which the strikerswere able to extract from Mr. Frank-lin.

In a statement accompanying his de-cision, the arbitrator praised the cooper-ation shown him both by the radio op-erators and the steamship company.

" Your cooperator has found that thecompany has recognized the spirit of thetimes and is willing to grant the mentheir rights of bargaining collectivelythrough an agency of their own choos-ing," the statement read. "The policylaid down by the United States Govern-ment, as evidenced by the Wagner LaborDisputes Bill, has been strictly followedby the company.

''Your arbitrator further feels thatthe association of radio operators hasshown itself to be genuinely interested inbettering the laboring conditions of itsmembers, and that it has shown an un-derstanding and appreciation of theproblems of the steamship company. Theassociation has secured for its members

Page Eighteen

W10XX

W2XDRW8XANW9XKW9 X A T

Call PowerLetters (watts) Company Location

W2XDR2000-2100 kilocycles

500 Radio Pictures, Inc. Long Island City, N. Y.W8XAN 100 Sparks-Withington Co. Jackson, Mich.W9XK 50 University of Iowa Iowa City, Ia.W9XAK 125 Kansas State College of Agri- Manhattan, Kan.

culture and Applied ScienceW6XAH 1000 Pioneer Mercantile Company Bakersfield, Calif.

2750-2850 kilocyclesW3XAK 5000 National Broadcasting Co. PortableW9XAP 2500 National Broadcasting Co. Chicago, Ill.W2XBS 5000 National Broadcasting Co.W9XAL

Bellmore, N. Y.500 First National Television Corp. Kansas City, Mo.

W9XG 1500 Purdue University West Lafayette, Ind.W2XAB 500 Atlantic Broadcasting Corp. New York, N. Y.

42000.56000, 60000- 86000 kilocyclesW2XAX 50 Atlantic Broadcasting Corp. New York, N. Y.W6XAO 150 Don Lee Broadcasting System Los Angeles, Calif.W9XAL 150 First National Television Corp. Kansas City, Mo.W1XG 500 General Television Corp. Boston, Mass.W9XD 500 The Journal Company Milwaukee, Wis.W2XBT 750 National Broadcasting Co. PortableW2XF 5000 National Broadcasting Co. New York, N. Y.W3XE 1500 Philadelphia Storage Battery Co. Philadelphia, Penna.W3XAD 2000 RCA Manufacturing Co., Inc. Camden, N. J.

& 3000050 RCA Manufacturing Co., Inc. Portable -mobile (vicinity of

Camden)1000 liadio Pictures Long Island City, N. Y.100 Sparks-Withington Company Jackson, Mich.100 University of Iowa Iowa City, Ia.500 Dr. George W. Young Portable

Relay Broadcast Stationsin the United States

Fre-quency Power Call

Ice kw Letters6040 5 W1XAL6040 2.5 W4XB

6060 1 W3XAU6060 10 W8XAL6080 .5 W9XAA6100 35 W3XAL6100 10 W9XF6120 5 W2XE6140 40 W8XK9530 40 W2XAF9570 40 W8XK9570 10 W1XK9590. 1 W3XAU

11790 5 W1XAL11830 5 W2XE11830 .5 W9XAA11870 40 W8XK15210 40 W8XK15250 5 W1XAL15270 5 W2XE15330 25 W2XAD17780 40 W8XK17780 35 W3XAL17780 .5 W9XAA17780 10 W9XF21460 5 W1XAL21540 40 W8XK

CompanyWorld Wide Broadcasting Corp.Isle of Dreams Broadcasting

Corp.WCAU Broadcasting Co.The Crosley Radio Corp.Chicago Federation of LaborNational Broadcasting Co. Inc.National Broadcasting Co. Inc.Atlantic Broadcasting Corp.Westinghouse Elec. & Mfg. Co.General Electric CompanyWestinghouse Elec. & Mfg. Co.Westinghouse Elec. & Mfg. Co.WCAU Broadcasting Co.World Wide Broadcasting Corp.Atlantic Broadcasting Corp.Chicago Federation of LaborWestinghouse Elec. & Mfg. Co.Westinghouse Elec. & Mfg. Co.World Wide Broadcasting Corp.Atlantic Broadcasting Corp.General Electric Co.Westinghouse Elec. & Mfg. Co.National Broadcasting Co. Inc.Chicago Federation of LaborNational Broadcasting Co. Inc.World Wide Broadcasting Corp.Westinghouse Elec. & Mfg. Co.

LocationBoston, Mass.Miami Beach, Fla.

Newtown Square, Penna.Mason, Ohio.Chicago, Ill.Bound Brook, N. J.Downer 'a Grove, ft.Wayne, N. J.Nr. Saxonburg, Penna.So. Schenectady, N. Y.Nr. Saxonburg, Penna.Millie, Mass.Newtown Square, Penna.Boston, Mass.Wayne, N. J.Chicago, Ill.Nr. Saxonburg, Penna.Nr. Saxonburg, Penna.Boston, Mass.Wayne, N. J.So. Schenectady, N. Y.Nr. Saxonburg, Penna.Bound Brook, N. J.Chicago, Ill.Downer 'a Grove, Ill.Boston, Mass.Nr. Saxonburg, Penna.

both a substantial increase in wages anda reduction in working hours.

" The intelligent cooperation on bothsides will go far to avert unnecessary in-dustrial strife."

The decision also calls for a continuousvacation of three weeks with pay foreach radio officer for each three-yearperiod. In the past, radio operators re-

ceived no vacations.

Roy A. Pyle, vice president of theAmerican Radio Telegraphists Associa-tion, called the decision "fair and satis-factory." While the decision of the ar-bitrator does not establish working con-ditions as good as those now existing onthe Pacific coast, it does mark a "no -

(Continued on Page 21)

COMMERCIAL RADIO

ASSIGNMENTS

Radio officers assigned Mackay Radio,New York:Yorba Linda-T. J. BurnsShawnee-P. B. Kimball (Jr.)San Jacinto-E. H. Cole (Chief)Black Osprey-R. C HorscroftManhattan-F. W. Kent (4th)Manhattan-W. E. Smith (5th)Thos. P. Beal-J. J. BambergSage Brush-A. AdamsonCherokee-T. J Cain (Jr.)W. R Keever-C. R. HamiltonScanpenn-H. Weinstein (Chief)Edouard Jeramec-.H. McGoldrick (Ch.)Edouard Jeramec-M. Gardiner (2nd)Edouard Jeramec-R. C. Williams (3rd)City of Fairbury-W. R. WeberShawnee-A. Sopko (Jr.)

Short Wave Programsfor Waldorf Guests

(Continued from Page 12)proximate lengths of 12.5, 25, and 50meters, arranged as shown in the illus-tration at the head of this article. Thisarrangement permits reception of allfrequencies from 2200 to 25,000 kilo-cycles except for a slightly lower re-sponse over the narrow range 3600to 4800 kilocycles. This low fre-quency range is extended and re -en-forced, however, by using the verticallead-in wire from the horizontal doub-lets as a vertical antenna. Such anarrangement, with the lower end of thevertical antenna connected to groundthrough the coupling transformer, actsas a vertical doublet with its lower halfburied in the ground, and responds toodd multiples of wave -lengths of fourtimes its length. By suitable "loading"the effective length of this vertical sec-tion may be considerably modified and,as arranged at the Waldorf, the verticalsection of about 100 feet which is "load-ed" by the doublets responds to fre-quencies of 800, 2400, 4000, 5600 kilo-cycles, etc. By design, however, the re-sponse of this vertical section to fre-quencies above 6000 kilocycles is pro-gressively nullified in the special coup-ling transformer to the radio -receivertransmission line.

The manner of covering the wide fre-quency range by these horizontal doub-lets and the vertical half doublet is indi-cated in Figure 3. Here the odd -multi-ple response frequencies of the variousantennas are indicated by the verticallines, while the horizontal lines indicatethe frequency range brought in, allowinga 20 per cent spread on each side of themultiple frequencies. The vertical lead -

JULY -AUGUST; 1935

in consists of two wires twisted togetker-one wire being connected to each halfof the horizontal doublets. The currentfrom the horizontal antennas comes downone of these wires and up the otherthus traversing the vertical section inboth directions. The current induced inthe vertical section, however, travels inthe same direction in both conductors.The special transformer at the foot ofthe vertical lead allows both of thesecurrents to be fed to the radio appara-tus, but shuts off the higher frequen-cies from the vertical part of the an-tenna.

Most transmitting antennas are ef-fectively vertical rods, and the walesthey emit are vertically polarized-pp(

Fig. 5-In the intermediate -frequencyamplifier, shown undergoing inspectionby F. Stevens, Radio Technician of theWaldorf, the power of the signal is in-creased a hundred thousand million fold

riding the greatest effects on vertical re-ceiving antennas. In traveling great dis-tances, however, these waves undergo aseries of reflections between the earthand the ionized regions of the upper at-mosphere. By this multiple reflectiontheir vertical polarization is changed toan elliptical polarization, with the resultthat they may produce even greater ef-fects on a horizontal antenna than on avertical one. For this reason the hori-zontal structure used at the Waldorfis very sensitive to waves coming fromremote points, where because of thegreat distances involved the greatestsensitivity in reception is required. Thisform of antenna will also minimize in-terference by nearby stations, the wavesof which are vertically polarized. Ithappens, moreover, that the waves frommost man-made sources of interferenceaffect a horizontal doublet much lessthan a vertical antenna. Most of thisform of interference is at the higher fre-quencies and thus does not prove objec-tionable over the range from 2000 to6000 kilocycles where the vertical sectionof the antenna becomes effective. Sta-tions operating at these lower frequen-cies are for the most part local, repre-senting mainly police, aviation, and am-ateur radio telephone channels. Thesewaves retain sufficient of the verticallypolarized component to be readily pickedup by the vertical antenna.

This multiple antenna system is thushighly suited to picking up high -frequen-cy signals coming from great distancesand lower frequency signals from near-by stations, both with a large signal-to-noise ratio compared to vertical re-ceiving antennas. The effectiveness of theantenna is further enhanced, however, bytaking advantage of the directional char-acteristics of a horizontal doublet.Greatest sensitivity is obtained for wavesarriving in a direction at right anglesto the doublet. In Figure 4 is a mapof the world in gnomonic projectioncentered at New York. The distinguish-ing feature of such a scheme of projec-tion is that a line joining New Yorkand any part of the world lies in thetrue direction over which radio waveswould travel. The horizontal antennasystem of the Waldorf-considerably en-larged in scale-is superimposed on thismap at New York, and it is at once ev-ident that waves from most of the in-ternational broadcast stations wouldreach the antenna from a favorable di-rection. The end -on directions of theantenna are toward the South Atlanticand North Pacific oceans where thereare practically no stations, but evenend -on, the antennas have some responsebecause the short-wave signals arrive ata slight angle above the horizontal.

With these facilities the Waldorf isnow in a position to offer its patronsshort wave radio broadcast programs ofa high order of merit. Short-wave sta-tions in London and Daventry, Eng-land, in Paris, France, in Madrid, Spain,in Koenigswusterhausen, Berlin, Ger-many, at Rome and in the Vatican, canbe as readily heard as local broadcaststations under favorable conditions. Ev-en the short-wave stations in remote lo-cations such as Moscow, Tokyo, Rabat inMorocco, Melbourne in Australia, andthe various South American stationswill at times be available for instruc-tion and amusement.

Page Nineteen

An Efficient Ma-rine Transmitter

rE Internationa I Marine Radio Com-pany 's type M. 100.D. radio trans-

mitter provides facilities for C.W. andI.O.W. telegraphy on the medium andshort wave ship -to -shore bands.

The installation possesses several fea-tures which have not hitherto been in-corporated in a ship's radio equipment.The short wave transmitter, for exam-ple, has been specially designed to meetthe high standard of frequency stabilitynow called for by the Regulations ofthe International Radio Telegraph Con-vention. In addition to its wide rangeit is notable for two special features,viz., master oscillator control over thewhole wave band and crystal control onany two selected spot waves. These fea-tures not only ensure that its operationmeets international requirements but al-so that communication is maintained atmaximum efficiency on the medium waveband.

Particular attention has been given tothe requirements of safety to life at sea,an automatic sending key being sup-plied with the equipment which, in theevent of distress, enables the operator tosend out the alarm signal without handmanipulation, thereby leaving him freeto attend to other important matters atsuch a critical moment. At the sametime the mechanical accuracy of thistransmission ensures the reception of thealarm signal by the auto alarm appara-tus installed on other ships in the vicin-ity.

The wavelength range and power con-sumption of this equipment are:

Wavelength Range: 22.4-24.4 and 33.7-36.6 metres, 550 to 850 metres.

Power consumption from Mains: 1.9kw.

Power Consumption from Batteries(Emergency): 300 watts.

The equipment has been approved bythe British Board of Trade and the Brit-ish Post Office as meeting all the re-quirements of the Safety of Life atSea and International Radio -telegraphRegulations.

The following is an extract from theNautical Magazine, describing the excel-lent results obtained by the Anglo-SaxonPetroleum Company with this type ofequipment, which has been installed aspart of the radio equipment on theirmost recently commissioned tankers.

"The four 12,000 ton tankers built inGreat Britain for the Anglo-Saxon Pe-troleum Co., have all passed into com-mission after very successful trials. Allthese vessels had a speed of 13 knots inloaded trim. They are fitted with allthe latest appliances including the newshort and medium wave wireless equip-ment supplied by the International Ma-rine Radio Co. of London. The firstship Ancylus while on trials off the Tynecalled up an American station which re-ported the reception was excellent. Thesecond vessel Acavus, while on trials inBelfast Lough, called up and spoke toher sister ship the Ancylus which wasthen over 3,000 miles away and nearingthe West Indies. Again the sending andreception from both ships were excel-lent. Acavus communicated with theshort wave station at Portishead everyother day during her voyage to Curacaoand was then ordered through the Panama Canal to San Pedro. It then be-came a real test, for while in the Pacificand right up to the day before arrivalat San Pedro, she was in direct commu-nication with Portishead, a distance of5,400 miles. The direct line to ship'sposition was across the Atlantic andright across the United States. Thelast two ships, Anadara and Amastra,while on trials at the entrance to theFirth of Clyde, were both in communi-cation with the Ancylus which was then2,000 miles out in her voyage to theWest Indies. These results will aston-ish the average shipowner and seafaringman because we have imagined up to thepresent that the range of an ordinarywireless as fitted in our ships was 500 to700 miles at the utmost. But what hasbeen a dream has now come true, andthis new direct service with Portisheadas the receiving station for Great Bri-tain is in full operation. What has beenthe privilege of the big liners up to thepresent is now open to the MercantileMarine as a whole. This new develop-ment has only been made possible bythe introduction by the InternationalMarine Radio Co. of their new crystalcontrol short wave. It was introducedfor the first time on a cargo boat ortanker on the Ancylus, this crystal con-

trol having hitherto been exclusively con-fined to large passenger vessels. Insteadof waiting days for a reply to a messagesent, while it was being relayed by othervessels, the direct communication nowoffered enables a reply to be received thesame night of the next day. Then againthese ships are acting as wireless trans-mitting stations sending messages fromother vessels which have only mediumwave equipment. This is indeed a greatstride ahead and shipowners will bequick to see its advantages."

NIKOLA TESLA NOW 79On July 10, 1935, Nikola Tesla, well

known member of the scientific worldcelebrated his seventy-ninth birthday.Tesla, as is usual on his birthday celebra-tions called attention to several of his"pet" developments. Listing them him-self, he believed would come to be hisgreatest development, the one by whichmechanical energy can be transmitted toany part of the terrestrial globe. Thosewho have followed Tesla's thoughts formany years will be familiar with the ma-ny plans he has worked on for this.

Second, he placed a new method andapparatus for producing direct currentwithout a commutator. He said he hasfound a solution to this problem, but de-tails were not made public.

New Orleans Airway RadioStation on Ancient Graveyard

During the last two months the FERAand Tulane University have been under-taking excavations in the marsh landalong the banks of Lake Pontchartrainand have discovered some extremely interesting material in the old shell banksnear Hayne Blvd. and the road fromShushan Airport along the lake front.

Several skeletons were removed fromthe shell right under the loops of theNew Orleans Radio Range Station andIndian pottery, beads, arrowheads, andother relics and remains are constantlybeing unearthed. The skeletons are be-lieved to be those of Indians and whilethe Smithsonian and Tulane experts havenot made a, complete study as yet, it isthought that the graves are very old,probably pre-Columbian.

At the present time many of the bonesand skulls are lying on the ground asthey were first uncovered preparatory tobeing photographed and it is a rathergruesome and ghostly sight to see theseold boys grinning at one with their emp-ty eye sockets staring so intently. Theseskulls show wonderful teeth almost with-out exception.

Gov't Price for CommunicationOn June 27, 1935, the Federal Com-

munication Commission, in Order No. 15,sheet 13,518, issued a lengthy order cov-ering "Rates of Pay for GovernmentCommunication by Telegraph." Thoseinterested' may secure copies by writingthe Secretary of the Commiasion.

Page Twenty COMMERCIAL RADIO

MULTIVIBRATORS(Continued from Page 9)

divide into 1; this gives the timeslant in seconds.

ory of oscillations," Proc. IRE,Vol. 22, No. 9, Sept. 1934

-Papers dealing exclusively with thecon- theory of oscillations produced in

the multivibrator:

(2) Divide the time constant by theSUM of the condensers in micro -farads;the result gives the value of each gridleak resistor in ohms.

ILLUSTRATION: Given a frequen-cy of 50 KC/sec. and two 500 uufd con-densers. Find the value of the grid leakresistors to obtain the given frequency.

SOLUTION:

1

(1) .00002 or 2 x 10' seconds50,000

2 x 10 5 2 x 10-5(2)

(5 x 10-10) + (5 x 10'") 10 °

= 20,000 ohms per grid leak resistor

Producing Sinusoidal Oscillations in aSymmetrical Circuit

In an engineering paper by Y. Wa-tannabe7 (Japan), it was shown that sin-usoidal oscillations could be produced ina symmetrical multivibrator if capaci-ties Cx and Cy were shunted across theplate resistors in the respective circuits.Mr. Watannabe says, "If the shuntedcapacities Cx and Cy has some givenvalue, sinusoidal oscillations could beproduced under the following conditions:

1 1 1 CxGm = - - (1 -)

Rp R, R2 Cy

Where G. and Rp are respectively themutual conductance and the plate re-sistance. The angular velocity of thevector representing the sinusoidal oscil-lation is

1 1 1 1

R,C Cx 11 ri

When the system is arranged to func-tion as a producer of sinusoidal oscilla-tions, the operating condition of eachtube must be adjusted to give the maxi-mum value of mutual conductance; thatis, the point of equilibrium with respectto the direct current must be nearly inthe middle of the characteristic curve.It is an interesting fast that one canproduce either sinusoidal or relaxation -oscillations by means of a two -tube sym-metrical multivibrator by simply vary-ing one of the anode capacities over acertain setting.,'

(To be continued)cID cD

Bibliography of Part 1

1-A. Andronow and A. Witt, "Un-stetige periodische Bewegungen unddie Theorie des Multivibrators vonAbraham und Bloch "-ComptesRendus de l'acad. des Sci del'URSS, pg. 189, 1930

2-B. van der Pol,gen 1," Physics,1926

.3-B. van der Pol,

"Relaxatietrillin-Vol. 16, pg. 154,

"Non linear the -

7 See loc. cit. No. 6.JULY -AUGUST, 1935

4-B. van der Pol, Jahr. de draht Tel.und Tel., Vol. 28, pg. 178, 1926

5-E. Friedlaender, Arch. f. Elektr.,Vol. 17, pg. 103, 1926

6-.43. van der Pol, Jahr. der drahtTel. und Tel., Vol. 29, pg. 114, 1927

7-E. Friedlaender, Arch. f. Elektr.,Vol. 20, pg. 158, 1928

8-E. Sehirl, Arch, f. Elektr., Vol. 20,pg. 346, 1928

9-Y. Watannabe, Jahr. de draht Tel.und Tel., Vol. 32, pg. 77, 1928

10-J. Mercier, "Oscillateurs Symmet-riques et Multivibrateur," L 'OndeElectrique, Vol. 13, No. 149, May,1934

RADIO OPERATORSWIN A RISE IN PAY

(Continued from Page 18)

table" advance over the "abominable''situation preceding the strike, he said.

The detailed monthly pay schedulefollows:

Class A Ships

Chief Radio OperatorFirst AssistantSecond AssistantThird Assistant

Class B Ships

Chief Radio OperatorFirst AssistantSecond Assistant

Class C Ships

Chief Radio OperatorFirst AssistantSecond Assistant

$155140125120

$155130120

$120110100

Class D Ships

Operator $110(N. Y. Times, July 6, 1935)

CAN SERVE ONLY ONETen prominent officials of communi-

cations companies who sought permissionof the Federal Communications Commis-sion to serve as officers or directors ofmore than one carrier subject to theCommunications Act, were denied thatright, on June 10th, by the FederalCommunications Commission.

The petitioners were: SosthenesNewcomb Carlton, Edwin F. Carter, Ed-win F. Chinlund, E. Y. Gallaher, FrankL. Polk, Walter S. Gifford, John J. Hal-pin, David Samar, and Lewis MacCon-neck

Commissioners Walker, Payne, Case,Sykes and Prall voted in the negative,Commissioners Stewart and Brown voted

in favor of granting said petitions.

The order was made effective August9, 1935.

Federal Communications

Commission Memorandum

The Commission on July 2, 1935, di-rected that the present Rule 258 be re-numbered as Rule 258(a). In addition,the Commission adopted Rule 258(b) asfollows:

258(b) Airport marker beacon trans-mitting equipment will not be separatelylicensed, but shall be described in the ap-plication for construction permit andlicense for the airport station with whichit is associated. When such an applica-tion is approved the marker beacontransmitting equipment will be consid-ered as an integral part of the airportstation and its authority for operationwill be included in the instrument of au-thorization for the airport station. Air-port marker beacons may be operatedduring periods when no interference willbe caused to airport radiotelephone com-munication. The frequency to be usedby marker beacons shall be 1000 cyclesplus or minus the frequency assigned theairport station, and the transmittingequipment shall be installed so that thedirection of radiation will be substan-tially vertical.

HERBERT L. PETTEY, Sec.

NEW APPARATUSONE radio development of the year is

the announcement of P. R. Mallory& Co., Inc., that the well-known line ofMallory Replacement Vibrators is nowcomplete-and completely competitive.At the moment more than 50 per cent ofthe two million vibrator units new inuse en all makes of automobile radioreceivers are Mallory Vibrators. In thefuture this will be greatly increased. Inthe past the service man was limited byreason of limitations of the line. Hispractice, based on performance, was toreplace with a genuine Mallory Vibratorwherever he could. Now new types andnew low prices enable him to meet vibra-tor replacement requirements with Mal-lory Replacement -Vibrators.

In 1934 Mallory Replacement Vibra-tors were available for the followingsets: Admiral, Airline, Arcadia, Audio -la, Belmont, Blackhawk, Bosch, Cadillac,Captain, Colonial, Commander, Console,G -E, Governor, Gulbransen, Lafayette,Lt. Governor, Majestic, Motorola, Pilot,President, R. C. A. -Victor, Recorder, So-lar, Star, Stromberg-Carlson, Tropic -Aire, Truestone, Truevalue, Wells -Gard-ner.

Additional auto radio sets for whichPage Twenty-one

Mallory Replacement Vibrators are nowavailable include Buick -Olds -Pontiac980383, 980393, 980455, 980459; BuickPontiac 544245, 544246; Chevrolet 364-441, 600153, 600566, 600249, 600565, 601-038, 601176, 601177; Clarion 100, TC50;Consolidated 51; Crosley 98, 99, 102, 103,119, 5 A2, Detrola 60, 1100, 1100A; De -weld 52, 61, 640; Electric Auto-Lite 062,062A; Emerson 965-667, 5A, 678-1, 678-2; Erla Sentinel 5500, 602, 603; Fade101, 102, 104B; Fairbanks -Morse 346,347; Ford (Majestic) 40, 18805; Ford(Philco) all; Ford (Lincoln) all; Fed-erated Purchaser 92, 92A, 94A, 460;Freed A9; General Motors (Canada)135; Graybar 15 (Chassis) Grebe 61-R;Harley-Davidson, all; Hudson Terra -

plane (Majestic Head) ; InternationalK-60; Larkin Company 91; Mission Bell10A, 11, 12, 14, and 25A; MontgomeryWard 87, 62, 118; Auto Radio 5Y chas-sis; Oldsmobile 393885, 393884; Philco(all) ; Rebler 27 (Scotty) -35; SearsRoebuck 7188, 7117, 1859A; Simplex T;Sparton 33, 33A, 333; Stewart Radio 60;Stewart Warner 1171, R1112, 1121, 11-22; United Motors Service 2035, 4036, 40-37, 4038; Utah (B Eliminator Non-Synchronous) ; Westinghouse WR25, WR26;Wilcox Gay 4B6; Zenith 7, 460, 462, 650HD, 651 HE, 660 TD, 661 TE; Wurlitzer460, A60.

Mallory's announcement of a Replace-ment Vibrator line is an important an-nouncement -and the news of new lowprices, standard distribution and dealerdiscounts is good news. Another bit of in-formation equally interesting concernsthe preparation of the new Mallory AutoRadio Service and Replacement Manual.This new manual, to contain accurateschematic charts of more than 200 popu-lar automobile radio receivers, will beone of the finest works of its kind everpublished. It will be available, withoutcharge, to all authorized service men.

"The House that Radio Built" is thetitle of a 36 page issued by the Nation-al Broadcasting Co., R. C. A. Building,New York City. It is a story of the ex-perience and research which went intothe building and equipping of the NBCstudios in New York, and was preparedby Mr. 0. B. Hanson, Chief Engineer.Well worth the time of any broadcaststation engineer taken in the time ofreading and many ideas may come fromyour interest.

"The Educational Program" by Mer-rill Denison is the title of a 20 -pagebooklet published and distributed by theRadio Institute of the Audible Arts, 80Broadway, New York City. Mr. Denisonoffers many suggestions along the linesthat should be understood by the partygiving an educational talk before the mi-crophone. Other booklets also available

Page Twenty-two

from the same organization are entitled,"The Use of Radio in Leisure Time","Music as Presented by the Radio","Radio Music. for Boys and Girls","Women and Radio Music," and writtenin general character may be had for thewriting.

"Western Electric Radio Transmit-ter No. 14A" is the title of a 12 pagebooklet issued by the Western ElectricCompany, 195 Broadway, New York Ci-ty, describing their transmitter of thatdesignation for CW, ICW, or Telephonework, with Frequency Range Pread-justment to any 10 frequencies in rangeof 2 to 18.1 megacyces, with carrierpower output of 400 watts at the lowerfrequencies, and 300 watts at the higher.

Lear Developments, Inc., 125 West17th st., New York City, have issued abeautiful booklet with the title "Air-craft Radio," covering their productsof receivers, transmitters, and direc-tion finders for aircraft. For free copyaddress Mr. Johnson, business manager.

WHERE YOU WILL FIND ITIn an art isle under the title of "Noise

and Its Measurement," by A. J. Mu -chow, in the G. E. Review, the authorsays the following measurements weremade using sound level meters made upof Microphone, Amplifier, and outputmeter.

(Painful Sound: Threshold ofFeeling 120 db)

Noise in Subway Car 90 dbNoise in Railroad Car 80 dbNoise in Automobile going 40

mph. 70 dbQuiet Street 50 dbAverage New York office 40 dbCountry Residence 30 dbNoise in Room specially construct-

ed for sound measurements 10-20 db

(Minimum of Audible Sound: Thresholdof Audibility)

The author makes reference to an ar-ticle in the January Electrical Engineer-ing, by R. G. McCurdy, under the ti-tle of "Standardization of Noise Me-ters," as a good basis for manufactur-ers to follow.

2,000,000th PATENT ISSUEDJoseph Ledwinka, Chief Enganeer of

the Edward G. Budd Mfg. Co., of Phil-adelphia, recently had the honor of re-ceiving U. S. Govt. Patent No. 2,000,000.The first million patents were issued be-tween the years 1790 to 1911, and thesecond million since that time.

The first patent was issued with thesignatures of President George Wash-ington, Secretary of State Thomas Jef-ferson, and Attorney General EdmundRandolph in 1790.

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Police Radio Combatting Crime(Continued from Page 6)

due to the actions of the shorter wavefollowing the straight line radiationprinciple of light, and metal absorptionquality.

The other factor that must be con-sidered here is that in two-way communi-cation from patrol ears on ultra highfrequency the headquarters receivingantenna must be well elevated to receiveas the patrol car cannot have a hightransmitting antenna.

Distance Covered

Where the suburban points toreached are of great distance ultra highfrequency becomes a matter of heightfor the transmitting antenna, as the dis-tance is largely a matter of anlintiaheight. If the surrounding territory isfairly flat and a suitably high transmit-ting antenna point can be established byeither the flag pole of a large building,or a very high transmitting antennatower the ultra high frequency transmis-sion will reach a large area. Other thanthese conditions medium high frequencyaffords the -better system.

Elect Heal and other disturbancesMUM be considered in business industrial localities when considering Shrange of transmitters. Where a signalstrength of 1.0 millivolt is considerednecessary in the receiving antenna inbusiness sections, a 2 millivolt antennasignal will often serve in residential ter-ritory, and a .05 millivolt antenna sig-nal will serve very well in rural terri-tory. The reason for this is that theantenna at former locations is bound topick up some slight impulse as signaland when amplified in the receiver th unwanted signal will be proportionatelyamplified with the desired on2, and it hasbeen found that at least 1.0 millivolt signal is necessary to prevent this condi-tion in business territory.

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Just Off the Press

COMMERCIAL RADIO - 7 West 44th St., New York City, N.Y.

Generally speaking a good table tofollow on this matter of transmission isafforded by the following prepared byone large manufacturer as average;Medium Iligh Frequency:Power State Police Municipal PoliceOutput 1658 to 1706 Ice. 1712 to 2490 ke.

50 watts 8 to 12 mi. 2 to 4 mi.100 watts 12 to 18 mi. 3 to 6 mi.500 watts 25 to 40 mi. 6 to 12 mi.

1000 watts 35 to 60 mi.2000 watts 45 to 80 mi.5000 watts 60 to 120 mi.

On Ultra High Frequency, MunicipalPolice only:PowerOutput Distance15 watts 3 to 5 mi.

100 watts 5 to 10 mi.500 to 1500 10 to 15 mi.

The above distances of course beingin any direction in a straight iine fromthe transmitter antenna.

Allowing for night time approximately200q greater range, and 40% largerrange during winter.

The cruising car tratismitturs of 5watts hare proved very satisfactOry in -

CLASSIFIED ADSCU AI II I. KC .11, RA MO will accept clas-

sified advertising at the special rateof five cents per word.

Remittance in full must accompanycopy. Closing date for classified adver-tisements is the 15th of the mouth pre-ceding publication.FOR SALE-Radio Model V ibroplex,

heavy contacts, $10.50. Like new.Guaranteed. John Morgan, 54 HardingDrive, Glen Oaks, Rye, N. Y.ONE NEW SET Van Nostrand Mathe-

matic books: Arithmetic, Algebra,Trigonometry, Calculus and Home Study,4 vols. $3.50, list price $7,00. LD.; careCommercial Radio, 7 W. 44th St., N. Y.

operation, having crystal control theseare able to maintain frequency within.023 per cent. Most up to date cruisingcar radio receivers are of the super het-erodyne type using 7 tubes, locked to re-ceiving channA, and mounted either ondash or on top of rear partition behinddriver in a coupe.

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