SEPTEMBE35

CommunicationEngineering

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AssignmentsNews, Review

"Wrinkles"

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irway News

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The most popular basic text on ra-dio in existence, used by students,schools, technicians and experimen-ters the world over. Everythingfrom fundamental electrical theoryright up to the latest applicationsand developments. Clear. concise.complete, upto-date. written In langunge easy to understand, withover 500 diagrams and illustrations.Invaluable for broadcast techniciansfor rounding out their radio back-ground. You need this greatIn your work. 1972 pages, $4.00 postpnid.)

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, 5%x8, 96 illustrations

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Practical Radio Communication, Nilson & Hornung $5.09How to Pass C. S. Govt. License Examinations,

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GENERALPrinciples of Radio, Keith ItenneyRadio Theory 1111(1 Operating, Mary T. Loomis 41.510111

Elements of Radio Communieation, J. It, Morecroft 3.011Radio Engineering Handbook, Keith !felonry

55..Radio Engineering. F. E. 'FermanRadio Engineering Principles. Lauer & Brown

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Radio Handbook, Moyer & Wastrel 5.00Radio Telegraphy and Telephony, Ouncion & Drew 7.50Experimental Radio, Prof. It, H. Ha 2.75Fundamentals of Radio, Prof, R. R. Ramsey 8.51)

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WastrelTelevision -Its Methods and Uses, E. J. Felix

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VOLUME IV NO. 10

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

THE"Red Herring'' will not be

downed. The first rumblings werethe announced policy of "drilling fromwithin." This means the policy of cer-tain members of communistic leaningsof joining as good members of units ofThe American Federation of Labor, withthe vicious forethought of advancingsuch ideas and leaders in the organiza-tion.

The later voieings in Russia by thewell known Pacific Coast shipping groupleader Darcy in Russia, followed by thisgovernment 's protests to such actions ina friendly nation. The periodic officialannouncements through official channelsof the A. F. of L. that they are famil-iar and fighting against communisticgroups acting under their banner, re-quire more than passing notice.

The radio man is organized. Underone group or another he has now takenhis place. It is unfortunate that everyaction to gain ground is often brandedcommunistic, but it is high time thatevery radio man look well about him.Especially should he be careful in pick-ing, or voting for leaders. A carefulattention to the working of any organ-ization of which he is a member is apersonal obligation. After all if an at-tempt by a minority to inject communisminto an organization is tolerated by thelack of grouping of the majority, eachindividual member not holding suchideas is equally responsible for his share.

(FORMERLY "C -O")

The Only Magazine in America Devoted Enti-ellOg) the Commercial Radio Man

*,

Contents for September, 1935°-

WPFH, Baltimore Police .Radio Transmitter

Page

Front Cover

A New Development in Commun,cation Engineering 5

Here and There ' 6

Broadcast Station News, .. 7

By William D. Kelly

Foreign Press 7

Austin Y. Tuel Dies 8

Random Notes - 8

Forms for Making AppliCations 8

Multivibrators, 9

By Bernard Ephraiin

Designing the Midwest .A11 -Wave -I8 12

By Walter. Shirlc:

Airway News - - 12

How Eastern Handles Itealthei ReP61-tSMonteagle, Tenn., Station,.. . -New Radio Stations in Second District

The Barkhausen Oscillator. 13

By F. B. Llewellyn .

With the Technical Editor 14

New Apparatus 15

Press Wireless to Ethiopia 15

Actions of the Federal Communications commission 16

Published Monthly..by CQ Magazine Company, 7 West 44th Street, New York.N. Y.. Phone VAnderbilt 8-9461. Yearly subscription rate 82.00 it U. S. and Canada;22.60 foreign. Make all checks, drafts and money ordorr payable to the Company.Single Copies, 20 cents. Teri and illustrations of this Magazine are copyrighted, andmust not be reproduced without permission.

LONG before the dew has vanished from thefields, the farmer is at work ... the harness of his

team creaking sharply in the dawn . . . the plowshearing through the earth . . . long furrows turningin a measured arch and fall of brown loam . . . un-locking the fields, opening the earth to the sun andthe rains of Spring-and Summer. ... .

The story of farming is as old as the Earth. But thepresent-day methods of farming are new-new asthe Age of Science. Today farming is a business forprofit. Harrowing, planting, cultivating, harvesting,marketing-each step is a matter of knowledge. Noseed is sown without careful reference to experi-ence and information in books.In this day and age the Serviceman's job is a gooddeal like the farmer's. Like farming, making servic-ing pay is a matter of specialized knowledge. In-creased complications in set development make itnecessary, more than ever before, for the Servicemanto have at his fingertips, reference data that canbe easily located and instantly applied to questionsabout diagrams, color -coding, capacities, resistancevalues, operating voltages and location of differentparts.

IT'S A LITTLE COUPON,BUT IT MAY MEAN A

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Dear Rider:

Send me "Successful Servicing" right away

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Page Four

will help you

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dis FALLThousands of Servicemen have found the scientificbasis for their business in Rider's Trouble Shooter'sManuals. Aro other manuals contain as many schematics,I -F peaks, alignment data, circuit descriptions, etc.

Over 5,200 models and thousands of schematic diagrams givingcomplete detailed information are illustrated. Easily under-stood descriptive text, with an excellent index system, makesreference a matter of ease.

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SERV:CING SUPERHETSA comprehensive, easily understood explan-ation of the superheterodyne.288 pages $1.00

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1440 BROADWAY NEW YORKMention Commercial Radio when answering Advertisements

10

Diagrut 1.

Three way Duplex Radio TelegraphSystem.

[RI

A LEADING communication was21 faced with a major problem. Hand-ling reports, frem point to point, thruthree key radio stations, they foundtheir facilities overloaded by traffic. Theannoying part was that the traffic real-ly was not more than could be handledby steady transmission over the twenty-four hours each day, but due to the na-ture of the transmitted material sucha schedule was impossible.

Handling communication is handling ahighly perishable commodity. A part:graph schednled to make the noon edi-tion of a San Francisco paper is worth-less if held up two hours because theChicago transmitter is tied up handlingimportant press to New York. Sportsevents, such as ball games, tie uptransmission for hours on end andfrequently are of only localized interest.If you have ever listened to the broad-cast of a running report on a ball gameyou will realize that the time on the airactually used to convey pertinent infor-mation is only a small fraction of thetotal and that the same words, bereft offill-in and given in continuity fore' atthe end of the event, would upabout one quarter of the tin Of

SEPTEMBER, 1935

To PRINT iRCIRCUIT NO 1

To RINTERCiRCLIT No t

Diagram 2.

Scheratic Diegrea1 or

one ate -Um in the

Three flay Duplex.

ANew

Developmentin

CommunicationEngineering

course, the news value would suffer pro-portionately.

The communications company feltthat to stop transmission to New Yorkin order to break in with material nec-essary for San Francisco was often notonly impractical, but absolutely impos-sible. Too many times some receivingcenter had to get "the short 2nd," muchto their disgust and dissatisfaction withthe company's service. What was need-ed to solve the problem was either acomplete additional set of transmittingand receiving channels, whose incomewould never justify the tremendous ex-pense involved, or some means of split-ting the present channels for simultane-ous two communication. With wiredchannels this is feasible, with radiotransmission it sounds impossible.

William A. Bruno, of the Bruno Lab-oratories, a transmission engineer, wascalled into consultation. His solutionof the problem was simple and satisfac-tory, but before it can be set forth wemust review briefly the method; of hand-ling press transmission for the benefitof those not acquainted with this branchof the art.

Material to be automatically transmit -

IN WHICHA NEW

DEVICE ISUTILIZED

TO AFFORDTHREE WAY

DUPLEXOPERATION

ted is first "printed" by perforating atape on a machine which looks somethinglike a typewriter. Thil perforated tapeis then fed into a sending machine whichcontrols the "keying" of the trans-mitter. At the receiving end the signalis caused to perforate another tapewhich becomes a duplicate of the origi-nal. This second tape is fed into a decod-ing machine which translates it into atypewritten duplicate of the originalmessage.

Mr. Bruno reasoned that as at manytimes the' channel was tied up in trans-mission of material of a semi -continuousnature (that is, one having momentary

'pauses such as sports events previouslyreferred to), advantage could be taken ofthese pauses to transmit news of otherinterest. He proposed a synchronousswitching system to be operated at highspeed and to be applied at both re-ceiving and transmitting ends. The fun-damentals are these: Suppose the Chi-cago transmitter to be in operation andsending two sets of material, one of in-terest to New York, the other to SanFrancisco. Two separate tape machinesare feeding the transmitter. The opera-tion of the tape transmitters is eon -

Page Five

trolled by the synchronous switch whichturns them on and off alternately manytimes per second.

In New York and San Francisco arelocated duplicate synchronous switchescontrolling the operation of the printingmachines attached to their respective re-ceivers. The New York synchronousswitch allows its printer to operate only(Turing that portion of the time that thesender handling New York material isfeeding the Chicago transmitter. Simi-larly the San Francisco printer is onlyin operation during the time news in-tended for it is being transmitted.Switching takes place at the rate of 240switches per minute. In this way twocomplete channels are available and agreat percentage of "waste time" elim-inated. Of course, any number of de-sired channels could be made availablein the same manner.

The apparatus developed by the Bru-no Laboratories to answer this purposeis illustrated in the photographs. Itconsists of a rotary switch arm whichcontacts a number of segments in turn.One segment for each desired channelplus one comparatively small segmentused for synchronization. The switch

controlling the transmitting type ma-chines rotates continuously. Each timeit passes the synchronizing segment itcauses the transmitter to send a syn-ehronizing pulse. At the receiving end,the switch is arranged to make one com-plete revolution and then stop on thesynchronizing segment until releasedfrom this position by the incoming syn-chronizing pulse. In this way it. is im-possible for the two machines to get outof step as they are automatically re -syn-chronized at each revolution.

Diagrams 1 and 2 illustrate how afour segment synchronous switchingsystem can be used to give two-waycommunication between any and all ofthree points. Diagram 2 shows the in-stallation at the individual station. Itis self explanatory when studied in con-junction with Diagram I. The seg-ments have been developed in order tofacilitate interpretation of the schemat-ic. The solid center bar representingthe switch arm which in this instance isconstructed in such a way as to makethe contact with two segments at a time.It should be noted that there is no idletime, all transmitters and receivers work-ing full time.

Tor VI C.

HERE AND THEREQAN FRANCISCO, CAL.-The Mari-

time Federation composed of allmarine groups on the \Vest Coast wasasked to vote on the British Columbiacargo plan recently as a basis of opera-tion.

cto ciD cip

NEW YORK, N. Y.-A war againstelimination of noise was declared. Thiswill probably spread to other parts ofthe country. Sound measurement instru-ments on radio lines described in our lastissue are utilized with the decibel as ameasurement unit of sound.

ctp cb cp

CAMDEN, N. J.-Interest aroused bythe three months ship yard strike of theemployees of the New York Shipbuild-ing Corp. bring to mind the October 1,1928, announcement of the AmericanBrown Boveri Electric Corp. that fromthat time on a completely owned subsid-iary under this name would take overall existing ship contracts of the Amer-ican Brown Boveri. American BrownBoveri has since been taken over by Al-lis Chalmers. Work on seven naval ves-sels have been delayed on account ofthe strike.

CID

DETROIT, MICIL-A radio device isused to transmit a musical note of defi-nite pitch to a lightship in the harbor.The transmitted signal starts a gener-ator on the lightship to supply the ra-dio beacon, and an air compressor tokeep the fog signal in operation. TheEleventh Lighthouse District developedthe equipment, and no one is regularlyof duty on the lightship. It is saidother units will he so equipped if thisone is successful.

CID CID CIO

LONDON, ENGLAND.- Will i am('live Bridgeman, better known as Vis-count Bridgeman, head of the BritishBroadcasting Corporation, died in Lon-don, August 14th.

c't3 clo cID

NEW YORK, N. Y.-Wired Radio,Inc., subsidiary of The North Ameri-can Company, is again trying out radioover lighting wire circuits in Ohio, sup-plied to customers of their operatingcompany there on a rental basis-noadvertising announcement of any kiwiis allowed.

CTD 4D ct)

LOS ANGELES, CAL.-The RCACommunications, Inc. have opened up aLos Angeles office. This now givesthem offices in Baltimore, Boston, Chi-cago, Detroit, Los Angeles, New Orleans,New York, Philadelphia, San Francisco,Seattle, and Washington, D. C.

cp CYD CiD

WASHINGTON, D. C.-Another at-tempt is to be made to put through Con-gress at the next session a ship subsidybill. The last session had little successin bringing the different interests con-cerned to an agreement. PresidentRoosevelt is known to be for a subsidy,but has ideas of his own along whatlines this should be.

Page Six COMMERCIAL RADIO

Broadcast Station News

111.11M10.=

THEgigantic, stupendous, colossal

Third Annual Outing of the I. R. C.was held Sunday, July 28th, at Solm-son's-on-the-Severn. Members of theclub and their friends met at the studiosof WCAO. After a tour of the studiosand transmitter there, provisions weremade for those who did not have auto-mobiles with those who did, and the car-avan proceeded onward to the SevernRiver with the honking of horns, someof the boys sending code on auto hornslike a farmer at sea sending with hisleft foot. This all happened in Balti-more, you must remember. The I. R. C.is a club of Baltimore radio men fromall branches of radio-broadcast, tele-graph, public address men-all of thesebeing represented at the; outing. I. R. C.is Institute of Radio Conferees.

At the shore there was plenty of beerand eats and a good time was had byall. There was a base ball game, mouserace, tug of war, etc.., but the biggestevent of the day was a husband callingcontest for the ladies. Much credit goesto Lt. Wm. E. Taylor and Charles El-lert, the entertainment committee. Well,that covers that.

Joe Rubin, radio telegrapher on theSS Carolyn, was married July 7th. Bonvoyage, feller. On the sea that isn't al-ways smooth and calm.

Paul Ruckert of WFBR Control Roomcelebrated a birthday August 5th witha big cake 'n everything. Paul treatedhimself to a Scott All -Wave Imperial,too.

By WILLIAM D. KELLY

.14,4M.,.=.,10111.4,41M.4.1M1.1 411.000041MPI/O=.1.111M1,04=1P114M14/4M1.041001,4=1.11.1414M.0411.4M0011104=104M.:.

Bob Briel is back in town after work-ing as vacation relief at WJEJ in Ha-gerstown.

Gus Lynch is with EAT in Savannah,so 'tis said.

Morris Blum took the job as reliefoperator on the SS Dorchester duringAugust.

Summers T. Carter is down in Spar-tansburg, S. C., at WSPA.

Norman O'Hearn, WFBR's vacationrelief man, is an automobile salesmanin his spare time. Wanna buy a car

James Shultz, WCAO's chief, is sport-ing a new Ford automobile. There'sgonna be a lot of new things up WCAOway soon-new transmitter 'n every-thing.

Amateur radio shows seem to be thething nowadays. In Baltimore, threestations, WFBR, WBAL and WCAO, arebroadcasting the same amateur showfrom one of Baltimore's local theaters.

Speaking of amateur shows-WCBMhad a show called Amateur Night inHarlem-the show being picked up frontone of Baltimore's colored theaters.

Harry Boone just blew into town andis going to take a trip on the SS BeachMaru for a little while.

From down Norfolk way comes wordthat Robert L. Kennedy left in July,His place was filled by John Carl Mor-gan.

Down at WTAR, J. L. Grether is thechief engineer and John C. Peffer isthe chief operator at the transmitter,

with Wm. L. Davis as transmitter oper-ator and Charles R. Pattee in controloperator.

Myril Harrison left WTAR recentlyand when last heard of was in NewYork City.

George A. Boisseau is pounding brasson the SS Clare.

On the City of Havre we find: RoyBartels, chief; Forest Flander, second;and Baker, third opr.

The Baltimore Mail Line is carryingthree operators now, so I am told.

George Brewer is the chief engineerup at WJEJ, Hagerstown, Md. WillardBetts is the assistant.

Sam Canter is the Sparks on the SSMillinocket.

Edward McDowell is down at WIOD,Miami, Fla.

Eddie Stover took a "Postman's Va-cation"-took in all the radio stationshe could find on his vacation.

Harry A. Mills is new man at WCAOcoming to Baltimore from Cumberland.Harry says that he is going to movehis family and W8DSO to Baltimoreabout October 1. W8DSO will be knownin Baltimore as W3UO and has a powerof 1 kw.

Martin Jones of WCAO is also sport-ing a new Ford auto.

Porter Houston and his brother Sam-my down at WCBM are in training forannouncer. Both have had a shot at iton the air recently-it's a long story.

FOREIGN PRESSLinguistic Transmissions from Italy

DONEE: The "Duce" not only be-lieves in modernity but "ne plus ul-

tra'' for his subjects' radio transmis-sions; hence, Italian news goes forth toall points of the compass in twelve dif-ferent languages: English, French, Ger-man, Spanish, Italian, Hungarian, Greek,Bulgarian, Esperanto (the universal lan-guage), Arabic, Roumanian and Albani-an.

Transmitters are located in Rome, Mi-lan, Florence, Turin, Bolzano, Trieste,and Bari. Latter station broadcasts les-sons in Italian for the edification of theneighborly Greeks and Albanians

Progress in Radio Conintunientlon

LONDON: In a paper published byCol. A. S. Angwin, which appeared inthe Journal of Electrical Engineers,February 1935, tells of the technicalprogress made during the last two years.Briefly, Mr. Angwin says: At the begin -

SEPTEMBER, 193:

Reviewing the March of World Progress

ning of 1932, the number of licensed lis-teners in Europe was nearly 14 millions,and two years later it was nearly 20millions (see next item). In 1929 thetotal power used in broadcasting was420 kilowatts, whilst 5 years later itwas more than ten times greater. Nowthe average high-powered station con-sumes more than 2 million watts yearly;it is, therefore, important to use trans-mitters of high efficiency. The extendeduse of short-wave telegraph working inships has enabled the British Post Of-fice stations to communicate regularlywith whaling boats in the Antarctic andin Eastern waters. Directive antennashave been erected at these stations cov-ering all the main shipping routes of theworld, and this has greatly improvedservices. Additional radio -telephone ser-vices from Great Britain to South Afri-ca, Egypt and India have been openedup, while services to Japan, Shanghai,Kenya and Iceland are projected. Byextension to circuits already existing, ra-dio communication is now possible with

nearly all South American states. Theoutstanding feature in radio researchhas been the intensive study with thehelp of the cathode-ray oscillograph onthe propagation of waves in the iono-sphere. The methods now in use indi-cate that the reflected signal from asingle pulse incident on the ionosphereconsists frequently of a doublet, thecomponents of which are separated by asmall time interval. The reflected com-ponents are apparently electrically pol-arized waves of opposite rotationalsense.-Extracted "Nature," No. 3424,Vol. 135

More than 21,000,000 Receivers inEurope

PARIS: Statistics issued by the In-ternational Union of Radio -diffusion, inGeneva, and published by the Frenchtechnical press, indicate a 19 per centincrease in the number of Europeanbroadcast receivers. The report statesthat in 1933 there were over 17 million

Page Seven

-`7~ 7,-4:4704e 3'."*T171.rt-7!:,""1-cf.

rs, while today the figure is wellover 21,000,000.

Below are tabulated comparative fig-ures which indicate the number of re-ceivers per 1000 inhabitants:

Denmark 160.00-1000Gr. Britain 147.25-1000Sweden 118.03-1000Holland 108.96-1000Switzerland 97.75-1000Germany 94.22-1000Iceland 90.00-1000Austria 78.00-1000Belgium 73.52-1000Danzig 63.90-1000Norway 54.85-1000Czechoslovakia 47.10-1000Luxembourg 45.83-1000France 41.97-1000Hungary 39.15-1000Italy 10.08-1000Spa in 8.90-1000Roumania 5.49-1000Bulgaria 1.48-1000Greece .05-1000

On the continent, Great Britain hasapproximately 18 million receivers, Ger-many 6 million, and France 2 million.In the United States there are betterthan 20 million sets which barely eclip-ses the European total.

,I.

Television in Germany

BERLIN: During the last few monthsthe German Post Office authorities havebeen giving public demonstrations ofthe progress made on television appara-tus. Reports indicate that the Germanpublic is not yet ready to accept televi-sion as a commercial product. Two rea-sons are given for this reluctancy: first,the high cost of television receivers (200to 1600 dollars); and second, loss ofdetail in reproduction. Of course, de-velopment continues, but until such timesas price, incongruous distortions, fog-ging, optical lattice phenomena, and distortion are eliminated, television willremain as one of the scientific wondersof this electrical age.

An article in a German paper "Rid --triadic Nachrichten Teehnik" says: thatGermany proposes national coverage byinstalling a group of 5:7 meter trans-mitters having output powers from 2 to20 kilowatts. By selecting the best ge-ographical sites for transmitters, a fieldstrength of 1 millivolt per meter isplanned. Transmissions will be of the180 line type, 25 scannings per minute.Band width allocated will be 2,400 kilo-cycles, practically all stations will besynchronized. At the receiver a heterodyne oscillator will be employed forsimultaneously receiving both frequen-cies.

South American 50K11' Transmitter

RIO de JANIERO: The great SouthAmerican newspaper "Jornal de Bra-sil," (Radio TUPY) will inaugurateamidst neo-Bra zilia a pomp and beau-tiful senoritas its new 50 Kilowatt trans-mitter, broadcasting on 325 meters. Pre-liminary tests made by installators ofthe new equipment, which is of Americanand British manufacture, indicate thatthe entire country will be amply servedby the super -power station. The immensi-ty of the signal coverage can be visu-alized by taking into account that thearea of Brazil is very much greater thanPage Eight

AUSTIN Y. TUEL DIESAustin Y. Tuel, vice president and

general manager of the Mackay Radio I

and Telegraph Company who had been 1in radio since 1909, when he was con-nected with the United Wireless Com-pany, died in New York City on Aug- 1ust 27th.

Mr. Tuel had been a telegraph op-erator, and early went into wireless. I

He was for a long time in charge ofthe Federal Telegraph Company's San ;Francisco station in the early days.During the war in his capacity of ra- 1

dio man he served as lieutenant withthe navy. He later returned to Feder- !

al, and continued on with Mackay. Mr.Tuel was one of the pioneers who be-came a rapid sender of code and set amark that was hard to get near, aver- I

aging close to fifty words a minute.

that of the United States. Unfortunately,more than 90 per cent of the inhabi-tants of Brazil are illiterates; hence,broadcasting in that country in a gran-diose style requires a plenty or cour-age and initiative. Incidentally, thereis a dearth of radio receivers outside ofthe country's five key cities; one is notsurprised to find no sets of any descrip-tion in some well -populated regions.-Scarcity of money, compatible with thelow I. Q. are factors which prevent salesof receivers.

Laws and Restrictions in CubaHAVANA: An ultimatum has been

issued by Nicholas G. de Mendoza, Ra-dio Commissioner, that all transmitterslocated within urban areas having pow-ers of 250 watts or over must either re-duce power by August 31st or have theirpermits revoked. A report from an as-sociate of the Secretary of Communica-tions states that this new ruling willclear up present congested conditions onthe air.

A new law which was signed on the2nd of July, under the revised CubanRadio Code, states: that no electricaltranscriptions characterizing things Cu-ban, such as music, song or compositionmay be broadcast. All other types ofrecordings suffering no prohibition.

RANDOM NOTESR. S. Polk is holding down his job of

chief of the Santa Rita of the GraceLine.

George Fitzsimmons, on the S. S.George Washington, of the Old Domin-ion, is doing a nice job as chief.

Roy Hester Roberson (we put in theHester so there will be no confusion ofidentity) is running on the Rosa Queendown off the South American Coast forthe Grace Line.

Steve Kovacs is looking for a lift todear old Budapest. "I must see itagain," says Steve.

Alex Vadas is in Steve's heart's de-sire-summering in Hodmezovasarhaly,Hungary. Sometimes it's whistled andsometimes it's sung.

Richard Golden, up Boston way, is do-ing well these days. "Boston is a goodspot for me," says Dick.

J. E. Brockway, well known old timeron the West Coast, is now in San Fran-cisco, working on a Diesel Engine pro-

ject. Say, J. E., when do you shipagainI

Karl Baarslag, well known author of"S 0 S to the Rescue," is just takingit easy working twenty-five hours a day,but it won't be long so Karl says untilwe will have some nice reading matterfrom him for COMMERCIAL RADIO. Infact you can look forward to seeing itin the next issue.

Brother Delaney has taken out a boatfor Mackay, and is looking much "cheerup" these days. Good luck, Jim, andmay your boats always come in.

Forms for Making ApplicationsFCC FORM NO.:

301-Application for Radio BroadcastStation Construction Permit or Modifi-cation Thereof.

302-Application for Radio BroadcastStation License.

303-Application for Renewal of Ra-dio Broadcast Station License.

304-Application for Modification ofRadio Broadcast Station License.

305-Application for Authorization toInstall Automatic Frequency Control-

306-Application to Determine Oper-ating Power of Broadcasting Station byDirect Measurement of Antenna Power.

307-Application for Radio BroadcastStation Special Experimental Authori-zation or Extension Thereof.

308-Application for Permit to Lo-cate, Maintain, or Use Studio or Appa-ratus for Production of Programs to beTransmitted or Delivered to ForeignRadio Stations.

401-Application for Radio StationConstruction Permit (Other than Broad-casting).

402-Application for Modification ofRadio Station Construction Permit (Oth-er than Broadcasting).

403-Application for Radio StationLicense (Other than Broadcasting).

404-Application for (New) or (Mod-ification of) Aircraft Radio Station Li-cense.

405-Application for Renewal of Ra-dio Station License (Other than, Broad-casting).

407-Application for Modification ofRadio Station License (Other thanBroadcasting).

410-Application for ExperimentalBroadcast Station Construction Permitor Modification Thereof (for the fre-quencies 1530, 1550, and 1570 kilocyclesonly).

411-Applicat ion for ExperimentalBroadcast Station License.

501-Application for Ship Radio Sta-tion License.

602-Application for Amateur StationLicense (under Special Provision ofRule 366).

610-Application for (New, Renewal,Modification, Duplicate, or Replacement)Amateur Radio Station and OperatorsLicense.

701-Application for Additional Timeto Construct Radio Station.

702-Application for Consent to As-signment of Radio Station ConstructionPermit or License.

703-A ppl ica t ion for Consent toTransfer of Control of CorporationHolding Construction Permit or StationLicense.

756-Application for Radio Operator'sLicense.

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IMILT1V TIM'S

ITERNARIPControlling the Multivibrator-Unsymmetrical Systems

Phenomena of Frequency Demultiplication

IN FOUR PARTS-PART 2Controlling the System

IN reviewing the theory and circuitalfunction of the multivibrator, it is ob-

vious that no precautions have been tak-en into consideration to stabilize thesystems against variations in plate, fila-ment, or heater supply voltages, orchanges in the circuit constants. If re-medial measures are not taken to rec-tify the instrument against these transi-tional effects, small frequency excursionswill occur in the system making the mul-tivibrator of little use in measurementswhere stability of frequency is of primeimportance. Fortunately, any spuriouseffects may be cancelled out by simplycontrolling the time of relaxation thrusynchronization with energy supplied byan external frequency standard. Undersuch external influence, the stability ofthe multivibrators' oscillatory system de-pends upon the accuracy and operatingparameters of the controlling agent, andnot upon any other influence exceptthose which tend to either impair theprecision of the standard or alter the re-laxation time or circuit constants of thedevice. A scheme by which the multivi-brator is being controlled by an externalfrequency Is shown in Figure 7.

Primary and Secondary Frequency -Con-trol Standards

Oscillators used for controlling themultivibrator may be classed as eitherprimary or secondary control -frequencystandards. A primary standard, accord-ing to late engineering bulletins of theGeneral Radio Company, is a standardknown to keep its frequency accurate tobetter than one part in a million (0.0001per cent). It is unquestionable that thisis certainly high precision and implies amuch higher degree of accuracy than isgenerally sought. Al secondary standard,while not quite as accurate as a primarystandard, may include any calibratedfrequency -measuring device whose accu-racy can be determined by direct or in-direct comparison with a known accurateor better standard. It is common forsecondary standards of the crystal -con-trolled type to continuously maintain afrequency accurate to within 20 partsin a million (0.002 per cent). Othertypes of frequency standards using sta-bilized oscillators ofttimes can maintainaccuracies comparable to that of a pri-mary standard for short periods oftime. The period during which ordinaryoscillators may remain stable dependsprincipally upon the operating parame-ters of the circuits. Hence, for workrequiring continuous use of a highly ac-curate frequency, a primary standard

SEPTEMBER, 1935

would be the instrument to use; wherelesser accuracy can be tolerated, the sec-ondary standard is the ideal instrument.On the other hand, if an ordinary oscil-lator is employed as a temporary stan-dard, and has been carefully construct-ed to minimize frequency variations, itis possible to obtain frequencies of highprecision for short periods of time. Thesefrequencies will have sufficient stabilityto be satisfactory for practically alllaboratory measurements.

Ove a.e

There are numerous factors which en-ter into the design of an oscillator ofhigh stability, that a discourse on thissubject is outside the scope of this pa-per. It matters little, however, what.type of oscillator is employed to con-trol the multivibrator so long as it islightly loaded.' It is paramount thatthe frequency be highly stable duringfrequency measurements, standardiza-tion, monitoring or calibration work. Ifattendant precautions are not taken intoconsideration, the oscillator frequencywill deviate and the multivibrator fre-quency will change accordingly causingmeasurements taken at the time to bein error.

Coupling the Multivibrator to theControl Standard

In properly controlling the multivibra-tor, success lies in the type of coil usedto couple the controlling frequency tothe system. If the inductance of thecoil is not of the proper value, oscilla-tions generated in the multivibrator mayreact back and cause disturbances in thecircuit of the control oscillator. The

details entering into the design are giv-en herewith:

The loading inductance designated inthe circuit wiring diagrams as L-1 maybe either a honey -comb, duo -lateral, oruniversal wound coil. It is essentialthat the coil have such an inductive re-actance at the control frequency that theamplitude of the voltage in the coil issmaller than that of the oscillations gen-erated in the main oscillatory circuit.In other words, the resonant frequencyof the coil MUST be above the funda-mental frequency and not equal to anyharmonics produced in the circuit of theexternal oscillator. When this conditionis obtained, no circuit interaction canexist between the natural frequency ofL-1 and the main oscillatory circuit. Theinductance of the coils shown in the var-ious diagrams in these articles are ofthe optimum value for the frequenciesgiven.

Input Coupling Methods

In coupling the multivibrator to thecontrol oscillator, it is optional whetherinductive or conductive coupling be em-ployed. Whatever method is selected, itis very important that no load be im-posed or reflected upon the oscillatorycircuit of the controlling medium. Thisprecaution must be closely observed inorder to preclude the possibility of afrequency drift occurring in the system.The factors which may impair the stabil-ity of the controlling device are princi-pally caused by changes in the multivi-brators' load, coupling or circuit con-stants. These factors may be preventedfrom appreciably exerting their influenceupon the controlling device by simplyisolating the multivibrator from itssource of control. This measure can becarried out by either electron -couplingthe oscillator to the multivibrator, or bycoupling through a shield -grid amplifier.Figure 8 shows some common methodsof coupling.

Output Coupling MethodsThe output of the multivibrator may

be coupled by, the same methods used incoupling to the input. Therefore, in thecase of inductive coupling, a small coilof low inductance need only be insertediu any branch of, the oscillatory systemnot forming a portion of the controlcircuit. By referring to Figure 8 willbe seen diagrams of output couplingschemes. The output coil L-2 consists ofa few turns of wire wound on any suita-ble form. If the inductance of the wind-ing is made resonant to the fundamentalor to an harmonic frequency of the sys-tem, and a variable condenser shunted

8 R. Gunn, "Stabilized oscillator systems,"Proc. IRE, Vol. 18 No. 9, pg. 1560, 1930

Page Nine

in the circuit to assist tuning, the out-put signal strength can be multipliedseveral times. If purity of wave formis desired, a series tuned filter may beinserted into the output as a possibleshunt for removing undesired frequen-cies.

It will be noted that an auxiliary am-plifier stage has been added to the out-put as well as to the input stages of themultivibrator. These amplifier stagesserve to isolate the multivibrator systemfrom any external coupling influencewhich may tend to affect the frequencystability of the system. The amplifiersalso augment the strength of the input -control and output frequencies.

Preface to the Unsymmetrical Multivi-brator

To present a satisfactory explanationapplicable to all types of unsymmetricalstructures is a difficult problem. How-ever, after an exhaustive search of engi-neering archives, three excellent expla-nations have been found. The first, byMessrs. L.M. Hull and J. K. Clapp"(US) deal with a multivibrator havingonly dissymmetrical plate resistors; oneof these has a value 5 to 50 times great-er than the other. Such an unsymmetri-cal relationship in the respective plateloads causes greater changes in platecurrent across the smaller resistor thanacross the larger. Thus, allowing thesymmetrically loaded tube to function asa straight resistance -coupled amplifier,and the unsymmetrical tube to operateas an unstabilized amplifier over thecomplete tube characteristic front satu-ration to cut off. The Hull and Clappsystem can be analyzed by practicallythe same methods used in studying thesymmetrical multivibrator, except that itis necessary to consider the dissymmetryin the plate resistors, all other factorsremaining substantially equal.

The second and third engineering pa-pers of technical interest, written by F.Vecchiacchi (Italy) and R. N. Harmon'"(US), respectively, describe a system inwhich the ratio of the condenser dis-charge time -constants are not equal,plate circuits, however, being symmetri-cal. A small difference exists betweenthe Vecchiacchi and Harmon circuits,the latter containing a small inductancein the common plate lead. This induc-tance causes periodic interruptions tothe relaxation frequency which stabilizesthe operation of the system. Incidental-ly, this is one of the features of theHarmon patent. Upon a careful studyof the aforementioned circuits, it hasbeen found that both may be investigtted by practically the same analyses. For-tunately, the technical material embodied in the Harmon patent contains acomplete complement of analytical datafreighted with such clarity that por-tions of this interesting paper have beenabridged and appear below in the ex-planation.

Explanation of the Unsymmetrical Mul-tivibrator

An unsymmetrical multivibrator cir-cuit is shown in Figure 9. Attention iscalled to the time constants of the two

9 Hull & Clapp, Proc. IRE. Vol. 17. No.2, pp 252, 1929

10 US. patent No. 1.936,789 ; assigned tothe Westinghouse Elec. & Mfg. Co., Pitts-burgh, Pa.

Page Ten

condensers Ca, C, which are adjusted sc.that the ratio between them T1/T2 is, asnearly as possible, an integer. The ad-justment merely consists of either mak-ing condenser C1 considerably smallerthan C, or by making resistors R, andR, considerably smaller than resistorsR, and R2, or both of these expedients.

GENERAL EXPLANATION: Whenthe multivibrator is controlled by a vol-tage such as illustrated in Figure 10,curve "a", a voltage like that shown incurve "b" will be obtained in the out-put of tube VT -1 which gives rise, in theoutput transformer to a voltage repre-sented by curve "c." It will be observedthat curve "b" has a square wave -form

InputControlH

R1

R1

B3

Harmonic FilterNetwork

Figure 9

ginning at the beginning of the periodrepresented at point 3 and continuingthroughout this period. At the end ofthe period, the amplitude returns to itsoriginal value. A similar but much lessconspicuous decrement is illustrated bycurve "c" and may be observed bynoticing the peak, see point 4, is not ashigh as its neighboring peaks and thetrough, point 5, is not as deep as theneighboring troughs.

If a voltage is injected into the cir-cuit corresponding to curve "c", theoutput wave -form will closely resemblecurve "a." When this is done,. the onlyreadjustment of the constants of theapparatus required is in the output eir-

IR4

RFC

Out

n nnfinnn n r<r

-7-1nnnnn"z1 f\A

of uniform character except that, atpoint 1, a single wave has been omitted.

The omission of a single cycle of thehigh -frequency, square -wave -form poten-tial corresponds to the adjustment inwhich the time constant of condenser C1is nearly equal to the time constant ofcondenser C. If these constants are lessnearly equal, the potential delivered byVT -1 will be similar to that shown incurve "d," and the period :luring whichthe square -wave -form pulses will not bedelivered is greater, as illustrated atpoint 2. Curve "e" illustrates the po-tential which will be delivered by theoutput transformer under these circum-stances. It will be observed that a (lee-rement shown by curve "e" occurs, be -

PIA. 30cuit which now must be changed to alow frequency.

The following results have been ob-tained experimentally: if the inductanceof coil Lx is omitted from the circuit,a more critical adjustment of the con-densers and resistors is required in orderto produce the results described. Thecondition pending upon the multivibra-tor being under control. If the system isnot controlled, and inductance Lx isomitted, the apparatus will give rise toa square -wave -form in the output ofVT -1 which may be controlled, tosome extent, by adjustment of the ratiobetween the time constants of the twocondensers, but under these circumstanc-es, the adjustment is exceedingly critical,

COMMERCIAL RADIO

many harmonics will be present and theinterruptions to high frequency, repre-sented at points 1 and 2, will not occur.

When the controlling voltage and Lxis omitted, similar results may be ob-tained by inserting an inductor in theconnection between resistor R, and theplate of VT -1 or between R, and theplate of VT -2. The results obtained arenot very stable when the inductor is in-serted at the points mentioned.

Analysis of Circuit OperationsThe anaylsis about to be given here

differs from that previously given on thesynunetrical multivibrator, because thetime constants of the condensers are un-equal in the structure here proposed andare equal in the structure previously an-alyzed in these parts. There is a fur-ther difference which results from thepresence of inductance.

Oscillographic observations show thattubes VT -1 and VT -2 are alternatelyconductive and non-conductive, becauseof the grid potential changing past thecut-off point. Curves which have beenprepared from oscillographic observa-tions are represented in Figure 11.Curve "f" represents the plate currentthrough VT -2. Curve "g" representsthe charge on condenser C,. Curve "h"represents the potential on the grid ofVT -1. Curve "i" represents the platecurrent through VT -1. Curve "j" repre-sents the charge on condenser C,. Curve"k" represents the grid potential intube VT -2. Curve "L" represents thepotential across Lx. The part of thecurve above the zero axis represents thepotentials directed upward in Lx. Curve"in" represents the control voltage.

Refer now to Figure 12. The momentat which the tube VT -2 changes from aconductive and approaches a non-con-ductive condition is represented by point6 in curve "f'' of Figure 11. As a con-sequence, although not all of the conse-quences, of the change of current thruVT -2, is that of the potential of theplate of the tube rises, because of the po-tential drop across R, which approacheszero. As the plate voltage on VT -2 in-creases, the condenser C, will receive acharge from battery 1 over the circuit 1,2, 3, 4, 5, 6, 7 and return. The increasein the charge on C, is represented by theupward trend at point 7 of curve "g"of Figure 11. The charging current flowsdownward in R, as the diagram is drawn.Therefore the grid of VT -1 which isconnected to the upper terminal of thisresistor, is positive relative to the fila-ment of the tube, which is connected tothe lower end of said resistor. This isindicated by the fact that point 8 ofcurve "It" is above the line.

VT -1 becomes conductive because itsgrid is positive. At the same time, thereis some current flow from the grid to thefilament in this tube and, therefore, thecharging circuit for C, includes the grid -filament path in VT -1 in parallel with R,.The current drawn by the plate of VT -1during this time is represented at point9 of curve "i."

Condenser C1 will continue to charge(luring the time fixed by its capacity andthe resistance of the charging circuit.The conditions just described, namely,VT -2 non-conductive, VT -1 conductive,will continue until the charging of C, iscompleted.

When the condenser C, is completelycharged, as indicated at point 10 ofcurve "g," no more current will flow in

SEPTEMBER, 1933

7 .s' 34

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r(r[-. ,.h:V=1 nn n

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Figure 1:2-Unsymmt tricalof Parts:R,-60,000 ohmsR,-60,000 ohms123-11,000 ohms

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R,-11,000 ohmsL.-5 henriesC,-.015 microfarlds

the charging circuit. The drop over Rtherefore, becomes zero, and the poten-tial of the grid of VT -1 will fall, asshown by point 11 of curve "h."

Even though the potential of the griddoes not fall below the cut-off point forthe tube, it falls enough to cause a dim-inution in current through VT -1. Dimi-nution in this current causes an increasein the plate potential of VT -1. The in-creased potential is impressed upon con-

microfarads

denser Q. which begins to charge asshown at point 12 of curve "j."

That the condenser C, was, at thismoment, either completely or partiallydischarged, is a consequence of the factthat VT -1 had been conductive duringthe period C, was charging. The dis-charge circuit for C, was thru VT -1 toground and from the ground thru theelements 7, 6, and 8.

(Continued on Page 18)

Page Eleven

DESIGNING THEMIDWEST ALL -WAVE 18

By WALTER SHIRK*THE difficult designed problem encoun-

tered in developing the receiver hav-ing enormous range of 4% meters to2400 meters is without a doubt the os-cillator. It is a very serious task to de-velop a circuit giving uniform oscillatorvoltage for the American broadcast bandwhich covers only a tuning ratio of threeto one frequency range. It is muchmore difficult to obtain a circuit thatwill cover the enormous range of 530to 1. Both the oscillator and radio fre-quency circuits require special atten-tion. In addition, the terrific losses en-countered at sixty-five million cycles persecond almost prevent even feeble oscil-lation. At these frequencies it is neces-sary to deliver very large amounts ofenergy to the grid of the mixer tube inorder to produce proper heterodyne ac-tion.

/.1.,,o

Or

FiCoOitti OrcAVor

The customary oscillator circuit con-taining a "tickler" coil in the platecircuit for feeding back energy to thegrid circuit, fails to deliver sufficientfeed -back to sustain oscillation unlessthe period of the plate circuit is veryclose to the period of the grid circuit;or unless the coupling is exceedinglytight. Both of these methods limit thetuning range of the grid circuit, eitherbecause of the exceedingly high distrib-uted capacity introduced or because ofthe period of the primary, interferingwith the tuning of the secondary.

A further difficulty encountered withthe customary type oscillator circuit isthe non -uniformity of the output thru-out these higher frequency bands. It isnoted that the output tends to decreasevery rapidly at one end or the other re-gardless of what circuit is used. All ofthese difficulties can be solved by meansof the "Colpitts" oscillator, providedthat a two -gang condenser is used fortuning the coil, thus insuring uniform-ly increasing feed -back proportionate tothe frequency. In this manner the lossesare successfully overcome.

The "Colpitts" circuit is fundamen-tally a tapped condenser rather than atapped coil as shown in Figure No. 1.The voltage generated across the coilis divided in inverse portion to the ca-pacity of the condenser as shown.

In the event that one of these condens-ers is fixed the feed -back is not uniform,therefore, it is very desirable that thetwo condensers should be equal at alltimes, thus a two -gang condenser is re -

(Continued on Page 17)

*Midwest Radio Corp.

Page Twelve

AIRWAY NEWS1:341r--0.Nnr-4.41/.--...41P-041/-41r......41r-trAille-wAltHOW EASTERN HANDLES

WEATHER REPORTS

AN octopus -like system of teletypelines and radio channels, tapping

the 25 cities on the 3,755 -mile EasternAir Lines routes, is centered in, the wea-ther -operations office of the airline atWashington, D. C., comprising the elab-orate new weather department which op-erates 24 hours of the day, out -guessingnature in all her angry moods.

The Air Mass Analysis System of wea-ther forecasting, proved practical forairline operation only a few years agoon the Pacific Coast, has been institutedby Joseph George, chief meteorologistof Eastern Air Lines. In 1932 he col-laborated with scientists of the Califor-nia Institute of Technology in testingthe method over a western airline.

The communications tentacles of thecompany weather bureau follow the threegreat air routes of Eastern Air Lines;New York to Miami, New York to NewOrleans, and Chicago to Miami. Weath-er information is not only received byteletype and radio from the 15 statesserved by the airline, but two generaland 46 trip forecasts are issued fromthe "octopus -like brain'' (luring the 24hours, or practically one every one-halfhour.

In the general forecasts sent to everystation at 9:30 a.m. and 9:30 p.m., theEastern Air Lines Air Mass forecastsadvise what trips will complete or can-cel and where delays will occur beforethe weather clears. The special trip -forecasts are sent to pilots and dispatch-ers an hour before scheduled departuresat the six major terminals so that astudy can be made before any particularflight takes off.

Supplementing hourly reports fromvarious eastern points, the United StatesWeather Bureau also supplies the East-ern Air Lines Weather Bureau with twogeneral weather reports from the 250major weather bureau stations as farnorth as Point Barrow, Alaska, Cana-dian stations, and 10 ships at sea inthe Atlantic Ocean. These reports arereceived at 8:25, a.m. and 8:25 p.m.

The information received by the air-line and also that disseminated, givesceilings of clouds, visibility of stationsand the airway, general conditions, suchas rain, snow, haze, fog and type ofcloud formations, temperature, dewpoint,wind direction and velocity and baro-metric pressure.

In connection with the new weatherdepartment, Eastern Air Lines has in-augurated scientific treatment of eachof the 24 flights made during the 24hours over its vast system. After col-lecting information on winds aloft, theirspeed, and general weather conditions,the weather department determinesmathematically the correct altitude,course, and cruising speed for the pilotto use to reach his destination in thefastest time with the greatest comfortto passengers.

Monteagle, Tenn., StationTHE Monteagle Airway Station is on

top of Cumberland Mountain, thehighest point on the Chicago -Miami run,and is the midpoint between Chattanoo-ga and Nashville. Since being commis-sioned in November 1930, the stationhas been in operation twenty-four hoursa day. There are three operators orkeepers assigned to this post and in ad-dition to operating and maintaining theradio and teletype equipment and wea-ther observing, they are required to keepup the grounds and station building andequipment in general.

The station has a marker type radiorange transmitter that is used when ceil-ing and visibility are low and for an-swering calls from passing ships. Tworadio receivers are used for ground toplane communication and for monitor-ing the Nashville Radio Range Trans-mitter. There is a tape teletypewriteron the Nashville -Atlanta line which isused for dispatches and to gather wea-ther data to and from all stations onthe line to be used by weather forecast-ers at the larger airports.

The three keepers are William A. Cole-man, Dentis Milam and G. E. Knight.Mr. Coleman came to Monteagle in 1932andcame to Monteagle in the same year andMr. Knight was transferred fromAdairsville, Ga., about four months ago.

Monteagle is a summer colony popularwith people from Nashville, Chattanoo-ga and Atlanta. The elevation is 2000feet and one sleeps under a blanketeven in July. The station is, in a beau-tiful location and can be seen to the leftof the Chattanooga -Nashville highwayjust before starting the descent on thenorth side of the mountain.

NEW RADIO STATIONIN SECOND DISTRICT

THE Second Air Navigation DivisionDistrict of the Bureau of Air Com-

merce is opening or about to open eightnew stations. These are located in thesoutheastern part of the United Statesin the following places: Vero Beach,West Palm Beach and Daytona Beachin Florida, Savannah and Brunswick inGeorgia, Warrentown, North Carolina,and Lane and Beaufort, South Carolina.

Beaufort, Lane and Warrenton willbe weather observing and teletype sta-tions in all probability, and there willbe a keeper and three assistants at eachof these places. It is expected that theother stations will be larger and equip-ped with radio facilities and that an as-sistant radio operator and three juniorswill be assigned to each of these radiostations.

There is some talk of a radio stationfor Florence, south Carolina, but theOffice has not announced what the per-sonnel would be for Florence.

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The Barkhausen Oscillator

THE Barkhausen oscillator for ultra-high frequencies has been the sub-

ject of many complicated analyses. Aswith other developments, the history ofits theory has gone through three stag-es starting with a simple but incom-plete concept advancing through a moreand snore involved mathematical analy-sis, and finally yielding the importantproperties in simple enough form to bestated in everyday language.

The elementary concept upon whichthe explanation of the Barkhausen os-cillator was originally based was thatof an electron or group of electronswhich danced back and forth through theopening, in a positively polarized grid,Among other things this concept did notshow why the number of electrons go-ing in opposite directions through thegrid was not always the same. Themathematics which followed led in manycases into strange paths, but finally wasplaced on a sound basis. When this hadbeen done it was found that the expla-nation could be made in a perfectlystraightforward way, and that the orig-inal concept of the dancing electroncontained only enough truth to delayand complicate the process of arrivingat the correct answer.

Physically the Barkhausen oscillatorconsists of a filamentary cathode sur-rounded by a cylindrical grid and plate,as shown in Figure 1. The grid is oper-ated at a positive potential, the plate isbiased to a slightly negative potential,and a tuned circuited LC is usually con-nected between them.

Electrons starting out from the cath-ode are attracted by the positive grid,and move with increasing velocity in thatdirection. Many of the electrons hit thegrid, and become of no further concern.Many others, however, pass between thegrid wires without hitting them andmove toward the plate with decreasingvelocity, coming to rest just beforereaching the negative plate and thenstarting back toward the grid again. Asbefore, a given electron may hit the gridor may miss it again and continue ontoward the cathode, when the cycle isrepeated.

If the tube were not oscillating, thestory would now be complete. A con-venient way of seeing what causes theoscillations in the tube is to investi-gate what happens when a transient os-cillation is produced in the LC circuitby some external means. If the forcesproduced on the moving electrons bythis transient deliver energy to the elec-trons, the transient will die out; but ifthe electrons, having acquired kinetic -en-ergy frolit the grid battery, can opposethe forces set up by the transient andthus deliver energy to the circuit, thetransient will persist or build up as acontinuous oscillation instead of dyingout.

In the absence of the transient, anelectron starting from the filament movesin the direction of the force from thepositive grid, and so draws energy from

SEPTEMBER, 193

By F. B. LLEWELLYNMember of Technical Staff ; Bell Telephone Labs.

the grid battery. After passing throughthe grid wires, the electron movesagainst the force from the grid, thusreturning energy to the grid battery.When it comes to rest in the grid -platespace, the entire amount of energypicked up in the cathode -grid space hasbeen restored to the battery. During thereturn trip, the same sequence again oc-curs: the energy which was abstractedin moving toward the grid is restoredin moving away from it. The net resultis that energy is neither absorbed fromnor delivered to the external circuit andbatteries by such an electron. This factis made graphically evident in Figure 2,where the force from the batteries whichacts on the electron is plotted as ordi-nate while the distance the electron hasmoved from the cathode is taken as ab-scissa. The area under the curve conse-quently measures the work done on theelectron during its trip across the tube:the positive work done between cathodeand grid is just equal to the negative

Fig. 1-This general arrangement oftube elements and circuit is used in theproduction of Barkhausen oscillations

CATHODE PLATE

Fig. 3-Because the work done on anelectron of the useless type by an alter-nating force is positive, the electron ab-stracts energy from the alternating -

current transient

work done between the grid and theplate.

When the transient is introduced intothe LC circuit, conditions areconsiderab-ly changed. Superposed on the force dia-grammed in Figure 2 is the force set upby the alternating grid potential. Sincethe latter force alternates the resultantforces acting on electrons which startout front the cathode at different timesin the alternating -current cycle will bequite different. For purposes of illus-tration, it is sufficient to trace the his-tory of two electrons only. One of thesestarts out just at the time when the al-ternating force begins acting in thesame direction as the constant force of

Figure 2. The other starts out a halfcycle later, when the alternating forcebegins to oppose the constant force.

In the first case, the alternating forceincreases in intensity as the electronmoves along, then decreases to zero, thenreverses and opposes the motion, and fi-nally completes the cycle by becomingpositive again. If the electron passesthrough the grid mesh just before thealternating force returns to its first zerovalue, the action of the force upon it isas shown in Figure 3. At the instantthe electron passes through the grid, ofcourse, the direction of the force actingoa the electron reverses, not because ofany abrupt change in the grid potential,but because the grid is now located be-hind the electron instead of ahead ofit. As the electron moves on toward the

Fig. 2-When a constant is applied tothe grid of a vacuum tube constructedas shown in Figure 1, the force exertedon the electron at various points in itstrip acrossi the tube is as shown by thecurve. The work done on the electron istherefore measured by the area under the

curve

CATHODE

1.1

GRID PLAT

Fig. 4-With ass alternating farce, anelectron of the useful type delivers en-ergy to the transient, at the expense ofthe battery producing the constant force

plate, however, the alternating force de-creases to zero and then reverses. Thusduring both halves of the cycle the forcearts in the same direction as the electronis moving, and delivers energy to it, ascan be checked by reference to the areaunder the curve in Figure 3. In otherwords, the transient in the external cir-cuit has done work on this particularelectron, and the electron, by taking en-ergy away from the circuit, has produceda tendency for the transient to die out.

There is nothing in this behavior thatgives encouragement to the maintenanceof oscillations. The only consolationcollies from noting that the electron is

(Continued on Page 17)

Page Thirteen

Win

Tin EDITORr Contributions to these columns are

invited from readers. They should be ii concise and may deal with technicalj articles published in previous issues, I

or other subjects of some general in- iI terest and professional importance.

Statements made by writers do notnecessarily carry the endorsement of

! this publication. Address all corn-Lunications to the Technical Editor.

Upon the Propagation of Micro -WavesHere is an interesting question ex-

cerpted from an article appearing in anItalian radio journal: How can ultra -short waves that were not reflected bythe ionosphere be carried beyond the op-tical horizon/

The author of the above article, Mr.I. Gianfranceschi, answers this perplex-ing question by saying: "Transmissionoccurs by defraction and refraction; ofthe latter, the curvature of the upperatmosphere deflects the trajectory ofthe rays-similar to that of optical phe-nomena."-E. Scientiarum Nuncio Radi-ophonico, No. 24, July 27, 1933. (Seealso COMMERCIAL RADIO, W. Goodall,"The Ionosphere," Vol. IV, No. 6, pg.9, 1935.

*

Note on Designing Noise ControlsThe noise control which masquerades

under the so-called name of "tone con-trol" functions only to by-pass such fre-quencies that are not desirable in theoutput. Usually, noise frequencies arein the upper end of the spectrum and,their attenuation sometimes helps inclearing up QRM; more often the use ofthe device distorts all definitive qualitiesof reproduction. However, those wish-ing to properly design a noise controlwill find the following data of inestima-ble value.

A formula to represent the attenua-tion of any frequency above a standardauricular frequency of 16 cycles for usein designing a noise control is given be-low:

(6.28 CR)2 .0039DB = 5 Log

1(6.28 CRY

symbols: C, farads; R, resistance inohms; f, loss frequency

If, for example, an optimum value of150,000 ohms was given to R, and .01microfarad to C, noise frequencies in theupper end of the spectrum would begreatly (not completely) attenuated;and conversely, if R had a low value,say 50,000 ohms, and C, 1 microfarad,noise frequencies from 5000 down to3000 cycles would be completely sup-pressed. The response below 3000 cyclesbeing augmented to a certain degree.-(See also COMMERCIAL RADIO, "FactorsAffecting Sound Reproduction," Vol.III, No. 21, pg. 5, 1934.)

* *

Release of Gas During Storage BatteryCharging

(J. Lester Woodbridge, The ElectricStorage Battery Co., Phila., Penn.) Theconversion of lead sulphate (PbSO4) in-

Page Fourteen

to lead peroxide (PbO,) in the positiveplate and lead in the negative plate isnot the only reaction occurring whilecharging current is passing. These arethe preferential reactions and take placeso long as there is sufficient sulphatedactive material accessible to absorb thecurrent, and diffusion can take place ata rate which will prevent excessive acidconcentration in the pores of the plates.Whenever the charging current exceedsthis value, the excess which cannot beused for charging the active materialcauses decomposition of the water of theelectrolyte into hydrogen and oxygenwhich are released as gas bubbles-thehydrogen at the negative plate and oxy-gen at the positive. A higher voltage isrequired to release Igas than to chargethe active material so the beginning ofthe active gassing is indicated by a com-paratively rapid rise of voltage at thecell terminals.-According to Faradayslaw a given amount of current passingthrough an electrolytic cell can produceonly a definite amount of electro-chemi-cal reaction. Hence, that part of the cur-rent which produces gas by decomposingthe water in the electrolyte cannot haveany effect in charging the active mater-ial. This applies separately to the posi-tives and to the negatives that is, thesame current which produces gas (oxy-gen) at the positive plate after the plateis fully charged may still be chargingthe active material of the negative plate,if the plate is not fully charged; butany part of the charging current whichproduces gas at both plates is absolutelywasted as far as charging the active ma-terial is concerned.-Electrical Engineer-ing, Vol. 54, No. 5, 1935

*

Amplitude and 'Frequency ModulationDefined

(J. G. Chaffee, Bell Tel. Lab., N. Y.)One of the fundamental differences be-tween the two systems of modulation isthe following:

In amplitude modulation the varia-tions in the energy associated with thehigh -frequency wave which occur duringmodulation are primarily supplied bythe source which energizes the transmit-ter.

In a system employing frequency mod-ulation the energy in the high -frequencywave remains constant during modula-tion, and the energy which is associatedwith the useful output of the detector issupplied by the source which energizesthe receiver.-Proc. I. R. E., Vol. 23,No. 5, 1933.)

* * *

Conduit Microphone Developed(P. W. Williams, Muirhead & Co. Ltd.,

London) A conduit microphone designedby P. W. Williams, and exhibited atKings College, London, represents amarked departure from existing practice.The basic idea is effective removal ofthe microphone from the sound field byattachment to its input side of a longconduit. The standing waves set up be-tween the microphone and the open endof the conduit are damped out by meansof an acoustic resistance, which consistsof a second conduit fill will wool "be-

yond" the microphone. The microphoneassembly, which consists of a fine alumi-num ribbon suspended between polepieces (velocity microphone), is so de-signed that no reflection of sound wavestakes placd at the strip, with the resultthat the vibrations of the strip are sub-stantially proportional to the vibrationsof air at the mouth of the conduit. Oneadvantage of the conduit microphone isthat it has the quality of "acousticsmallness," and thus gives rise to lessdistortion of the sound waves withoutthe disadvantage of insensitivity and fra-gility which must necessarily be presentin the use of microphones which are in-trinsically small. - Electrician, Vol.CXIV, No. 2954, 1935 "

* * *

Push -Pull vs. Parallel Operation(J. N. A. Hawkins, Eng., Pac. Bldg.,

San Francisco, Cal.) The recent devel-opment of low C tubes makes it easy topractically eliminate former difficultiesencountered from parasitics and insta-bility which accompany parallel opera-tion of vacuum tubes. Parasitics arelargely caused by stray inductance andcapacity in the tubes themselves, as wellas in the connecting leads between thetubes and the associated grid and platetank circuits. Parasitics are not con-fined to tubes in parallel, but are in factnearly as common in push-pull circuitsbecause the inductance of the leads whenconnected through the tank tuning con-densers can form an ultra -high frequen-cy tuned -grid tuned -plate oscillator. Thiscauses oscillation at a frequency otherthan that desired, with consequent lowefficiency and reduced power output, aswell as resulting in a poor note.

Parallel operation has many advan-tages over push-pull operation, even atthe higher frequencies, provided low Ctubes are used. The plate tuning con-denser can be one of a cheaper varietyfor a given tuning capacity and oneneutralizing condenser is eliminated forparallel operation. The tubes are usual-ly easier to drive to a given output whenused in parallel, due to the higher trans -conductance of the two tubes in parallel.The amplification factor is the same fortwo tubes in parallel as it is for on3tube, whereas the plate resistance is cutin half.

High C tubes, such as the 45, 2A3, 10,211, 203A and 204A should generally beused in push-pull below 40 meters be-cause the high capacity shunted acrossthe plate tank when high C tubes areused in parallel makes the use of a lowC, low loss tank circuit impossible.

Another advantage of parallel opera-tion is that it permits the use of thesimplified PI antenna coupler systemfor effective reduction of illegal radia-tion of harmonics. This system alsogives continuously variable antennacoupling.

When three tubes are used in paral-lel there is less tendency for parasiticsthan when two tubes are paralleled. Thisis because the addition of the third tubeunbalances the TPTG ultra -high fre-quency oscillator effect which sometimesresults from the inductance of the leadswhen two tubes are used in parallel.-"Radio," Vol. 17, No. 7, Pg. 26, 1935

COMMERCIAL RADIO

NEW APPARATUSGRINDER USED IN

SOUND EFFECT

MANY successful sound effects havebeen created using the DeLuxe

Hand-ee Grinder as the motor power.Doubtless in your connection with theradio broadcasting field you are familiarwith the reluctance sound effect menhave in divulging details of their pro-fession. To our personal knowledge atleast three effects were created and theDeLuxe Hand-ee used, together with the

foot speed control, replacing larger andheavier equipment formerly used for thesame effect.

The foot speed control is a rheostatdevice we have developed for control-ling the speed anywhere within a rangeof 300 to 25,000 r.p.m. Of course in thesound effects created velocity plus speedof the tool was used to give that particu-lar sound created only by high speed.In one case the rise of an elevator in alarge building was imitated, the speedof the tool being varied by using footspeed control to designate the progressof the passenger car upwards. This ef-fect was as a background to dialoguewhich was carried on during the radiosketch.

The unit has been successfully used ina barber shop scene of a rather promi-nent sketch which recently was heard ov-er one of the large networks. In this casethe set screw on the chuck was loosenedwhen the tool was revolved, the clickingserved as a perfect imitation of bar-ber 's clippers. The dialogue called forthe man in the chair to fall asleep andthe barber to increase his speed of con-versation as he progressed with the hair-cut. As the conversation was increasedthe motor was also increased in speedby the foot speed control and the ef-fect created was most realistic.

In addition to the foregoing manysound effects have been created withthe Grinder, details of which we are un-able to divulge. In addition, the serviceengineers have found use for the toolsin polishing jacks, removing pit marksfrom relays to secure a smooth contact.

SEPTEMBER, 1935

NEW CRYSTALMICROPHONE

A new diaphragm -type crystal micro-phone, especially designed for highly -effective communications service in air-ways, police, commercial and amateurradiophone systems, has recently beenannounced by Shure Brothers Company,

"Microphone Headquarters," 215 West.Huron Street, Chicago. The new modelis known as the 708, and is furnishedwith a convenient desk mount and two -conductor shielded cable.

The 70S has been designed to producea higher effective percentage modulationon "intelligibility" speech frequenciesthan can be obtained with the ordinaryspeech -input system. It is well knownthat low -frequency speech components,with their high peak amplitudes, establish the overload level of the speech -inputand modulator, yet they contribute verylittle to the intelligibility of the signal.This limiting factor has been largelyeliminated. The response increases lin-early a total of 20 db in progressingfrom 60 to 2,000 cycles, is substantiallyuniform from 2,000 -to above 4,000 cycles, followed by gradual cut-off. Theresponse curve is 'entirely free fromsharp peaks which tend to produce"harsh" reproduction. The rising characteristic attenuates the low "overload"frequencies and results in clear speechwith effective side -band power doubleor more than usually obtained from thetransmitter. Front a communicationsstandpoint, this is equivalent to doub-ling the carrier power with its attendantincrease in signal-to-noise ratio. In ad-dition, there is a real improvement inthe output signal quality from highlyselective receivers.

Candler Moves to Asheville

Walter H. Candler, President of theCandler System Company, announcesthat he has moved his school to Ashe-ville, N. Car. Mr. Candler, althoughborn in the vicinity of Asheville, hasbeen a resident of Chicago for twentyyears or more, during which time hehas been teaching his original method ofhigh-speed telegraphing to thousands ofradio and American Morse operators.

SPECIAL SPARK PLUGFOR RADIO CARS

A new type spark plug for carsequipped with radio, has been developedby engineers of the AC Spark Plug Co.The new development makes possiblebetter radio reception along with goodengine performance, AC engineers de-clare.

The new spark plug is designed witha resistor unit built into the insulator.

To replace resistor, remove terminal (A),take out screw (B), and shake out thespring (C), and resistance unit (D).Clean both ends of spring with emerycloth. (E) indicates the center electrode

The resistor unit can be removed andreplaced when it becomes ineffectivewithout replacing the entire spark plug.Because the resistor unit is close to thepoint where the actual spark takes placein the cylinder, noise or click from theradio receiver is reduced to a minimum.

Press Wireless to EthiopiaAUTHORITY was granted to Press

Wireless, Inc. on July 19th to in-clude Addis Ababa, Ethiopia, as a pointof communication. Press Wireless wasthoroughly explained in our October1934 issue, as rendering a service to cer-tain member newspapers.

Complete news from the Ethiopianfront is expected to come over this newradio link first hand to those papersserved by Press Wireless, Inc.

Airway NewsGeorge Shuman, at the Airway Radio

Station, Shushan Airport, New Orleans,is a hustling chap. Stands his watch,then goes to his shop and turns outcracker -jack keys for telegraph work.George, to you old timers, is the samewho used to work the United Fruit line.

If present plans work out, the samesystem of blind approach landing now'in operation at Newark, will be in useat Washington Hoover Airport, Wash-ington, D. C., Atlanta, Buffalo, Chey-enne, Indianapolis, Los Angeles and St.Louis.

Page Fifteen

Actions of The Federal Communications CommissionCALL SIGNALS ASSIGNED

Name ofStation

CallSignal Owner and/or Licensee

"Princeton"

Unda MarisIdleo 48Kinkajou

Gallant LadyF. B. SquireSeminole

Va TianNaugatuck

Brown Bear

Clearwater, Fla.Oak Park, Ill.Green Bay, Wis.Wilkes-Barre, Pa.Winter Haven, Fla.Ada, OklahomaLafayette, Indiana

Springfiehl, Ill.

Redwood Falls, Minn.

Portable

Aniak, AlaskaHyder, Alaska

(changedDestrehan, La.Kasilof, AlaskaDeering, AlaskaPortableDeering, AlaskaHawk Inlet Camp

Alaska (Portable)Kasilof, Alaska KIOZ Territory of Alaska

Aeronautical and Aeronautical Point to PointSummit, Ill. WEEO Aeronautical Radio, Inc.Casper, Wyo. KNCK Aeronautical Radio, Inc.Cheyenne, Wyo. KNCL Aeronautical Radio, Inc.Billings, Mont. KNCM Aeronautical Radio, Inc.Sheridan, Wyo. KNCN Aeronautical Radio, Inc.Denver, Colo. KNCO Aeronautical Radio, Ing.Motor launch "Midway" KNCP Pan Amer. Airways, Inc.Motor launch "Wake" KNCQ Pan Amer. Airways, Inc.Portable -mobile KNCR Pan Amer. Airways, Inc.West Yellowstone, Mont. KNCS Aeronautical Radio, Inc.

Commercial AircraftNC -876M KHAFK C. P. HoafeyNR -10239 KHAFL Thor Solberg Aviation CorNC -13464 KHAFM Reginald H. Jackson, Jr.NC -14924 KHAFN American Airlines, Inc.NC -14925 KHAFO American Airlines, Inc.NC -14566 KHAFP Westchester Airplane SalesNC -6V KHAFQ S. ('. Johnson Son, Inc..NC -11176 KHAFR Delta Air CorporationNC -11177 KHAFS Delta Air CorporationNC -11174 KHAFT Delta Air CorporationNC -14599 KHAFV Delta Air CorporationNC -10846 KHAFW Delta Air CorporationNC -14598 KHAF X. Delta Air CorporationNC -15061 KHAFY Inter --Island Airways, Ltd.NC -15062 KHAFZ Inter--1st:Ind Airways, Ltd.NC -14945 KHAGA Max C. FleischmannNC -15551 KHAGB Pan Amer. Airways, Inc.

Aviation Obstruction Marker BeaconMason, 0. (near) WOEW The Crosley Radio Corp.

Commercial BroadcastRockville, Md. WRMD The Monocacy Broad. Co.Brady, Tex. KNEL G. L. BurnsPage Sixteen

Commercial ShipWOFT

WOFSWOFUWOFV

WOFWWOFYWOFZ

Board of National MissionsPresbyterian Church

Edward K. HauseElectric Boat Co. of N. Y.Dwight H. Baldwin of Maui,

T. H.Mendle C. RiggsBuckeye S. S. CompanyFederal Emergency Relief

Adm.WOGA F. B. WoodworthKJSJ Radiontatine Corporation of

AmericaGovernment ShipWWFZ Dept. of AgricultureMunicipal PoliceWQFK City of Clearwater Police DeptWQFL Village of Oak ParkKNHB City of Green BayWQFM City of Wilkes-BarreWQFN City of Winter HavenKNHC City of Ada Police Dept.WQFQ City of Lafayette Police Dept.

State PoliceWQFP State of Illinois, Dept. of

Public Works and Bldgs.KNHD Bureau of Criminal Apprehen-

sion, State of MinnesotaWQFR State of New York, Division

of State PolicePoint to Point Telegraph

KIOQ Lee S. GardnerKIOP Hyder Radio & Telephone Co.

from KDF)WOEU RCA Communications, Inc.

Territory of AlaskaTerritory of AlaskaAlaska Empire Gold Min. Co.Territory of AlaskaAlaska Empire Gold Min. Co.

KIOWKIOVKIOXKIOR

P.

Name ofStation

CallSignal Owner and/or Licensee

Del Monte, Calif. KDQ.N' Richard Field Lewis(changed from KFUH)

Boston, Mass. WCOP. Joseph M. Kirby(changed from WMFH)

Hilo, T. of Hawaii KHBC Honolulu Broadcast. Co., Ltd.Broadcast Pickup

Portable WOEB Agricultural Broadcasting Co.Portable KNEC Puget Sound Broad. Co., Inc.Portable -Mobile KNED Carter Publications, Inc.Portable -Mobile KNEF Radio Service Corp. of Utah

General ExperimentalHull, Mass.Portable -MobileWoodbridge, N. J.Portable -MobilePortable -MobilePortable -MobilePortable -MobilePortable -MobileAlpena, Mich.Portable -MobilePortable -Mobile

Portable -MobilePortable -MobilePortable -MobileStorrs (College Cam-

pus), Conn.PortablePortable -MobilePortable -MobileBelmar, N. J.MobilePortable -MobileTerre Haute, Ind.MobileMobilePortable -MobileSt. Cloud, Minn.

Burlingame, Calif.MobileMobile

Portable(Pacific Islands)

Portable(Pacific Islands)

Avon, Conn.

Portable -MobilePortable -Mobile

W1XEEW9XHAW2XICW2XIDW2XIEW4XASW4XATW1XEFW8XENW9XHBW9XHC

W9XHDW9XH EW9XHF

Town of Hull, Fire Dept.Donald A. BurtonTownship of WoodbridgeBell Telephone LaboratoriesBorough of Deal, N. J.Aeronautical Radio, Inc.Aeronautical Radio, Inc.East Providence Police Dept.City of AlpenaAnderson Broadcasting Corp.Kansas State College of Agri-

culture & Applied ScienceAgricultural Broadcasting Co.Agricultural Broadcasting Co.Agricultural Broadcasting Co,

W1XEG Connecticut State CollegeW7XBK Puget Sound Broadcasting Co.WIOXFQ National Broadcast. Co., Inc.W1OXFR National Broadcast. Co., Inc.

W2XIF Borough of BelmarW2XIG Borough of BelmarW1XEI Westinghouse Elec. & Mfg. Co.

W9XHG City of Terre HauteW9XHH City of Terre Haute\V9XHI City of Terre HauteW9XHJ The Pulitzer Publisher Co.W9XHK Frank 0. Knoll & Julian F.

MeCutchanW6XJK City of Burlingame, Calif.W6XJL City of Burlingame, Calif.\\'6XJM City of Burlingame, Calif.

Special ExperimentalK6XJI Dr. Dana Coman

Dr. Dana ComanK6XJJ

W1XEH Travelers Broadaistisig Ser-vice Corp.

GeophysicalWAAY Sun Pipe Line Co.IYAAZ Sun Pipe Line Co.

SUMMARY OF APPLICATIONS FOR NEWTRANSMITTERS GRANTED

(Telegraph Division)

AeronauticalAeronautical Radio, Inc. Tulsa, Okla.

PoliceCity of Wilkes-Barre, Pa. 2412 Ke

Co. City of Winter Haven, Fla, 2412 KeState of Illinois, Dept. of Pub-

lic Works and Bltigs., Spring-field, Ill. 1610 Kc

City of Green Bay. Wise. 2382 Kc.City of Ada, Okla. 2450 Kc.Bur. of Criminal Apprehen-

sion, State of Minn., Red-wood Falls, Minn. 1658 Kc.

Village of Hibbing, Minn. 2382 Kc.City of Lafayette, Ind. 2412 Kc.

Point -to -PointNorthern Commercial Co.

Hamilton, Alaska :1092.5 Kc.General Experimental

City of Alpena, Mich.Borough of Belmar, N. J.City of Terre Haute, Intl.

:10 watts

50 watts50 watts

1 KW.50 watts25 watts

500 watts50 watts

50 watts

2 watts

25 watts25 watts25 watts

COMMERCIAL RADIO

-.-1C0P7PP.X..T,--r77Frit7,17(4.7,17.1"TV' .Aur,T57F4174-t 111W-trilth

_4,11;

Loftfield & Mathison, Terminal 50 wattsIsland, Calif.

Rockland Co., New City, N. Y. 150 wattsSpecial Experimental

New England Tel. & Tel. Co. Motor vessel Fauci 10 wattsNew England Tel. & Tel. Co. Motor vessel Whalen 10 wattsNew England Tel. & Tel. Co. S. S. Hekla 10 wattsRCA Mfg. Co., New York City 100 watts

UnusualPioneer Sea Foods Co., Cordova, Alaska. Granted temporary

authority to W. Lewis and Harold Tvest to operate radioequipment aboard tenders "Cora B" and "Taku" for 90days, provided these men qualify for proper class licenseswithin that time.

SUMMARY OF APPLICATIONS RECEIVED FORNEW INSTALLATIONS

(Telegraph Division)

Aeronautical Radio,Summit, Ill.

Aeronautical Radio, Inc.Miles City, Mont.

Aeronautical Radio, Inc.St. Louis, Mo.

. AeronauticalInc. 1000 watts

50 watts

125 watts

Peoria Air Associates,Peoria County, Ill.

PoliceCity of Prescott, Prescott, Ariz. 2430 Ke.City of Fort Smith, Fort 2406 Ke.

Smith, Ark.City of Augusta, Augusta, Ga. 2414 Kc.

Point -to -PointKoyukuk Community Radio 252 Kc.

Serv., Wiseman, AlaskaElwin P. Dell, Hooper Bay, 3092.5 Kc.

AlaskaGeneral Experimental

Huntington Police Dept., Hunt-ington, Ind.

City of Hamilton, Hamilton, 0.City of Burlingham, Burling-

ham, Cal.City of Petaluma, Petaluma,

Cal.Wayne Miller, Des Moines, Ia.Star Chronicle Pub. Co.. St.

Louis, Mo.Special Experimental

Press Wireless, Inc., Hicks-ville, N. Y.

Press Wireless, Inc., nr. DalyCity, Cal.

15 watts

10 watts50 watts

250 watts

50 watts

25 watts

15 watts

150 watts50 watts

10 watts

50 watts100 watts

1.2 watts

1.5 watts

The Barkhausen Oscillator

(Continued from Page 13)

moving faster when it approaches theplate than it would if no alternatingforces had acted on it, and consequentlyit will hit the plate even though the lat-ter be at a slightly negative potential.Thus this useless, and in fact harmful,electron is at least prevented from doingstill further harm by being removedthrough the plate from the scene of ac-tion.

Fortunately the other electron, thatleaves a half cycle later than the worth-less one just dismissed, is more useful.From the very start the alternating forceopposes the motion of the new electron,but cannot stop it because the alternat-ing force is never larger than the con-stant force of Figure 2. The electronis therefore doing work against the al-ternating force, delivering energy to thetransient in the external circuit. As theelectron progresses, the phase of theforce changes as shown in Figure 4. Un-like Figure 3, the reversal in directionoccurs before the electron has reachedthe grid, because the force opposing themotion has decreased the speed. Whenpassage through the grid mesh againreverses the direction of the force, theagreeable electron continues to deliverenergy to the circuit transient, as it ap-proaches the plate. Having lost much ofits velocity in transferring its energy tothe circuit, the electron conies to restbefore hitting the plate, and then, urgedby the constant force of Figure 2, startson its return journey toward the grid.At about the same time, the phase of thealternating force again reverses andagain opposes the motion, so that thehapless electron must give up still moreof its energy to the growing transient.

Another passage through the grid fol-lows, accompanied by another reversalin the phase of the alternating force, andthe tormented electron must again yieldenergy acquired from the constant forceto the hungry transient. The energyloss brings the electron to a halt beforeit reaches the cathode, the phases againreverse, and the cycle starts over again.

In its round trip, the useful electron

SEPTEMBER, 1935

of Figure 4 supplies to the transientnearly twice as much energy as the use-less one in Figure 3 abstracted in itsone-way trip. Moreover, the useful elec-tron reaches the cathode again at justthe right time to join with other elec-trons of the useful type and augmenttheir relative number. The action isconsequently progressive, building upmore and more useful electrons.

In practice, operating conditions mod-ify somewhat the mechanism described.For example, space charge near the cath-ode produces more harmful electronsthan useful ones and is to be avoided.Space charge near the plate causes ashift between the phase of the grid vol-tage and the force acting on the elec-trons, which in general tends to raise thefrequency of oscillation. On the otherhand, space charge in general makes theelectrons move slower. Since the slowermotion tends to decrease the frequency,the net result of space charge near theplate is only a small decrease in fre-quency. The tuning of the external cir-cuit can also modify the frequency byabout thirty per cent, but for fixed val-ues of plate, grid, and filament batteryvoltage, there is a particular tuning ad-justment which gives maximum output.

There is a simple approximate expres-sion for determining the proper grid vol-tage and size of vacuum tube to produceoscillations of a given wavelength. Forexample, a tube with a plate diameterof one centimeter, and with 100 voltsapplied to the grid, will produce oscil-lations with a wavelength somewherebetween 100 and 50 centimeters, corre-sponding to a frequency between 300and 600 megacycles, depending on thecircuit adjustments.

It is interesting to note that the samekind of analysis here used to illustratethe workings of the Barkhausen oscil-lator can be applied to the well-knownfeedback oscillators operating with neg-ative grid and positive plate, and showsthat the two are not very different fromeach other after alL The Barkhausenoscillator will probably prove very use-ful in the fields of ultra -short-wavetransmission, which are rapidly cominginto commercial application.

Designing the MidwestAll -Wave 18

(Continued from Page 12)quired for tuning the oscillator circuit

In a commercial receiver it is desirablethat each variable condenser should have

trimmer as indicated at Tg and Tpfor making the minimum capacities uni-form for high speed production. Like-wise in order that the oscillator circuitmay tract with the other condenser re-quired to tune the R. F. coils, the pad -der is inserted as indicated at P. Thus,the entire circuit becomes complicated.

In addition there are by-pass condens-ers and isolating condensers required toprevent the B+ voltage from being ap-plied across the tuning condenser.

With such an oscillator it is foundthat the output is entirely satisfactoryto less than four (4) meters with con-ventional equipment. If all dielectricsare limited to isolantite the frequenciesmay be still further increased.

Design of radio frequency circuits tohandle signals to sixty -million cycles persecond demands very careful design toprevent losses which can easily be sogreat as to cause attenuation of the sig-nal rather than amplification of it. Cer-amics, materials which have the lowestlosses of any materials known, must beused exclusive of any other coil form ortrimmer condenser insulating material.

All parts must be so designed and lo-cated that even very short leads whichwould radiate much energy are unneces-sary. The parts themselves must be usedas lends.

The coils must be so wound, spacedand designed that both the inductanceand capacitive coupling are aiding. Thisis imperative as tight coupling must beused at high frequencies to obtain suffi-cient amplification.

A double ratio tuning knob (fast andslow) is necessary in order that one mayreduce the apparent selectivity of the re-ceiver sufficiently to tune in ultra -shortnave stations.

A careful choice of the type directionand location of the antenna is of espe-cial importance at sixty million cyclesper second.

Page Seventeen

1401\ ---7r,t47.4fir'TeWV4F-N' .44g ","74AKinwOof"'",-IFI-tvi'P"t:XT4t17164-VrrciftVX4/1s,-.

Multivibrators(Continued from Page 11)

The charging circuit for C2 is frombattery 1 thru elements 2, 9, 10, 8, 6, 7and return. The direction of the charg-ing current for C, is downward thru R,and, therefore, the grid becomes positivewith respect to the filament, as soon asthe charging of C2 begins. This is rep-resented at point 13 of curve "k." Thisresults in VT -2 drawing current asshown at point 14, curve " f."

VT -2 being conductive opens a dis-charge path for C1. The discharge cur-rent flows thru VT -2 to ground, thencethru elements 7, 6, 5 and to the conden-ser. Since the discharge current is up-ward thru R, the grid of VT -1 becomesnegative with respect to the filament andVT -1 becomes non-conductive. Moreov-er as there is substantially no inductancein the discharge path, the change in thepotential of the grid of VT -1 is abrupt,as shown at point 15 of curve "h."

It should be noted that the conse-quence of the small decrease in currentthru VT -1 which resulted from the cessa-tion of charging current for C1 causesan abrupt termination of all current thruVT -1 as shown at point 16 of curve "i."

The condition, VT -2 conductive andVT -1 non-conductive, will continue untilC1 discharges. During this time, C, is re-ceiving a charge. (NOTE: UP TO THISPOINT THE DISCUSSION IS SIMI-LAR TO THAT OF THE SYMMETRI-CAL SYSTEM, FROM HERE ON,THE DIFFERENCES SHOULD BECAREFULLY OBSERVED.) This willbe added to the charge which remainedin C, at the moment of change in con-ditions, represented at point 12 of curve"j." The condenser C, will not havebeen completely discharged because itstime constant is slower than the timeconstant of C1. The change from dis-charging to charging was brought aboutby the completion of point 10 of thecharge upon C1, which happened beforethe discharge of C, was completed.

The period now under considerationwill continue until C1 has completed itsdischarge, as indicated at point 17 ofcurve "g." When this discharge is com-pleted, discharge current will cease toflow over R1. The potential of the gridof VT -1 will, therefore, rise from a neg-ative value to zero, as indicated at point18 of curve "Ii," and the tube againwill become conductive. As soon as thishappens, C, will begin to discharge thruVT -1, as indicated at point 19 of curve" j." VT -2 will, thereupon, become non-conductive, the plate potential across thetube will rise, and C1 will begin tocharge, as indicated at point 20 of curve"g." When C, begins to charge, thegrid of VT -1 will become positive, as in-dicated at point 21 of curve "h," andthe tube will become even more conduc-tive. All the changes just noted areabrupt because no inductance is in-volved in any of them. The current thruVT -1, therefore, rises abruptly from ze-ro to maximum value, as indicated atpoint 22 of curve "i."

Conditions are now as they were atthe beginning of this analysis exceptthat the charge upon C, is somewhatgreater than at first. Operations willrepeat themselves in this way until thecharge on C, has increased sufficiently torequire less time for the completion ofthe change than is required for the dis-charge of C1.

Page Eighteen

The analysis that has so far been, giv-en to the unsymmetrical multivibratorsapplies equally well to both Vecchiacebiand Harmon circuits. The remainderof this discussion will deal exclusivelywith the function of inductance Lx, afeature of the Harmon invention.

Consider the moment when C, beginsto receive charging current after thecharge which has been accumulated there-in is nearly sufficient to fill it, as indi-cated at point 23 of curve "j." At thatmoment, VT -2 is conductive, as indicatedat point 24 of curve "f," and the con-denser C, is discharging, as indicated atpoint 25 of curve "g," but C, completes

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its charge, as indicated at point 26 ofcurve "j," before C1 has completed itsdischarge, as indicated at point 27 ofcurve "g." When this happens, thecharging current thru R, falls to zero.The potential in the grid of VT -2, there-fore, becomes zero, as indicated at point28 of curve "k," and the tube, whilestill conducting draws less current thanbefore, as indicated at point 29 of curve"f." VT -1 is, at this moment, in a non-conducting condition, as indicated atpoint 30 of curve "i." The total cur-rent drawn thru inductance Lx, there-fore, diminishes.

The diminution produces an electro-motive force downward in Lx, as repre-sented in the diagram at point 31 ofcurve "L." The increase in plate po-tential across VT -2, which result from

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the diminution in the drop thru R isadded to the EMF from Lx, and the in-crease in plate potential across VT -2 is,therefore, greater than heretofore. Thecharging effect upon C, is, therefore,greater. The condenser charges, not on-ly to a higher potential, but more rapid-ly, as indicated at point 32 of curve"g." VT -1, therefore, becomes conduc-tive, as indicated at point 33 of curve"i," and, if anything, more abruptlythan before.

The extra rise in plate potential uponVT -2 was temporary. The effect of Lxdisappears and the higher potential towhich C, has been charged soon exceedsthe potential impressed upon the plateof VT -2. Condenser C, will, therefore,discharge, but not thru VT -2. It willdischarge over the path from 9, 3, 2, 1,7, 6, and 5 until the potential on C,falls to the potential impressed by bat-tery 1 as indicated at point 34 of curve

Since C, discharges over a path includ-ing battery 1, the potential producingthe discharge current is only the differ-ence between the battery potential andthe potential to which C, is charged. Thisdifference is small. Consequently, therate of discharge is slow. The currentthru R, is therefore small, and the gridof VT -1, although it becomes negative,does not become sufficiently negative torender the tube non-conductive.

Since the time during which C1 is dis-charging is brief, as may be seen by ob-serving point 34 of curve "g" that theportion of the curve which slopes down-ward is short, the slightly negative po-tential of the grid was not caught bythe oscillograph, which is the reasonwhy it is not exhibited by curve "h."

When the potential of C1 has fallen tothat impressed by the battery, it willnot continue to discharge over the pathlast traced, because of the opposing po-tential of the battery. It will not dis-charge over the path thru VT -2, becausethis tube is, at this time, non-conductive(see point 35 of curve "f"). Thecharge of C, will, therefore, remain stea-dy, and there will be zero current thruresistor R1. Consequently, VT -1 will besomewhat conductive (see point 36 ofcurve "i") and C, will discharge (seepoint 37 of curve "j"), thereby main-taining the grid of VT -2 negative (point38 of curve "k") and VT -2 non -con-ducting until C. is completely discharged.

When C, is completely discharged, thepotential of the grid of VT -2 becomeszero (point 39 of curve "k"). This tubebegins to conduct. The condenser C1 can,therefore, discharge, and the cycle ofoperations repeat.

It will appear upon the study of theaforegoing analysis that one really sig-nificant action of Lx is to bring to passthat, during a short time, condensers C,and C, are both discharging, (comparepoint 34 of curve "g" with point 40 ofcurve "j"). This changes the controlfrom the fast condenser to the slow con-denser, and the high -frequency impulseswill not appear until the slow condenserhas discharged.

There are ninny peculiarities of theelectromotive force across Lx as shownby curve "L" beside the one just men-tioned, but this one alone produces sig-nificant results. For this reason, the oth-er peculiarities are not described in de -

SEPTEMBER, 1935

tail. The several sharp peaks correspondto the moments when the total of thecurrent in tubes VT -1 and VT -2 is in-creasing. The portions of curve "L"which fall below the zero line correspondto times when the total is decreasing.

Tubes continue to be conductive aftertheir grid potential has become nega-tive. It is not until the grid has be-come several volts negative that the cur-rent is cut off entirely. This is the ex-planation of the fact that curve "f"slopes downward at point 20 at the sametime curve "i" slopes downward atpoint 22, and this accounts for the neg-ative portion of the curve "L" verti-cally in alignment with points 20 and 22.

The portion of the curve immediatelyto the left of point 31 is explained inthe same way but, considering the pointson curves "L" and "i" vertically inalignment with 31, it will be seen thatthe portion of the curve "f'' betweenpoints 29 and 35 slopes downward, whilethe portion of the curve "i" at point 36is horizontal. The decrease in total cur-rent is, therefore, very small, and theportion of curve "L" to the right ofpoint 31 will rise rapidly towards thezero line.

The time constants of the two con-densers are 80 adjusted that the ratio be-tween them is, as nearly as possible, aninteger. If this adjustment is inexact,condenser C, may complete the last stepin its charging action somewhat toogoon, but the inductance Lx will producethe effect described. Consequently, thepresence of the inductance in the com-mon plate lead makes the adjustment ofthe resistors and condensers non -critical -

In conclusion, the advantages of theHarmon circuit over other unsymmetri-cal schemes wherein the discharge timesare unequal are: (1) circuit adjust-ments are not critical; (2') means forobtaining any selected harmonic with-out the use of multitubes which haveheretofore been required for this pur-pose.

Factors Govering Frequency at Time ofControl

The most popularly used unsymmetri-cal multivibrator is the Hull and Clapptype, wherein the condenser dischargetime -constants are equal and the platecircuit unsymmetrical. This type ofmultivibrator structure will form thebasis of the following discussions.

It is generally understood that an un-controlled multivibrator is controlled byits fundamental frequency or by an har-monic of this fundamental. This is amistaken idea, as it is practically impos-sible to control these frequencies by syn-chronization. Moreover, control can on-ly occur when the controlling voltage hasbeen sufficiently raised to supply enoughreal energy" to the multivibrator to ac-celerate the normal relaxation time upto such a frequency that the relaxationtime itself greatly depends upon thevalue of the voltage injected. (Controlvoltage is seldom over 3 volts.) To prop-erly control the multivibrator, the an -controlled frequency (real fundamental)must be raised to such a value that whenthe system is under control of the gov-erning agent, either the fundamental orharmonic of the new frequency assumesa definite phase relationship to the con-

trolling frequency. To make the controleffective, the constant of the multivibra-tor must be adjusted so that the uncon-trolled frequency is slightly below thefrequency of control.

Relation Between Control Voltage and

Harmonic Demultiplication

When the control voltage is carriedbeyond the region necessary to maintaincontrol at the fundamental or synchro-nizing frequency, the relaxation time willsuddenly change to a new value. Thetransition occurs without actual changesin the circuit constants. In general,when the control -voltage is increased be-yond the value necessary to maintaincontrol, the multivibrator will produce astill higher frequency. On the otherhand, if the control voltage is at a fre-quency which is a harmonic of the mul-tivibrator fundamental, then increasesin the control of voltage will producecontrol at lower and lower harmonics.At this juncture, it should be borne inmind that any factor which tends to ac-celerate or retard the multivibrator con-denser discharge times makes the sys-tem act as though the CR product hasbeen either raised or lowered, whicheverthe case may be.

The relationship existing between thecontrol voltage and the production ofhigher harmonics, called harmonic de -multiplication", is explained as follows:

Suppose that a 10 kilocycle control os-cillator was controlling a 1 kilocycle mul-tivibrator, necessitating, of course, thatthe 10th harmonic of the multivibratorbe in phase with the controlling device.Curves !representing the wave compo-nents, not apparatus areshown in Figure 14. Here, the 1KC mul-tivibrator and its 10th harmonic, are su-perimposed upon the 10 KC oscillatorsinusoid. Now, if the control voltageshown at the left of the illustration, isslowly raised from "a" to "b," morevoltage will be injected into the multivi-brator which will accelerate the con-denser discharge time and so tend toraise the fundamental frequency of thesystem. Here, the word "tend" is usedadvisedly, because the fundamental willremain at a fixed frequency (1KC), ir-respective of the forced acceleration, un-til the voltage gas reached such a mag-nitude "b" to cause the fundamentalto SUDDENLY JUMP to a higher fre-quency (1.11KC). The value of thisjump depends upon the ratio of the con-trol frequency to multivibrator frequen-cy. If this ratio is 1 to 10, the first in-crease in the multivibrator fundamentalwill be equal to 1/9th that of the con-trol oscillator. In other words, the fre-quency of the multivibrator will increasein steps at a rate of one -ninth, one -eighth, one -seventh, and so on, in ratioto the frequency of the controlling device.For a 1KC multivibrator, the progressionof the control order may be followed byreferring to the tabulations shown be-low.

11 J. Groszkowski, "Frequency division."Proc. IRE. Vol. 18, No. 11. Nov. 1930

12 B. van der Pol and J, van der Mark."Frequency demultiplication." Nature (Eng-land) Vol. 120, pp. 363. 1927

Page Nineteen

411.

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Control Table Showing Harmonic Demultipbcation Frequencies forSynchronized with a 10KC Osoillator

1 or 10KC Multivibrator

10 9 8 7 6 5 4 8 2

0.000 0.000 0.900 0.000 0-000 0.000 0.000 0.000 0.0002.000 1.111 1:250 1.429 1.667 0.000 0.000 0.000 0.0008.000 2.222 2.500 2.858 0.000 2.000 2.500 0.000 0.0004.000 8.838 3.750 0.000 3.334 0.000 0.000 3.333 0.0006.000 4.441 0.000 4.287 0.000 4.000 0.000 0.000 0.0006.000 5.555 6.000 5.716 5.000 0.000 5.000 0.000 5.0007.000 6.667 6.250 0.000 6.667 6.000 0.000 6.667 0.0008.000 7.778 7.770 0.000 0.000 0.000 7.500 0.000 0.0009.000 8.889 8.750 8.674 5.834 8.000 0.000 0.000 0.0000.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000

Decimal values only approximate

Explanation of the Frequency "Jump"What caused the frequency to

" junip" when the control voltage israised, is a question seldom answered.here appears an explanation clarifyingwhat might be conceived as a complexphenomenon.

In a communication to the writer,says Mr. W. F. Curtis, Naval ResearchLaboratory, "that the multivibratorworks between two critical voltages, sayv and v'. The time taken for a con-denser to discharge from potential v° topotential v is RC log v'/V. (The so-called time -constant RC is simply thetime in which the potential falls to ze-ro 1/e times its initial value.) Now bysuperimposing a higher frequency poten-tial upon the condenser potential, it willbe found that the lower critical voltageis reached sooner than it otherwise wouldbe; that is, the higher frequency tripsthe device. It can be readily seen thatas the amplitude of the high frequencypotential is slowly increased, see Figure13, that the phase of the tripping pointwill correspondingly advance, but theorder of division (and hence frequency)will remain fixed until the amplitude hasreached such a value that the next earliercycle will trip the device; whereuponthere will be a sudden and discretechange in frequency''

In other words the frequency jump oc-curred because the cross -synchronizingcurrent supplied by the control oscilla-tor is insufficient to maintain properphase relationship with the condenser

charge and discharge voltages at thefrequency in question. The instant thesynchronizing current can no longer sup-ply enough power to maintain synchro-nism, the multivibrator mometarily"falls out of step," but is immediate-ly pulled back "in step" at the nextlowest harmonic. The system is actuallypulled into synchronism through extrapower supplied to the multivibrator bythe synclionizing current. This currenttransmits energy to accelerate the con-denser discharges up to such a frequencythat an harmonic of the fundamentalcoincides in PHASE with the control-ling frequency.

( To be Continued)ct3

BIBLIOGRAPHY OF PART 211 J. K. Clapp, "Universal frequen-

cy standardization from a single fre-quency source," Rev. Sci. Inst., XV(July, 1927), 25

12 Clapp and Crawford, "Frequencystandardization," QST. Mar. 1930

13 J. W. Horton and W. A. Marrison,"Frequency standard," Proc. IRE Vol.16, No. 2, pp., 137, 1928

14 " Frequency Measurements at RadioFrequencies," Bulletin 10, General Ra-dio Company, Cambridge, Mass., U.S.A.

15 R. Jouast, " Temps, Frequence,mesure des Frequence," L 'Onde, Vol.8, pp. 421-35 Oct., 1929

16 V. J. Andrew, "Simplified fre-quency dividing circuit," Proc. IRE,Vol. 21, No. 7, pp. 982.3, July, 1933

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BACK ISSUES AVAILABLEWe have just a few back copies of each ofthe following issues. First Come-FirstServed. 1934 No.'s 25c each; 1935 No.'s 20ceach. Complete Your Files Nov BeforeDepleted.

1934JAN.-(Inductance Authority, Complete data, Tables, Figures, etc.)FEB.-(Radio Trans. Used for Central American Phone Service, Schematic, Engineering

Articles, etc.)MAR.-(Mercury Arc. Rectifiers, Sound, Speakers, Bridge Measurement)APR.-(Modulation and Carrier, Band. Pass and Line Filters)MAY-(Budapest Anti -Fading Antenna, Press Skeds, Brit. Empire Broadcasting)JUNE-(Disc Recording, Sound Measurement Through Walls)JUL.-AUG.-(Airport Receivers, Airplane Receivers, Inductance Measurement)SEPT.-(Calculation of H. & T. Attenuation Pads, Volunteer Comm. Reserve)OCT.-(Direction of Arrival of Radio Wavep, Radio Story of Marro Castle)NOV.-(Speech Input Equipment, Police -Airway Wrinkles)DEC.-(Gas Filled Thermionic Rectifiers, KYW Transmitter)1935JAN.-(Velocity Microphones, Six String Oscillograph, Under Voltage Relay)FEB.-MAR.-(WOR Antenna, Ethereal Effect on Transmitters, High Freq. Vacuum Tubes)APR.-(The Ionosphere, Vacuum Tubes as High Freq. Oscillators)MAY-(Photo Electric Effect, Telephone Lines for Radio to a Nation, Telephotographic

System)JUNE-(Constant Frequency Monitor, Cathode Ray Tube Explained)

The above copies are immediately available while the supplylasts. When they are gone we cannot supply any more backissues. We are clearing our shelves, and now is the time toorder at once.

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