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August 1936 - ELECTRONICS

www.americanradiohistory.com ELECTRONICS

radio, communication and industrial applications of electron tubes design, engineering, manufacture

HOWARD EHRLICH KEITH HENNEY DONALD G. FINK H. W. MATEER Vice -President Editor Associate Editor Manager

Contents August 1936

COVER: An expert glass blower sealing one of the new Western Electric 316-A triodes, which can deliver 6 watts at a wavelength of 60 centimeters in conventional negative grid circuits.

NAB in Convention 7 Canadian Field Strength Meas- News of the broadcast industry as revealed in Chicago urements 20 BY H. M. SMITH Methods used by the Canadian Radio Commission Theory of Electron Oscillators .. 9 BY J. E. ANDERSON Modulation Measurements 23 A new explanation of the properties of positive grid (B -K and G -M) circuits BY C. G. SERIGHT Peak vs. r -m -s methods of evaluating modulation performance

Cathode Ray Aircraft Compass . 12 BY SAMUEL OSTROLENK Resistance -Coupling Data 25 A visual indicator of the CR type greatly im- proves performance of direction finders BY GLENN KOEHLER Gain of resistance coupled amplifiers for all audio frequencies, in chart form for reference use U -h -f Signal Generator 16 BY C. J. FRANKS Mean Level Determinations .... 27 20 to 100 mc. In a new instrument of countless BY uses in G. H. LOGAN ultra -high frequency practice Decibel chart for sound -power levels

Remote Tuning at KDYL 19 Delay -Relay Circuits 28 BY JOHN M. BALDWIN BY D. E. NOBLE Collecting short-wave press at a distance by ten - Time discharge (RC) circuits for timing photo- mile tuning, thus avoiding noise graphic printing, ringing class -room bells, etc.

DEPARTMENTS

Crosstalk 5 Tubes at Work 32 Manufacturing Review ... 48 Reference Sheet lectron Art 40 Index to Advertisers 61

Volume 9 . . . Number 8 Contents Copyright, 1936, by McGraw-Hill Publishing Company, Inc. ELECTRONICS, August 1936. Vol. 9. No. 8. Pub- lished monthly, Price 50e a copy. Subscription rates- McGRAW-HILL PUBLISHING COMPANY, INC. United States, $5.00 a year. Latin America, $5.00 a year. Canada, $5.00 a year. All other countries, $6.00 Publication Office, 99-129 a year or 24 shillings. Application for entry as 2nd North Broadway, Albany, N. Y. class matter at Albany, N. Y., pending. Printed in Editorial and Executive Offices U. S. A. 330 West 42d Street, New York, N. Y. Branch Ornees: 520 North Michigan Ave., Chicago; 883 James H. McGraw, Jr. Malcolm Muir James H. McGraw Mission St.. San Francisco; Aidwych House, Aldwych, Chairman President Honorary Chairman London. Howard Ehrlich B. R. Putnam D. C. McGraw W. C. 2; Washington; Philadelphia; Cleve- Vice -President Treasurer Secretary land; Detroit; St. Louis; Boston; Atlanta, Ga. Cable Address: MCGRAWHILL, New York. Member A.B.P. Member A.B.C.

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August 1936 ELECTRONICS

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4 August 1936 - ELECTRONICS

www.americanradiohistory.com ELECTRONICS

AUGUST KEITH HENNEY 1936 Editor

Crosstalk

HAMS AT WASHINGTON . . . On Dr. Paul Weiller, Welding Timer Cor- twenty-four hours a day, five days a all sides we hear of the excellent pre- p3ration (see Electronics May 1936) week, five thousand hours are approxi- sentation made at the FCC June UHF states: "We have been making welding mately a year's service. Add to this in meetings by the amateurs. This is but control equipment for over a year and a shop working only eight hours a day, natural. Most experienced of all users a considerable number of our units five thousand hours are approximately of the frequencies above 1500 kc. the have been in operation for about that three year's service. This is more than amateur knows his stuff, and he con- long, a good proportion of them on sufficient for radio tubes which can be tributed much to clarify the extensive twenty-four hour service. Most of the purchased anywhere at a low price. loose talk at the meeting by those others are working about nine hours a "Conditions are not quite so favorable whose desire for allocations was based day continuously. when it comes to grid control rectifiers. more on hope than on exact knowledge. "Our timers are operated by two 27 These seem to have a life of about Most conservative of all groups in re- tubes as control elements and two 80, three thousand hours, occasional short quest for additional ether space, the 5Z3 and 83 as rectifiers. In one year, life tubes being covered by a guarantee. amateurs want the harmonic band of we have not had a single complaint The tube replacement cost of this type 112 to 120 mc. and without shutting from customers or a request to furnish is therefore rather high. This is not cur eyes to the needs of other services, new tubes. Several of the 83 tubes very important for equipment control- especially new governmental services, have given out. Because of the low ling large powers. If there is three or we believe the amateurs should get cost and because failure can be easily four hundred dollars worth of tube re- their request. Having grown up as noticed without resorting to test equip- placement on a total equipment cost of amateurs through the coherer, Electro ment, there has been no complaint. Of say ten thousand dollars, this is not so Importing Company, spark and tube the other tubes, we have never heard. serious. A tube replacement cost of days our hearts are with the amateurs "I assume, therefore, that the simple sixty or one hundred dollars on equip- in spirit and practice. There is no more types of radio tubes made by prom- ment controlling only a few kilowatts, avid experimenter, no greater producer inent manufacturers if used conserva- however, creates considerable sales re- of concrete practical knowledge of tively have an actual life of several sistance. We have, therefore, a peculiar methods or apparatus, no pioneer more thousand hours. In a shop working condition that users of tube controlled eagerly looking for new frontiers than equipment do not frown on the cost of the "ham"-and probably no more use- the large tubes but seriously object to ful citizen in case his experience and the cost of the smaller tubes. capabilities are ever called upon by the "It would be very desirable to make government. the life of the mercury vapor types of tubes fifteen or twenty thousand hours TUBE LIFE . . . In June we asked even if their cost should be thereby infor experience on tube life, especially creased. This period of service would from industrial users. We quote below. approach the obsolescence period of the "In the Center Theater, Rockefeller equipment and would be sufficient for Center, Westinghouse installed a West- all purposes." inghouse Ward -Leonard Hysterset con- HONORS . . . Morris E. Leeds, trol theater switchboard. There were president of Leeds and Northrup, in- 186 individual circuits with a rectify- ternationally known as manufacturers ing tube in each circuit. These cir- of electrical measuring equipment, has cuits were in use morning, noon and received two signal honors recently. night during months of rehearsals and The Institute of Management gave him had been in service considerably over a its Gant Medal for "distinguished year. This means an average of 15 to achievement in industrial management" 16 hours per day service. The total and Polytechnic Institute of Brooklyn cost of tube replacement for renewals made him Doctor of Engineering for has been $30. In the Music Hall a "great service to society." A keen stu- Hysterset control replaced storage bat- dent of relations in industry, Mr. Leeds teries and generator for telephone is widely known for his far-sighted service for over a year, on continual philosophy of the factors which under- service. There have been no tube lie harmony between employer and failures." Morris E. Leeds, D.Eng. employee.

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www.americanradiohistory.com NAB in Convention

National Association of Broadcasters avoids membership split, votes money for research, reappoints James W. Baldwin managing director, elects Charles W. Myers as president, discusses superpower, frequency allocation, new wavebands

CLOSING its annual meeting at after the October hearing on reallo- ity of broadcasting stations now sur- Chicago on July 8, the National cation. The stations known to be passes the reception capability of a Association of Broadcasters may considering 500 kw. include KDKA, majority of broadcast receiving sets. sum up the results of its convention KFI, KNX, WBBM, WBZ, VGN, I hope and believe that the set manu- as having stalled off an incipient WHAS, WHO, WJR, WJZ, WOAI, facturers will improve the fidelity of split within its membership over the WOR, WSB, and WSM. receiving sets." copyright (and other) questions, as Reallocation A hearing on reallocation has been having reappointed James W. Bald- called for October 5th, and is ex- win as managing director (at an in- Reallocation of frequencies is the pected to last about ten days. This creased salary), as having elected next momentous technical question hearing will deal with frequencies Charles (Chuck) W. Myers of KOIN confronting the industry. At the last between 550 and 1600 kc. and will and KALE as the new president. general reallocation in 1928, 90 per be similar in scope to the hearing Matters of great interest to the cent of the stations were changed in held in June on ultra high frequency broadcast industry naturally were frequency. Since that date great allocation. Subjects discussed in the discussed at this convention. The technical advances have been made hearing will include the future sta- following notes, augmented with in radio, and it must now be deter- tus of cleared channels, superpower, technical data furnished by engin- mined whether public interest will horizontal increase in power of re- eers closely associated with the art, best be served by another general gional stations, duplication of as- will indicate the trend of these dis- reallocation. signments, and possible opening of cussions and outline the present new classifications of stations. The thinking of men identified with Davis Amendment which has re- broadcasting. quired the quota system in distribut- ing radio Superpower facilities to states and zones was repealed by the last ses- The anticipated increase in power sion of Congress, and the effects of to 500 kw. by several cleared chan- repeal on allocation are not yet nel stations was opposed by many certain. other stations of all classifications. The most obvious improvement to The Texas representatives were par- be expected from a reallocation at ticularly strong in their opposition. this time is a better utilization of the A resolution to petition the Fed- lower frequency end of the broad- eral Communications Commission to cast band for covering large areas. grant no more superpower licenses The difference in the absorption of was defeated in the Resolutions Com- the ground wave at the two ends of mittee and again in a general meet- the broadcast band is so great that ing. Such a petition was consid- Western Electric 316A tube de- a 50 -kw. station at the low frequency ered outside the proper field of the scribed on page 8 end can serve an area many times as association, and many considered it large as a 50 -kw. station at the high useless to fight the inevitable. The Judge Sykes of the FCC addressed frequency end. Within a few miles situation resembled the bitter op- the convention, explaining the Com- of the transmitter, there is only a position in a 1924 meeting to the mission's plans. He said, "The con- slight difference in performance at creation of high power stations, stant effort of the Commission has different frequencies. Since there which at that time meant 5 kw. been to improve broadcast service are large areas in the United States At a meeting of the cleared chan- to the listening public. A great step which must rely for service on sta- nel group it was decided to oppose in this direction is through better- tions several hundred miles away, any limitation on the maximum ment of station broadcasting equip- it seems that the stations with loca- power of cleared channel stations. A ment. The Commission has no juris- tion, power, and desire to serve these minimum power limit of 50 kw. was diction over receiving sets and can audiences should have the most fa- urged. The date for the FCC hear- not prescribe standards for their vorable channels. This principle is ing on applications for 500 kw. has production. I am informed, by en- already partially applied in the con- been postponed from September to gineers, that the transmission qual- fining of local stations to frequencies

ELECTRONICS - August 1936 7

www.americanradiohistory.com between 1200 and 1500 kc. The cur- project is to be a joint one between give a very rapid rise and slow fall, rent plans to open broadcast chan- the radio broadcasting industry, which is considered necessary for nels above 25 mc. are an extreme radio advertisers, and advertising proper control of level. application of this principle, but agencies. The important feature is The most outstanding feature of there is no prospect of these chan- that the findings are intended to be the WE-Graybar exhibit was the nels taking over any large part of such that all three groups will accept demonstration and illustration with local broadcasting service for at least them as authentic. It is intended meters and a cathode ray oscilloscope three or four years. to get more complete and authorita- of the new Doherty high -efficiency The technical difficulties in putting tive data than is now available, and linear power amplifier. In this cir- a reallocation into practice are quite to eliminate disagreements in exist- cuit, two tubes are used, one carry- formidable; much more than they ing data due either to variations in ing no load when there is no modu- were in 1928. Many vertical radia- methods of taking data or to per- lation. The signal to one of the tors are in service, or will be by fall, sonal interests of those for whom it tubes is shifted 90 degrees ahead and when a station is changed to is compiled. The greater part of before being applied to the grid, and such a high frequency that the ra- the research will be of a commercial 90 degrees back after leaving the diator becomes much more than one nature, but some of it will involve plate. Plate efficiencies of 60 to 65 half -wave -length long, it will not be engineering. It is proposed that per cent independent of modulation usable. Such radiators must be the research be done in a university are obtained. shortened, or may be insulated and for the sake of impartiality and Several new transmitting tubes loaded to convert them into Franklin economy, and the University of were shown. The 316A has a con- antennas. Where stations are as- Pennsylvania is recommended for struction comparable with "acorn" signed to lower frequencies, it is the commercial portion of it. The tubes. It delivers 6 watts at 500 probable that the more desirable cost of the project is estimated to be megacycles. The 304B is intended channels will be so welcome to the $50,000, which is half the annual for operation between 30 and 300 managements that there will be gross income of the NAB. Similar mc. The anode of this tube has no objection to installing higher work has already been begun with been changed from graphite to radiators. funds supplied by NBC and CBS. metal. Graphite proves unsatisfac- Numerous manufacturers ex- Engineering Committee Report tory at such frequencies because of hibited broadcast station equipment. its high resistivity, and the fact that The Report of the Engineering Transcribed programs, transcription the higher frequency currents are Committee was made by Chairman libraries, and transcription equip- confined more closely to the surface of DeWitt of WSM. The advantages ment are rapidly increasing in im- by skin effect. The 305A is a 25 a good antenna, which were stressed portance to broadcasters. The new watt amplifier intended primarily in Mr. both DeWitt's report and in studio equipment and transmitters for police transmitters up to 60 mc. Judge Sykes' talk were of particular differed not so much in fundamentals Very short leads from the screen interest to many station owners and as in construction details and and the center of the filament are managers, and lead to considerable appearance. necessary for this service. discussion of the value of half-wave Apparatus Displayed Type 22A remote pickup amplifier antennas, and means for determin- A Fairchild -Proctor recorder was and mixer shown weighs less than ing whether a half -wave antenna is fifteen pounds. It may be used with economically justified a exhibited which makes records suit- for particu- either battery or a -c power supply. lar station. Judge Sykes stated able for either immediate use or duplicating. It uses a piezoelectric The new 23A input equipment con- that, based on the FCC survey, he tains everything necessary for a believed 50 cutting head, driven with about one that per cent of the sta- local station with two studios, and is tions, by an improvement in antenna, watt of audio energy. The UV -892 shown at the conven- constructed in a console for table could vastly expand their radio cov- mounting. erage without increasing power. tion is a new water cooled tube used Collins Radio Company exhibited Mr. DeWitt also called attention in 5 kw. transmitters. It has a samples from their line of speech to fact center tapped filament intended for the that the improvement in input equipment, transmitters, and frequency stability required 1932 operating from two phase a.c. in transmitting tubes. Among their and improvement New RCA speech equipment has the in modulation new items were type 12F speech in- performance being required many novel features, the most con- this put rack and a frequency control for year are equivalent increase spicuous being modernistic design. to of broadcast transmitters. Type power of the station so far as serv- Individual meter lights are pro- C -375A mercury vapor rectifier tube ice to the listener is concerned. vided. Ventilation louvres have been converted into chromium panel orna- is suitable for 5 kw. transmitters. Research Proposed ments. The front panels are hinged It can be used in many places where A proposal made by Church of to give access to tubes, and the the larger 869 has been necessary KMBC, as head of the Commercial chassis is hinged so that it can be heretofore. Committee, was considered to be of turned over to the rear for access to The electron image tube and the great importance to the NAB. Mr. other parts. A particularly desir- electron multiplier of Dr. Zworykin Church recommended creation of a able feature is the fact that all parts described in Electronics in January cooperative bureau of radio research, are accessible without removing 1936 and November 1935 were to compile data on station coverage power or disconnecting any circuits. demonstrated at this NAB conven- and listener habits. The proposed The volume indicator is designed to tion. 8 August 1936 - ELECTRONICS

www.americanradiohistory.com Theory of Electron Oscillators

A review of the Barkhausen-Kurz and Gill-Morell circuits, and a new explanation of their oscillating peculiarities, of timely interest because of their ability to generate power at extremely high frequencies

AN OSCILLATOR employing a An electron oscillator which be- haves according to the findings of thermionic triode in which the BY J. E. ANDERSON grid is highly positive with respect Gill and Morrell is called a Gill - to the cathode and the plate is at a Morrell (G -M oscillator). In this low potential, which may be nega- the generated wave was not inde- paper, however, an oscillator of the tive, zero, or positive, is called an pendent of the external impedence, Barkhausen-Kurz form in which the electron oscillator. Such oscillators but that it varied somewhat as ex- generated wave is independent of are usually operated at ultra -high pected. However, at certain values the grid potential and dependent frequencies. One of their character- of the impedance the oscillation was only on the external impedence will istic features is that the generated most intense, and at these intensity be referred to as a G -M oscillator. frequency depends more on the grid maxima the generated wave was re- As here defined, the B-K and the potential and on the tube structure lated to the grid potential in the G-M oscillators are opposite ex- than on the impedance connected to manner found by Barkhausen and tremes. No actual oscillator can the tube for the purpose of deter- Kurz. Later Gill modified the for- belong exclusively to either type, mining the frequency. mula to the form X2I9/ (E9) %=k, but must be a compromise between The first electron oscillator was which reduces to the original for- the two, sometimes approaching one, brought out in 1920 by Barkhausen mula if the grid current, I9, varies sometimes the other. The reason and Kurz. The wavelength generat- as the 3/2 power of E9. Both the for this is that the effects tending ed by this circuit varied from 43 original and the modified formulas to produce the two types co -exist in to 200 centimeters, and it was found depend on the assumption that the every oscillator circuit. This will to be related to the grid potential plate potential is zero. be discussed later. Since Gill and Morrell various investigators have reached different conclusions regarding electron oscillators. Thus in 1924, Scheibe reported results similar to those of Bark- hausen and Kurz, whereas in 1927, Tonks reported the results of mathematical investigations which supported the conclusions of Gill and Morrell.

Fig. 2 (below) The equivalent circuit of the electron oscillator in Fig. 1

Fig. 1 (above) The circuit diagram of a typical electron oscillator

by the relation ?2E9= k, where k is a constant. Apparently, the wavelength did not at all depend on the external impedance connected to the tube. An oscillator of this type will be referred to hereafter as a B -K oscillator. In 1922, Gill and Morrell, working with an oscillator similar to that of Barkhausen and Kurz, but covering a wavelength range from 200 to 500 centimeters, found that ELECTRONICS - August 1936

www.americanradiohistory.com Fig. 3-Computed curves giving relation between length of Lecher wires and the generated wave in an Ultraudion with negligible effect of the grid and plate resistances

modes of vibration by suitable impulses, it cannot oscillate in any but the first mode when it con- stitutes the frequency -determining impedance of a self-excited oscillator That is, it cannot oscillate in any but the first mode unless there is some constraint internally or ex- ternally that forces it to oscillate in one of the higher modes In the electron oscillators there is no external constraint, unless one is deliberately established, and therefore there must be anexternal one. What is it? In order to find this constraint, it is necessary to return to the well- known theory of the conventional feed-back oscillators; for that theory suffices, provided only that no essential factors are omitted as being in- consequential. It is customary to omit the effects of the grid and plate resistances, but in electron oscillators their retention is imperative. An important paper on the behav- rule, is just the equation given by Aside from the fact that the or- ior of electron oscillators was Barkhausen and Kurz and also by dinary oscillator theory leads to a brought out in 1929 by Hollmann, Gill and Morrell. That is, the wave- satisfactory qualitative explanation in which he showed that these oscil- length squared multiplied by the of the behavior of electron oscilla- lators would follow the G-M pattern grid potential is equal to a constant, tors, is there justification for apply- for certain values of the external provided the plate potential is zero. ing this theory, approximate as it impedance and the B -K pattern for This formula explains B -K oscilla- must be at best? Well, the circuit other values. The change from the tions very well, but it fails to explain is the same as that of a conventional G -M type to the B -K type, on in- the results of Gill and Morrell and oscillator, the tube used remains the creasing the length of the Lecher also those of Hohmann. The for- same even though the relative values wires, was gradual and continuous. mula does not admit any variations of the grid and plate potentials are The change in the opposite direction, in wavelength as a result of changes changed, and it should make no dif- that is, from B -K to G -M, was sud- in the external impedence. Neither ference whether the power is sup- den and discontinuous. Several of does the theory plied in the grid these discontinuities occurred along of the uniform circuit or in the the Lecher wires. The absolute transmission plate circuit. amount of the change in wavelength line explain the Along this line at each break depended on the grid iterative behav- innwAnuarí it is interesting potential and on the position along ior of an elec- to quote Llewel- the wire at which the break oc- tron oscillator d111ZMIMIE lyn.1 After he curred. The change th the wave- as observed by b111VAMEMINZ has considered length varied from about 20 to 50 q111/MMIll Hollmann. If the 1111532311111111131 the forces act- centimeters. The wavelengths ob- oscillations were ing on the elec- tained by Hollmann varied from 20 purely of the trons in a B -K to 140 centimeters G -M type, there oscillator he In order to explain the existence should be no comments in of B -K oscillations investigators jumping from Fig. 4-Computed curves giving re- conclusion : "It usually return to one mode of os- lation between length of Lecher to first principles and wires and the generated wave when is interesting consider the forces acting on the cillation to an- the product of the grid and plate note thát. the electrons inside the tube, the dis- other but the resistances is low same kind:' of tances they have to travel, and the wavelength analysis her e dimensions of the elements. The should increase continuously as the used to illustrate the workings of the "time of transit of an electron" from length of the line is increased. Barkhausen oscillator can be applied the cathode to the plate is also a con- While a transmission line can be * The Barkhausen Oscillator, Bell Labora- sideration. The conclusion, as a excited in any one of its natural tories Record, Vol. %III, No. 12. 10 August 1936 - ELECTRONICS

www.americanradiohistory.com to the well-known feedback oscilla- oscillation in the circuit. The real This wo is of prime importance in an tors operating with negative grid part is the amplitude condition and electron oscillator. By definition it and positive plate, and shows that the imaginary part the phase condi- is the geometric mean of the time the two are not very different from tion. They must be true simultan- constants of the end meshes of Fig.

each other after all. . . ." If that be eously. Since all the impedances 2. By equations (4) and (5) it is true, the converse should also be have been assumed to be pure re- the lowest frequency at which the true. That is, the theory ordinarily actances, the two conditions may be circuit can oscillate, which holds for applied to the feedback oscillator written: any Colpitts. It is the frequency, in should be applicable to the electron radians, of the pure B -K oscillator oscillator. - µr,Z,Z, = r,Z,Z. + r,ZpZ, + r,Z,Z, + and the frequency at which the Gill r,Z,Z, (3a) The circuit of a typical electron r,r,(Z, + Z, + Z,) + Z,Z,Z., = 0 (3b) and Morrell circuit oscillates most oscillator is given in Fig. 1. When intensely. It is also the frequency this has been stripped of strictly d -c When reactances are inserted in at which the Hollmann oscillator branches and when elements inherent 3a it reduces to, jumped from the B -K type to the in the tube have been added, the G -M type. The condition w?w», ob- rm (r,C, + r,C,) 3.w (4) equivalent circuit may be represented = tained from (4) and (5), is the in- as in Fig. 2. Here Cg, Cm, and Cg in which rm = tiro + r + rp and w ternal constraint that is necessary to are the usual tube capacities; and is the frequency of the oscillation in force the circuit to oscillate at the they are assumed to be lumped at the radians per second. Since all the re- higher modes. end of the transmission line, the sistances are positive, this equation The effect of w is present in all impedance of which is represented by Z in shunt with Cm. The grid - cathode and plate -cathode resistances loo are represented by rg and rp, respectively. All other resistances will be 1 neglected. For convenience "the im- BO 1 pedance of Z and Cm in parallel will be denoted by Zs. Impedance sym- bols will be retained for brevity until 60 ,.c 1 reactances are needed. Cm=O 1 It will be noticed that the equiva- 1 lent circuit is that of a simple Col- 40 pitts, or more particularly, the UI- traudion form of the Colpitts. Hence . , any conclusions drawn from the , analysis of Fig. 2 will apply equally 20 o 20 40 60 80 !00 120 well to any simple Colpitts. It is L cm. understood that Z need not neces- sarily be the impedance of a trans- Fig. 5-Curves similar to those in Fig. 4 but computed on the mission line. assumption that the grid -to -plate capacity, Cm, is zero. The solid The circuit can most easily be lines represent regions of oscillation solved by treating it as an amplifier that feeds itself, and then computing can be satisfied only by positive val- Colpitts oscillators, unless it should the amplification. As soon as the ues of Xs. This means that oscilla- happen that either rp or r, is infinite, steady state has been reached, the tion can occur only if the impedance for then wo is zero. However, in amplification must be identically between the grid and the plate is most feedback oscillators the limit- unity, for there can neither be a inductive. This holds true for all ing frequency is so low that it af- change in amplitude nor in phase. Colpitts oscillators. Whereas X, is fects the oscillation frequency, only On this basis the solution is readily restricted only to positive values, X to a negligible extent. But when a effected by solving for one of the as- is much more restricted. Since the tube is operated so that for any rea- sumed currents, say I3, in terms of line reactor is in shunt with Cm., we son rprg is low, becomes high. It itself and of the circuit parameters. wo have X, = X/(1-XwC,,,). Thus X may easily become higher than the By summing up the voltage drops is hemmed in by conditions natural frequency of the tuned cir- in the three meshes we have: O

www.americanradiohistory.com The Cathode -Ray

Use of a fluorescent screen as an indicator for radio direction finders overcomes many serious disadvantages of other instruments, permits accurate night flying

A. On course. The voltage from the loop is zero

Fundamental circuit of the compass, showing how the loop and stationary 1 "mast" voltages are applied to deflecting plates

BY SAMUEL OSTROLENK New York, N. Y.

RECENT aircraft disasters have intervals to apprise him of his focused attention upon the se- course. Accurate determinations by rious need of an absolutely reliable this system prove the reliability of and foolproof radio -directional guid- the null type direction finder. ance for aircraft. Although the re- However, very few planes can com- liability of the loop antenna for di- mand such elaborate ground facilities rectional indication is well-known, to guide their flight. The trend has the requirements for aircraft radio been toward a self-contained, light directional apparatus differ vitally weight equipment which automatical- from established land or marine ly determines the direction toward equipment. a radio station and automatically One of the first developments of indicates the deviation air- C. Circle image showing plane of the 2 directly over towers of station an automatic on -course indicator for craft to the right or to the left of the pilot was the A -N beacon system. the on -course direction. The presen- The disadvantages of the system are tation "Aircraft Radio Compass" a report of the Radio Technical Com- well-known. If the beam is acci- (Electronics, Oct. 1935, page 7) de- mittee for Aeronautics, published on dentally lost, it is difficult to return scribes the details of a radio com- pages 163-164 of Air Commerce Bul- to the predetermined course. The pass extensively used today. The letin of January 15, 1936. pilot has to depend upon special bea- basic principle underlying these 1. The indicated bearings of con stations and special courses of devices, invented by Dieckman and a satisfactory radio direc- flight. Hell in 1925, depends upon properly tion finder should depend liì;the article "Flying the Pacific phasing the received signals by a upon the angular relation of by Radio" (Flactronics, April 1936, loop and a non -directional antenna to the loop with respect to the page 7) there is described an elab- produce the cardioid reception pat- transmitting station only orate directional system employed by terns (page 9) and actuate an indi- and should not depend upon the Pan American Airways for their cator to the right or left of a zero critical phasing of the elec- Clipper ships. Signals transmitted null position in accordance with the trical circuits. We believe by the aircraft are picked up by two orientation of the loop antenna and that the lack of this feature separate ground stations. The posi- the signal wave front. in the present equipment, tion of the craft is calculated and The fundamental faults of this which requires accurate ad- transmitted to the pilot at regular system are adequately summarized in justment of circuits, is the 12 August 1936 - ELECTRONICS

www.americanradiohistory.com Aircraft Compass

Lissajou figures formed by loop and stationary antennas give course indications accurately. Phase errors immediately detected and corrected

B. Indication when ofj-course to left

3 Improved circuit using superheterodyne principle, which p-events inter- coupling

compass circuits are in proper rela- which Mr. Hefele is Chief Radio En- tion. Flight errors up to ten degrees gineer, have been submitted to the and more are attributable to mis - U. S. Coast Guard. This direction phased conditions over which the finder has been tested extensively pilot has no control. When it is under various flight conditions un- realized that the electrical parame- der the supervision of Chief Radio ters of the loop antenna do not re- Electrician C. T. Solt of the Com- main constant, but change in accord- munications Division, Coast Guard ance with temperature, humidity and Headquarters, Washington, D. C., mechanical vibration or shock, it will which division functions under the be evident that the absolute reliabil- immediate jurisdiction of Com- ity of the cardioid system is impos- mander F. A. Zeusler, Chief Com- sible. Temperature variations in munications Officer. Mr. Solt, ac- flight of two degrees Fahrenheit per companied by Coast Guard pilots J. minute me usually incurred and R. Orndorff and W. R. Durham con- D. Elliptical pattern showing improper phase adjustment serve to destroy the phasing char- ducted numerous test flights over acteristics for the cardioid reception bodies of water as well as over flat, pattern and in turn destroy the ac- hilly and mountainous terrain during principal disadvantage of curacy of the indications. A mis - daylight and darkness. During these these units. phased condition will prevent a tests it was noted that night effect, 2. A direction finder, to be `null' indication when on -course. although evident by the character of satisfactory, should be free Mistuning of the loop circuit is an- the cathode ray pattern, did not ma- from course errors resulting other serious factor for misphasing terially affect the directional ac- from interference by other and the pilot generally has no means curacy. Flights through heavy at- stations on adjacent chan- for realizing this condition. Slight mospheric disturbances, which would nels. mistuning errors cause directional preclude any other type of radio com- errors of two to four degrees. pass have been made `blind' by this The cardioid reception pattern ra- A right -left indicating direction cathode ray right -left indicator with dio compass system requires accu- finder, operating on a radically new excellent results." rate adjustment of the antenna cir- principle, for which patents are The basic improvement of the cuits, particularly the phase rela- pending, has been invented by Ed- Hefele system resides in combining tion between the loop and the non - ward J. Hefele. This device employs independently amplified directional directional antenna. Periodic elec- a cathode ray tube as a means of vis- and non -directionally received signals trical servicing of the equipment is ual indication. Several models, manu- at the indicator, which is preferably necessary and the pilot has no indi- factured by the Airplane and Marine a cathode ray tube, in a manner cation during flight that his radio Direction Finder Corporation, of which continuously apprises the pilot ELECTRONICS - August 1936 13

www.americanradiohistory.com The CR compass in the Coast Guard plane. Note ceived signal, a zero or null signal vertical arrangement of condition exists therein. By position- navigation instruments ing the plane of the loop perpendicu- lar to the axis of the plane, a null loop signal condition will provide homing flying. If the plane deviates to the left or to the right of the on - Magnetic compass course path, the loop antenna will be impressed with corresponding signals to deflect the normal vertical indication (due to the mast antenna system) to the right or the left. The Artificial Horizon angle of deviation depends upon the sensitivity adjustment of the loop amplifier and also upon the angle of deviation of the aircraft from its course. Directional gyro compass The pilot tunes to a radio station in the vicinity of his destination by means of the audio unit, and maintains his flight directly towards the station by manipulating his controls to keep the deflecting fluorescent image vertical. The vertical indication of a normally functioning instrument accurately determines when the plan of the loop antenna is per- pendicular to the wave front of the received signals. Failure of either amplifier unit is of all the necessary information sajou figure) upon the fluorescent immediately ascertained by the pilot which he needs for reliable direc- screen of the cathode ray tube ac- by absence of the corresponding com- tional guidance. cording to principles well known. The ponent of the indication image. The Figure 1 is a simplified schematic deflection of the image from vertical bearing accuracy of the system de- representation of the electrical cir- is dependent upon the relative inten- pends only upon the physical posi- cuit of this new radio compass. The sity of the loop or directional signal tion of the loop antenna with respect radio station is tuned in by means component. A straight line image to the transmitting station and is of a common tuning control. The results when the vertical and hori- independent of critical phasing or non-directionál antenna is preferably zontal deflecting plate signals are in amplification ratios of the electrical á vertical mast located upon the ex- phase. Otherwise, an ellipse appears equipment. terior of the aircraft. The mast sig- on the screen (see Fig. 2). Since A misphased condition between nals are amplified by a corresponding the wave shape of the component si'g- the directional and non -directional radio frequency amplifier, the output nals is the same, a stationary image antenna systems is immediately evi - of which is connected to the vertical results. The ellipse shows evidence deflecting plates of a cathode ray of misphasing between the two com- tube. The loop antenna is tuned by ponent signals. By adjusting the the variable condenser C and is con- vernier condenser C' connected in nected to the input of the loop radio parallel across the loop antenna, the frequency amplifier. The loop sig- relative phase of the loop signal is nals are connected to the horizontal changed and is brought into coinci- deflecting plates of the cathode ray dence at the cathode ray tube with tube. Continuous aural reception' is the vertical mast signals as evidenced feasible by closing switch S, connect- by the straight line image upon the ing the audio detector and amplifier cathode ray screen. to the output of the non -directional The horizontal component signals radio frequency amplifier. impressed upon the cathode ray tube The mast signals produce a ver- due to the loop antenna causes the tical image of predetermined ampli- null reference vertical indication to tude upon the fluorescent screen. The deflect to the right or to the left as loop signals impressed upon the hori- illustrated in Fig. 2. The angle of zontal deflecting plate, being of the deviation depends upon the relative same wave shape as the vertical plage intensity of the loop component. signals, act with the vertical image If the plane of the loop is perpen- to produce a resultant image (Lis - dicular to the wave front of the re- Streamlined loop for the new compass

14 August 1936 - ELECTRONICS

www.americanradiohistory.com dent as an elliptic image and can be Receiving unit installed immediately corrected by the tuning in the plane vernier C'. However, it is to be noted that the automatic directional indication is independent of the mis - phased conditions, even though an elliptic image is produced, since its axis is deflected similarly to the cor- Loop control wheel for responding straight line image. taking off -course bearings The tuned radio frequency amplifier system illustrated in Fig. 1 causes signals of corresponding radio frequency to be impressed upon the cathode ray tube and special precautions must be taken to avoid inter - coupling reactions. Fig. 3 illustrates Receiving control unit for tuning, phase adjustment, a more practical modification utiliz-' audio output ing superheterodyne reception. A common beat -frequency oscillator is employed with independent antenna r -f amplifier sections. The resultant intermediate frequency signals are accordingly of identical frequency and wave shape due to the common beat -frequency oscillator. The output of the i -f amplifiers are impressed upon the corresponding deflecting plates of the cathode ray tube. The principle of operation of the superheterodyne modification in Fig. 3 is identical to that of Fig. cent image will be to the left or re- direct indication when the aircraft 1 with the added advantage of higher versed to the normal condition. This is directly over a transmitting an- stable amplification and in arrange- reversed effect is due to the recipro- tenna. In flight over the. ment of circuits. cal or opposite position of the incom- the indicator sense will change from It is important for the pilot to ing signal waves with respect to the normal to reversed. However, when know whether he is flying towards predetermined orientation of the directly over the station, the vertical or away from the station even loop antenna. The signals are ac- indication broadens to -an ellipse and though he is on -course on the beam. cordingly 180° out of phase and pro- then to a distinctly circular image The cathode ray tube direction finder duce an inverted sense indication on which moves slowly off center. When provides such automatic sense direc- the indicator. the over-station position is- passed, tions in the following manner : When The pilot is immediately apprised the vertical line on -course indication the plane deviates to the right of the of reversed flying. When he deviates returns but with reverse sense. Con- course, the deflection of the fluores- to the right of on -course and the in- tinued flying with proper sense is dicator deflects to the left of the null accomplished by the loop - reversal reference indication, the pilot nor- switch. - mally believes himself to be flying Hefele's cathode ray right -left in- at an angle to the left of the beam. dicator may be used to indicate the He accordingly controls his plane to direction of any type of -radio sta- turn more toward the right to bring tion, such as a broadcasting; station, him from his apparent left position radio beacon of the A -N type and to on -course. However, due to his commercial or telegraph stations. reversed bearing, the deflection will ICW telegraph signals may be read deviate still more towards the left. directly on the indicator 4ince the The pilot accordingly immediately image line will appear and disappear knows that he is flying away from in accordance with the telegraph sig- the beam. It may be sometimes con- nals. However, the deflectioj-of the venient to fly on "reversed sense" image is unaffected by the IÇW and when flying away from a beacon or accordingly the directional aeuracy transmitting station. This is accom- is maintained. Continuous aural re- plished by merely reversing the ception of weather reports, flight in- terminals of the loop to the input of structions and the like are Feasible its radio frequency amplifier by a while maintaining continuou ,di rec- simple reversing switch. tional indication on a catho le ray The drag is two pounds at í200 m.p.h. This indicator will also give a Continued on page 45

ELECTRONICS' August 1936 15

www.americanradiohistory.com 20-100 mc. Signal Generator

Allwave receivers now tune as high as 40 to 60 megacycles. To engineer and test them and other apparatus in the UHF region calls for a generator with characteristics not found in the broadcast band

THE modern allwave receiver is a ators, and one which kept them from pretty marvelous machine. Tun- By C. J. FRANKS being usable, was the lack of proper ing over the range from 0.5 to 20 provision for this connection. Al- Ferris Instrument Corporation though the correct microvoltage mc., any frequency in that range Boonton, N. J. quickly and easily selected, sensitive might actually appear at the output enough to reach noise level in most haps 20 mc.; some go higher, but terminals of the instrument, there locations, selective, and reproduced not very satisfactorily. Now we wasn't any way of making use of it. in quantity at a surprisingly low know that above 20 mc. is a region When the usual connecting means price, it presents a striking contrast of great potential usefulness. Trans- were used, strange and unaccount- to the insensitive, hard -to -tune, un- mission characteristics are begin- able things happened, and measure- selective, expensive receiver of a few ning to be known, antenna design is ments didn't mean anything. When years ago. Receiver design has gone well advanced, and transmitters can a pair of leads becomes comparable ahead at an amazing rate in the last be built for almost any desired in length to one -quarter of a wave- ten years, chiefly because we have amount of power at frequencies up length, which can easily happen learned how to measure what we are to perhaps 100 mc. And there is an above 30 mc., the voltage at one end doing. enormous number of channels avail- usually bears very little relation to There never has been any sub- able-yet this frequency region is that at the other end, sometimes be- stitute for a signal in receiver test- little used. Why? ing ten times as much, and some- ing. The most convenient source Largely because we have no satis- times as little as one-tenth. of such signals is the signal genera- factory receivers for use on the The magnitude of the lead step- tor. Placed on the bench in front higher frequencies. For proof look up effect and the surprisingly low of the engineer, it is in effect a com- at the number of freakish, unsatis- frequencies at which it can become plete distant transmitter, operating factory attempts which have been important are shown by the curves with the type of transmission he made and still are being made to of Fig. 1 taken on a typical setup, wants, at any hour of the day or design ultra -high -frequency receiv- the generator and receiver being night, transmitting on any desired ers. There is always the old stand- connected by leads three feet long. frequency with any desired signal by, the superregenerator, but that is The termination at the receiver end strength, and with all of these fac- scarcely a solution. was a tube grid. The largest error tors under control. With it he can The superheterodyne is a usable shown on the curves is only 8 to 1, make performance tests, compare circuit, but to realize the possibilities but in some special cases errors as one receiver with another, trace of this type a good signal generator large as 25 to 1 have been found in down defects, study the effect of de- is required. Even the mere aligning the same frequency region. Since a sign changes. Without its aid we and tracking of a UHF superhetero- slight change of load capacitance, should still be a long way from the dyne is almost impossible without at load power factor, or lead configura- perfected allwave receiver of today. least a test signal of some sort. tion will produce large changes of But the "allwave" receiver is not The difficulty of building a good step-up at the critical frequencies, truly all -wave. It goes up to per - and useful UHF generator does not, measurements can seldom be repeat- strangely enough, lie in the internal ed or checked and the engineer ends design of the instrument itself, al- up with a hopeless feeling and a com- though such a generator is much plete loss of confidence in signal Setup for Fig. generators. 2 on page ]8 more difficult to build than one for use at lower frequencies. The first On going to higher frequencies generators for the high frequencies the natural thing is to shorten leads, were built several years ago, and the to eliminate errors, but this usually model described here differs only proves disappointing. In the case slightly from those earlier models. shown in Fig. 1, shortening the leads The real difference lies in the method to six inches raised the resonant fre- used to connect the generator to the quency to only 55 mc., due to the receiver to be measured. The prin- residual self-inductance of about 0.1 cipal difficulty with earlier gener- microhenry within the signal-gener-

www.americanradiohistory.com Left Signal generator "knocked down" to show components

Output Below potentiometer Modulation transformer Generator connected to receiver under test ator proper. To be successful at frequencies above about 50 mc. it is essential not only to reduce the residual inductance of the generator to the vanishing point, but to reduce the connecting leads to something under about two inches in length. It is not too difficult to accomplish the first requirement-that is only a design problem-but the second is harder. Leads less than about a foot long seriously cramp the style of the user, yet these are too long for accuracy. Next was tried a setup of an experimental signal generator ought to be nearly flat. The trouble apparently made its own rules. There and an experimental superheterodyne turns out to be mostly in the ground seemed to be unpredictable reso- receiver, both covering the range 50 lead, for when this is shorted out, by nances in the complex circuit made to 75 megacycles. They were placed moving the receiver until its chassis up of the generator, receiver, their on the test bench as close together contacts the signal generator case, capacitances to ground, the induc- as was possible and connected with a the largest bumps disappear and the tances of the leads, the power sup- ground lead six inches long and a curves B and B' are obtained. How- ply cords, and the wiring under the high potential lead twelve inches ever, this is still not the correct re- test bench. Measurements could long. Figure 2 shows the results of sult, for when the leads are reduced never be relied upon or repeated un- measurements made with this setup. to about one half -inch in length, by til the ground lead was eliminated The measurement is that of antenna dint of great effort, the curves C and and the receiver chassis brought to circuit voltage gain, made in the C' are obtained. These are proved the same potential as the case of the usual manner by determining the to be correct when further effort at generator. However it was appar- microvolts input for standard output shortening and rearranging the ent that until this limitation could with the generator connected alter- leads fails to produce any appre- be overcome, and the necessity for nately to antenna terminals and to ciable change. propping apparatus up at crazy the first grid, the ratio of these In this and many similar tests the angles to shorten leads could be values being the voltage gain. Curves ground lead was the worst offender, eliminated, the whole thing was fan- A and A' were taken with the setup since it put entirely unexplainable tastic and impossible from a com- shown. Of course it is highly im- bumps and holes in the curves. The mercial standpoint. probable that such curves could be high lead was bad enough, but at The use of a properly terminated correct, particularly the one of volt- least it behaved according to reason- transmission line on the output of age on the grid (A') which able theory, while the ground lead the generator finally solved the prob - ELECTRONICS - August 1936 17

www.americanradiohistory.com output of the oscillator is of the diode type, provided with a bucking circuit to allow compensation for

8 varying cathode temperatures due to sv varying line voltage. This meter s = 7 indicates the voltage set up by the >0 oscillator across a single turn of -4- D heavy brass strip which forms the a 6 c first, continuously variable, portion .I. of the attenuator system. Provision m 5 m is made to adjust the output of the s oscillator to permit bringing this > 4 voltage to the correct value. Any desired portion of the voltage exist- 3 ing across the single turn is picked up by a moving arm contact, the O 2 + position of the arm being shown on s a panel control calibrated directly in microvolts output. This, together with the customary multi -position ladder type resistance attenuator 10 12 14 6 18 20 22 24 26 28 30 32 34 Frequency Megacycles network permits the customary values of output microvoltage to be obtained. The inductive type of po- Fig. 1-Effect of leads on gain measurements tentiometer has proven reliable in service and should give longer life than the resistive type, although the lem. A three-foot section of flexible without difficulty, and work on re- chief reason for abandoning the re- concentric line was used, its outer ceivers in the ultra -high -frequency sistive potentiometer was the fact end terminated in a resistor of the region became almost as easy and that no design suitable for use at proper value, and the whole output reliable as in the now familiar lower - high frequencies was available. system arranged so that the indi- frequency bands. On page 17 is shown a preliminary cated microvoltage appeared across The next step was to employ the the resistor. This resistor was model of a 20 to 100 mc. generator new transmission line output system connected housed in a very small box which to a receiver for measur- in a generator which would embody ing showing also served as a mounting for the sensitivity the manner those features of ease of control and in which the transmission line per- output binding posts, the whole as- convenience of operation which we sembly being small enough to permit mits the output voltage to be in- have become accustomed to expect of serted into the receiver. The ground its insertion into almost any part modern generators. Line operation, of a receiver into which the voltage terminal of the output box is clamped output metering, direct -reading out- on shielding of the receiver, was to be introduced. In many cases the put controls, were all easy enough. while high lead is only an it was possible to clamp the "ground" the about Self-contained coils for band -switch- inch long. terminal directly onto some portion ing looked harder, and the unde- of the receiver shielding, eliminating sirable plug-in coil seemed inevitable. the ground lead entirely. Now, ob- But a trial oscillator built with the taining leads short enough to elim- coils mounted in a rotating drum inate resonances became easy, in- proved unexpectedly successful and 1000 stead of calling for and 900 ingenuity was adopted. The use of the acorn öó gymnastic ability of a high order. triode tube, small components, and 600 The use of line 500 the transmission short leads gave satisfactory opera- 400 placed unusual requirements upon tion at frequencies up to 100 mc. and 300 the remainder of the output (attenu- fairly good results up to 150 mc. At ator) system. This was finally this point, however, practically all ó 200 worked out to provide proper at- of the inductance is in the leads and P tenuation, to terminate the line prop- contacts and very little is left for erly under all conditions all set- 100 and the coil itself, so that 150 mc. is 8Ó tings of controls, to compensate for about the practical limit 70 for this type 60 the shunting effect of the line upon of construction. Frequency modula- 50 .rc the attenuator, and to correct for the tion was held down to a point where 40 \ transmission loss of the line so that the modulated signal could be re- 3o the correct voltage would actually ceived on a superheterodyne of the 20 50 60 70 80 90 appear at the end of the line. There selective communications type with Megacycles was no more trouble with unexplain- out difficulty or mushiness in the able bumps in the curves, measure- audio tone. Fig. 2-Measurements made with ments could be made and repeated The voltmeter which indicates the setup described 18 August 1936 - ELECTRONICS

www.americanradiohistory.com Tuning a shortwave receiver over a phantomed line

Remote Receiver Tuning at KDYL

the phantomed line and ground. In John M. Baldwin describes a solution the other two positions of the switch, however, the phantomed line is bi- to a short-wave press service problem ased either positive or negative in respect to ground, and controls the plate currents of the two sections of the type 53 double triode control STATION KDYL, subscribing to description is given below, so that tube. The switch itself is a WE one of the short wave press other stations confronted with the control key, such as used for ringer services, has found it necessary to same problem may avail themselves service on telephone switchboards, install the receiver at the trans- of it. and connected as shown. In the nor- mitting terminal, to obtain more An inspection of the circuit dia- mal (no bias) positicón of the con- reliable reception than would be gram, shows the equipment to be trol key, the two plate circuits of obtained at the studios, located in merely a vacuum tube polarized re- the 53 control tube pass about 20 a center of high noise level. The lay, actuated by changes in grid bias, ma. When the switch is thrown in output of the receiving equipment controlled from the studio news either position however, one grid is transmitted to the studios through room and in turn operating a spe- goes positive and the other negative. a telephone line, where it is copied cially constructed electromagnetic This unbalances the plate currents by an operator. Using this system, switch, which controls the starting, so that one plate draws 100 ma. two men are normally required- stopping and direction of rotation of and the other drops to zero. This one to keep the receiver in tune and a small commutator type motor, causes the electromagnetic switch to the other to copy. In practice, fre- driving a vernier condenser through throw off center position, closing the quent retuning of the receiver is an 800 to 1 reduction gear. This motor start and field polarity con- necessary during a news transmis- vernier condenser is a three gang tacts and causing the vernier con- sion, and the operator at the ter- unit and is connected in parallel denser to rotate slowly as long as minal has a double duty to perform with the three gang tuning con- the control switch is held closed. -to watch the press receiver and denser in the receiver, which tunes The windings of the electromag- monitor the broadcast program. the first r -f, detector, and oscillator netic switch consist of 6000 turns This has its obvious disadvantages, circuits respectively, in an ACR 136 each of number 34 enameled wire. and so a remote control system has receiver. Although this size wire is not rated been designed to enable the copyist At the studio end of the line, a to carry 100 ma. continuously with- to tune the receiver from the studios. small lever type switch is so connect- out heating, the intermittent use to Inasmuch as there are a few novel ed that in the center position there which it is put prevents any diffi- features in this control system, a is no potential difference between [Continued on page 31] ELECTRONICS - August 1936 19

www.americanradiohistory.com By H. M. SMITH Engineering Division, Canadian Radio Broadcasting Commission

Map of boundaries of various grades of broadcast service

HE development of any engi- basically important phases of radio S = a reduction factor known as the neering activity or process is transmission-the measurement of "attenuation factor." S is characterized by increasingly rigor- the electro -magnetic field of a radio always less than 1. ous test and measurement technique. transmitting station. Its significance A rigorous analysis of antenna Indeed, tests and measurements is appreciated with the realization radiation indicates the presence of occupy a very prominent part in that it is the strength of this field another field, known as the "induc- soundly establishing the application which determines whether or not the tion field." It can be shown to vary of any new principle. This is justi- transmitting station can be heard at as 1/d' and is 90 degrees out of fied, not only in widening existing any given receiving point. In other phase with the field under considera- knowledge regarding a particular words, the strength of this field de- tion. Its effect is not significant at activity or process, but also eco- termines the area throughout which distances greater than 4 or 5 wave nomically in minimizing empirical a given radio station can render lengths from the transmitting an- factors in application, with the gen- service. The discussion in this paper tenna, and it will not be considered eral consequence of increased yield will be confined to broadcasting sta- further here. or efficiency per unit cost. As appli- tions and frequencies. The same As shown above, the relation be- cation increases, refinement of general considerations apply to the tween field intensity and antenna processes and methods occurs, re- other radio services, though the height, current, wave length and dis- quiring more and more precise requirements and methods may vary tance is a simple one. The term production control. greatly. HI/A may be replaced by k'Vw Radio is no exception to this Theoretical investigation indicates representing the radiated component general rule, and its increasing that the field intensity of any radio of the antenna power input. economic and social importance has station, expressed in terms of the The factor S, however, cannot be ex- brought with it a need for more voltage induced in a conductor passed over so lightly. It is an precise information on its abilities posed to that field, is given by the extremely complex function of wave and limitations. The need is further relation, length, distance, ground conductivity emphasized where a specialized KHI and earth's dielectric constant. At- technical service is intimately asso- E= XS tempts have been made to evaluate it ciated with the lay public as in the d by several investigators, both theo- case of broadcasting. Varying opin- where E = volts induced per meter retically and empirically, with vary- ions are bound to exist with more of receiving conductor; usually ing degrees of success. Any such or less knowledge of the technical known as "field intensity" process, of necessity, must be of lim- considerations involved. Such opin- K = a number dependent on HI/A ited value for the evaluation of S ions can only be justified by facts, can only be accurate over flat antenna height terrain and unfortunately the facts are all H = transmitting having constant ground conductivity too frequently rather obscure. It is I = transmitting antenna current and this condition is extremely rare the purpose of this article to discuss = transmitter wave length. in nature. Irregularities such as some general considerations involved d = distance from transmitter to hills, cities or towns, and variations in one of the less well known, but receiving point of ground conductivity with strata 20 August 1936 - ELECTRONICS

www.americanradiohistory.com Field Strength Measurements

The days in which stations are rated by antenna power as a measure of their effectiveness are, fortunately, coming to a close. Exact measurements prove to be better criteria of performance than argument

of various depths all operate to complete survey of the area covered vary with the station's power defeat even approximate calculation by a station. The data is plotted on and efficiency and is determined by of S. It is obvious that S must be a map and equal signal contours field strength measurements. An determined precisely if there is to be drawn to indicate the boundaries of endeavour is made to protect each any accurate prediction of radio the various classes of service ren- station against radio interference coverage in a given area. dered by that station ; these, of ne- within its fair service area. The Measurement of field strength per- cessity, will vary widely. Examples Commission has had recourse to field mits the S for any territory to be are shown above. For example, a strength measurements on many determined readily. If measurements field intensity which would be unsuit- occasions to determine whether or are made at intervals along a radial able in the business section of a city, not such interference occurred within line from the transmitter the data due to artificial interference pro- the fair service area of the plaintiff. may be plotted in the form Ed vs. d. duced by elevators, street cars, de- A transmitting antenfna propagates It is apparent, from the relation fective electric signs, etc., might be a field in practically all directions in given, that if S were equal to unity capable of rendering good service a vertical plane above ground. The the product EXd would be a con- over many square miles of rural component of the transmitted field stant (for a given frequency and area where the artificial noise level included in the angle formed by the antenna power). For constant fre- is very low. earth's surface and a line 10 degrees quency and ground conductivity it Due to the necessity of allocating above the horizon, with the transmit- can be shown that S is a variable a large number of stations to com- ting antenna as origin, will be desig- function of d, decreasing as d in- paratively few channels, interfer- nated, for this discussion, as "ground º. creases: In addition, hills and ence is often a problem. The wave" ; the remainder, propagated in other changes in topography and Canadian Radio Commission asses- directions making an angle from 10 subsoil conditions further contribute ses each Canadian station with to 90 degrees above the horizon, will to variations in S so that its value, a fair service area. This will be termed "high angle radiation" or always less than unity, will vary widely along one radial and, very Portable field strength frequently, in different directions measuring equipment from the transmitter. With the measurement data plotted in the form noted above, the value of S in any region may be determined, and when broken down yields the value of the ground conductivity in that region. Once the ground conductivity is known, fairly simple calculations permit the prediction, with fair accuracy, of field strength from a station of any power and frequency at any point within the area investigated.

Measurement Avoids Conjecture Applications of the general problem, as outlined above, are many and varied. It is readily apparent that with measured values available, there is no valid ground for conjecture regarding the grade of service rendered by a station in any particular area. This usually requires a ELECTRONICS - August 1936

www.americanradiohistory.com "sky wave." It is apparent that the is known as the "zone of first use is to show to what degree auto- ground wave is most useful in areas fading." matic volume control in commercial adjacent to the station. This ground If dll is greater than dl, as is fre- receivers will permit a fading pro- wave, however, is subject to rapid quently the case with stations of low gram to render useful service. attenuation, due to the factor S power, fading becomes a minor prob- The proportion of ground wave to discussed above and the fact that lem within the fair service area of sky wave can be controlled to some even without attenuation the field the station. If, however, d1 is extent by the physical height of a would decrease inversely with the greater than d11 the night service transmitting antenna for a given distance from the station. At some area of the station becomes less than wave length. The costs of antenna distance then, its value becomes so the day area. Since broadcasting is structures depend on a factor which low as to be of no further use in pro- useful to a greater number of listen- varies roughly between the square ducing suitable reception because of ers during the evening hours than at and the cube of the height so it is artificial noise level, limitations in any other time of the day, this point readily apparent that the economics receiver sensitivity, or both. Let us becomes of serious importance in the of such moves warrant reasonably call this limiting distance dl miles. case of stations of medium and high close consideration, particularly since The high angle radiation is almost power. The sky wave and ground the increase in service area and completely the absorbed in daylight; this wave components are both increased reduction in fading which can be does not occur during darkness, and in the same proportion as the trans- effected in this manner are limited. at broadcast wave lengths it is effec- mitter power is increased; the zone This immediately suggests that tively reflected from the ionosphere of first fading is therefore independ- transmitter efficiency, or more prop- located some 60 to 70 miles above the ent of transmitting power and power erly antenna efficiency, must contain, earth's surface. Depending upon the increases alone would appear to pre- in addition to factors determining its angle of propagation this reflected sent no proper economic solution to electrical efficiency, a term which spe- component returns to the earth at the problem. cifies the degree to which high angle varying distances from the transmit- Chart below shows the night field radiation is suppressed. Any exter. The combined action of the strength of a station measured at a pression of this nature is extremely ground and sky wave components point 150 miles from the station. involved and radiation theory is not then produces the voltage in the re- A daytime measurement would indi- yet sufficiently clarified to permit ceiving antenna. If the sky wave cate a steady field strength showing such an expression to be generally component is of the same order of the absence of reflected components. useful. One can, however, calculate magnitude as the ground wave, fad- The night measurements show the with reasonable accuracy the field ing of various types usually exists, wide variations of field intensity strength which would be obtained due to amplitude and phase varia- which may be encountered. Record- from a perfect antenna with a given tions of the reflected component to- ings of this type are useful from power at any point. From the meas- gether with polarization. There is several practical standpoints. Analy- ured value of field strength at such a always some distance d" miles from sis of the record shows the actual point, together with a knowledge of the transmitter at which these re- time, during a given period of re- S, a measure of antenna efficiency in flected components become appreci- cording, in which the signal exceeds terms of the ideal can be obtained. able as compared with the amplitude certain specified values; in this way This is very useful in practice and of the ground wave at that point and the exact amount of valid interfer- provides an excellent index regarding where amplitude and phase varia- ence is determined for a given set of the degree of usefulness of any stations of the resultant defeat the use- conditions, throwing the light of fact tion in terms of the best performance fulness of automatic volume control upon what may or may not be possible for a given power and wave systems in the receiver. This region reasonable claims. Another obvious length. Field Measurements It hardly needs to be pointed out that a survey of a given area, using 500 a low power portable transmitter, supplies 400 very valuable information (which could not otherwise be obtained) for use in the most efficient 300 location of a new station. In this case S is evaluated, as discussed pre- viously, to provide the range of 200 ground conductivities existing within > the region under consideration. From this the best site, as determined by 100 coverage vs. economics, may be obtained. Experience has indicated that it is unwise to take liberties in predicting coverage of a projected /0.40P.M.E.5.7 /0.50P.M. station beyond the region investi- Night fib strength 150 miles from station [Oontinued on page 38] 22 August 1936 - ELECTRONICS

www.americanradiohistory.com Modulation Measurement

Which to use-peak voltmeter, r.m.s. meter, or average -value meter? A diode rectifier followed by a linear d -c amplifier is the solution offered in this design article

R -F signal ImaxIrvin By C. G. SERIGHT % modulation - X 100 (1) 2Xiav Radio Products Company But sometimes the modulation per- wave types were chosen for better centage as thus determined is not illustration. the most valid coefficient. This is The inference to be drawn from the case, for instance, in production the foregoing discussion is that ex- gain -testing of radio receivers-and cept for such uses as determining in most laboratory tests of similar over -modulation, an r. m. s. or recti- nature because almost invariably in this work output meters are used Measured Peaked Obtuse by Sinusoid wave wave which indicate more nearly r. m. s. meter ....100% 100% 100% r. m. s. Peak than peak amplitudes. When an R.M.S. meter...100% 71% 110% output meter is used and the signal Rectifier meter.100% 61% 112% modulation is other than sine wave shape, an error is introduced if the fier type meter will frequently give more legitimate indication of mod- Afi-er rectification modulation percentage is determined a by the standard method outlined ulation per cent than can be ob- above, that is, with a peak meter. tained with a peak meter. It must the Substituting an r. m. s. meter for the be understood, however, that peak meter, the "effective" modula- writer does not overestimate the im- of the point. The modula- Fig. l. --Relation between modulated and tion per cent becomes : portance rectified currents tion of signals used in measurements 1.41 I a -c wave form, % modulation= X 100 (2) usually approaches sine d c N making quantitative measure- in which case all of the meter types ments with modulated r -f cur- Rectifier type meters are widely discussed give equivalent indications. rents, the degree of modulation, used for evaluating Furthermore, t h e usually expressed in per cent of the radio receiver out- error in measure- average r -f amplitude, is of tanta- put. The indica- ment of modulation mount importance with the r-f am- tion of this type per cent is in near- plitude itself. of meter is most ly all cases over- Modulation percentage is deter- nearly proportional shadowed by great- mined by subjecting a portion of the to the average cur- er errors in meas- signal to linear rectification, and rent, but the cali- urement of small then comparing the magnitudes of bration is in terms signal voltages. On Fig. 2.-High energy meter. the d -c and a-c components of the of r.m.s. of cur- the other hand, current developed by the rectifica- rent of sine wave there are probably tion. The d -c component is propor- form. Substituting a rectifier type cases in which precautions need tional to the average r -f amplitude. meter in the circuit of Fig. 2 and to be taken to insure the most Superimposed on this is an a -c com- again obtaining the modulation per- valid determination of modulation ponent having the same wave form centage from Eq. (2), we find that percentage. as the imaginary line connecting suc- for a departure from sine wave mod- The circuit of Fig. 2 would be cessive peaks of like sign of the im- ulation a different percentage will be suitable only for high energy sources, pressed r. f., and bearing the same indicated than with either a peak or such as transmitters. Even with the amplitude relation to the d -c com- r. m. s. meter. The percentage of substitution of a rectifier type a -c ponent as the imaginary line bears modulation indicated by peak, r.m.s., meter, the load imposed on the meas- -f amplitude. This to the average r and rectifier type meters on signals ured circuit would in many instances in Fig. 1. The per- is illustrated as shown in Fig. 3 are be greater than could be tolerated. meter must measure modulated cent -modulation The figures are An r -f amplifier between the meas- minimum-peak, average, and tabulated below. the effects ured and measuring circuits would maximum -peak values of the cur- approximate, and neglect the non- introduce a probability of large er- rent passed by the rectifier. Know- of frequency discrimination; and is a linear d -c ing these values, the modulation per linear rectification in the rectifier rors. The alternative amplifier following the rectifier. A cent is given by : type meter. Greatly exaggerated ELECTRONICS - August 1936 23

www.americanradiohistory.com A ,,--,. the resistance in the diode circuit. A /! high resistance potentiometer is Obtuse Peaked \\ Sinusoid wavc wave therefore to be preferred. An r -f / A / filter is advisable between this poten- Z ,r l t--f / tiometer and the grid. The capacitance of this filter, plus that of the / i diode input condenser, must be low

i 11 ä _i enough in relation to the potentiome- -TI-' V 1 ter resistance that the modulation component of the rectified signal is Il not attenuated. The plate supply potential need be

r only sufficient to accommodate a plate current change of slightly more ' . than twice the required d -c increment on the straight portion of the Fig. 3.-Types of waveforms encountered Ec-Ib curve. 200 volts is a satisfactory value. For accurate measurement, a cor- circuit worked out by the writer in sion scale, and correspondingly indi- rection must be made in the d -c in- connection with the development of cates fractional modulation directly cremental reading. To make this a production gain -testing system is in per cent. calibration, the d -c meter is adjusted diagrammed in Fig. 4. Inasmuch as rectifier meters have to the end of the scale by means of The diodes of an 85 tube are a non -uniformly -divided scale, and the bucking circuit. Then a small coupled to the circuit carrying the this departure from linearity is a d -c voltage is introduced in series signal to be analyzed. A portion of function of the resistance in series with the grid bias battery. A smaller the rectified voltage is impressed on with the meter, the a -c meter should sine wave a -c potential of accurately the grid. The plate circuit contains be equipped with a scale compensated known magnitude is also connected the indicating meters, a ballast re- for a multiplier approximately equal in series in the grid circuit. The a -c sistance, and a filter to separate the in resistance to the total plate cir- potential is adjusted to a value that a-c and d -c components of the plate cuit a-c impedance. A 100 v. scale gives some convenient reading, say current. A rheostat and bucking was used in the writer's meter, but 50, on the plate a -c meter. The d -c battery around the d -c meter enable a 25 or 50 v. scale would have been voltage is then adjusted to: needle end of slightly more in measure- setting its to the the accurate 1.41 X a -c grid volts (r.m.s.) scale when the r -f input is reduced ment of low percentages. Also, the Edc - (3) to zero. The a -c meter has a range a-c meter scale could be calibrated % reading of plate a -c meter of 1 ma., r. m. s. If the input is up to 125 or 150% (and a corre- whereupon the d -c increment is read. increased from nil by an amount sponding compensation made in the This increment is subsequently used sufficient to produce an increment d -c meter increment) so as to read in lieu of 1.4 ma. in per cent of 1.4 ma. d -c meter reading, modulation in excess of in the "effective" measurements. and the a -c meter then reads full 100%. Push-button switches as shown scale, the indication is 100% modula- The on measured load imposed the add greatly to the convenience of tion. The a -c meter has a 100 divi - circuit is inversely proportional to [Continued on page 38]

1MA B5 a.r.

0-'-111 I Coupled _ to - signa/ ; I L_ R -F 1.5 Flash- choke o/fs light 3 ce// ohms 10,000 to tooo o 200 o 01_4 f o Pus but ton switches Bottom makes /00 ohms before top breaks

Fig. 4.-Modulation measurement circuit used in production testing I/O volts a. c.

24 August 1936 - ELECTRONICS

www.americanradiohistory.com Mean Level Determination

GEORGE H. LOGAN 1000 100 iº 1.0 0.10 0.01 Sound Department, M. G. M. Studio 900 90 9 0.9 0.09 0.009 Culver City, California 800 80 `. 8 0$ 0.08 0008 700 70 7 07 0.07 0.007

600 60 6 06 0.06 0006 WHEN the relative energy output of a source (such as a 500 50 5 0.5 0.05 0005 speaker system, for example) is ob- 400 40 4 0.4 0.04 0004 tained on a high speed level 0 recorder, the chart in general ap- t K pears as standing waves which vary 300 30 3 03 0.03 0.003 in amplitude about some unknown mean energy level. Figure 1 represents such a chart, with decibel 200 20 2 0.2 002 0.002 ordinates, and frequency abscissae. To study the system characteristic, it is desirable to plot the mean level in decibels against log frequency. Deci eia It must be remembered that the 100 10 0.1 0.01 0.001 energy level, when recorded in de- -30 -29 -28 -27 -26 -25 -24 -23 -22 -21 -20 cibels, does not vary arithmetically but changes logarithmically. The -20 -19 -18 -17 ..-16 -15 -14 -13 -12 -11 -10 correct procedure, then, is to read -10 -9 -8 -7 -6 -5 -4 -3 -2 -I 0 from the chart the maximum and 0 1 2 3 4 5 6 7 8 9 10 minimum decibel values for a particular frequency, convert these to 13 14 15 16 17 18 19 20 corresponding power ratios, average 20 '21 22 23 24 25 26 27 28 29 30 the power ratios, and finally convert this average power ratio to de- Fig. 2-Unusual form of power ratio -decibel chart from which values cibels. In this manner is found the for formulas may be secured true average level for a specific frequency. Finding a number of such points throughout the frequency To convert to average decibel To illustrate use of the formula, range, and connecting them with a values- solution for mean level at 50 cycles smooth curve produces the true mean is given. level curve. D.... = 10 logio PR.... D1 D, In deriving the mean level equa- Reading D, and D Figure 1- tion, let D, and D, be the maximum 1010 = 10 logio and minimum recorded levels at a 2 D1=9 D,=6 given frequency. D1 DQ r 9 6 D.... = lO logio + antilog- D = lO logio [1010 -1-1011 ] - 10 logio 2 10 10 D = 10 logio PR or PR = (10)5 lantilog- rr D1 Ds At the extremes D, and D,- = lO logio + antilog- -3.010 Lantilog-10 10 D1 D2 = 10 logio [7.943 + 3.981] - 3.010 -3.010 = 10 logio [11.924] - 3.010 PR1 = (10)i;PR, = (10)71. = 10[1.0764) - 3.010 = 10.764 - 3.010 Hence the average power ratio is- Therefore, to compute the mean = 7.754 decibels decibel level at a certain frequency, D1 D2 the extremes D, and D, are read from In practice it will be found satis- 1010 + 1010 the chart, substituted above, and the factory and appreciably faster to 2 equation solved for Day. obtain Day. using Figure 2. Taking D, and D, at 50 cycles, Figure 1- Fig. I-Response curve for demonstrating average level determination D1 = 9 from Fig. 2, PR11 = 7.7 D2 = 6 from Fig. 2, PR2 = 3.9 -12j

J.Inearnqe111111111L'..riYA nlewlmaIwlln L1 \ rn 11wr'1111'll1'1111i.Mll1na6 w11...mn1.1.. 1 ..un1 ",I.m 1 7.7 + 3.9 iüiilY 1111.1. ..,..r1:1.1.'I,F:::111111ri'.1'nT.l'::.11...... 11 PR.... _ -5.3 2

100 200 300 400 500 700 900 1000 1100 1200 1300 1400 1500 1600 1700 1800 1900 600 800 from Fig. 2, D.... = 7.8 decibel» ELECTRONICS - August 1936 27

www.americanradiohistory.com By DANIEL E. NOBLE Assistant Professor of Engineering Connecticut State College

Limited Impulse & Delay Relays

Many circuits using tubes for relays have been devised; Professor Noble contributes his share in a class room bell timer, and a photographic printing time control. They operate from a.c.

THE widely used electronic relays because the impulse may be limited closes to ring the class -starting bell. are either designed for d -c oper- to any fraction of the original con- The electron relay has these charac- ation or for a -c use with a rectifier tact time, will find many uses in teristics: system in the unit. While no claims process timing. In the author's lab- 1. The contact sparking current of startling originality are made by oratory, two such units are in use. is negligible since the contacts the author the relays described below One is connected to an electric clock, operate in series with a half operate on a.c. without a rectifier as shown above, for the purpose million ohm resistor. system and offer a simplicity of de- of timing classes. When the hour 2. The ringing time of the bells sign which will appeal to the engi- hand brushes the insulated contact is limited (in this case to three neer or scientist concerned with con- at ten minutes to the hour, the relay seconds) to a predetermined trol problems. closes to ring the class -ending bell impulse. The slowly moving The limited impulse relay so-called and on the hour the relay again minute hand may move errati-

6A6

Re/ay contacts

En/arPin,q or printing /amp, V

Heater Swi+ch Positions' I -Lamp off 2 -Lamp onforexposure determined by Ry 1 & 3 - Lamp on. Manua/ control

2 Photographic printing light control 3 Twin triode limited impulse circuit 28 August 1936 - ELECTRONICS

www.americanradiohistory.com 1 Limited ring impulse clock timer

equal to the drop across the relay circuit. Therefore, when the switch is closed, the plate current rises to close the relay and then falls to open the relay when the grid condenser has charged sufficiently. On a d -c supply there are no special problems to be solved for satis- Bell factory operation of the relay. When used with a. c. the design must com- 1).9Q.QQQ.040..0 pensate for the fact that current will flow in the plate circuit of the 000 ` tube only during positive plate half 110v. 60 N cycle. Fortunately, a power factor adjustment of the relay circuit can be made which will eliminate entirely the chattering of the relay cally over the contact for a half of duplicate prints are to be made. and the unstable timing. Since the minute or more without affect- The operation of the limited im- values of Rr and Cr will depend upon ing the bells beyond the length pulse relay depends upon the well- the characteristics of the relay, no of the original pulse. known condenser charging principle. general values can be assigned but When switch S (Fig. 2) is thrown in the unit built by the author Cr In the second unit in the laboratory, to Position 2, the condenser C9 was 8µf and Rr, 5,000 ohms for a the resistance Rg is a variable unit charges through Rg. The charging rugged relay which closed on ap- equipped with a dial calibrated in voltage is the drop across the relay proximately 10 m. a. For the same seconds (Fig. 2). The lamp circuit circuit. The grid bias before the unit, Rg equals 250,000 ohms and Cg, of either a photograph contact print- switch is thrown is also equal to 8 µf for a three second impulse. The er or enlarger is connected through the voltage across the relay circuit time can be altered several hundred the relay circuit. Used in this way, but at the instant the switch makes per cent by changing the relay the device is a magnificent saver of contact the condenser charging cur- spring tension. This should make time and patience. The photog- rent is a maximum. The grid bias it clear that the relay characteristics rapher places his paper in position, is then equal to the drop across must be considered together with the sets the dial for proper exposure the relay circuit minus the drop product RgCg when determining the and throws the switch. The relay across Rg. As the charging of the time factor for the relay. then turns on the light for the ex- condenser proceeds, the current Where rapid recycling is not re- posure and automatically turns it through Rg decreases resulting in an quired, a resistance of 5 megohms off at the end of the predetermined increase in the negative grid bias. or more may be placed across Cg. exposure period. The unit is espe- When the condenser is fully charged, For rapid recycling the arrangement cially valuable when a large number the grid bias is again approximately shown in Fig. 2 may be used.

6A6

Neate

R3» R1, used only when second switch position is not used

4 Limited impulse relay as flasher control 5 Time delay relay using single tube 6 Self rectified, time delay relay ELECTRONICS - August 1936 29

www.americanradiohistory.com Limited Impulse Time Delay for a limited part of the contact time, the upper limit of the impulse can be determined by setting the condenser and resistor values of A. B will not respond to impulses unless they are of longer duration p Relay contacts o y than a predetermined minimum. Sw. o Thus, short impulses applied to the switch at A will not operate the relay at B and long impulses will Q9000 OQQ90 operate B only for a period equal to IIIPPIII the difference between the A timing and the B A timing. B must always be adjusted to a shorter time than A if any impulses are to be allowed Production of impulses above (A) and below (B) certain duration limits 7 to operate B. The author has found that the unit a rugged reliable unit. is reliable and free from relay chat- The time relay relay will also Tolerance Relays tering. The relay may be adjusted function properly as a single tube or for any impulse period between one - twin triode tube ac operated circuit. The arrangement shown in Fig. 7 twentieth of a second and three min- Figure 5 shows a circuit that has could be used for the automatic sort- utes and will maintain the timing operated very satisfactorily in the ing or checking of resistors or con- of the impulse within five per cent author's laboratory. When the densers within set tolerances. Cir- if the supply voltage is constant. switch is placed in Position 2, the cuit A would then be arranged for Figure 3 shows the circuit used condenser Cg begins to charge the insertion of either a condenser with a 6A6 twin triode for full - through R2. During the charging or a resistance into the operating wave self -rectification. This circuit process the current through R2 pro- position depending upon which was permits the use of a very rugged duces a drop between the cathode to be tested. Two B or time delay relay since a large current change and grid negative toward the grid. circuits would be connected to the may be produced when the switch While the charging continues, this A circuit. With one adjusted for a is moved to Position 1. The elim- negative grid bias prevents the relay required delay and the other ad- ination of relay chatter is also sim- from closing. When the charging justed for a slightly shorter delay plified by the full -wave rectification. process is complete, the grid will be the circuit would operate in this Another use of the limited impulse zero in respect to the cathode and manner: relay is shown in Fig. 4. A single the relay will close. By adjusting If the condensers are to be tested, tube is shown but a 6A6 twin triode the values of R2 and Cg the delay each condenser will be inserted in would serve as in Fig. 3. The ac- can be varied from a fraction of a the operating position in place of tion is as follows: second to several minutes. R1 and C1. The size of the condenser will Lever 1 in Position 3 with zero Cf are essential to the operation of determine the length of the impulse. bias on the grid controls a current the circuit. Their function is to If the impulse is too short, neither through the relay large enough to filter the fluctuations from the charg- time delay relay will operate and pull it closed. The lever then con- ing voltage. Without the filter the the condenser is rejected as under tacts 2 and C1 begins to charge. The ripple voltage will pass through Cg capacity. If the condenser capacity grid bias equals the drop across the to produce a continuous fluctuating is correct, the short delay relay will relay minus the drop across R1. As bias on the grid resulting in no operate and light a signal light or C1 charges the drop across R1 de- time delay action. Again, the twin start an automatic selector, but the creases and the bias approaches the triode 6A6 circuit shown in Fig. 6 second time delay relay will not have drop across the relay. This bias is is somewhat more reliable. In each time to operate with the limited im- great enough to open the relay and case the resistance shown across Cg pulse. If the condenser is oversize, the lever drops back to Position 3. is there to bias the grid negative the impulse will be long enough to C1 now discharges through R1 and before the charging operation starts. operate both time delay relays and R2 until the bias reduces to a point The magnitude of the resistance light a rejection light or start a re- where the relay will be closed again across Cg should be much larger than jection lever. The tolerance could and the cycle repeated. R1 and R2 R2. Five or ten megohm leaks may be set for each size condenser or may be selected to provide a wide be used in the position. resistance as closely as desired. The range of time on to time off ratios. The two relays may be combined accuracy of the system and all the Extra contacts operate the light cir- into a very interesting circuit which other systems described is largely cuit. For more complex flasher sys- will produce impulses only within a function of design. For extreme tems several limited impulse relays certain predetermined limits. Fig- accuracy an automatically regulated may be connected in cascade. Re- ure 7 shows one version. Two tri- constant voltage d -c supply should lays which close on currents from odes could be used with a single be used instead of a.c. but for many 20 to 40 ma. may be used in the transformer to produce similar re- applications the a.c. circuit is suffi- twin triode circuit, thus providing sults. Since circuit A will operate ciently accurate. 30 August 1936 - ELECTRONICS

www.americanradiohistory.com gang unit, specially constructed to fit Remote Tuning at KDYL on top of the main tuning gang. The 1 in diameter [Continued from page 19] plates are about inch and spaced about + inch. The capacity range is small enough to re- culty from this source. The contact equipment, and it was a distinct give a frequency control of about points are made of coin silver, and lief to find that all the anticipated 5000 cycles at 8000 kc. and about so arranged that a slight wiping troubles were non -existant. 20,000 cycles at 16000 kc. At the consists of a action occurs when the contacts The gear reduction beginning of a press schedule, the close. Ford coil contact points combination of worm and ring gears plates are meshed about of their should be even more suitable than giving a reduction of 800 to 1. This range, and the controlling operator condenser coin silver ones, and would make is ample, as the vernier has a plus or minus variation avail- the capacity a more lasting job. The contacts rotates so slowly that able by proper manipulation of his enable are mounted on spring brass arms change is small enough to control key. long enough to insure a good spring- close tuning. The output of the gear Trouble with leakage ground cur- ing action without being too stiff. reduction box is coupled to the con- rents was expected before the appa- Close fitting is essential in construct- denser with a section of speedometer ratus was installed, but to our grat- ing this relay, as it is the most crit- shaft and two universal joint coupl- ification none was encountered, al- ical item in the entire assembly. ings. No mechanical noise is trans- though no common ground connec- Commercial relays capable of permitted to the receiver, and the flexi- obtainable, other than that forming the same functions should tion was furnished by the city wiring system. be easily obtainable, but as the con- found necessary to use a trol unit was an experimental one, It was -f choke in the lead from the the expense of specially constructed small r line transformer to elim- relays was not felt justifiable. phantomed inate pickup of the intense r -f field The motor is a six volt commutator in the vicinity of the transmitter type, originally used on an automo- building. bile horn. The field connections were changed from series to shunt, In case any readers of this de- and although the result is a woefully scription wish to build up a control inefficient motor, at least it has a unit similar to this, we will be glad good starting torque and plenty of to give further information, pro- power. No trouble has been experi- vided a stamped envelope is included enced from commutator noise and for reply. This control unit has operation now for some the motor runs very well on a -c sup- at transmitter build- been in steady Mechanism as installed reliable ply. Although the control unit is ing where receiver is located months, and given completely mounted immediately adjacent to the service. The transmitter operators receiver, no precautions have been check the tuning at the beginning necessary to eliminate operating bility of the speedometer shaft en- of each schedule and from then on noises, because there just aren't ables the control unit to be placed give it no further attention. It is any. All sorts of dire forebodings in the most convenient location. indeed a labor-saving device and were felt before actual test of the The vernier condenser is a three well worth the trouble of building.

Book Review

phones and the electrical phonograph terms and by sketchy descriptions of The New Acoustics is given in some detail. Although the the principle of operation of the various of con- By N. W. McLACHLAN. Oxford Uni- author's principle contributions have devices. The book should be York been in the field of loud speakers, the siderable interest to readers of the versity Press, New City. A sur- scientific vey of modern development in acous- sections covering these devices are not other two groups who have a out of proportion to the rest of the background but are not posted on the tical engineering (Five tables, 111 The figures. Price $2.75). work. There are also chapters deal- present state of the acoustic art. ing briefly with telephone receivers, the value of the book to the more serious THIS IS AN INTERESTING ACCOUNT Of measurement of frequency, analysis of student is limited by the non -mathe- the contributions of "The New Acous- sounds, behavior of the ear, auditorium matical treatment, the paucity of ref- tics." There is a brief review of the acoustics, sound absorption, and one erences and by the fact that the author background provided for these con- describing a number of deaf aids. The has been handicapped in his choice of tributions by the classical theories. contributions which circuit theory had illustrative material by an attempt to The author considers that the World made to the design of the various describe British apparatus. Since War, with its need for navigation, sub- devices is discussed. most of the contributions in this field marine and aircraft detection devices, While an effort has been made to have come from the United States and gave the first impetus to recent devel- reach "scientists, engineers and gen- Germany, the author might have made opments. The second big impetus was eral readers", the value of the book to the book of more general interest by given by popular broadcasting. the last of these is restricted by inade- making additional references to prog- The evolution of loud speaker, micro - quate definitions of many technical ress in these countries. ELECTRONICS - August 1936 31

www.americanradiohistory.com TUBES AT WORK

CONSTRUCTIONAL details of a VT voltmeter using the 954 acorn pentode, a microwave link for WNYC, photo - tubes for auto -race timing and mine -door control, and a tube for generating kilomegacycles.

A Highly Flexible of its small size and indifference to filament fluctuations. By connecting VT Voltmeter the plate, screen and suppressor to- BY H. G. BOYLE gether a hi -mu triode is produced with Delco Radio Division, General Motors desirable cut-off characteristics. The mounting ring of bakelite or iso- OF THE MANY electronic tools available lantite is arranged so that the lugs on to the development engineer the the mounting clips are bent down and vacuum tube voltmeter can be of tre- the whole assembly slipped in a brass mendous value for routine checks. lamp socket from which the threaded Most of these units as normally con- shell and snap switch have been re- structed are bulky, awkward, and have moved. This is attached to a standard banks of associated batteries. Usu- eighteen inch flexible gooseneck and the filament, cathode and plate wires run inside. A rounded "bullet" nose was soldered to a thin brass ring, threaded to fit the open end of the The complete unit in use socket and all surplus metal ground away. This results in a completely enclosing shield and has proven adequate with its clip to connect to the tube. A for any frequency. In this nose is lead of flexible braid with a similar also mounted a very small switch to clip is soldered to the shielding shell. short the grid when the instrument is The normal line fluctuations caused not in use or shunt the grid when used some trouble originally but the net- with circuits containing open -circuit work shown, with the assistance of the direct current voltage. neon tube, obviates this difficulty en- A small hole in the cap, containing a tirely. By removing the resistance A lamp socket houses the 954 rubber grommet, allows the grid lead from the base of the neon tube, a very

ally the input capacity is high, and changeable, and the shielding is inade- quate at high r -f frequencies. VACUUM TESTING WITH A VENGEANCE All of these facts assist in producing the attitude that the work can be carried to a tube voltmeter as a last re- sort. Actually it should be regarded as indispensable as an d-c voltmeter. The unit described here was developed for general use in measuring gain and selectivity, and, with the assistance of other simple apparatus, the "Q" of coils and the effects of impreg- nating compounds. It is a very sensitive indicator for use with an absorption type wavemeter. Advantages of the unit are its complete portability, a -c operation, input capacity of less than five micro micro - f arads, no load on the circuit, complete shielding, and self check of calibration. The normal range is two volts r -m -s, grid current occurring at five volts input, giving adequate safety range for peak inputs of distorted micro microfarads wave forms. Where it is desired to extend the range to higher voltages a series of non -inductive resistors may be used to make up multiplier units of five, ten, and fifty times the voltage mentioned. This unit puts a load on the circuit, however, and can be used only where This Heintz and Kaufman Type 354 Gam -matron is being subjected to an the load is of no moment. "over-all" high -voltage test at sixty cycles. Evidence of high vacuum in The tube selected for the voltmeter the envelope was disclosed by the fact that no glow discharge occurred circuit is the "acorn" type 954 because inside the tube although heavy arcing did occur in the air outside 32 August 1936 - ELECTRONICS

www.americanradiohistory.com Read the "Inside Story" of this Radio Styling

TODAY, even the mass market for small radio receivers de- mands high quality in the styling and construction of cabinets. For success in this field, set manufacturers must supply it, often at mod- erate prices. For cabinets of this type, as well as for the larger, more expensive table models, Bakelite Molded offers outstanding advantages. Its fine lustre and rich colors contribute much

to the styling. Its ability to repro- even the three external ridges, duce practically any form or pat- which replace the usual cushioned tern provides broader opportunity legs, are accurately formed in the for originality in design. mold. Polishing and finishing are In addition, the production short- unnecessary because the color is cuts furnished by Bakelite Molded inherent in the material, and the afford striking economies without lustre is imparted by the mold itself. sacrifice of quality. For example the Radio manufacturers are invited new Emerson five -tube receiver cab- to consult us regarding methods of inet pictured, is completely formed obtaining maximum styling and pro- in two operations of the molding duction advantages through use press. of Bakelite Molded for proposed Metal inserts are permanently designs. Also, to write for our help- positioned; grooves, cut-outs and ful booklet 13M,`°BakeliteMolded." BAKELITE CORPO RATION, 247 PARK AVENUE, NEW YORK, N.Y. BAKELITE CORPORATION OF CANADA, LIMITED, 163 Dnfferin Street, Toronto. Ontario, Canada BAK _LITE rho r000000d ood moth , .,-. ..- , .-.,,,.-a.. -.Mm...,.a e. awwr cam.,o u.a.. w .onori r o -. ova. a a.« -a iw- n w, a m.wr Corcw-.o., THE MATERIAL OF A. THOUSAND USES ELECTRONICS - August 1936 33

www.americanradiohistory.com value the net voltage between plate and two cycle log paper. It was found con- cathode is 25 volts. Resistor Re of venient to write the reading for one 50,000 ohms is used to supply bleeder half volt, one volt, one and one half current for the bias control. R, of volts and two volts on a small card 1,000 ohms, R5 of 400 ohms and R. of and attach it directly to the top of the 025 20,000 ohms combine to supply bucking metal case with a cover of clear cellu- 2 current for zero adjustment. R. is set loid to prevent soiling. Thus a point is hand for 63V so that R5 will adjust smoothly to zero of calibration always at A.C. meter reading near the center of its reference. £ó CRR travel when the switch S2 is thrown In conjunction with this feature a RNió R,s ös to zero position. This switch opens self checking tap was provided. A the bucking circuit in its other position small 1,000 ohm potentiometer across 400+ to allow adjustment of plate current the filament was adjusted at the time to the correct value. R14 of 100,000 of calibration so that one volt is al- ohms is the current limiting resistor ways available for checking when the for the bucking network. line voltage is adjusted to 115 volts. Resistors R;, Rs, R9, Rio, and R11 in This tap is connected to a terminal ex- conjunction with the neon lamp make tending through the back of the up the voltage control network while cabinet. R12 is the power supply filter. This A small screen door handle bolted to Riz entire network should be of 10 watt the top of the cabinet assists in carry- Bmfd é~fd. wire -round resistors to lessen the ef- ing the unit easily. The power supply II fect of heating after long continued and all condensers and resistors are t 400V.D.C. from reclifier- fiHere- operation. The filter condensers, recti- mounted on the steel sub-panel and fier tube and power transformer are bakelite panel. A terminal board proof standard type, and supply 400 volts vides easy connection to the leads from VT voltmeter connection diagram d -c, at about 50 ma. the tube when the sub -panel assembly The three 0.25 microfarad con- is slipped into place in the cabinet. good voltage control can be obtained densers should be of low impedance The metal cabinet was finished in and by using a heavy bleeder the addi- type with adequate grounding. Any crackle and the gooseneck, handle and tional 100 microamperes drawn by the fifty microampere meter may be used screws left in their original brass. voltmeter tube on full input, does not providing the shunt is made of equal Completed, the unit is very neat and affect the regulation at all. resistance. workmanlike in appearance. Referring to the circuit diagram With this arrangement it will be In development of r -f coils and i -f resistor R, of 5,000 ohms is used to found that one volt input gives a read- transformers, checking oscillators and supply sufficient bias to the tube so ing of approximately thirty-five and the "Q" of coils it is very handy, al- that adjustment of R2, the 3,000 ohm an input of two volts will give full ways within reach and instantly mov- bias control, will not cause damage, scale deflection with the shunt on. able. The long, flexible gooseneck and even at zero setting. With this limit- Thus the most used ranges are well small size of the tube mounting head ing resistor the maximum current with up on the scale and easily read. allow it to be inserted within a chassis, a new tube is approximately 30 micro- The instrument should be calibrated connected to the desired circuits, and amperes. This current should not fall against a very accurate standard with not produce undesirable regenerative or to less than half this value during the some means of supplying either 60 degenerative effects. useful life of the tube. Resistor R2 is cycles or 1,000 cycles of the required The total cost of the unit including adjusted before each reading to a plate voltage. The calibration should be the type 600 Weston meter was ap- current of five microamperes, at which square -law and can be drawn up on proximately seventy-five dollars.

ULTRA -ULTRA -HIGH: A 30 KILOMEGACYCLE TRIODE New York to Use Micro -wave Beam THE COMMISSIONER OF PLANT and Structures, Frederick J. H. Kracke, of the City of New York has announced that before the end of the year New York City will possess a micro -ray beam radio link, the first in regular service in this country. The beam will connect the Municipal Building in City Hall Park with a transmitting plant of Station WNYC, which is now under construction at Greenpoint. The beam will be used as an emergency link only, but it will be a permanent feature of the station equipment and available for regular programs. In the event of wire failure between the Municipal Building and the station, the beam can be put into operation at once; neither rain, fog nor smoke will affect the transmission. The wave length of the micro- Claimed to be the world's smallest, these tube elements (left) generate wave will be approximately 20 centi- waves about one centimeter long. Drs. G. W. Potapenko and C. Y. Meng meters and the power output about 1.1 of Caltech have already used the waves in studying molecular structure, watt. The new Greenpoint transmit- find that they cannot penetrate fog. The fly gives an idea of the size; ting station is expected to be ready for the grid (on point of pin at right) is 0.02 inch long operation late this summer. 34 August 1936 - ELECTRONICS

www.americanradiohistory.com - August 1936 -

FACTS ABOUT FLEXIBLE CASINGS

for Auto Radio Remote Controls

The CASING is more than just a protective covering for the flexible shaft.

To assure entirely satisfactory shaft performance and proper installation and protection, the CASING should possess the following characteristics:

1. Necessary Flexibility combined with Sufficient Firmness to retain a given flexed position. 2. Minimum Radius of Curvature correct- ly proportioned to the minimum radius of curvature of the shaft.

3. Spring Tension sufficient to prevent the casing from kinking or bending too sharply.

4. Size of Bore properly proportioned to shaft diameter.

5. Resistance to Elongation to preserve predetermined length and facilitate assembly of unit. 6. Oil -Tightness and Corrosion Resist- ance.

S. S. WHITE METALLIC CASINGS S. S. WHITE CASINGS for auto radio ap- for Auto Radio Remote Controls plication do possess all of these characteristics ... They were developed ex- 1. Casing with plain end. pressly for use with S. S. WHITE Radio 2. Casing with integral enlarged end. Shafts ... They do assure the proper 3. Casing with integral flanged end performance of these shAfts. and female nut. 4. Casing with integral flanged end So we stress the importance of always and male nut. using the combination of S. S. WHITE CASINGS can be supplied with both Casings with S. S. WHITE Shafts for ends the same or with any combination auto radio. of ends. All casings are,oil-tight and corrosion -resistant. They can WATCH FOR THE be furnished with dull parkerized SEPTEMBER BULLETIN finish for exposed controls, or with In it we will give you the engineering galvanized finish for contrcls mount- data on S. S. WHITE CASINGS for auto ed on the dash. radio remote controls.

The S.S.W H ITE Dental Mfg. Co. INDUSTRIAL DIVISION IO EAST 40tk.ST. ROOM 2310 E, NEW YORK, N.Y.

ELECTRONICS August 1936 35

www.americanradiohistory.com MODERN JEAN VALJEAN world's pioneer broadcast station, will standing in the doorway. As the end rise to a height of 710 ft. The tower of the train passes either beam "W" will be triangular with cross sections or "E" which permits reestablishment and only 51h feet on a side. The of the beam, the door immediately entire weight of the tower, 60 tons closes. will be mounted on a porcelain insula- The installation functions properly tor 18 in. in diameter. Unusual fea- for any length of train. In the event ture of the antenna is the fact that it the locomotive operator is instructed to will be insulated at the half way point move the train backward after passing in its height, permitting operation as a so-called half wave doublet. Anten- nas of this type have been used for re/ays-___ some time in short-wave and ultra- /íi, iiii(iiiiiiiaiiiííaii/i//i high frequency transmission, but it is . believed that it is the first application 'Car Car C`, i E © ss in the broadcasting field. A powerful iiiiiiiiii/Ife44.7i`i`iiiiiiiiiiiiiiiiio+ iiiiiiiiiiiiiiiiiiii///!.S aviation beacon will be mounted on --Light sources ----- the top of the tower for warning to itinerant fivers. Interlocked mine -door control

either beam "W" or "E" which causes the door to open, the door will reclose Photo Tube Timers on after a predetermined time. By automatically controlling the op- Indianapolis Speedway eration of the mine door, the train does DURING THE RECENT auto races held at not have to slow down and, therefore, Reuben F. Brown, Assistant Sewer Main- the Indianapolis Motor Speedway increased haulage speeds are maintenance Engineer of Los Angeles, takes a checks were made with new photo- tained and accelerating power saved. leaf from %'ictor Hugo as he begins an electric equipment for timing and extensive inspection of the six -mile sewer photographing the finishes of the vari- system of the city. Let into the sewer ous races. The equipment takes a canal from a manhole, Brown rides in a picture of each car for each lap, and special boat several hundred feet a day, marks the time at which the car went searching for acid erosion, earthquake by on a strip of motion picture film. WAVE ANALYSIS FOR cracks, measuring The problem of motor speedway timing current flow and tem- is considerably different from that of THE MOVIES peratures. He maintains contact with the horse race timing, since the cars in- surface crew by means of an earth induc- tercept the beam of light which enters tion communicating set. Special clothing the photocell at a speed of 140 miles and an oxygen mask protect him from an hour which is in excess of 155 feet lethal gases per second. Even at this speed the equipment will operate when only the head of the mechanic or driver inter- cepts the beam. At the recent races there were 33 cars starting and each made 200 laps, which makes a total of New Antennas for 660 pictures if all cars had finished KDKA and WJZ the 500 -mile race. The equipment was designed and installed by Ralph Two APPLICATIONS for approval by the Powers of the Electronic Control Cor- FCC of tower construction have re- poration in Detroit. cently been made by Stations WJZ of Bound Brook, N. J., and KDKA at Sax- onburg, Pa. The WJZ tower, for which approval has been obtained will be a steel structure 640 ft. high, with constant cross-section throughout ap- Photoelectric Mine proximately 8 ft. in width. The tower Door Control will be supported by two sets of steel guy wires. In the earth directly be- ONE OF THE MOST interesting installa- neath the tower will be placed a copper tions of photoelectric relays and light screen 150 ft. in diameter which will sources used in the production of coal minimize sound losses which might is installed in a Pennsylvania coal mine occur at this point, and extending for for automatically controlling the opera- more than 600 ft. in every direction tion of mine doors. The installation will be more than 85,000 ft. of heavy consists of three photoelectric relays copper rivets. Power will be fed to and three light sources as shown in the the tower through a 10 -in. copper figure. transmission line. Because of the haz- When either the "W" or "E" beams Douglas Shearer of MGM and the "densi- ards which such towers present to air- are interrupted by the train the door tometer" he developed for analyzing the craft travel engineers of the Depart- immediately opens. A timing relay voices of the movie stars. Acting on the ment of Commerce and of the National causes the door to be reclosed after a Broadcasting Company have been work- definite time interval unless the beam principle of a reflecting galvanometer, the ing together to perfect a system of "C" is interrupted. The interruption machine makes a photographic record of night lighting, which is expected to be of the beam "C" cancels the timing the sound -pressure variations. Above is a one of the most effective ever to be cycle of the beams "W" and "E" to in- pure-tone record made by Jeanette Mac- designed for this purpose. sure that the mine door will not close Donald; below, the baritone voice of The new tower for KDKA, the while the train is passing through or Nelson Eddy 36 August 1936 - ELECTRONICS

www.americanradiohistory.com the s e4Ba2 7heABC f 7heABCof they are the basic and fundamental Sturdy Good reasons for the overwhelming popularity of CENTRALAB parts for Resistors Volume Control original equipment with the major- A Center core of resistance mate- A ity of the outstanding set manufac- rial is surrounded by a dense Resistor strip on inner circum- shock -proof ceramic, providing ference of Bakelite case has of country. strength and protection against longest possible length to in- turers this humidity. sure smooth volume control and low noise level. CENTRALAB Div. of Globe Union Mfg. B Core and jacket are fired to- B gether at 2500 degrees F. into Highly polished non -rotating a single, solid unit, hard and metal band contacts the resistor durable as stone. over a large area. Result, low contact resistance with light pressure, low -noise level, no re- C sistance change or wear. Pure copper covers the resistor end for wire lead contact. Con- tact to the resistance material C MILWAUKEE, WIS. is at the extreme ends only, Oilless wood bearing provides uniform resistance pressure and glides providing the contact and load distribution over en- over the polished metal band End contacts do Per- tire length. when control is rotated. British Centralab, Ltd. Centralab not short circuit part of resist- manently quiet and smooth types. turning. Canterbury Rd., Kilburn 68-70 Rue Amelo+ ance as in other London N. W. 6, England Paris, France ELECTRONICS - August 1936 37

www.americanradiohistory.com Modulation Measurement non-linear. Beyond this point com- parative readings can be obtained, [Continued from page 24] but the per cent calibration is no longer valid. operation. Button No. 1 permits slightly detuning the input circuit. The accuracy of the percentage in- rapid checking of the no -signal ad- With high r -f input, the diode d -c dication at low and medium modula- justment of the d -c meter. Button voltage due to the signal is many tion frequencies is comparable to No. 2, of the lock -down type, shunts times greater than the no -signal that obtained with more complex the d -c meter and disconnects the voltage, and the d -c incremental peak meters. For non -sinusoidal or bucking battery when up, thus pro- reading can be obtained by merely asymmetrical modulation, the circuit tecting the meter. Convenience of adjusting the potentiometer. will give a more logical per cent operation is further enhanced by This circuit is applicable up to reading than a peak meter. For high connecting the d -c meter backwards, very high signal frequencies, and modulation frequencies, the per cent so that signal input increases its will be found especially useful when indication must be corrected for fre- reading, and by connecting the input working with high -frequency, low - quency discrimination by the recti- potentiometer and bucking battery power generators. As shown by the fier meter. A further refinement for rheostat so that clockwise rotation curves, r -f input of less than 0.5 covering a wide range of modulation of the knobs also results in increased milliwatt at 5.5 volts will produce the frequencies is the substitution of re- reading on the d -c meter scale. necessary d -c plate current change sistance in each branch of the plate The diode places a slight bias of 1.4 ma. It is entirely feasible to circuit for the choke and ballast re- across the grid potentiometer even use more sensitive meters, the limit sistance indicated in the diagram, in the absence of signal input. in sensitivity being reached when and recalibration of the d -c meter Therefore if the signal input is low, the diode rectifier becomes seriously increment according to Eq. (3). it is necessary to recheck the no - signal reading of the d -c meter whenever the grid potentiometer Field Strength Measurement setting is changed, because the por- [Continued from page 22] tion of the no -signal diode bias included in the grid circuit changes gated by field strength tests. ment) and the increased flexibility with the potentiometer setting. If Within this region predictions of warrants the cost of the additional the r -f input circuit is tuned, as the fair accuracy can be made from a apparatus involved. writer prefers, the potentiometer can thorough consideration of the test It may be said that apparatus suit- be set so as to obtain greater than data; ground conductivity and topog- able for measurements of this type the required d -c plate current in- raphy can change so rapidly, how- is one of the most useful tools avail- crement, after which push-button ever, that subsequent results may able to radio transmission. The No. 1 is pressed and the d -c meter vary by a seriously wide margin economic value of the data which can reset to zero. The required d -c in- from the test predictions beyond the be obtained more than justifies the cremental reading is then obtained exact area which was investigated. cost of the equipment. by releasing the push-button and Another difficulty, obscure but The Canadian Radio Commission very practical, arises in some cases recognizes the value and importance Grid Volts due to the geology of the territory. of such measurements and has been -10 -5 0 If an investigation a given e of area consistently active in utilizing them, SYtú be is made on an existing or a portable and in developing equipment 1.4 MA. of wider Eb-250

www.americanradiohistory.com .64P

On this little ring you'll find the answer to your Locking Problems - send for yours nowl

THE SENSATIONAL LOCKING POWER OF SHAKEPROOF'S NEW 4w/dewed TOOTH LEARN for yourself by actual trial on your own product, or by the most severe tests you can devise, how Shakeproof's Triple -Action Locking Principle defies vibration. Look closely at the exclusive tapered -twisted teeth and you'll quickly appreciate why a Shakeproof Lock Washer holds any nut or screw absolutely tight. Note how each tooth is tapered, the width decreasing as the degree of twist increases, producing a substantial line bite at initial contact -the top edge biting into the nut or screw head, the lower edge digging into the work. This construction places a sturdy strut between nut and work, positively preventing backward movement of the nut, and also provides a strong spring -tension which keeps the locking force continuously active. This triple -action lock cannot be loosened by vibration. In fact, the greater the vibration the deeper the tapered - twisted teeth bite in-making the lock tighter than ever. PROTECTS PERFORMANCE- CUTS COSTS! If you use bolts or screws in your assemblies, you need the definite, positive protection STRU'-ACTION+SPRING-TENSION+LINE BITE against the loosening effects of vibration that Shakeproof Lock Washers provide. Don't be satisfied with ordinary lock washers-be sure you have the best. Test Shakeproof Lock Washers against any other type and the results will tell you why thousands of America's leading manufacturers have adopted Shakeproof. Mail the coupon today for your free Test Ring!

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www.americanradiohistory.com THE ELECTRON ART

RADIO in France as revealed by the International Exposition Volume Expansion in Paris. High frequencies, their measurement and genera- CROSLEY'S method of volume expansion tion continue to occupy a major place in contemporary literature. by which the low passages are de- pressed somewhat below their normal volume so that a wider range of volume is experienced has been described in Notes on the Paris 120 stations to be received by simply Electronics (March 1936, P. 9). The pressing two buttons. method practically applied with its International Radio The most noticeable defect in all the mathematics worked out for several Exposition sets displayed was the lack of fidelity. test cases will be found in The Wire- absent and less World, May 22, 1936 in an article By WINSTON E. KOCK The bass was completely highs above 4,000 cycles were ex- by R. H. Tanner and V. T. Dickens. THE THIRTEENTH ANNUAL Interna- tremely weak. Since about 90 per cent tional Radio Exposition was held in of the sets sold in France are table tre Hall Citroen in Paris from May models, the baffle area would prevent 20 to June 2, 1936. There were 163 high fidelity reproduction even if it A Wave Meter for exhibitors represented and the display were present in the received signal. Decimeter Waves covered an area of one square mile. However, this is not the case; the Exhibiting U. S. set manufacturers studio cables and studio equipment [LOTHAR ROHDE, LABORATORY FOR IN- included Zenith, American Bosch, are such that high quality reproduc- DUSTRIAL PHYSICS, MUNICH] When Scott All -Wave, Universal (Kadette), tion as we know it is not obtainable working with wave-lengths between 30 Motorola, and Lyric Radio; parts even with high fidelity receivers. The cm. and 60 cm. it becomes necessary to manufacturers were more fully repre- frequency separation of broadcasting ascertain the presence of oscillations sented. stations is less in Europe than in in the desired range or to make sure Television and metal tubes were the America, being usually 9,000 cycles that the wave -length remains constant. features of the exhibition. Television and sometimes 8,000 cycles which ac- Lecher wires are not very convenient broadcasts of 180 -line pictures were counts for the receiver cut-off at about for this purpose, and it is simpler to made regularly each day from 4 to 5 4,000 cycles. The poor fidelity of the use tuned circuits which have been o'clock from Paris, and at the exposi- receivers shown was so noticeable that calibrated with the aid of Lecher wires. tion one large hall was used solely for unquestionably a sensation could have Four tuned circuits consisting of a loop showing examples of television recep- been created by the display of one of wire and a two -plate condenser ad- tion. Throughout the main exposition high fidelity U. S. set playing high justed by means of a micrometer screw several individual exhibitors also dis- quality recordings of symphonic works. which may be read to 0.001 mm. cover played television receivers in operation. Nevertheless, there is as yet no quantity production of television receivers in France; one German Exhibi- tor, Radio A.G.-D.S. Loewe, has been FACSIMILE TELEPHONE IN GERMANY prepared for several months for mass production of sets but complications in Germany have prevented such a step. Good images in black and white are obtainable with the Loewe set. The television broadcasts consisted solely of vocal solos, recitations, and an- nouncements; so that good lighting was easily available for the subject. Metal tubes were used in many of the receiving sets displayed and the majority of these tubes were of Ameri- can manufacture. However, several French firms are manufacturing the all -metal tubes and also the type having a glass envelope and metal shell. A great many French sets utilize American parts in various places in the set, such as speakers, tubes, condensers, etc. Prices are still very high in France. A typical table model set lists at 2,750 Francs, the equivalent of $180, and an auto radio set lists at 1,500 Francs or $100. Console models range from 5,000 to 12,000 francs ($330 to $800). Several novel designs were displayed, including a radio modelled after a This highly portable scanning outfit is used as the transmitter for sending famous French castle, one built in the form of a baby -grand piano (3 feet photographs by wire in Germany, where it was developed by Siemens and high and 21 feet long), and a set with Halske. The photocell (in the T-shaped member) views a tiny spot of push button tuning. In this set, two light directed on the photograph by the 4-volt exciter lamp, while the rows of push buttons connected to drum revolves 60 times per second. Photos 5%" by 71/8" can be handled; fixed condensers permitted any one of the carrier frequency used is 1300 cps 40 August 1936 - ELECTRONICS

www.americanradiohistory.com NJ r (- o 4-'` 0 e N e& 4- 4- 4- 4- 4 44 ee 4- O 4`j` \'' -tr`yAo°Pr Q 45°* 4."1(59 4te O S)"%g<4 et> 44C "Pt" 44,<< ate SIIPSL*1**41.P1V a 1'44? Join This Network %e4e4stec.). OF GOOD stations who are using the General Radio ep,44.4- Type 731-A Modulation Monitor. There are four main reasons why these stations are G -R equipped: er,.4 7,40 I. The General Radio Modulation Monitor is reasonably priced. Complete with tubes and accessories, ready 40.**44 to operate, it costs $195.00. re-Zeze:Z2e.e 2. It not only guarantees that your station will comply with the FCC regulations, but it assures you of a A\04-40`' better signal in all modern high-fidelity receivers, with 4,4 increased coverage. te9 3. It is a separately operated part of the General Radio Class 730-A Transmission Monitoring Assembly which is in use by many of the finest stations to insure abso- 4741.1 ization. Years of useful service, as is the case with all G -R prcducts, are assured. We are havinc_ a difficult time keeping up with orders, but if yours is received soon we should be able to make delivery from the next production lot sometime early in AC"94"; September. * Only a partial list of purchasers of the G -R Monitor 449 For additional details write for Bulletin 41-E. 401;;St 2 so:$ste- t 4%, ,>+ Nee c- r4% 4

ELECTRONICS - August 1936 13

www.americanradiohistory.com LONDON'S TELEVISION New York MEASURES 10-28 GRAM TOWER Y.M.C.A. Offers Electronics Courses THE TECHNICAL SCHOOL of the New York Y.M.C.A. at 5 West 63rd Street, New York, announces the formation of courses in Electronics, available in both day and evening classes, which will begin Monday, September 21st, 1936. The courses are intended to give a thorough grounding in all phases of electronic science, and are given in two ternis, the first of a more elementary character for students not familiar with the fundamentals of electricity, and the second for more advanced students and engineers who already have a working knowledge of the fundamentals. Each term of the day course is given in approximately four months; the evening course requires approximately eight months per term. Both the elementary and advanced courses are given simultaneously, and it is possible for properly qualified students to take the elementary work during the Univer- the day, and the advanced work in the The latest mass spectograph at sity of Chicago will detect differences in steel structure, installed on the Alex- evening. This weight of the order of 10' gram. Atoms in North London, will radiate The elementary course includes in- andra Palace from a hot spark are drawn through a sound signals in the forthcoming struction in a -c and d-c circuit theory, sight and algebra, and the simpler vacuum tube slit, acted on by magnetic and electric BBC tests circuits, particularly as applied to fields, finally hit a photographic plate, radio. The advanced course is open to forming a spectrum which reveals the rela- students who have completed the ele- tive weight of the atoms mentary work, and to others who have substantially equivalent training; it is Radio Abroad intended for men who are familiar with THE FOLLOWING notes are made up the basic principles of electricity and from bulletins of the Bureau of its engineering applications but who Foreign and Domestic Commerce, of the Department of Commerce. desire specialized training in the newer Uruguay - Better market for im- and more advanced applications of elec- ported receivers, especially American, tron tubes. This latter course, which because of better economic condition TUBE -CONTROLLED LATHE may prove of interest to readers of and lack of enthusiasm for locally made Electronics, contains the following divi- sets. Market for auto radios is dull sions: Basic Electron Theory, includ- because many cars are imported with ing charge and mass relationships, radios already installed and owners of modes of electron emission, vacuum old cars are not taking to radio very tube structures; Electron Tube Cir- fast. cuits; Practical applications, including Venezuela-New stations, YV14RC, lecture demonstrations and trips to out- 6,270 kc. and 882 kc. and YV15RC, side installations; Electronic Systems; 5,910 and 1,400 kc. and Industrial Electronics, including Czechoslovakia -863,326 licensed re- control and measurement functions of ceiving sets as of March 31, 1936. thermionic and photoelectric tubes in Licenses now must indicate number of industrial use. Approximately one tubes, brand and chassis number. third of the course is devoted to Germany-Registered listeners on laboratory work. April 1, 1936 was 7,583,841 or 110,520 The teaching staff of the Electronics more than a month previous. First 5 Courses includes Mr. J. L. Hornung, months of 1936 saw a turn over of formerly radio instructor at New York 520,000 sets compared to 699,030 the University and coauthor of "Radio Op- year before. erating Questions and Answers" and United Kingdom - 776,663 new "Practical Radio Communications"; licenses during February making a Mr. Ralph Batcher, consulting engineer total of 7,573,793. and member of the Board of Editors Sweden -883,845 licensed sets are in of the I.R.E. Proceedings; Mr. Paul A. use in Sweden, a saturation of 141.8 Von Kunits, Chief Engineer of the per 1,000. The first three months of Bruno Laboratories; Mr. Chester this year saw the greatest increase for Smith, instructor in motion picture any quarter. projection and operating. The eve- South Africa-134,233 licenses are ning division advanced course will be in effect. The first locally made re- given by Donald G. Fink, Associate ceiver is on the market; known as the This automatic metal -working lathe shapes Editor of Electronics. Further informa- Viking it sold to the extent of 150 dur- its work from a black-and -white pattern tion may be obtained directly from the ing the week of their Rand Agricul- which is scanned by a photocell. It was office of the school at 5 West 63rd St., tural Show. designed by a Russian, V. S. Vikhman New York City. 44 August 1936 - ELECTRONICS

www.americanradiohistory.com Another useful contribution of Aircraft Hefele for aircraft radio guidance is an ingenious stream line loop an- Compass tenna. A loop wound on a coil of relatively small diameter such as 8" TRUTHS [Continued from page 15] is rotatably mounted within a stream lined housing which is in turn rigidly attached to the aircraft. The U. S. screen since an independent AF unit Coast Guard has adopted this type A man can work with maxi- is connected across the constant in- of stream line loop as standard equip- skill and speed only a tensity non-directional antenna am- ment. This loop may be seen mount- mum plifier system and does not effect the ed upon one of the Coast Guard certain number of hours per directional circuit. Strong static or The planes of the photographs. day. It is a mistake to work nonperiodic atmospheric disturbances effective reception by the 8" diameter produce corresponding erratic spot- loop is equivalent to the common him too long and too hard -- images of short duration. How- ted tubular metallic shielded loop of 18" in produc- ever, the continuous, normal super- any small gain diameter. by imposed directional indication is The aerodynamic resistance of the tivity is sure to be offset clearly visible in conjunction with stream lined loop is negligible, par- losses in quality. the static disturbances. Accurate ticularly as compared to the tor- flight through storms has been ac- roidal metallic loop. It is to be noted complished in spite of poor signal that the low aerodynamic resistance Help your men maintain conditions. The directional indicator of the loop inclosed in the stream may be used to determine the direc- lined housing is independent of the their physical well-being. tion of a distant storm in order that angular position of the loop coil Reward them sufficiently to the pilot may fly around it. within. The stream line housing is An interfering station would nor- mounted with its minimum resist- make jobs worth while-and mally superimpose its signal upon a ance in the line of flight. you have made loyalty their null indicator to destroy its accurate The total weight of the cathode null indication. However, an inter- ray right -left indicator has been de- first thought-that is worth with Hefele's right -left fering signal signed under seventy pounds and is more than the outworn word indicator merely produces a minor comparable with the weight of other "efficiency." pattern of its own and the major pat- types of radio compasses. The sensi- tern due to the preferred station is tivity of the receiver is such that a due clearly distinguishable. Errors field strength of two microvolts per to interfering stations are thus vir- meter may cause a full deflection of tually impossible. the indicator. Automatic volume Night effect, the bug-a -boo of control provides predetermined sensi- night flying with radio guidance, is tivity of deflection during extended overcome with the cathode-ray direc- flight periods. The power supply tion finder. In this case, the erron- may be directly operated from the eous polarization of the wave front, plane 12 volt storage battery with a although presenting an out -of -phase power drain of about 100 watts. The SUPERIOR component, has for its major com- deflection sensitivity of the indicator ponent the normal flight direction may be adjusted so that a 2° depar- TUBE which produces the proper direc- ture from on -course would deflect tional and sense indication upon the the indication 15 or 20 degrees from cathode ray tube. vertical. COMPANY Night flying tests have shown that Other designs embodying Hefele's the directional accuracy of the in- basic principle have been made with NORRISTOWN, PA. strument is not only unaffected by dynamometer and electrostatic indi- the night effect but night effect is cating meters in place of the cathode 25 miles from Philadelphia evidenced upon the indication as a ray tube. However the cathode ray non -correctible ellipse, the width of tube is particularly useful during ad- 100 Miles from New York which continually changes according verse weather conditions where the to the polarization effects. Flight signal is visually distinguishable during the night using the narrow from the static. The cathode ray "ellipse" instead of the straight line tube has proven itself to be a reliable, We Manufacture is very practical since the inclination rugged instrument on board an air- Fine Tubing of the ellipse is the determining fac- craft. The life period of a cathode tor of the right left indication and ray tube is at least that of the in Small Sizes its deflection from the vertical is vacuum tubes employed in the radio readily ascertained and the pilot can circuit and therefore regular servic- keep the indicator "on -course" to his ing and replacement precautions only destination. need be effected. ELECTRONICS - August 1936 45

www.americanradiohistory.com and some of the more likely will be discussed. Electron Oscillators In order for the curves to approach X=10 slowly and thus make from page 11) (Continued the oscillator one of the B -K type over considerable portions of the Lecher wires, the right hand member should be as large as possible Morrell on the other got such diver- Cp=Cm.=3.2, C5=2.2, K=1.3035, and when A=Ag and it should become as gent results when they used similar C=0.0684, all in micromicrofarads; small as possible for the slightest deviation circuits is undoubtedly that in the L=16.25 cm and A0, when finite, from this equality. The B -K case the filament emission was 100 cm. only way to make the tangent infinite when A=X0 is to make Cm zero. The much more copious than in the G -M The curves in Fig. 3 have been curves in Fig. 5 have been computed case. With the higher emission, computed from rprg would be lower. on this basis. It will be observed If equation (6) expresses the fre- 2l XC that these curves are more nearly tan- _ (9) like the experimental curves than are quency of the B -K oscillator, it X 2ir(C, + K) should be possible, without making the curves in Fig. 4. But still the any absurd assumptions, to throw obtained from (8) on the assumption angle of incidence of the curves at this equation into the form 102Eg=k, that ), is infinite. One of the curves X=aa is so large that there is no sug- gestion of B -K where ao is the wavelength corre- is for Cm=3.2 and the other for the condition. The change in wavelength at the jumps sponding to cog. The transformation Cm=O. The interesting feature about from one mode to the next is also is readily effected by assuming that these curves is that A increases unin- too both rp and rg are proportional to the terruptedly as l increases. There- great. first derivative of the grid voltage fore equation (9) represents pure It will also be noticed from (8) with respect to the grid current and G -M oscillations. that if Cm is zero and C/K is small, the curves will approach A=A0 that the grid current varies as the The next set of curves, shown in the more slowly in the region of oscilla- 3/2 power of the grid potential. Fig. 4, has been computed on the tion. One set of curves was com- assumption Äg =100 cm. Equa- that puted in Application of Phase Equation tion (8) gives directly the values of which the type was nearly pure B -K, but it was not retained l in the first mode only. The values Suppose X is the reactance of an because the required value of for the second and modes have C/K inductance coil instead of the re- third was absurdly small. been obtained by adding A/2 and X actance of a transmission line. Then Is there any justification for as- to each of the computed values. This X=L,u,, where L, is the inductance suming that Cm is zero? There is. is now allowable since the circuit can- between the grid and the plate. Equa- The assumption was first made not oscillate at a wavelength greater that tion (5) can then be written, Cm was lumped at the end of the than 100 centimeters. line. In practice this is not so, for 1 Although the inverse tangent is .º _ (7) Cm is distributed over the leads to the L,(C., -}- K) multiple -valued, there is only one grid and the plate and over the ex- value of A for each value of 1. The tent of these structures themselves. This equation shows how cog affects circuit continues to oscillate in a There is also distributed inductance the frequency in an Ultraudion oscil- lower mode until the condition A=Xo lator or any simple Colpitts, and also in this region. Therefore Cm and forces it to drop to a lower wave in the internal inductance constitute a how the tube capacities affect it. the next higher mode. The circuit Now let us suppose that X is the non uniform extension of the exter- "prefers" to oscillate at the longer nal line. Hence there is more reason reactance of a shorted transmission wave, as was pointed out by Gill and line having a characteristic resist- for assuming the Cm is zero than as- Morrell, and the reason for this pref- suming it has the value obtained by ance Zo= (L/C) i, length 1, induc- erence is obvious. When the circuit static measurement. tance L per unit length and capacity is oscillating near the limiting wave, C per unit length. Then, writing Another factor that should not be the inductance in the circuit is great- overlooked is that the first observed A for w, X=Z0tan (27í1/a), and equa- est for a given capacity. Any oscil- tion (5) may be written, mode may actually be the second. lator will oscillate more easily and The first may be so close to the tube 2Fl XC intensely when the inductance/capac- that it cannot be observed convenient- tan -_ ...... (8) ity ratio is high than when it is low. ly. It may even be entirely inside X 2a[Cm+K-K 1 Although the curves in Fig. 4 show the tube. As will be observed, the 20 the characteristics of the experi- slope of the computed curves becomes With the aid of (8), the length of mental curves of Hollmann, there is less the higher the mode. line required to generate any given a sharp contrast between the two in Again, if the two meshes account- wavelength can be computed if the the manner they approach the limiting for A° be regarded as a tuned other factors are known. By coming wave. In the computed curves circuit, there would be a tendency for puting l for a large number of values the angle of incidence is large; in the this circuit to take control over the of A, a graph can be constructed. experimental curves it is small, al- oscillation from the line. This ef- The following values were used in most zero. Several reasons may be fect would be greater the higher the computing the curves herein: adduced to explain the difference, resistance in the line. The com- 46 August 1936 - ELECTRONICS

www.americanradiohistory.com puted curves are for zero line resistance. That resistance in the line affects the course of the curves is Assure better performance corroborated by experiment. Still another possibility is that the reactance of the bridge affects the curves. If the bridge reactance is *S.S.WHITE 1,000 appreciable, the reactance of the open MOLDED OHMS end of the line beyond the bridge TO also must be taken into account. A 1,000,000 set of curves was computed for a RESISTORS line of total length 100 cm, a bridge MEGOHMS with inductance of 32 cm, and Crn=O. The effect of the terminating impedance from about 80 to 100 centi- Featured by noiseless operation, permanent re- meters was to decrease the slope of sistance value, rugged mechanical strength and the curves slightly. At 80 cm, non -hygroscopic material, S. S. tan (2x10/a) became infinite for the WHITE Resistors first time and for lower values the meet and satisfy effect of the terminating reactance NOISE TESTED every resistor need of the commercial, and the laboratory and was most erratic. For certain values At slight additional cost, re- of A the required value of tan (21s//X) sistors will be supplied indi- experimental fields. Recommended vidually "noise -tested" was complex. Here to for the to this particularly for air craft radio and stands specification: "For the com- total length of the line and l for the plete audio frequency range, for all applications where noiseless length from the bridge to the tube. resistors shall have less noise performance is vital. WRITE for than corresponds to 1 part in The B -K oscillator has always been 1,000,000." descriptive circular showing types associated with ultra -high frequen- and capacities. cies, and it has gained the reputation that it is especially suited for such frequencies. This reputation it does The S. S. WHITE Dental Mfg. Co. INDUSTRIAL DIVISION not deserve. The best that can be 10 East 40th Street, Room 2310E, New York, N. Y. said for it is that it is incapable of oscillating below a certain critical frequency, which may be made high by making the product CpC9rpr9 small. The Ultraudion with a pair Newly of Lecher wires connected to the grid and the plate is just as suitable for the generation of ultra -high fre- Designed EMLE quencies, provided that the line be made short enough, or if long, pro- AR -69 Preamplifier vided an external constraint be for placed on the line to force it to oscil- VELOCITY or DYNAMIC Microphones late in one of the higher modes. The Circuit: Two stage, resistance coupled. Highest quality, self - feedback oscillator would be more shielded transformers. Input trans- efficient than the electron oscillator. former cushioned in rubber. Out- put Since A. is practically infinite in transformer parallel fed. 2 Type 77 tubes, triode connected. the feedback oscillator, the curves in Gain 42 db. Response: plus 1/4 Fig. 3 may be taken as the relation to minus 13/4 db. from 1000 between the wavelength and the line cycle reference over the range 40 to 12,000 cycles. Also available length in the first mode of oscillation. at 36 db. gain with rising high To get the higher modes it is only frequency response (plus 4 db. at necessary to add multiples 10,000 cycles) to compensate for of half other apparatus. wavelengths to the abscissas. Imput: 30 Ohms standard, 250 It might be pointed out that Cp Ohms on special order. Imput is balanced and C9 are essential to oscillation in to center tap. Output: 200 Ohms. (May be paralleled any Colpitts circuit. They need not for 50 Ohms.) be as large as they usually are. In Power Required: 180 to 250 smaller volts plate (less than 2 mils drain) fact, the they are the more and 6 volts A. C. or D.C. (at .6 intense will the oscillation be for a amperes drain). Plate current May be had in Dural or Black finish Panel. Dimensions: jacks on given wavelength, and the shorter 19" z 51/4". Depth, including Dust Cover, I1N". Very front panel. Tubes acces- the wavelength that may be gener- moderately priced. Write for details. sible from front. ated with a given intensity. Cm, on REMLER COMPANY, Ltd. 2101 Bryant St., San Francisco the other hand, is not essential to oscillation and is always a nuisance. REMLER-THE RADIO FIRM AS OLD AS RADIO ELECTRONICS - August 1936 47

www.americanradiohistory.com MANUFACTURING REVIEW

New Products

molded lead wire connection. A Transformers Portable Engine Generator double loop conductor is used as the pick-up element. The unit weighs A GASOLINE ENGINE generator listing COTO -COIL COMPANY, 229 Chapman St., 6 lb., individually packed, and lists at Providence, Rhode Island, offers a line at $198.50 is manufactured by the $2.95. Gruenhagen-Callwell, Inc., 216 Santa of r -f transformers of the iron core Domingo Ave., Lomita Park, Calif. type. These transformers are made in The unit which contains a single Harmonic Filter two groups, the 50 series and the 60 cylinder 4 -cycle engine operating at series. The 50 Series is available for communication receivers requiring the 3600 r.p.m. and a 150 -watt continuous THE RADIO ENGINEERING & MANU- duty generator, weighs less than ultimate in selectivity, while the 60 FACTURING Co., 26 Journal Square, series is best suited for broadcast ap- Jersey City, N. J., announce a new plication demanding high gain and full harmonic filter for operation on the band-width response. Both types use output circuits of broadcast and com- the newly developed magnetic alloy munication type transmitters. Known material known as Magiccore which as type LP -10A Harmonic Filter exhibits no eddy current or hysteresis each unit is individually engineered to losses when used in a radio frequency the specified undesired harmonic. The field. All coils are wound with Litz type illustrated may be supplied for wire with the exception of the 175 kc. suppressing one frequency in the types. Padding condensers are zero bands 1100 to 3000 kilocycles and drift mica type on Isolanite bases. The 1650 to 4500 kilocycles when the fun- capacity range is sufficient to permit damental operating power does not readjustment of 465 kc. units to other exceed 1 kilowatt. A bulletin describ- popular I. F. frequencies from 550 to ing the filter is available upon 456 kc. request. 20 lb. The unit runs 12 hrs. on a gallon of gasoline, the gasoline tank holding 1 quart. By using new two type magnetic alloys for the steel Voltage Regulator livering the rectified d-c current to the structure, no exciting unit is neces- WARD LEONARD ELECTRIC COMPANY, Mt. shunt field of the exciter in an amount sary in the generator. Generator Vernon, New York, has developed an which is a function of the a-c gener- output is at 360 cycles, used rather electronic voltage regulator which per- ator potential. The diagram shows the than the conventional 60 cycles be- forms the same functions as do the elementary circuit involved which has cause of the much smaller generator other and older types, but the method the following advantages: 1. No mov- thus made possible. It may be used by which regulation is effected is en- ing parts. 2. No maintenance. 3. No "for lighting or with any other type tirely independent. Type EF regulators replacement except tubes. 4. Simple to -of load capable of using 360 cycle are control rectifiers deriving their install. 5. Low initial cost. 6. Quick_ alternating current at 125 volts. power from the a-c generator and de - acting.

"Ultra High Range" Resistor

THE INTERNATIONAL Resistance Co., -401 N. Broad St., Philadelphia, announces a line of stable, high range, non -inductive, high voltage resistors, types "FH-1" and "MG." The type FH -1 resembles a metallized filament resistor, but is made with special stabilizing processes. Available in -values up to 10,000 megohms for low ed. Arm. Md. Arm voltage application. Type MG is Exciter A. C.Generanor available from 20 megohms to 100,- 4000 megohms and in voltages up to VT -3 "4,000 volts. Both types are described in a catalog available on request. Circuit of Ward Leonard tube -controlled voltage A de- VT -4 regulator. bulletin R -I scribes its operation fully. Automobile Aerial

AN AUTO AERIAL known as model 4 R.C. Streamline is announced by the Control "Ward Products Corp., 2135 Superior frcrnsFornror Ave., Cleveland, Ohio. This aerial is Control .of the running board type, completely rheostat rubber covered and containing a 48 August 1936 - ELECTRONICS

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Model 521 Volt Ohm Milliammeter INSTRUMENTS fLET This flee inch model is just one R of the many styles and sizes available. Model 521 Volt-Ohm-Milliammeter PRECISION WITHOUT EXTRAVAGANCE Accuracy guaranteed within 1 c/

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This five inch model is just one of Triplett's large line INCORPORATES THESE NECESSARY AIDS FOR of instruments manufactured on a quantity basis at PRECISE INSTRUMENT MANUFACTURING attractive prices. Precision accuracy has been maintained through design improvements, highly efficient equipment, gauges and check methods by skilled labor working DUST CONTROL under ideal conditions in the new TRIPLETT FACTORY. TEMPERATURE REGULATION BLUFFTON, OHIO. Triplett Manufactures AIR CONDITIONING EQUIPMENT a complete line of electrical measuring instruments embracing MANUFACTURING round, square, rectangular molded and metal cases, twin meters NEW AND OF LATEST TYPE and multi range with changeable individual scales, for radio, electrical and general industrial applications. If you have an THIS COUPON TODAY ! electrical instrument problem write to TRIPLETT. MAIL

TRIPLETT ELECTRICAL INSTRUMErT CO. 238 Harmon Drive, Bluffton, Ohio, U. S. A. Please send me at once- More information on your Model 521. NAME ADDRESS ELECTRICAL INSTRUMENT CITY STATE ELECTRONICS - August 1936 49

www.americanradiohistory.com Literature

+ Sprink-la-stat Leaflet. The, Game - well Company, Newton, Massachusetts, HEARST describes its new automatic fire alarm system. Contains details on range of thermal ratings available and instruc- tion for installation. + Amplifiers. A booklet describing the complete line of preamplifiers offered 80git by Audio Development Company, Min- neapolis, Minnesota. 1 NSTALLS + Instruments. Leeds & Northrup Company's catalog No. N -33A, containing photographs, descriptions and maintenance data on Micromax thermocouple pyrometers. + Resistance Instruments. Loose-leaf binder type catalog covering precision type resistance instruments and allied products (volume control attenuators, L, T and H pads, precision attenuators, volume indicators, etc.), published by Tech Laboratories, 703 Newark Ave- nue, Jersey City, New Jersey. PRESTO + Transmitting Equipment. Sheets INSTANTANEOUS picturing and describing transmitting condenser, modulation monitor, field RECORDERS strength indicator and antenna coupling Outstanding performance of the equipment, and not cost ... was the final de- units. Doolittle & Falknor, Inc., 1306 ciding factor in the selection of PRESTO W. 74th Street, Chicago, Illinois. INSTANTANEOUS RECORDING EQUIP- MENT!

+ Welding. Specifications for Mallory The inherent sturdy construction - - dies, electrodes and water-cooled High fidelity characteristics . . Extreme portability ... and lasting dependability holders, contàined in handy booklet for in operation quickly demonstrated the insertion in file. P. R. Mallory & Com- money -making and money -saving possibilities of this equipment, to Hearst pany, Inc., Indianapolis, Indliana. Engineers. + A When time is not availale for local talent Foote -Prints. booklet issued by PRESTO RECORDERS will fill the the Foote Mineral Company, 16th & breach by making the necessary recording. This recording can then be played Summer Streets, Philadelphia, devoted back at any time. to the history, properties and potential sources of Zircon.

+ Sound Recording. A pamphlet issued Presto Green Seal Discs by the Fairchild Aerial Camera Corpo- are available ration, describing the Fairchild -Proctor in all sizes for immedi- studio recording system for broadcast ate delivery tstations. Woodside, New York City. All orders filled and shipped * Photoelectric Apparatus. Photocells, same day. colorimeter, relays handled by Pfaltz & Bauer, Inc., designed by Dr. B. Lange, and described in pamphlets giving characteristics, uses, and internal Technical ass stance and complete descrip- views. Distributed by Pfaltz & Bauer, tive literature gladly supplied on request. Inc., 300 Pearl Street, New York City. At Presto Headquarters, you will find everything for your recording requirements from a needle to a disc . ". to a complete + Transformers. Variac transformers high fidelity studio installation. for voltage control described by Gen- Export Division (except Australia and Canada) eral Radio Company in a newly dis- M. SIMONS & SONS, INC. tributed pamphlet. 25 Warren Street, New York Cable: Simontrice, N. Y. + Industrial Control. Ward Leonard Electric Company, Mount Vernon, New York, has issued a complete catalog with general descriptive material on their field rheostats, d-c and a -c manual starters, manual regulators, contactors, automatic starters and automatic transfer switches. + Calliflex. Callite Products Company has published description of its new RECORDING CORPORATION thermostatic bimetal, giving deflection formula and characteristics. 139 West 19th Street, New York, N.Y. 50 August 1936 - ELECTRONICS

www.americanradiohistory.com New Products

Small Metal -Can Electrolytic Condensers

A NEW SERIES of metal -can electrolytic condensers of large capacity is announced by the Aerovox Corp., 70 Washington St., Brooklyn, N. Y. The new condensers are uniform 1 in. diameter varying in height from 2 3/16 to 4% in., the latter being the 16 microfarad size. Two -voltage ratings, 450 and 250 d.c., are available. Capacities of 4, 8, 12 and 16 mfd. are offered. It is claimed that the capacity of these units is approximately twice that of the former units of equal size.

Cathode Ray Oscillograph and Accessory Units ELECTROLAB, INC., of Bloomfield, N. J., announces type PR 100 oscilograph list price $84.50. This cathode ray unit has a sweep oscillator capable of separating cycles from 6 to 1,000,- 000 cycles per second and a self-con-

tained amplifier. An electronic switch (type PR 200) for use with the cathode ray oscillograph permits simultaneous observation of any two 4 recurring or transient phenomena; A complete series of CaI-Lux Fluorescent Materials, list price $48.50. Type PR 300 direct coupled amplifier has controllable fully tested, and of measured characteristics, is now current and covers low frequencies up to to 100,000 cycles, lists at $34.50. available for the first time the electronic industries. Type PR 400 alternating" current amplifier, also $34.50, .has' an ampli- Our electronic laboratory is fully equipped to furnish: fication of 1000 over the range between 10 cycles and 2,000,000 cycles. spectral characteristics, rates of decay, and complete data on the response to Cathode Ray, X -Ray, Ultra- Communications Attenuator violet and Visible Radiations.

A NEW ATTENUATOR type "T-330" is announced by the 'Daven Co., 158-160 Write for full particulars Summit Street, Newark, N. J. At- tenuators are furnished with terminal impedances bëtween 30 .and 600 ohms, CAL -LUX FLUORESCENT MATERIALS and listed at $17.50. The attenuation is obtained in 30 steps with a standard With Measured Characteristics For All Applicaiions range from approximately 114 db. to a total loss of 128 db., accuracy within 5 per cent and with no«frequency dis- CALLITE PRODUCTS DIVISION crimination over the range from 300 to EISLER ELECTRIC CORPORATION 17,000 cycles. Shipping, weight is 544- 39th STREET UNION CITY, N. J. 22 oz. The diameter is 23 in. and depth back of panel 2 1/16 in. ELECTRONICS - August 1936 51

www.americanradiohistory.com Wave Trap

1pEiFECTt ALADDIN RADIO INDUSTRIES, 466 West Superior Street, Chicago, Illinois, announce several new products. One pre- AM 1(0w vents code interference from commercial ship -to -shore stations. This wave - Engraving Stock 7025-'7031 trap is tuned by the movement of a magnetic core made of "Polyiron". It lists at $2.50 with shield. Another

For Engraved Panels, Signs, Name Plates, Number Plates Panel shown was fabricated by lustrous black surface. Also avail- Insulating Fabricators, Inc., New able with white surface and black York City, for the Lepel High Fre- core, Lamicoid #7031. Engraved quency Diathermy Machine. Made lettering is permanent, clean-cut, of a laminated sheet of Lamicoid easily cleaned. Engraving stock #7025, having a pure white core and furnished in glossy or satin finish.

MICA INSULATOR COMPANY item is a type P, i -f transformer, in which the cores are adjustable with a 200 Varick St., New York; 542 So. Dearborn St., Chicago; 1276 West Third St., Cleveland. screw thread and the inductance values Branches at: Birmingham, Boston, Cincinnati, Loa Angeles, San Francisco, Seattle, Montreal, Toronto. are not affected by vibration, humidity or temperature changes. Fixed sealed condensers are permanently connected across the inductors. Type P transformers are characterized by high gain and a width. Insulated . . . narrow band The third Wire item is the type D-101 selective band three -circuit i -f transformer. Contained Whether it requires a Simple Free in an aluminum shield can 2" x 2" Push Back or a Line Cord in Rubber by 4", the transformer has three trim- or Silk-or even a multiple cable- mer condensers, a link -mechanism so Thousands of manufacturers depend that selectivity may be adjusted. on us for their production.

Write us for quotations.

General Sales Office Twin Multimeter

GENERAL INSULATED WIRE CORP. R A W S O N ELECTRICAL INSTRUMENT 53 PARK PLACE, NEW YORK CITY COMPANY, INC., Cambridge, Massa- chusetts, has developed a new twin multimeter. This instrument com- bines the older type 501 D -C multi - meter and type 502 thermal multi - meter into one compact unit. This is TELEVISION? accomplished by the use of a single movement switched from one side to SOUND? the other without disturbing either circuit. Each side is well insulated INDUSTRIAL? from the other and the range shunts Whatever. your interest may be in photo cells-there is a or voltage series resistors remain in dependable super-sensitive CETRON available for most circuit to the individual binding post, purposes. independent of the position of change- As specialists in the manufacture of photo cells we are over switch. The scale is easily read- prepared to supply a wide range of standard cells or, if you able. Eight millivolts are dissipated prefer, we will make them to your specifications. on the approximately 10 ohms resistance of the junction and on We invite your inquiry. eight the 10 ohm resistance of the meter circuit. The resistance of 10 ohms is CONTINENTAL ELECTRIC CO. constant on both the two and ten milli- ST. CHARLES 7 ILLINOIS volt ranges, permitting correct over- lapping of scale. , August 1936 - ELECTRONICS

www.americanradiohistory.com Literature + Time switches. Zenith Electric Company, 607 S. Dearborn Street, Chi- cago, Illinois, announce several bul- modern letins. Among these are Bulletin 702A describing remote control switches and magnetic contactors. Bulletin 500 describes automatic time switches and PLATE -SUPPLY high amperage time switches. Bulletin 780 covers automatic reset timers; 780C automatic timers that are manually TRANSFORMER reset and 780B motor driven automatic timers.

+ P. A. Amplifiers. Wholesale Radio Service, 100 Sixth Avenue, New York for Broadcast City, has published a catalog describing the complete line of 1936 Lafay- ette public address amplifiers, systems Station and accessories. Copies may be obtained by request addressed to the above address. Service

+ Sound Apparatus. Leaflets "Sound Advice" describing various types of audio frequency equipment, pick-ups, turntables, etc. for recording and re- by RPM producing. Issued by the Sound Ap- paratus Co., 150 West 46th St., New York City.

+ Wax on Recording. "A Treatise AmerTran Type RS plate -supply transformer. These units are Practical Wax Recording," by Ever- of the oil -immersed type and are furnished in standard steel itte K. Barnes. Issued by Universal tanks. High -voltage bushings through cover; low -voltage leads Microphone Co., Ltd., Inglewood, through bushings in corner pocket; tap -changer operating handle Calif. Price 50 cents. A 35 -page through front of case; available in sizes from Ph to 100 Kva., booklet describing methods and appa- single phase or three phase. ratus used in modern wax disk recording technique.

+ Insulating Varnish. A catalog de- HETHER you require plate transformers and scribing the complete line of Irvington reactors for a small rectifier or a 500 -kw. insulating varnishes. Also a folder broadcast transmitter, AmerTran can furnish describing Harvel 512C, an insulating AMERTRAN proper equipment of latest design. Transformers varnish for coil windings, manufac- PRODUCTS of either air -insulated or oil -immersed construc- tured under Harvel patent, by Irving- Transformers tion are assembled from standard stock parts, thus ton Varnish & Insulator Co., Irving- Audio -frequency Modulation insuring quicker delivery, lower cost, and proved ton, N. J. Plate -supply Filament -supply dependability. Power (5000 Kva.) The standard plate transformer illustrated is + Distribution oil -immersed rectifier equipment fur- Welding Apparatus. "Electric Instrument typical of Welding Machines and Welding Tips," Air-cooled nished to many broadcasting stations. Features a 64 -page reference book (36-W) on Special-purpose include: coils vacuum impregnated in varnish, resistance welding published by Reactors Audio & Filter ample oil ducts for proper cooling and high over- Charles Eisler of the Eisler Engineer- Volume Regulators load capacity; syphonproof bushings of coordi- ing Co., 750 So. 13th St., Newark, Rectifiers N. J. Available upon request to Testing Sets nated flashover type; tanks of weather-proof, those interested in using resistance Spot welders splashproof construction which may be shipped welding apparatus. filled with oil. May we send engineering details of equipment to meet your requirements? + Laboratory Instruments. "Galvano- meters and Dynamometers," Catalog ED 1936, issued by the Leeds & Northrup Co., Philadelphia, Pa., including a description of several newly developed instruments, a narrow -coil galvanometer of high voltage sensitivity with a short period, and a dual galvanometer. The specifications and listings of all instruments have been brought up to date throughout the catalog. Obtainable upon request American Transformer Company & Co., 4934 from Leeds Northrup Sales Offices: Boston, Chicago, Cleveland. Council Bluffs, Dallas, Hartford, Ithaca, Knoxville, Los Angeles, Stanton Ave., Philadelphia, Pa. Montreal, Newark, New York City, Philadelphia, Pittsburgh. San Francisco, Seattle, St. Louis. ELECTRONICS - August 1936 53

www.americanradiohistory.com Broadcast Now- Pre -Amplifier a high-powered- A PRE -AMPLIFIER, type AR -83, designed for use with dynamic and velocity types of microphones in high- fidelity transmission is announced by the Techna Corp., 926 Howard St., San Francisco. The unit is a two stage, resistance -coupled, fixed gain (44 db.) and the frequency response is within ± 1 db. from 30 to 12,000 cycles, with harmonic content of less than 1% at zero level. Input and Saja recording unit using Soja Motor output transformers to match 30 or 250 ohm lines. Panel size 5/ in. x 19 in. Net price $67.50. A power SAJA MOTOR supply furnishing 180 to 250 volts of "Saja Synchronous Motors" designed RADIO highly filtered d-c for plate current for high quality disc recording and re- at a total of 17 milliamperes and 6.3 producing High Torque-no vibration ENGINEERING volts filament voltage for operation -constant speed-sturdy symetrical of up to six AR -83 units is also avail- construction. No gears in able at a price of $58.00. either LIBRARY single or dual speed motors. Dual speed motors change speed electrically. - especially selected by radio specialists of McGraw-Hill publications DURALOTONE DISCS - to give most complete, dependable coverage of facts needed by all whose fields HIGH I.EVEL RECORDING-WIDE FREQUENCY RANGE MORE are grounded on radio fundamentals Velotron - - available at a special price and terms DURABLE THAN PRESSINGS- Microphone PLAYBACK WITH REGULAR These books cover circuit pheno{nena, tube STEEL NEEDLES. theory, networks, measurements, and other THE BRUNO LABORATORIES, INC., 20 subjects-give specialized treatment of all fields of practical design and application. West 22nd Street, New York City, an- Write for literature They are books of recognized position in the nounce the Velotron Microphone, a literature-books you will refer to and be SOUND APPARATUS COMPANY referred to often. If you are a researcher new velocity microphone incorporating or experimenter-if your interest in radio is new principals of construction 150 West 46th St. New York, N. Y. deep-set and based on a real desire to go entirely further in this field-you want these books and employing a static rather than a for the help they give in hundreds of problems throughout the whole field of radio magnetic field. The output is very engineering. much higher than that of the conventional magnetic velocity microphone be- 5 volumes, 2981 pages, 2000 illustrations ing on the order of -53 db. It is a 1. Everitt's COMMUNICATION high impedance microphone but may ENGINEERING be employed with cable lengths up to 2. Terman's RADIO ENGINEERING 500', without detriment to the quality of the output. It maintains its high 3. Chaffee's THEORY OF fidelity characteristics even under close THERMIONIC VACUUM TUBES talking conditions. It has approxi- 4. Hund's HIGH -FREQUENCY mately the same directional charac- MEASUREMENTS teristics as the magnetic velocity micro- 5. Henney's RADIO ENGINEERING phone but the angle of pickup is some HANDBOOK degrees wider. It is rugged, dependable, and unaffected by temperature Special Low. Price and Easy Terms and atmospheric conditions. Comes Bought singly, the five volumes comprising equipped with a shock absorber, swivel, this library would cost you $26.00. Under and cable connector. Finished in gun- this offer you save $2.50 and, in addition. have the -privilege of paying in easy install- metal. Weight 1 lb., overall measurements beginning with $2.50, 10 days after ments 6t" x 2k" x 1v". List price receipt of the books, and $3.00 monthly there- after. Already these books are recognized as $20.00. Twenty -five-foot cable and standard works that you are bound to require carrying bag. sooner or later. Take advantage of these con- ' venient terms to add them to your library now. AY-a^iQ{QPQPl^aa.. SEND THIS ON -APPROVAL COUPON McGraw-Hill Hook Co Inc 330 W. 42nd St., New York, N. Y. I Send me Radio Engineering Library 5 vols., for 10 days' "Super Pro" examination on approval. In 10 days I will send $2.50, plus few cents postage, and $3.00 monthly till $23.50 is paid, or return boni, I HAMMERLUND MANUFACTURING COM- postpaid. (We nay postage on orders accola 3 panted by remittance of first installment.) PANY, 424 West 33rd. Street, New York City, has developed Name just a sixteen tube WRITE FOR OUR EN- superheterodyne for the professional Address and amateur operator. This "Super GINEERING TUBE FOLDER City and State Pro" model covers from 540 kc. to 20 NO. 102 mc. by means of 25 coils. It has an Position electrostatically shielded input, variable HEINTZ AND Q Company selectivity, high fidelity, variable beat 4áD KAUFMAN LdTD (Books sent on approval in U. S. and oscillator, tone control and other cir- SOUTH \ CALIFORNIA Canada only). RAN FRANCISCO U. S. A. I cuit features. 54 August 1936-ELECTRONICS

www.americanradiohistory.com Relay AMERICAN GAS ACCUMULATOR COM- PANY, Elizabeth, New Jersey, has a new time delay relay designed for use in conjunction with any electrical apparatus requiring a delay interval. It has a delay range from a fraction of a A specially designed, general purpose microphone for remote second to several minutes. The design pickup, "P. A." and commercial interstation transmission work. of the timing head is based on 25 years Low in price . but built to Brush's traditionally high mechani- of experience. A volume of gas is cal and electrical standards. Wide frequency response. Non - directional. No diaphragms. No distortion from close speaking. maintained in the timing head by two Trouble -free operation. No button current and no input trans- special diaphragms which are made former to cause hum. Beautifully finished in dull chromium. from the same special type of leather Size only 21i/ inches in diameter. Weight 5 oz. Output level that has been used in the AGA flashing minus 66 D. B. Locking type plug and socket connector for marine lighthouses. This unit is unaf- either suspension or stand mounting furnished at no extra cost. fected by dust, temperature or humidity Full details, Data Sheet No. 13. Free. Send for one. changes. The timing period is unaffected by fluctuations of voltage. BRUSH J!ape/ MICROPHONE Attenuator For after dinner convention speakers, A NEW ATTENUATOR and lecturers, etc. of improved de- Gives great mobility sign is announced by the Tech Labora- - the smallest, lightest microphone on the market. Size 11/2 x 11/ x 3/8. Weight with coat attach- 703 tories, Newark Avenue, Jersey ment less than I oz. Special internal construction and City, N. J. This new unit is especially rubber jacketed outer case insures quiet operation. No designed for broadcast and high grade interference from breathing noises, etc. Typical Brush sound cell response and trouble -free operation. Details on request.

DEVELOPMENT COMPANY PIEZO 1884 E. 40th St. ELECTRIC CLEVELAND, O.

MICROPHONES MIKE STANDS TWEETERS HEAD PHONES LOUD SPEAKERS UL ID sound recording purposes. It has a larger number of steps, lower noise V an adaptable material level, better frequency characteristics, better terminals, easier - 'wiring and smoother operation. Vulcoid is a chemically processed, laminated, fibrous insulating material that is permanently moisture resistant-adaptable for many insulating requirements-readily machined, and formed by heating. PROPERTIES Controlled Rectifiers THICKNESS WARD LEONARD ELECTRIC COMPANY, 1/16" 1/8" 3/16" 1/4" Mount Vernon, New York, has announced a new line of controlled recti- Specific Gravity 1.40 1.40 1.40 1.40 fiers providing d -c power, from an a -c Average Flexural Strength power supply for small public and pri- Pounds per Square Inch 23,000 21,000 20,000 19,000 vate telephone systems. This equip- Average Tensile Strength ment on an a -c line varying ±10 per Pounds per Square Inch 11,000 11,000 10,000 9,000 cent, supplies a d -c voltage maintained Dielectric Strength Volts per Mil 500 450 350 300 constant to -±1e -volt accuracy from no load to full load. In locations where the Vulcoid is a comparatively low cost non -hygroscopic material, a -c power supply is not continuously economical to buy in sheet, rod or tube form, economical to available and uninterrupted telephone fabricate, stable in both electrical and mechanical properties. service is necessary, a standby battery of proper voltage with emergency Ask for complete information. ampere -hour rating should be used. This unit consists of a Hysterset, rectifier and filter units assembled In CONTINENTAL -DIAMOND a metal enclosure and arranged for floor mounting. Both sizes are equipped with suitable d -c voltmeter and am- FIBRE COMPANY meter. NEWARK, DELAWARE ELECTRONICS-August 1936

www.americanradiohistory.com News

FAIRCHILD PROCTOR The New York Office of the Allen- Bradley Co., manufacturers of motor CRYSTAL control equipment and resistors has PICKUP been moved to larger quarters in the Underwood Building, at 30 Vesey Ideal for modern St., from the former location at 50 Church St. A complete consignment transcriptions stock of motor control equipment will Assures uniform response, extended be carried in the new headquarters. high and low frequency range, minimum record wear. Is non -resonant, non-magretic, and freely damped. A Complete Recording Service Calibrated needle Other Fairchild Proctor products in- +Ira J. Owen, well-known industrial pressure s c a I e. clude Portable Recorder and Sound Sturdy design and Recording System for Broadcast Sta- engineer, has been named president construction. Write tions, etc. Details on request. of the Utah Radio Products Co. to for Circular E- T. who FAIRCHILD AERIAL CAMERA CORP. succeed J. W. Caswell, continues 62-10 Woodside Ave., Woodside, N. Y. C. as director. Mr. Owen, a graduate of Cornell University, has been a consulting engineer for several years.

+ Edward J. McCarthy has been ap- DYNAMIC MICROPHONES pointed to the position of general Co., ARE INCREASING IN POPULARITY sales manager of The Gamewell according to an announcement of because they Mr. Vincent C. Stanley,p resident, Mr. -have greater sensitivity McCarthy has been in the employ of -are free from inductive pickup The Gamewell Co. for over 16 years, -have no background noise joining the Gamewell Co. in 1920 after -can work with long lines his graduation from Massachusetts -are sturdiest ever produced Institute of Technology. -are weatherproof -are small in size +Mr. H. J. Casey, manager of the -are reasonable in price Republic Radio Mfg. Co., announces Write for Bulletin No. 3012 the removal of their factory and general sales offices to larger manufac- RADIO RECEPTOR COMPANY, INC. turing facilities at 255 Grant Ave., 108 SEVENTH AVE. NEW YORK, N. Y. East Newark, N. J. Licensed manufacturers of radio tubes. An Ideal Midget RESISTOR for analyzer, meter conversion, etc. Literature The Type "R" MICROHM meets the popular demand for a compact. low priced Resistor. While small in size, it is of high + Pickup. Fairchild -Proctor's wide quality and accurate to within 1%. high fidelity crystal pickup de- The Type "R" is 1/2 -watt, with resistance up to 500,000 ohms. range, As a companion unit, we offer the type "S". 1 -watt, which is scribed in a pamphlet issued by the available in resistance values up to 1 megohm. Write for details. Fairchild Aerial Camera Corporation, Woodside Avenue, Woodside, New York City.

+ Amplifiers. A new 48 page bulletin including data and circuits on amplifiers from one half watt to 1,000 watts PRECISION REGISTOR CO., 334 Badger Ave., Newark, N. J. output, chapters on audio transformer design, charts on decibel conversion, reactance data, published by United Transformer Corporation, 72 Spring you can depend upon their Street, New York City. OPERATING RELIABILITY + Recording and Transcription. Presto Leach small size circuit control relay, Recording Corporation, 139 West 19th type No. 1357 is a compact, rugged and Street, New York City, has prepared reliable control relay ideal for your con- a catalog describing in detail the trol circuit. These relays have solid in cores, positive contact and low current latest developments equipment, consumption-built so that you can de- discs and parts, for instantaneous pend upon them! recording and transcription. Copies available upon request. LEACH RELAY COMPANY 591.5 Avalon Boulevard, LOS ANGELES, CALIF. + LEACH RELAY COMPANY, 5915 Avalon Boulevard, Los Angeles, Calif. Speakers. Catalog describing per- Please send your catalog. I am interested in type relay. manent magnet speakers for use in Name receiver, car and public address equip- Company ment, published by Cinaudagraph Address City Corporation, Stamford, Connecticut. 56 August /936-ELECTRONICS

www.americanradiohistory.com Vacuum Type Thermo Couple

THE SENSITIVE RESEARCH INSTRU- MENT CORP., 4545 Bronx Blvd., New York City, announces a new type of thermocouple mounted in a highly evacuated glass bulb, suitable for measurement of any d.c. or a.c. current of any frequency, including radio frequency. The thermo couples are mounted in a molded Bakelite base or can be supplied with a standard U tube base or unmounted. Other new items are announced in "Elec- trical Measurements," for April 1936, a house bulletin issued by the company. Sensitive Research has also added to its Polyranger instrument group a dy- nanometer current and voltage measur- Model 14C Standard Signal Generator ing instrument which measures a -c currents and voltages from 2 ma. to 10 An instrument for research and design laboratory use amperes and from 2 volts to 3000 volts with an accuracy of of 1% at com- IMPORTANT FEATURES: mercial frequencies. Built in coils cover 75 to 30,000 'kilocycles . . . Output up to TWO VOLTS across LOW RESISTANCE. (Never over 20 ohms) . . . Worm drive condenser with 30 FOOT scale length (10 kilocycles in broadcast band = 25 large scale divisions) . . . Operates on either Relay Equipment 115 volt 60 cycle AC or batteries (Without change in instrument) .. Low radio frequency harmonics. (Approximately one per cent) STRUTHERS-DUNN INC., 139 North Juni- per St., Philadelphia, Pennsylvania an- Price, $1250.00 F.O.B. Newark, N. J. Write for illustrated circular with full details. nounce a relay equipment for the control of crystal ovens. This equip- FERRIS INSTRUMENT CORPORATION ment consists of a sensitive relay and front contact relay. The thermoregula- BOONTON, N. J. tor controls the coil of the sensitive relay whose contact in turn controls the coil of the front contact relay. The contact of the front contact relay con- Featuring A BASICALLY NEW SWEEP trols the heating circuits, so that the contacts of the thermoregulator need AND AN IMPROVED SYNCHRONIZING CIRCUIT only carry a current of a few milliamperes to control the load circuit. THE MODEL 148 CATHODE RAY OSCILLOGRAPH The load contacts are 6 amperes at 110 This new oscillograph utilizing a five volts, a.c. for heating loads. This inch cathode ray tube incorporates equipment sells at $20.90 including the many advanced features, developed by glass cover. The relays are mounted DuMont, and offered for the first time on a base 7 in. high by 5 in. wide under in a commercial unit. a glass cover which is 317g inches high. Improvements are such as to assure ease of operation and accurate determinations. A basically new sweep circuit permits observation of waves from 10 to 500,000 cycles per second. A speeded up return trace which does not interfere with the pattern at high frequencies is another exclusive feature. Sweep can be synchronized easily with fractions as well as multiples of the wave. Amplifiers are arranged so that they may be used either as single stage for each set of deflection plates or as two stage for vertical deflection plates. Signal and sweep voltages in various combinations can be applied easily and conveniently by a single knob control. A calibrated scale is supplied for highly accurate determinations List Price with 5" tube $106.50 when used with a five inch cathode Du Mont also manufactures an improved and ray tube. Completely AC operated simplified Electronic Switch and other Osctllograph equipment as well as a complete from 110-120 volt supply. line of cathode ray and sweep discharge tubes. These products are in the sixth year Several motor operated timing de- Full technical data and the wide field of successful manufacture. of uses for which this instrument may vices have been added to the Struthers - Every Cathode Ray Tube used by Du Mont Dunn, Inc. line of thermo, inertia, air be effectively applied will be sent on is engineered and manufactured in the Du request. Mont Laboratories. Write for full information. dashpot and capacitor times. One type is of the immediately recycling type; another is of the continuously rotating ALLEN B. DUMONT LABS. INC., UPPER MONTCLAIR, N. J. type. ELECTRONICS - August 1936 57

www.americanradiohistory.com Audio Frequency Announcing deter GENERAL RADIO COMPANY, 30 State THE SIGMA Street, Cambridge, Massachusetts, announces the electronic frequency meter, SENSITIVE RELAY Type 834-A, a time -saving aid in fre- PROFESSIONAL quency measurements. The instrument includes a one -stage amplifier, the gas- discharge -tube counter circuit, diode switching tube, frequency -indicating SERVICES meter and power supply (with rectifier and voltage regulator). By arrange- $OA ment of the amplifier circuit provision INSrAUA is made for satisfactory operation over .... NI a wide range of signal input voltages up 200 no _ rylaar to volts, with change in ISABEL S. BEMIS indication of frequency. Five ranges MATHEMATICAL SOLUTIONS Radio Engineering Problems are provided, starting at zero and ex- Fifteen years experience covering. tending to 200, 500, 1,000, 2,000 and Calculation of Directive Antenna Diagrams, Analysis of Radio Field Intensity Data. Broadcast Cover- 5,000 cycles. age and Population Studies. Harmonic Analysis of The June issue of the Experimenter Curves. General Statistical Work. describes the new 605-A signal gen- 931 N. Walnut St., East Orange, N. J. erator covering a range of 9.5 to 30,000 Jewelled movement. kc. Designed by Messrs. E. Karplus, BLILEY ELECTRIC CO. Balanced to operate in any position. L. B. Arguimbau and A. G. Bousquet. Designers-Manufacturers Positive operation on 4 milliwatts, D. C. Quartz Crystals for standard or special radio frequency applications. Single pole, double throw. Low Cost Microphone Inquiries Invited. Mounts in standard 5.prong tube socket. 240 Union Station Bldg. Erie, Penna. A useful adjunct to A DOUBLE -BUTTON carbon microphone V. T. controls for which exceptional performance Supervisory and alarm circuits Signalling. and durability is claimed has been announced by the Shure Bros., 215 West EISLER ENGINEERING CO. Consulting, Designing ci Mfg. Engineers Huron St., Chicago, U. S. A. The Electric Welding Problems, High Com- SIGMA INSTRUMENTS, list is The model pound Vacuum INC. price $5.50. is flat Pumps, Soft and Hard within + 10 db. from 40 to 6000 Glass Working Equipment, Radio 358 Road, and Electronic Tube Machinery Trapelo BELMONT. MASS. cycles per second with a maximum Special Machinery built to your specifications button current of 12 milliamperes 753 So. 13th St. Newark, N. J. The output level is 30 db. below 6 mw in 200 ohms. ELECTRICAL TESTING Shure Brothers also announce a new LABORATORIES four-way utility microphone, for desk, Characteristics and stand, Life Tests of Vacuum Tubes direct hand or ring use. Testa of photo celle, glow lamps. crater lampa. Tests of electronic and optical devices. 80th Street and East End Avenue New York, N. Y. Plastics Phone: Butterfield 8-2600 GENERAL PLASTICS, INC., North Tono- wanda, New York, announces a new BERNARD EPHRAIM, E. E. line of resins by which wood, pulp and Expert Foreign Technical Translator cellulose materials in many forms can Patent Specifications Engineering Articles be strengthened and given greater re- French. Spanish, Italian, German sistance to acids, solvents, and alkalies. Better Filtering A new extra strength Durex molding Box 4049. San Francisco. California material known as 15/44 has been an- for .Midget sets nounced. It has higher impact strength, is light in weight and has good machin- THAD R. GOLDSBOROUGH Three entirely independent sections In com- REGISTERED PATENT ATTORNEY pact can, hermetically sealed for longest ing qualities. Still other new products Westinghouse Electric, 1925-1930 trouble -proof life-that's the idea of the new are improved thermosetting resin solu- Patent Attorney, RCA Victor, 1930-1935 Fifteen years familiarity with patent matters Series GGGL electrolytics. Six leads-two tions for impregnation and coating of relating to Talking Movies, Television. Radio and for each section. Units measure 1ÿi" dia. x motor and generator armatures. Fur- Electronics. 3%" or high. Inverted mounting. Two 201-205 McLachlen Building 4/a" thermore, metal castings may be im- Washington, D. C. ratings -250 and 450 v. working. In 4-4-4, pregnated with these resins to reduce 8-8-8, 8-8-16 and 8-16-16 mfd. combinations. Handy 3 -in -1 electrolytics for better filtering poracity. in tight places. HUDSON BROS. MFG. CO., Inc. 539-41 42nd St., Union City. N. J. for new catalog covering complete Door Alarm Designers and consultants for experimental glass * Write line of condensers and resistors. apparatus, pyrex and soft glass. Submit problems for engineering aid and Aspirator Pumps Ground Joints MEANS Graded Seals Stop -Cock Grease quotations. BY of the Photobell Model L Stop -Cocks Pyrex and McLeod Gauges electric eye signal any one entering a Soft Glass Traps of all types. Glass Apparatus Made to Blue Print Specifications. store or office door cuts a beam of light Tel. Palisade 6-2990 and rings a bell or chimes. The device can be used as a burglar alarm or an attention caller. It is good for dis- PROFESSIONAL ASSISTANCE up 15 CORPORATION tances to feet, costs one cent a in the solving of your most difficult 75 Washington St. Brooklyn, N. Y. day for electricity, is guaranteed for problems in the highly specialized field six months, lists at $49.00. Phorobell of electronic devices is offered by con- Corporation, 96 Warren Street, New sultants whose cards appear.on-this page.. York City. 58 August 1936-ELECTRONICS

www.americanradiohistory.com Beam system. Reversible undirec- tional antenna comprising two radi- PATENTS REVIEW ating elements, one of the elements having a two wire line connected thereto, and a switching mechanism PATENTS indicate trends. Next year's radio circuits, in circuit for shunting out a portion of electron tubes for non -communication of the line for reversing the direction applications of radiation. P. S. Carter, RCA. No. purposes, new tube types, new materials, may be discovered 2,040,079. See also No. 2,038,539 to by following United States and British inventions. Carter, RCA, on a directional system for radiation in two different directions differing by an angle which is less than 180 deg. Transmission Circuits ing electrical energy over commercial electrical power network. Antenna system. A bridge circuit Transmission line. Method of pre- involving a receiver, an antenna, a venting standing waves on a portion Signaling system. No. 2,041,830, C. of a transmission line by determining W. Hansell, RCA, on a high frequency the ratio of the maximum and mini- transmitter involving a magnetron os- mum standing wave amplitudes and cillator. connecting a pure reactance across the line at a maximum current point, the value of the reactance depending upon Duplex system. Separate antennas the ratio across the line at a point at for transmission and reception, the a distance from the ascertained cur- antennas displaced from each other so rent maximum point dependent upon that the receiving antenna is in the the ratio and less than an eighth of shadow of the transmitting antenna a wave length. P. H. Smith, B.T.L., at the same terminus. A. G. Clavier Inc. No. 2,041,378. and R. H. Darbord, W.E.Co. No. reflector and amplitude regulator. 2,043,347. Wilhelm Moser, Telefunken. No. 2, - Modulation circuits. The following 033,390. patents are on the general subject of Printing system. A combination of modulation: No. 2,038,992, J. G. Chaf- commercial telegraph printers in a Multiple antenna system. A method fee, B.T.L., Inc., ultra short wave radio telegraph system. W. C. Hill, of communication comprising energiz- system. No. 2,033,231, M. G. Crosby, Grand Island, Nebr. No. 2,017,458. ing several paths of different lengths RCA, phase modulation. No. 2,034,899, in the transmission medium between W. T. Ditcham, RCA, modulated trans- Fading reduction. Modulating the mitter. See also No. 2,038,526, to waves to a depth which varies ex- Ditcham. No. 2,037,756, Otto Böhm ponentialIy as the amplitude of the . M. modulation and Osnos, Telefunken, modulating potential varies. H. O. system. No. 2,042,748, G. L. Ussel - Roosenstein, Telefunken. No. 2,031,072. man, RCA, modulating means. No. 2,043,255, W. S. Marks, Jr., Fort Monmouth, N. J., screen grid modula- Carrier suppression. Combination tion. with an electric wave filter including a piezo-electric crystal of mechanical means for controllably damping the Synchronizing system. A common vibration of the crystal whereby its frequency broadcasting system, C. B. sharpness may be reduced. H. O. two stations and receiving at any one Aiken. No. 2,033,271. B.T.L., Inc. Roosenstein, Telefunken. No. 2,035,013. instant wave energy propagated along only one of the energized paths re- gardless of the proximity of the incom- Ringing circuit. No. 2,023,222, G. Antenna Systems ing energized paths. H. T. Friis, W. Fyler, G.E.Co., on a ringing cir- B.T.L., Inc. No. 2,041,600. cuit for radio -transmitters. Reflector. Unitary continuous reflecting web of curvilinear profile devoid Duplex transmission. A duplex sig- of salients partly enclosing the source Amplifier Circuits, Etc. naling system comprising a super- of energy. The web is made of an regenerative receiver at each end for inherently highly resilient material. Multi -element tube circuit. Com- Rene Jean Le Guillou, Paris, France, bination in ,a 'vacuum tube of a diode reception. E. H. Armstrong, New York, whereby the N. Y. No. 2,024,138. assigned S o c i et e des Applications element and an amplifier, "Guilux." No. 2,032,622. signal may be amplified and rectified in a single tube. K. C. Black, RCA. Airplane transmitter. No. 2,022,049, Reissue No. 19,943. L. J. Lesh, Associated Electric Labora- Duplex antenna. System for short tories, Inc. and long wave reception comprising an antenna, a pair of downlead conductors, Protective system. An incandescent overload prevention 2,026,382, transformers, etc. E. V. Amy and lamp used as an Frequency control. No. device, lamp comprising a dial A. Frum, Telefunken. Means for J. G. Aceves, reissue 19,854. the periodically checking the frequency of a transmitter by means of a photo- Relaying system. A repeating sta- electric cell, etc. tion having a reflector in a plane at an angle with respect to the hori- Broadcasting system. Multi -chan- zontal, another reflector in a plane at nel high frequency wire -broadcasting an angle with respect to the horizontal system. P. P. Eckersley, London. and inclined with respect to the first No. 2,031,528. See also No. 2,030,948 named plane, a parabolic reflector, etc. to J. L. Weston, Wired Radio, Inc., S. G. Frantz and J. Q. Stewart, RCA. light. Nicholas Raskhodoff, United on a method of transmitting signal - No. 2,042,302. American Bosch. No. 2,043,676. ELECTRONICS - August 1936 59

www.americanradiohistory.com Noise suppressor. M. E. Bond, United minimum selectivity is secured when a Demodulator and method of demodula- American Bosch Corp., Springfield, strong signal is received. G. V. Dowd- tion filed April 6, 1936, D. C., S. D. Mass. No. 2,034,970. See also No. ing, RCA. No. 2,031,034. Calif. (Los Angeles), Doc. E 890-Y, 2,034,974 to W. F. Cotter and M. E. Radio Corp. of America et al. v. M. Bond, Bosch, on an oscillator circuit. Patent Suits de Groot (Ambassador Radio Co.). 1,403,475, H. D. Arnold, Vacuum Same filed April 7, 1936, D. C., S. D. Detector circuit. A detector having tube circuit; 1,403,932, R. H. Wilson, Calif. (Los Angeles), Doc. E 892-Y, a fixed and a variable bias arranged Electron discharge device; 1,507,016, Radio Corp. of America et al. v. R. A. so that its efficiency increases in re- L. de Forest, Radio signaling system; Cottrell. Doc. E 894-S, Radio Corp. sponse to an increase in the amplitude 1,507,017, same, Wireless telegraph of America et al. v. E. Spigel. of an incoming wave. J. C. Warner, and telephone system; 1,618,017, F. 1,573,374, P. A. Chamberlain, Radio G.E. Co. No. 2,031,441. Lowenstein, Wireless telegraph appa- condenser; 1,795,214, 1,707,617, E. W. ratus; 1,702,833, W. S. Lemmon, Elec- Kellogg, Sound reproducing appara- Fidelity control. A detector followed trical condenser; 1,811,095, H. J. tus; 1,894,197, Rice & Kellogg, same; by an a -f amplifier with a rising char- Round, Thermionic amplifier and de- 1,728,879, same, Amplifying system, acteristic has a network such that tector; Re. 18,579, Ballantine & Hull, filed April 7, 1936, D. C., S. D. Calif. (Los Angeles) , Doc. E 891-Y, Radio Corp. of America et al. v. M. de Groot (Ambassador Radio Co.). Same, filed April 6, 1936, D. C., S. D. Calif. (Los Angeles), Doc. E 893-C, Radio Corp of Frequency Measuring Service Wo America et al. v. R. A. Cottrell. V! Doc. E 895-J, Radio Corp of America Many stations find this exact measuring serv- et al. v. E. Spigel. 1,811,095, H. Thermionic ice of great value for routine observation of J. Round, performance amplifier and detector; Re. 18,579, Bal- transmitter and for accurately lantine & Hull, Demcdulator and calibrating their own monitors. method of demodulation; 1,297,188, I. Langmuir, System for amplifying MEASUREMENTS WHEN YOU NEED THEM MOST variable currents, D. C. N. J., Doc. E 5261, Radio Corp of America et al R.C.A. COMMUNICATIONS, Inc. v. Atlas Laboratories, Inc.. et al. De- Commercial Dept. cree referring to Master Mar. 2, 1936. 1,973,277, A. R. Barfield, Electro - A RADIO AMERICA SERVICE CORPORATION OF acoustic translating device, filed Feb. 66 BROAD STREET NEW YORK, N. Y. 17, 1936, D. C. Md., Doc. E 2432, G. G. Cromartie et al. v. Montgomery Ward & Co. CLEEN-CUT The QUALITY BLANK for Instantaneous and transcription recording is STANDARD with the foremost recording studios as well as with the largest and most discriminating users of recording blanks.

We recommend RECO-LUBE to further prolong the playing life of recordings made on CLEEN-CUT blanks.

Write for literature and price list. ALLIED RECORDING PRODUCTS CO. Phone BRyant 9-1435 126 West 46th Street, New York, N. Y.

PIONEER DYNAMOTORS A Power Supply You Can DEPEND On! NOVV you can have a better power supply for Police, LESS than a year has elapsed since Air Craft, Marine Radio Service and Sound Sys- Cinaudagraph introduced t h e tems ! Pioneer "Silver Band" Dynamotors provide an MAGIC MAGNET SPEAKER. The unfailing-uniform-high voltage. They're not affected revolutionary principles embodied by vibration. They're compact, light weight and sturd- in this fine speaker have definitely ily built ! Sizes: 6 to 110 volts Input and up to 1000 given it first place in the radio in- volts Output. Write for full information ! dustry. Engineers, manufacturers, assem- blers of P.A. equipment, service technicians, have placed their stamn of unqualified approval on MAGIC Other Pioneer Products MAGNET SPEAKERS. PIONEER Red Seal Gen -E - MAIL THIS COUPON NOW! Have your secretary request descrip- Motors, Rotary Converters, "Blue l'IONE ER GEN -E -MOTOR tive literature and engineering Diamond" 110 V. 300 Watt AC CORP. data Gas -Electric Power Plant, with 464-X West Superior St., Chicago, Illinois . . . TODAY. DC winding for charging 6 volt Mail literature Silver -Band Dynamotors, D Gas batteries. Other Gas Electric Electric Plants, Converters, Gen -E -Motora. CINAUDACRAPH Power Plants from 6 to 110 volts CORPORATION and 150 to 1500 watts, either AC Speaker Division, Dept. "S" Stamford, Conn. or DC. Name . d ddreaa CI NAV DAG RAPII 60 ELECTRONICS - August 1936

www.americanradiohistory.com Oscillation circuits. The following ADVERTISERS' subject patents are on the general ONLY SHURE "ULTRA" of oscillation generation: No. 2,039,- INDEX 118, Kurt Schlesinger, Berlin, on a A Has All These Features! tilting oscillation generator. See also Page No. 2,039,119. No. 2,014,913, A. H. Acme Elec. & Mfg. Co 63 Wired Radio, Inc., precision Aerovox Corp. 68 A y it Taylor, Aladdin Radio Ind., Inc 63 control of master oscillators. No. Allied Recording Prod. Co 60 n41ß&.d rc N. E. Lindenblad, RCA, a American Transformer Corp 53 2,042,321, Astatic Microphone Labs 62 cathode ray tube oscillating system. Automatic Electric Co 64 See also No. 2,042,345 to Lindenblad, of oscillator. B on a braking field type Bakelite Corp. 33 No. 2,037,160, Malcolm Ferris, RCA, Biddle Co., James G 63 Crystal C. W. Brand & Co., Wm 62 signal generator. No. 2,037,897, Brush Development Co 55 Hansell, RCA, high frequency oscil- Microphones lator. No. 2,036,495, Max Pohontsch, C multiplica- Callite Products Co 51 Response approaching Telefunken, on a frequency Carter Motor Co 64 True High Fidelity . . . tion circuit. No. 2,036,562, Rudolf Central Radio Labs 37 high output through new Cinaudagraph Corp. 60 Shure "Cruciform" crys- Telefunken, ultra -short 2 Bechmann, Clough Brengle Co tal mounting . . wave oscillation generator. See also Continental Diamond Fibre Co 55 Screen -Protected cart- Continental Electric Co 52 ridge "Moisture - 2,024,864 to Dietrich Prinz and H. O. 63 Cornell Dubilier Corp S e al e d" Dual -Drive Roosenstein, Telefunken, on an ultra - Grafoil Bimorph crys- wave oscillation generator. No. D tal - These are but a short Dumont Labs., Allen B 57 few of the Right Engi- 2,041,408, D. W. R. Goddard, RCA, neering features that set crystal controlled oscillator. No. E new standards of per- Erie Resistor Corp 3 formance and dependa- 2,036,719, D. Prinz and W. Wehnert, bility in Shure "Ultra" Telefunken, on a relaxation oscillator. F Crystal Microphones. No. 2,043,242, L. A. Gebhard, Wash- Fairchild Aerial Camera Corp 56 "Grille" type as illustrated - also frequency Ferris Instrument Corp 57 "Spherical" and "Swivel" models - List ington, D. C., on a high Price only $25 complete with cable. Licensed oscillator. G under patents of the Brush Development General Insulated Wire Co 52 Company. General Radio Co 43 Write for Data Today! A having G -M Laboratories 62 "Mic ophone Headquarters" Variable Mu system. tube Goat Radio Tube Parts, Inc 50 SHURE BROTHERS, two cathodes having different electron Guthman & Co., Inc.. Edw. I ... 62 215 W. HURON ST. CHICAGO. U. S. A. emitting characteristics. J. M. No. H Schmierer, Berlin, Germany. Heintz & Kaufman, Ltd 54 2,040,341. L Leach -Relay Co. 56 Power supply system. Double recti- Littelfuse Labs. 62 MICROPHONES fier for plate voltages and bias volt- M ages comprising full wave and a half Mallory & Co., Inc., P. R 4 of electronic type, McGraw-Hill Book Co. 54 wave rectifiers the Mica Insulator Co 52 as indirectly heated cathodes for two Muter Co., The 64 AUDIO OSCILLATOR tfor rectifiers and a heating circuit P both cathodes. Otto H. Schade, RCA. Pioneer Gen -E Motor Corp 60 No. 2,037,659. Precision Resistor Corp 56 Presto Recording Corp 50 Power system. In a receiver operat- R Radio Receptor Co 56 ing on a -c or d -c, a circuit for trans- RCA Communications, Inc 60 mitting d -c without appreciable attenu- RCA Mfg. Co Back Cover Remler Co., Ltd 47 ation and a -c at a step-up voltage ratio. W. Lyons, Hazeltine Corp. No. S Shakeproof Lock Washer Co 39 2,036,343. Shure Brothers 61 Sigma Instruments, Inc... 58 Sound Apparatus Co 54 Constant current system. A high Stackpole Carbon Co. Inside Front Cover resistance connected in both input and Superior Tube Co 45 output circuits, the resistance designed Synthane Corp.... Inside Back Cover to maintain the total current there T through constant irrespective of Thomas & Skinner Steel Prod. Co. 62 whether the cathode current of the Triplett Electrical Instr. Co 49 TYPE CR -4 BEAT FREQUENCY AUDIO tube is saturated. Rudolf Urtel, Tele- U $77.00 funken, Germany. No. 2,034,011. United Sound Engineering Co 61 OSCILLATOR-Price W Portable, A.C. Operated. Broad band amplifier. Two tubes Weston Electrical Instr. Corp 41 connected in a direct current amplifier White Dental Mfg. Co.. S. S....35. 47 10 cps to 20,000 cps. system whereby potential drops across Reed for Calibration Check. a resistance due to the anode current High and Low Impedance Outputs. of the second are impressed directly Professional Services 58 upon the anode of the first tube. J. Direct Reading Dial. Accuracy 2%. See B. Knight, RCA. No. 2,026,944. SEARCHLIGHT Low Hum and Distortion. also No. 2,022,496 to Richard Feldt- SECTION High Output; 30 volts Max. keller, Siemens & Halske, Germany. Classified Advertising Drift after warmup Negligible. EMPLOYMENT 64 Direct current amplifier. System in- EQUIPMENT FOR SALE Write for Catalog Sheet of make -and-break con- American Electrical Sales Co 64 volving a pair Eisler Electric Corp 64 UNITED SOUND ENGINEERING CO. 64 tacts and an a -c amplifier. Paul H. Eisler Engineering Corp Manufacturers of Electronic Equipment Y. No. Electronics Machine Co 64 Macneil, Huntington, N. Kahle Engineering Corp 64 2235 University Ave.-St. Paul, Minn. 2,043,107. Winslow, Louis J 64 ELECTRONICS - August 1936 61

www.americanradiohistory.com ASIATIC NON -DIRECTIONAL METAL COVERED FUSE MOUNTING Designed for the new STUDIO metal covered tube sets Littelfuse No. 1126 Mount- MICROPHONE ing meets requirements of MODEL K-2 Underwriters' Laboratories for 1, 11/2, 2 or 3 amp. stand- :MULTI -UNIT ard 3AG fuses. No mounting ITS NON-1)IlREl'TIONAL screw needed-time and ma- pickup will reproduce the mul- terial saved. Only tiple instruments ofa; symphony 2/"x/"x as faithfully as the sàlo'perform- 3" over all. Supplied with ance of a single it strument or approved fuses or without star. A .dependable, clear -toned fuses. microphone with frequency response substantially flat from 30 Manufacturers, write for test samples. to 6000 c.p.s. with rising characteristics to 10.000 c.p.s.-and an Littelfuse Laboratories output level 'of -64 decibels (con- servatively rated). 4248 Lincoln Ave. Chicago, III. WRITE FOR BULLETIN 61 Licensed under patents of Brush De- velopment Company Astatic Patent Pending. Utilizing - grafoil bimorph D.C. crystal element. Featuring the ELECTRO MAGNETIC DUAL DIAPHRAGM RELAYS CONSTRUCTION These relays represent an improved form of sensitive electromagnetic relay which is espe- Exclusively Controlled cially suitable for use in direct current control circuits involving either "on -off" or marginal operation. The fineness and ease by of adjustment of operating current permits its use under conditions where an ordinary telephone type of relay would be impractical. Supplied in 25 resistances ranging from 0.2 ohm to 10,000 ohms. Prices in quantities as low as $1.44. FOR et IiIl'LETE INFVIltMMATION HEW :BT BULLETIN r. S, 559-A ASTATIC MICROPHONEI LABORATORY, INC. Youngstown, Ohio. U. S. A. G LABORATORIES INC. Pioneer Manufacturers of Quality -\t Crystal Devices 1734 BELMONT AVENUE CHICAGO, U.S.A.

Guthman Coils are dependable! No matter what your requirements, there's a Guthman coil that will fit the job! Send us your specifications - we' ll be glad to submit salnples and:quote SPE- CIAL LOW ERICES!

THIBTY different diameters, a dozen different colors, a stock I. sufficient to meet your most EDWIN GUTHMAN and CO., Inc. pressing production requirements. Engineers specify Brand 400 South Peoria Street, CHICAGO, ILLINOIS Smooth Inside Bore Turbo because of its ideal insulating- a n d mechanical properties, stable chemical structure that is unaffected when exposed to acids. oils, and high tempera- A TRIAL WILL CONVINCE YOU tures. Also manufacturers of Turbo 35 Years' Experience IIn+. tiattuated Sleeting and Var- nished Cambric. Cloths, Tapes Insures Dependability inri Papers. Complete catalog ,n request. Samples available. We Manufacture WILLIAM BRAND & COMPANY PERMANENT MAGNETS TOOLS and 276 Fourth Avenue. New York 217 No. Desplaines St.. Chicago DIES SINCE 1920 THE FINEST IN INSULATION METAL STAMPINGS LAMINATIONS Suppliers of ALNICO MAGNETS THOMAS & SKINNER I )) I », I 1 I ) STEEL PRODUCTS CO. 23d St. at Alvord Indianapolis, Ind. INSULATION ,uunumnunuuuuunuuunuuuunnuuunuuununuummmuulllllnlnllunnmuuuumuuwuuwuuuuuumnuumuw Fi2 August 1936 - ELECTRONICS

www.americanradiohistory.com 111111111111111111' nel l lltlll lll lllelttltnsinla nlnnul III III Il0 tIt nitllnll III BI111ny n een ene eeennllll l ll lll lellll llll ln tlll lll le ettllt INSULATION BREAKDOWN NEW TESTER Compact and complete. Not only indicates shorts, opens, or grounds, but actually provides for checking circuit at approved standard testing voltages. Operates from any 115 volt, 60 cycle primary circuit. Manually controlled tap switch for secondary CORNELL- voltages from 500 to 2500 volts. DU BILI ER THE ACME ELECTRIC & MFG. CO. FREE Bulletin 140 1447 Hamilton Avenue, DYKANOL CLEVELAND, OHIO gives all details. TRANSMITTING CAPACITORS High temperatures, high humid- BIDDLE ities and high voltages hold little SPECIALTIES or no terror for the Types T.1 and TB Dykanol Transmitting "ME GGER" Condensers. Specified by the Insulation Testers "FRAHM" United States Government, and and Ohmmeters FREQUENCY METER all leading broadcast stations the Dykanol Transmitting Series "MEGG ER" has established its worthiness Capacitance Meter through years of unfailing de- "FRAHM'" pendable service. Frequency Meters Available in a complete capacity range from 600 to 25,000 the and Radio Engineer JAGABI" 15901 Ej5I V.D.C. Catalog No. 127 for Industrial Rheostats 60 free on request. APIEZON" A MINIATURE "FRAHM" VIBRATING- Oils, Greases REED FREQUENCY METER of great rug- and Waxes for gedness and durability - now available for High Vacuum use on power frequencies. CORNELL-DUBILIER Work Write Jor descriptive Bulletin E-1415. CORPORATION JAMES G. BIDDLE CO 4380 BRONX BOULEVARDNEW YORK ELECTRICAL AND SCIENTIFIC INSTRUMENTS 1211-13 ARCH STREET PHILADELPHIA PENNSYLVANIA W m,111111'1 11.!:111 ,,ruu eici cir,c.'m 'r w:.r,uu ow u,, m.. :Imuuwl,

We recommend the 262 kc. trans- cally equal frequency increment former illustrated to endure ex- per turn. tremes in temperature, humidity, Characteristics vibration and shock. Both circuits Type Use Gain B.W. IOX smoothly tuned with Polyiron from L 150 cony. 78 17 kc. the top of 13/8" shield with practi- L 250 diode 54 31 kc.

These devices manufactured under one or more of the following Johnson Laboratories, Inc., U. S. Letters Patents: 1887380 2005203 1978600 2032914 2002500 Aladdi 1 1978599 2032580 1997453 1978568 2028534 Other patents pending. i._ 1982690 1940228 2018626 1982689 2035439

Write for technical data booklet 536 describing other ALADDIN products. 466-e W. Superior Str., Chicago, Ill.

ELECTRONICS - August 1936 63

www.americanradiohistory.com '_ I I I I I I I I I I I I8I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I l l I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I l l I I I I I I I I I I I I I I I I I I I I I I I I I ILa -HI-POWER FOR PORTABLE'

= SOUND EQUIPMENT = The Carter GENEMOTOR supplies the most reliable and economical "B" Power for Class A or B amplifiers from a 6 or 12 volt battery. Output up to 500 volts. Sturdy - Compact - Quiet in operation - Requires no o i l i n g - Guaranteed. fL Also can be supplied for A.C. output. 5. Write for Circular \ CARTER MOTOR CO. I\ 365 W. Superior St., Chicago We offer a comprehensive line of electrical ffillininninummiiiitinuumandinummumnimmuimminumumumiiiimmuninumniummutommummuninuaimmitimining

yllelml111I I III I t I I I II I1111111III I I I I control apparatus of proved dependability for n I I I I n I n I I I n I I II I I I II nlmuunhnnmmnnnmummmnmuuluaanunumnlulmmlnllmG adaptation to your products or for use in your production processes. Autelco control devices = include: RELAYS: Quick and delayed action types, for A.C. and D.C. circuits, any voltage, any contact combination. STEPPING SWITCHES: Electromagnetic mul.i- RED WIRE WOUND RESISTORS contact switches, for automatic selection of electrical circuits. R ELEVEN . LION IN USE .. SWITCHING KEYS: A variety of locking and non -locking types in any desired contact combination. MAY WE SAMPLE Also cords, plugs, jacks, signal lamps, sockets, counters, etc. Write for complete illustrated catalogs. AND QUOTE

American Automatic Electric Saks [ompany THE MUTER COMPAN 1023 W. Van Buren Street, Chicago 1255SO- MICHIGAN AVE., C

ñ,II11aIIII11Yt1111111111111111111111111111111111111111IIIIIIII11111111I III IIII1111IIII I II11111111111111111III1111111111111111111111111111111111111111111111111111111 ->+ +4. SEACMLWRT SE CTI ON EMPLOYMENT : BUSINESS OPPORTUNITIES : EQUIPMENT USED or RESALE

UNDISPLAYED-RATE PER WORD INFORMATION : DISPLAYED-RATE PER INCH Position Wanted, 5 cents a word, minimum Boa Numbers in care of our New York, 1 inch $5.00 $1.00 an insertion, payable in advance. Chicago or San Francisco offices count 2 to 3 inches 4.75 an inch 10 words additional in undisplayed ads. 4 to 7 inches 4.50 an inch Positions Vacant and all other classifica- Replies forwarded without extra charge. tions 10 cents a word minimum charge Other spaces and contract rates on request. $2.00. Discount of 10% if full payment is made in An advertising inch is measured vertically advance for four consecutive insertions of on one column, 3 columns -30 inches- Proposals, 40 cents a line an insertion. undisplayed ads (not including proposals). to a page. COPY FOR NEW ADVERTISEMENTS RECEIVED UNTIL 3 P. M. ON THE 3RD OF THE MONTH (Elect)

WANTED POSITION NEW AND USED EQUIPMENT Used Lab. Equipment Air Blowers Meters Flare ELECTRICAL ENGINEER desires location in Vacuum Pumps Rheostats Stem engineering department of radio receiver [email protected]., Etc. Aspirators Testers Winding manufacturer or component parts manufac- Meters -Bridges -Torsion balances -Inductors - Gas Boosters Spark Coils Sealing turer. Years experience in design of audio Decade boxes-Analytical balances-Oscillographe Spot Welders Bridges Exhaust and RF testing equipment for production of -Jagabi rheostats-Signal Generators --Condensers Gas Burners Decade Boxes Basing multi -band receivers. Alan, experience in re- Write for my list Accessories Transformers Machines ceiver design. Location immaterial, providing LOUIS J. WINSLOW AMERICAN ELEC. SALES CO. salary Justifies. Age 28, Eta Kappa Nu, Tau 200 Pennsylvania Avenue Hillside, N. J. 65-67 E. 8th St.. New York. N. Y. Beta Pi. P.W.-90, Electronics, 330 West 42nd nuuuumllum11,1u1lmuunll,,,,,u,u11,un,u,111111111,1111111,1101, 1,,,,,,111,,,,,111111111,111,111,1111111111111,111111,,,111l,,,l,,,,, ll111,111,111,111111,1 Street, New York City. DEPENDABLE E EQUIPMENT WANTED New and Used COMPLET ELECTRONIC TUBE EQUIPMENT New and Used for USED REVOLVING head stem machine that A complete line of equipment for the manufacture of can be used in manufacture of neon elec- Radio Tubes. New trodes. Six head preferred. State condition Tubes. Incandescent Lamps, eto. and price. P. O. Box 1113, Oklahoma City, Write for Bulletin showing savings from 25 to 75% ELECTRONIC TUBE MAKING, Oklahoma. EISLER ELECTRIC CORP. 539 -39th Street, Union City. N. J. LABORATORY, and SCHOOL UNITS HIGH GRADE NEW AND USED Air Blowers EQUIPMENT Flare Glass Cutters, Spot Welders, Annealers, Flare, Vacuum Pumps NOW-0E00NDITIONHD Stem ELECTRON TUBE EQUIPMENT Stem, Sealing, and Basing Machines, Aspirators for making Winding Gas Boosters sLEOTROxto TCERE, RADIO Sealing Huge Stock of Equipment of Vacuum Pumps, Burners Spot Welders TUEEa, INCANDESCENT Exhaust Every Type and Variety LAMPS, NEON COONS KAHLE ENGINEERING CORPORATION Gas Burners Special Raeint Accessories machines for Machines Specialists in Equipment and Methods for the cutting hard glass Manufacture of Neon Tubes. Radio Tuhee. Incan- ELECTRONICS MACHINE CO, EISLER ENGINEERING CO. descent Lamps, Photo Cells, X-ray Tubes. etc. 751 13th Street, Newark, N. J. 751 So. 13th St.. Newark, N. J. 941 DeMott St., North Bergen. N. J. 64 August 1936 - ELECTRONICS

www.americanradiohistory.com DECKS AWASH . . .

SYNTHANE LAMINATED BAKELITE Men go below, staking their lives on SHEETS RODS TUBES FABRICATED PARTS the best equipment known to marine Send for Sample Book engineering ... The use of SYNTHANE laminated bakelite in apparatus for the operation and control of submarines may suggest its applicability to your products where dependable insulation is required.

www.americanradiohistory.com ANNOUNCING!

THE RCA 892 Developed Especially for Longer Life AC -OPERATED Greater HIGH FIDELITY Reliability Broadcast Transmitters of 5 KW Power

STANDARD RCA Water Jackets will accommodate this new transmitting Tube. The improved Jacket and insulated mounting shown in the illustration can be furnished at very low cost to those stations not having RCA Jackets. Write for complete technical information on this tube to determine adapt- ability to your circuit.

TECHNICAL INFORMATION OUTSTANDING FEATURES: 1. Two phase filament for AC operation. Max. Plate Dissipation 10 KW distortion. Fil. Voltage 22 Volts 2. Improved emission characteristics, giving lower Fil. Current 59 5 Amp. 3. Filament operates at lower temperature, with resulting longer life. Amplification Factor 50 4. Shielded grid mcunting reduces corona. Transconductance 7000 Mmhos. Grid -Plate 5. Elements are trea:ed with new process, which eliminates gas flashes. Max. Plate Voltage (Broadcast Frequencies) 15000 Volts 6. Higher mutual conductance permits lower driving power.

NMI" IMP Timité2èqTaios Address TRANSMITTER SECTION, RCA MANUFACTURING COMPANY, INC., CAMDEN, NEW JERSEY 111 No. Canal Street A Service of the Radio New York, 1270 Sixth Avenue Dallas, 221 I Commerce Street Chicago, Corporation of America San Francisco, 170 Ninth Street Atlanta, 492 Peachtree Street, N. E. www.americanradiohistory.com