APRIL 1939

Vol. 17, No. 4

www.americanradiohistory.com ELECTRICAL COMMUNICATION

A Journal of Progress in the Telephone. Telegraph and Radio Art H. T. KOHLHAAS, EDITOR

EDITORIAL BOARD

E. A. Brofos G. Deakin E. M. Deloraine P. E. Erikson F. Gill W. Hatton R. A. Mack H. M. Pease Kenneth E. Stockton C. E. Strong

Issued Quarterly by the /nf-l!rnuil'1nu/ Sruunurd Elec/-ric Corpora/ion

67 BROAD STREET, NEW YORK, N.Y., U.S.A.

Volume XVII April, 1939 Number 4

PAGE PUBLIC ADDRESS SYSTEM AT THE THIRTY-FOURTH INTERNATIONAL EUCHARISTIC CONGRESS, BUDAPEST, MAY 22�29, 1938...... 319 By G. A. de Czegledy

ULTRA-SHORT WAVE OSCILLATORS ...... 325 By D. H. Black

ULTRA-SHORT WAVE POLICE RADIO TELEPHONE INSTALLATIONS IN

OSLO AND STOCKHOLM...... 335 . . By G. Weider

R-6 AUTOMATIC SYSTEM...... 346 By F. Gohorel and R. Lafon

}AMES LAWRENCE McQuARRIE ...... 358

}AMES LAWRENCE McQuARRIE-AN APPRECIATION...... 359 By F. B. Jewett

THE BUCHAREST-PLOESTI TOLL CABLE ...... •...... 360 By A. C. Nano

SOME INDUSTRIAL APPLICATIONS OF SELENIUM RECTIFIERS...... 366 . By S. V. C. Scruby and H. E. Giroz A LONG DISTANCE AUTOMATIC TELEPRINTER EXCHANGE WITH MANUAL

PRIORITY SERVICES ...... 375 By G. A. M. Hyde

THE EIFFEL TOWER TELEVISION TRANSMITTER...... 382. By S. Mallein and G. Rabuteau

RECENT TELECOMMUNICATION DEVELOPMENTS OF INTEREST...... 398.

www.americanradiohistory.com Jam es L. McQuarrie

1867-1939

www.americanradiohistory.com Public Address System at the Thirty-Fourth International Eucharistic Congress

Budapest, May 22-29, 1938

By G. A. DE CZEGLEDY, A.M.I.R.E.,

Chief Engineer, Standard Electric Company Limited, Budapest, Hungary

NTERNATIONAL Eucharistic Congresses fully for the benefit of multitudes, both at the I rank amongst the outstanding events in Congresses themselves and at distant points, the Catholic world of modern times. It is was extensively studied. As on previous thus natural that early recogmt10n was given occasions, it is an undoubted fact that the to the importance of communicating sermons elaborate public address and transm1ss10n and other items on the Congress programmes systems evolved for the Budapest International to the largest possible number of Catholics and Eucharistic Congress contributed to an import­ others not within the fold of the Church of ant degree to its overwhelming success. Rome. Since modern loudspeakers and power

In connection with previous Congresses, 1 amplifiers have attained a hi gh level of perfec­ the problem of utilizing loudspeaker systems, tion, sound effects covering a wide range could capable of reproducing the proceedings faith- be reproduced in a highly natural manner. Great care was needed to ensure the highest 1 See references at end of this article.

Fig. I-Main Altar at Heroes' Square.

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www.americanradiohistory.com 320 EL ECTRIC AL COMMUNICATION

fixed poles, lamps, etc., and the latter in wooden booths. The booths were inter-connected by a cable network which the Postal Administration placed at the disposal of the Congress. Telephone exchanges, in most cases, served as the distribution points of this network, over which the output of the microphone groups,

Fig. 2-Papal Legate, Cardinal Secretary of State Pacelli (now His Holiness, Pope Pius XII) before the Microphone. possible quality in transmissions from the microphones to the power amplifier stages of the loudspeakers. Standard Electric Company Limited, Budapest, handled all transmission and sound engineering problems and was officially respon­ sible for the success of the sound transmissions during the Congress. In addition to part of the loudspeakers and power amplifiers, Standard furnished all microphones and pre-amplifiers required in connection with mixers and volume indicator s, as we ll as the distribution amplifier s. The outstanding Congress events, attracting the largest mu ltitudes ever congregated in Budapest, took place at Heroes' Square, at St. Stephen's Cathedral, at the Congress Hall and at the Vigado (Concert Hall) . A prominent Congress feature was the Boat Procession of the Holy Eucharist on the Danube, when public address systems arrayed on both banks of the river transmitted the programme to the vast crowds aligned on its shores in devout adoration. Additional loudspeakers and power amplifiers Fig . 3-Group of Distribution Amplifiers. were placed alo ng the streets, the former on

www.americanradiohistory.com P U B L I C A D D R E S S - E U C H A R I S T I C C 0 N G R E S S 321 adeq uate ly amplified and MIXER CABIN eq ualized, could be faith­ r------, fully transmitte d. PRE·AMPLIFIHS MICROPHONES' MIXERS 1 I AND VOLUME : At He roe s' Sq uare , a ALTAR I. INDICATORS. 1 sort of te rrace was erec ted " II. I for the Prince s of the THRONE 1WORKING LINE STAIRS I Church, he ade d by the I Papal Le gate, Cardinal ORCHESTR. I R Se c re tary of State Pace lli CHO US I. SPARE: LINE (now His Holiness, Pope CHORUS JI. SPEAKER I Pius XII). The Main Altar I fI stood in the ce ntre of the I te rrace . The orc he stra and : DIRECT LINE I I TO ROME choir we re on the stree t L ______J le ve l be twee n the Millenary Me morial Column and the Altar (Figs. 1 and 2). All sound effec ts, from POWER AMPLIFIERS TO LOUDSPEAKER CROUPS i1>i1 AMPL 5Tiieurro"N-iIFIERS orc he stra and choir, and SPARE LINE 1 I from te rrace and Altar, I A we re transmitte d true to WORKING LINE life. Eight mi crophone SP. lines, consisting of shie lded 8 rubberca ble s 25 to 30 m w. in le ngth, we re utilize d, SP. te rminating in jacks at the c Altar te rrace and in a socket W. at the Millenary Column. It was ac cordingly possible SP. D to place the mi c rophones w. at any de sire d spot within SP. the ar ea, thus providing E gre at flex ibility in the w. I se le c tion of combinations I ______L _J of microphones and loud Fig. 4-Block Schematic of Transmission System at Heroes' spe akers-a pre re q uisite in Square and Surrounding Area. vie w of the rapid and var- ie d programme se que nce s. The shie lded pair mic rophone cable s we re mic rophones could be connec te d or dis­ conc entrate d at a cabin in the monitoring tower, connec ted witho ut the slightest noise . The to the right of the Main Altar. This cabin main function of the mixe rs, howe ve r, was to housed the mic rophone mixe rs and amplifiers ; give suitable music al colouring to the various from it, all transmissions we re controlled. soun

www.americanradiohistory.com 322 ELECTRICAL COMMUNICATION

choir. At the re he arsal, the choir of 1 200 was whe re signals had to be divide d be twee n se ve ral re groupe d in view of the predominance of groups of power amplifiers and loudspe akers. soprano voices. This choir was supple me nted Individual loudspe aker and power amplifier by a Gregorian choir forme d by 500 se minarists groups we re thus entirely independe nt ; also, and the Schola Cantorum Sabarie nsis. The a possible short circuit occurring in any one latte r re nde re d individual programme numbe rs group would not cause disturbance else where. which re quire d an additional microphone . The distribution amplifiers (Fig. 3) we re The allocution of the Holy Fathe r made locate d in the ce llar of a building adj ace nt to a profound impression on the vast multitude He roe s' Square . They we re provided in that attende d the Pontifical High Mass. It duplicate, as we re also the connections to loud­ was transmitted fromth e summer re sidence of spe ake rs and the ir associatedamplifi ers. Trans­ the Pope s in Castel Guandolfo ne ar Rome over mission could thus be effected ove r two inde­ se ve ral hundred kilometre s of te le phone line. pe nde nt channe ls ; and, in the event of failure Inasmuch as the sound volume of the Pope's of a loudspe aker group, the ne ce ssary switching address could not be ascertained in advance, an could be effected without special instructions adj ustable mixer-potentiometer was ke pt in to the pe rsonnel on point duty. Five loud­ re adine ss for practically instantane ous connec­ speaker-amplifier groups (Fig. 4) we re utilized tion to the loudspeaker system. at He roes' Square . Th e microphone and amplifier system used The nine mixers and the microphone pre­ at He roe s' Square and its environs is shown in amplifiers (Fig. 5) we re placed in a small cabin Fig. 4. The whole syste m was de signe d with in the tower ne ar the Altar. From this tower due re gard to the principle constantly the Altar was cle arly visible , so that the sound­ emphasized in conne ction with the Congress, enginee r could easily follow the ce re monie s. viz., re liability of pe rformance. Microphones Comparedwith open air transmissions, indoor and mixers we re connected in parallel to the transmissions involve d fe we r proble ms. two pre-amplifiers. From the ir output te r­ According to the occasion, three to five minals, independe nt le ads we re run to the microphones we re used in the Congress Hall. distributing syste m. In the Vigado and at St. Ste phe n' s Cathe dral, In order to increase the effective ne ss of the only two microphoneswe re ne ede d ; and mixing system, distribution amplifiers we re employed and pre-amplificationarrang ements we re similar

Fig. 5-Mixers and Pre-amplifiers at Heroes' Square.

www.americanradiohistory.com PUBLIC ADDRESS-EUCHARISTIC CONGRESS 323

EOTVOS PLACE --- -MicRoiluoii j - � I AMPLIFIE'RS MUSICAL HIGHSCHOOL PRE• I : MIXER / WORKING LINE iPRE-AMPL;;.�;;;1MICR0-! , I 1 I ______Y''--_.!f:.__ __;SC'CPA�R.,_..E'--'L"-' I N,_,,E �------l---"iiill--40PHONES1 _ ___ _ L ______TCREZ EXCH. I I ,------, ______1 ::i . L J ll L ____ _l

r--- I I I I I I _____ L J LAGYM.Al'fYOSEXCH. Eo tvo s Sq uare. Change-over from music to Fig . G-Block Schematic of the Transmission System speech, and vice versa, as well as mix ing, were for the Eucharistic Boat Procession. accomplished at the latter point. The resulting speech currents were passed thr ough distribution amplifiers located at the Terez, Belvaros, Krisztina and La gyma nyos to those described, ex cept that no distribution automatic ex changes to the five and seven loud­ amplifiers were employed inasmuch as the speaker groups, respectively, along the river microphone system was required to supply only banks. A schematic and plan of the system are one loudspeaker group. shown in Figs. 6 and 7. From the viewpoint of technique and per­ For transmission the telephone network was formance, the Danube Procession of the Holy used, the Postal Administration taking special Eucharist is perhaps unique in the history of precautions to assign the most suitable circuits. public address systems. The attenuation of all line sections had been The loudspeakers were placed along the river previously measured and, on the basis of the banks : in Buda, along the right shore fr om the results thus obtained, the frequency response Technical High School to Margaret Bridge ; curves of the line sections were eq ualized and, in Pest, along the left shore fr om Francis between 30 and 6 000 cycles by means of Joseph Bridge to Margaret Bridge. For the distribution amplifiers located at the individual feedi ng of the necessary loudspeakers, five and ex changes. seven power amplifier groups were used in As a result of this detailed and conscientious Buda and in Pest, respectively. effort, the freq uency response curve of even the Announcements were made in various longest line sections never deviated more than languages from Eo tvo s Sq uare to the public 2 decibels from a medium frequency value. arrayed on both shores. Transmission of the This good performance was, of course, of features of the Procession alternated with utmost importance in achieving high quality religious songs, conveyed fr om the Musical transmission. Safety of operation was increased High School where two microphones and their in this instance also by the provision of a associated pre-amplifiers were located. Trans­ spare network (Fig. 6). missions took place over telephone lines to Inasmuch as the Choir Master listened to the

www.americanradiohistory.com 324 ELEC TRIC AL COMMU NICATION

The mixers were the so-called type balanc ed potentiometers, the ou tput impedance"Hn of which is constant regardless of the degree of adjustment. The microphone pre-amplifying circuit gave a maximum gain of 100 db. The freq uency characteristic between 30 and 12 000 p : s showed a deviation of only one decibel, a result due to negative feed-back. The amplifier also MUSICAL HIGHSCHODL contained a volume indicator circuit, by means of which the volume could be checked accurately and ad justed accordingly. The distribution amplifier also contained negative feed-back, the maximum gain being 20 db. and giving approximately 300 mW into a 600-ohm impedance without noticeable distor­ tion. Its freq uency characteristic could be adjusted between 30 and 8 000 p: s for the purpose of line eq ualiz ation. The EucharisticCo ngress sound system, in­ cluding all eq uipment and apparatus components LAGYMANY'OS EXCH. utilized , was of impressively high quality and admirably adapted to the req uirements imposed.

POWER AMPLI Fl ER GROUPS · That the transmission of the programme was <1) ( l i2) FOR LOUDSPEAKERS. most satisfactory in every respect was due Fig. 7-Simplified Map of the Transmission System for largely to the painstaking effort devoted to the the Eucharistic Boat Procession. solution of the many constituent transmission and sound-engineering problems presented. speeches transmitted from Eo tvo s Sq uare with A further important factor contributing to the the aid of a radio receiving set, the Choir successful consummation of this outstanding renderings were timed with the greatest sound reproduction proj ect was the fine co­ precision. operation of the Hungarian Postal Administra­ By means of the distribution amplifiers tion, the clergy and those in charge of the located at the four telephone exchanges, the musical programmes of theCo ngress. volume of the individual loudspeaker-amplifier groups could be adjusted so that the loud­ speakers mounted on the right river bank could REFERENCES not be heard on the left, and vice versa. Since (1) "Vast Public Address System at Thirty-First International Eucharistic Congress, Dublin, the weather was calm, transmissions were not June, 1932," by W. L. McPherson, Electrical disturbed by atmospheric effects. Communication, April, 1935. Brief comments on the characteristics of the " Transmitting the Program of the Thirty­ eq uipments herein described may be of interest : Second International Eucharistic Congress," by Kenneth McKim, Electrical Communication, The microphones were of the Standard July, 1935. electrodynamic type, No. 4017-A. They afford " The Public Address System and Corollary the great advantage that their noise level is Installations for the Thirty-Second lnternation1l Eucharistic Congress," by Ricardo T. Mullea:ly, negligibly low ; they are not sensitive to and W. White, Electrical Communication, July, shaking, hum idity, heat, etc., and they do not 1935. req uire battery supply voltage. The level " Radiotelephone System Employed for th� supplied by the microphones was - 82 decibels Intercontinental Broadcast of the Thirty-S�con:l International Eucharistic Congress," by A. M. at normal sound pressure. Stevens, Electrical Communication, October, 1935.

www.americanradiohistory.com Ultra-Short Wave Oscillators* By D. H. BLACK, Ph.D., M.Sc., F.Inst.P., F.P.S., Standard Telephones and Cables, Limited, London, England

The various types of valve oscillators for obtaining ultra-high frequencies are briefly outlined, and the limitations of negative grid oscillators enumerated and discussed. Some practical examples are described together with methods of operation. An interesting oscillatory circuit in which a number of valves can be connected enables comparatively large powers to be obtained if required.

OR a number of ye ars many investi­ and, by suitable coupling circuits, the se indu ce d gators have be en workin g on th e curren ts may be made to de liver power to the F proble m of obtaining ele ctro-magnetic exte rnal circuit. The power is eithe r taken off oscillators of higher and higher freq uencies be twee n the grid and the cathode , or be twee n and of making the se oscillators de liver larger grid and anode ; but, in one specialized form powe r outputs. Extre me ly high fre q ue ncie s de ve lopedby A. G. Clavier of Le s Laboratoires, have be e n obtained using spe cial forms of Le Material Telephoniq ue , Paris, the oscilla­ spark ge ne rators but at the present time some tions are built up in a he lical grid and the power form of electron discharge tube is almost taken from the two ends of the grid. The universally used for the ge ne ration of the se fre quencies obtainable from this type of valve oscillations. The oscillators forming the subje ct are ve ry high, 6 000 me gacycle s pe r se cond of this pape r use thermionic valve s of the having be e n attaine d, but the output powers so-called ne gative grid type , but be fore de scrib­ are ve ry small. It should be re membe red, ing some re ce nt work on this subje ct other type s however, that a commercial system1 using of oscillators will be considered. valves of the Clavie r type has be e n in operation Ultra-high freq uency oscillators usmg be twee n England and France since 1931. This thermionic valves may be divided into four ope rates at a fre q ue ncy of approximately mam groups : 1 750 me gacycle s pe r se cond ; a view of the (1 ) Ne gative grid valves, type of valve use d is sh own in Fig. 1. (2) Positive grid valves, (3) Magnetrons, MAGNETRONS ( 4) Miscellaneous. The use of magnetrons to produce high freq ue nc y oscillations is too we ll known to make it ne ce ssary to de scribe the m in any de tail. POSITIVE GRID VALVES Whe re the highest powers at ve ry high fre­ Oscillators of the positive grid type are que ncies are re q uired, the magne tron is in a usually re ferre d to as Barkhausen oscillators class by itse lf and considerable ingenuity has and have be e n known for some considerable be e n shown in de veloping small high pe r­ time toge the r with the somewhat similar Gill­ formance valve s of this sort. It does, however, Morrell oscill ators. In its simplifie d form the suffer from one ve ry se rious disadvantage . valve use d to ge ne rate the oscillations is of the Owing to the fact that the oscillation freq uency triode type . The grid has a positive D.C. is de pe ndent upon the anode voltage it is ve ry potential applie d to it, while the anode is usually difficult to modulate the output from the valve, maintaine d at a ne gative potential. Electrons espe cially if a wide modulation bandwidth is emitte d from the cathode oscillate rapidly re q uired. A sys te m of so-called "pulse" be twee n the anode and the cathode be fore modulation has be e n applied to magnetrons finally coming to re st on the grid. The se with some success but only for comparatively oscillating electrons induce curre nts in the grid narrow bands.

*Paper delivered at the Emporium Section of the 1 "Production and Utilization of Micro-Rays," Elec trical Institute of Radio Engineers, 31st January, 1939. Communication, July, 1933.

325

www.americanradiohistory.com 326 ELECTRICAL COMMUNICATION

MISCELLANEOUS OSCILLATORS positive potential applie d to the grid in valves A number of other me thods for ge ne rating ope rating as Barkhausen oscillators. The use ultra-high freq uency oscillations have be e n of triodes in oscillators of this type dates back proposed from time to time . It is quite possible to the early days of thermionic valves. At first that some ne w me thod which will superse de all the freq uencies involved we re se ldom higher existing me thods may be de veloped in the than a fe w me gacycle s pe r se cond ; but, at future, and indee d some of the me thods already the pre se nt time, freq uencies of 70 me gacycle s proposed show considerable promise. All that pe r se cond are in common use , and the indica­ is intende d he re is to re cognise that other tions are that freq uencies up to 750 me gacycle s me thods of ge ne rating the se oscillations have pe r se cond will find exte nsive application for be en proposed. ce rtain classe s of work. Freq ue ncie s as high as the se have be en produced by me ans of ne gative NEGATIVE GRID OSCILLATORS grid triodes and still higher freq ue ncie s will no The te rm ne gative grid oscillators arise s from doubt be obtainable in the future, 3 000 Mc/s the fact that the D.C. potential applied to the having already be en attaine d expe rimentally. gr id is usually ne gative , as distinct from the FEATURES LIMITING THE OPERATION OF VALVES AT ULTRA-HIGH FREQUENCIES In considering the possible be haviour of a triode at ve ry high fre q ue ncie s a numbe r of limiting factors arise . Some of the se factors affect the ope ration of the valves at normal radio freq ue ncie s, but others do not have any marked effect until the ultra-high freq uencies are approached. The principal factors to be considered are as follows : (1) Maximum available emission from the cathode ; (2) Maximum anode dissipation ; (3) Grid emission ; (4) Die le ctric losse s in the enve lope and in- sulators; (5) Inductance of the valve le ads ; (6) Capacitie s be twee n the electrodes ; (7) Transit time of the electrons be twee n cathode and grid. The first three of the limitations also ente r into the de sign of valves for ope ration at normal freq ue ncies but the y have a much more marke d and, in some ways, a different effect on valves for ope ration at ultra-high freq ue ncies. Some of the limitations me ntione d above are inter­ conne cted, e.g., (1) and (6), and (5) and (7) ; and some of the se re lationships will be con­ sidered he re inafte r. Be fore doing so, however, it will be advantage ous to consider each limitation se parately. (1) It is obvious that if a valve is to de liver Fig . I-4036-A Micro-Ray Valve. power, ce rtain pe ak emissions must be obtain­ able from the cathode . The total emission available is proportional to the area of the

www.americanradiohistory.com ULTRA-SHORT WAVE OSCILLATORS 327

te mperature ; its rise in te mpe rature is due to the he at ge ne rated by the flowof electrons to it and by the absorption of he at from the cathode and the anode. Any te ndency for the grid to emit is gre atly increased if active material from the cathode be comes de posited on it. This is particul arly not iceable whe re oxide - coate d cathodes are use d. It can be counteracted to a ce rtain exte nt by constru cting the grids from mate rials such as mangane se -nickel alloys, or by coating the m with ce rtain substances which de cre ase the te ndency for emission to take pl ace . It has been observed that in valves having oxide -coated cathodes the te ndency for grid emission to take place increase s as the freq uency of ope ration increases. A number of explanations to account for this phenomenon has be e n put forward, but they are of a some­ what spe culative nature and ne e d not be considered he re . (4) Inasmuch as die le ctric losse s in most Fig . 2-4304-B Valve (S.T. &f C.). insulating materials mcre ase rapidly with freq uency, care must be taken to ke e p the se losses to a minimum by the use of low loss cathode and the emission per unit area. With­ insulating materials. In valves intended for out considering the re asons for the moment, it operation at the highest freq uencies, the only is fairly obvious that valves for ope ration at insulating mate rial use d is that of the hard glass high freq uencies must be sm all ; he nce the enve lope. are a of the cathode must be small and the total available emission from the cathode is limited. Conseq uently, the cathode must ope rate with as high an emission pe r unit area as possible . It is the refore customary to run the cathode of ultra-high freq uency valves at higher than normal te mperature s,ev en at the cost of re duce d life . Pure tungsten and thoriated tungste n filame nts are both use d ; and, later in this paper, some re sults obtained with oxide-coated cathodes will be de scribe d. (2) Similar re strictions apply to the anode of the valve . As the freq uency of the ope ration of a valve is pushe d towards the limit, the efficie ncy de crease s rapidly and a large proportion of the input power is dissipated by the anode ; as in the case of the cathode , the anode must be of small dimensions and it is a common practice to run the anode at a conside rably higher rating than the normal. (3 ) In any valve oscil lator grid emission may Fig. 3-4316-A Valve (S.T. &f C.). be the cause of a considerable amount of trouble . For a grid to emit electrons it must increase in

www.americanradiohistory.com 328 ELECTRICAL COMMU NI C ATION

Fig . 4-Double Lead Ultra-short Wave Valves (Bell Telephone Laboratories).

(5) The indu ctance of the connecting leads one-half the period of one complete oscillation. to the electrodes is also of great importance in these valves. Every effortis made to keep these INTERDEPENDENCE OF LIMITING leads as short as possible. CONDITIONS (6) The freq uency of an oscillatory circuit is The various factors which limit the freq uency given by the eq uation at which a valve can be operated have been mentioned above. Each one considered separ­ f=_}_J ately might be improved fairly easily. For 2n LC1' instance a tungsten filament could be run at a where Lis the inductance and C the capacity of high temperature in order to obtain a high the circuit. Assuming for the moment that L emission, or the spacings between the electrodes remains fixed, it is obvious that there is a could be increased in order to decrease the definite limit imposed on the frequ ency which inter-electrode capacities. Unfortu nately nearly can be obtained from a valve because of the all the limitations are interdependent, the only capacities between the electrodes. In order to exceptions being dielectric losses and, possibly, obtain high frequencies the inter-electrode inductance of the leads. It may theref ore be capacities must be small. As will be seen later, of interest to consider some of these relationships this means that the actual dimensions of the in a general way. valve must be reduced as the frequency is Consider first the cathode. One cannot increased, thus limiting the power which can obtain a high value of total emission by increas­ be obtained. ing the size of the cathode since this will (7) In valves operated at freq uencies of increase the size of the grid and anode, and so 60 Mc/s or less, the time which an electron increase the capacities unless the electrode takes to travel from the cathode to the anode is spacings are also increased; but this cannot usually negligible as compared with the time of be done. As has been seen, the capacities must one complete oscillation. As the fr eq uencies be kept to a low value. Increase in cathode are increased this transit time does not remain temperature is quite a common method of negligible but may be the limiting factor increasing the emission but, quite apart from determining the upper freq uency limit at which shortened life, there is a definite limit to which the valve will operate. It is generally accepted this can be carried. Increasing the temperature that it is the transit time between cathode and of the cathode increases the temperature of the grid which is of the greatest importance since grid, so that, if the cathode be of the thoriated the field acting on the electrons is lower in this tungsten or oxide-coated type, active material region than in that between the grid and anode. will be deposited on the grid at an increased It is also agreed that the limiting transit time is rate, consequ ently increasing the grid emission.

www.americanradiohistory.com ULTRA-SHORT WAVE OSCILLATORS 329

Increased emission, if used to its fullest extent, means increased power to be dissipated on the anode ; and, as in the case of the cathode, the size of the anode cannot be increased without increasing the capacities except at the expense of the electrode spacings. If the distances between the electrodes be increased, the inter­ electrode capacities will be decreased but, as a result, the mutual conductance of the valve will be decreased and the electron transit time increased. As has been pointed out, this latter effect may set a definite freq uency limit on the valve.

Fig. 6-LS.445 Valve.

It has been suggested that the necessary short transit time might be attained by operating a valve with high potentials, thus allowing the requirements of close inter-electrode spacing to be relaxed somewhat or permit higher fre­ quencies with a certain electrode spacing. High anode voltages, and the resulting high grid voltages, can be of assistance in some cases, but they do not offer a complete solution of the problem. If the inter-electrode spacing is fixed, it is at once evident that the application of high potentials entails increased space current, and thus the total emission from the cathode sets the limit to the magnitude of the potential which can be applied. If the freq uency of operation is fixed and attempts are made to Fig. 5-LS.486 Valve. increase the power handling capacity of the valve by increasing the inter-electrode spacings, then the same limitation is again encountered, Thus it is seen that, in order to keep both the although not to such a marked extent. capacities and the transit time to the low values required, the electrodes must be of decreasing size as the freq uency of operation is increased. In order to obtain maximum dissipation, the anode of such valves is usually provided with ribs and the surface roughened in order to improve its radiation properties. Carbon is freq uently used for the anodes owing to its extremely good properties in this respect. Grids are also provided with cooling fins in Fig. 7-Structural Details of the LS.486 Valve of order to keep their temperature, and hence Fig. 5. their emission, down to a minimum.

www.americanradiohistory.com 330 ELECTRICAL COMMUNICATION

supported from the leads. These valves have been very successfu l, the 316-A type having a higher fr eq uency limit of operation than any other valve on the market. It will oscillate at 750 Mc/s although the output at this freq uency is very small. Approximately 8 watts can be obtained from it at 300 Mc/s. The 304-B will deliver approximately 55 watts at 100 Mc/s, 15 watts at 300 Mc/s, and has an upper freq uency limit in the neighbourhood of 350 Mc/s. Fig. 4 shows th ree valves which have also been developed by the Bell Laboratories. They all differ fr om conventional triodes in that the anode and the grid each have two leads, one at each end of the bulb. The advantage of these double leads will be mentioned later. These valves also have finned grids to lessen any tendencies to grid emission ; and the filaments are of thoriated tungsten run at a somewhat higher temperature than the normal. Fig. 8-Structural Details of the Figs. 5 and 6 show two double lead triodes LS.445 Valve of Fig. 6. which have been developed by Standard Telephones and Cables, Limited, London. To sum up, then, we find that valves intended for operation at ultra-high freq uencies have a number of inherent limiting characteristics which do not affect their operation at normal 30 �l 25 freq uencies. These limitations are largely inter­ "' connected and the resulting valve must have 20 �' the following characteristics : � � 15 \ (1) High cathode emission per unit area; LS 48B (2) High anode dissipation per unit area; (3 ) Low temperature grids; I VLS445 10 I 'IV (4) Small electrodes and inter-electrode 9 _\ spacmgs; 8 (5) Short straight leads; 7 \ ''"" "' \ \ \ (6) Minimum ins l i material. \ \ \ 4316-A of u at ng 5 �si[i\ VALVE TYPES 4 \ \ \ A number of valves which have been specially 3 \ \\ \ designed for ultra-high fr eq uency operation are I\ shown in the accompanying illustrations. The first two were designed in the Bell Telephone \ Laboratories, Inc., and are referred to in the U.S.A. as the 304-B (Fig. 2) and the 316-A (Fig. 3). The same valves manufactured inEn gland I .300 400 500 600 are referred to as the 43 04-B and the 43 16-A. JOO zoo 700 Fig. 9-Relationship between output and In both these valves it will be noticed that the frequency for some indirectly heated Valves, leads to anode and grid are kept as short as and a 4316-A Valve. conveniently possible and both electrodes ar e

www.americanradiohistory.com ULTRA-SHORT WAVE OSCILLATORS 331

The se valves are similar to the Be ll Laboratorie s valve s in that they have double le ads to grid 100 and anode, and the grid is provided with a fin. 90 I 80 I I Figs. 7 and 8 illustrate de tails of the structure s. 70 I I 60 Their principle of construction, known as -...... _ �ARCE Tl/SE "micromesh," was de veloped by Standard 50 " 40 " Te le phones and Cables, Limited, some ye ars 4304-A \ ago and was applie d to high mutual conductance JO I\ \ triodes for radio re ce ivers. Each turn of the zo \ grid is we lded to the cooling fin and conse ­ \ quently ke e ps much cooler than the turns of a 1 NTEl{MEOJATE ""' /UBE conventional type grid. The grids used in the 10 9 \ Be ll Laboratorie s valve s differ in form but they 8 - 7 !".. , have adoptedth e same pr inciple s. The Standar d i> ' 5 valves differ from the othe rs in that they have r.. SMALL '- TUSE indire ctly he ated cathodes of the oxide- coated 4 \ type . Such cathodes run at a much lower \ te mpe rature than the tungsten or thoriate d 4316-A \ tungsten type and provide a comparatively high '' value of total emission.

METHODS OF OPERATION 100 zoo 400 600 BOO I 000 zooo At freq uencies up to 150, or even 200 me ga­ Fig. 10-Relationship between Output and Frequency for Bell Laboratories' Double­ cycles, more or le ss conventional oscillatory ended Valves and for the 4316-A and circuits may be use d. That is to say the 4304-A Valves. inductance is in the form of a coil which is tune d by a conde nser. Asth e se high fr eq ue ncies are approache d, however, the sizes of the coils efficie nt ope ration the open-e ndedlin e is re com­ and condensers be come ve ry small, and the me nded. It is also ne ce ssary to tune the inductance and capacity of the conne cting le ads cathode to obtain the most efficie nt operation. to the valve be come of increasing importance . This is conve nie ntly effecte d by conne cting the As the fre que ncy is raise d, increasing difficulty cathode to the ce ntre of a coaxial transmission arises through losses in the insulators used. line the effective le ngth of which can be varie d. Afte r considerable study of the various possi­ This line usually consists of a le ngth of copper bilitie s, Standard Te le phones andCa bles, Ltd., tubing with a copper rod along its axis, and has adopted the so-called "Linear" oscillator having a moveable plunger sliding on the copper as be ing the most efficie nt and conve nie nt for rod and making contact with the tubing. In freq uenciesabov e 200 Mc/s; and the re mainder the case of valves having indirectly he ate d of this pape r de als with some of the re sults cathodes, only one such tuning de vice is ne eded; obtained with the valves illustrate d above , but in filame ntary type valve s one is re quire d toge ther with some de velopments arising out of for each le g of the filame nt. The exte rnal the work done . supplies are conne cted to the valve through In the linear oscillator the oscillatory circuit small chokes, and in the case of the anode and proper consists of a le ngth of transmission line . the grid the se are conve nie ntly conne cted at the In its simple st form the transmission line con­ nodal points of the transmission line. The load sists of two paralle l rods conne cte d dire ct ly to into which the output works can be conne cte d the anode and grid pins. If the line is ope n­ across the rods at a point de pe nding upon its ended its le ngth is be twee n a quarte r and a half impe dance . of a wave le ngth. The line may be close d with Re duce d to its simplest te rms the oscillatory a condense r in order to de cre ase the fre que ncy circuit consists of two paralle l wires te rminated without using a long line ; but for the most at one end by a system, the valve , consisting of

www.americanradiohistory.com 332 ELECTRICAL COMM UNICATION a lumped capacity and inductance. Th e fre­ to have twice th e output of a single lead valve. quency is determined by th e length of th e In Fig. 9 th e output versus th e frequency transmission line, a vol tage anti-node occurring ch aracteris tics of four valves are sh own together at th e open end of th e line and a voltage node with th at of a 4316-A valve for comparison one quarter of a wavelength fr om th e open end. purposes. Th e valves all have th e same inter­ Th e length of line on th e other side of th e node, electrode spacings but diff er in th e following together with th e inductance and capacity of manner : VLS.381 is a single lead valve ; th e valve, constitute an equivalent quarter wave­ LS.486 is a double lead valve having th e same length , th e end of th e electrode system remote electrode length ; LS.488 is a single lead valve fr om th e line possibly forming another voltage having half th e electrode length of LS.486 ; anti-node. As th e length of th e line is reduced and VLS.445 is a double lead valve having th e th e valve oscillates at increasing frequencies and same electrode length as LS.488. Th ese curves th e nodal point enters th e valve envelope, do not bear out th e above conclusions very well eventually entering th e electrode system itself since one would expect LS.486 to have twice in some circumstances. th e output of LS.488 at all frequencies ; but it As mentioned above, a voltage anti-node is must be remembered th at th e output obtainable possibly formed at th e end of th e electrode depends on a number of factors and th at th ese system remote from th e point wh ere th e trans­ results are taken on a few experimental valves. mission line is joined to it. If such is th e case, Th e curves do, however, sh ow th e general one might consider th e possibility of placing a superiority of th e double lead valves, since it second electrode system against th is and taking will be seen th at wh ile VLS.381 and LS.486 a similar transmission line out on th e opposite have approximately th e same output at th e side. Th is becomes, in eff ect, th e double lead lower frequencies, LS.486 has a high er output type of valve, examples of wh ich have already at th e high er fr equencies. Th e same th ing is been sh own. From th e above reasoning one true of LS.488 and VLS.445. Fig. 10 sh ows would expect a double lead valve with a double similar curves forth e Bell Laboratories' valves. linear oscillator system, at a particular frequency, From th e results obtained with th e four valves illustrated in Fig. 9, it was found th at wh en th e length of th e transm ission line was plotted against th e wavelength a series of parallel straight lines was obtained wh ich could be - I 15 I I � . represented by th e formula VLS44.5 "A ·I ...... (1) ·09 l=3-k, - ·OB ...... LS.46G 488. wh ere is th e length of th e transmission line, 07 ""\.LS l OG - "A th e wavelength and k a constant wh ich varied ,. \I I\ 0 5 from valve to valve and wh ich depended upon \vL!>3611\ th e point from wh ich th e length of th e li ne was ·O 4 measured.

·O \ If th e origin of measurement was taken as 3 I th e point at wh ich th e leads joined th e electrode \ system, th e values of k for th e four valves in ·0 2 question were : I\ VLS.381 -9 LS.486 -7 LS.488 ...,7 ·OI 100 200 300 400 .500 600 700 800 VLS.445 -4. Fig. I I-Relationship between Equivalent Th us it is seen th at th e double lead LS.486 gave Capacity and Frequency for the Indirectly Heated Valves. th e same results as th e single lead LS.488 of half th e length. Since th e distance fr om th e

www.americanradiohistory.com ULTRA-SHORT WAVE OSCILLATORS 333

L Fig . 1'2-Double Valve Oscillator. l in. between centres. For a parallel wire open end of th e line to th e nodal point is 4.'A systemI th e impedance of propagation along th e distance between th e nodal point and th e = th e line, ( J �) is given by el ectrode system (x) is given by : Zp A A X= = 276 log 10�'b ••••••••••••(3) 3--k-- z? 4 a wh ere b is th e distance be tween centres and a = A ...... (2) 12 - k. is th e radius of th e rods. For th e system used, th e value of was approximately 300 oh ms. Th us wh en = 12k th e nodal point reaches Zp right to th e elecA trode structu re. Th e fact th at Assuming th e transmission line to be resistance­ wavel engths sh orter th an th is value have been less, th e impedance of an open-ended line me asured sh ows th at in some cases th e node is Z is given by th e expression : situated inside th e electrode structure. z) Z = cot ...... (4) If th e electrode system of th e valve could be -jZp �; replaced by a fixed inductance and a fixed If th is is tu ned by a capacity C th en Z must capacity th en one sh ould expect th e length cf 1 al so equal . and th erefore c th e transmission line to be proportional to �. JW 4 (2Ttl) _1 cot = Th e fact th at th is is not th e case indicates th at p - 1· z 'A jwC either th e inductance or th e capacity of th e ( valves ch anges wit h frequency. It is well or C = tan 2rd) , ...... (5) known th at th e capacity of a valve varies with T frequency and it is reasonable to assume th at wZ, wh ere = 2rrf , f being the frequency th e inductance remains fixed. In th e valves in w 10 = 3.�0 question th e inductance is small compared with ( ) . th e capacity and can be neglected to a first approximation. It is th en interesting to see Th us for th e valve VLS.381 th e value of C is how th e capacity of th e valve must ch ange with gi ven by : frequency in order th at equation (1) may be ( 3 240) C = 0.018 tan 60 + ...... (6) satisfied. A -:;:-· In all measurements referred to, th e grid­ Similarly, expressions may be found fo r th e anode transmission line consisted of two capacities of th e other th ree valves ; but it parall el copper rods in. in diameter and must be remembered th at th e values of l6 C

www.americanradiohistory.com 334 ELECTR ICAL COMMUNI CATION ob tained for th e double-ended valv es wi ll only Such a multi ple os cillator is not limit ed to repres ent half th e actual capacity, since each of two valves . Th ree valves , gi vi ng th ree ti mes th es e are regarded as forming two complete th e output of a si ngle valve have been operated os ci llator systems, placed back to back as it success fully ; and th ere seem s to be no reason were. Th e fact th at th e relations h ip between wh y th e system sh ould not be extended to and 'A for th e double lead LS.486 valve is gr eater numbers of valves . Tb is would appear idl entical with th at for th e si ngle lead LS.488 to be a very us eful method of obtai ni ng com­ havi ng half th e electrode length lends very paratively large outputs at ult ra-h igh fr equencies . strong support to th is as s umption. In Fig . 11 Fur th er more, it is not necess ary to space th e 1 valves one electri cal half wavelength apart values of are plotted agai ns t frequency and si nce th ey may be spaced at multiples of half C it can be seen th at th ey follow th e same generai a wavelength . Th is latter arrangement is tr end as th e output vers us frequency curves for es s ential wh en operating at fn :quenci es th es e valves . approaching th e upper li mit of th e valves ; for in th is case th e nodal points are si tuated inside MULTIPLE OPERATION th e valve envelope and it becomes imposs ible to An added advantage of th es e double lead space th e valves one electrical half waveleng th valves is th at th ey can be connected in multiple. apart. Us ing th ree LS.486 valves , an output Wi th th e double lead linear os ci llators , nodal of over 50 watts at 250 megacycles can be points ar e us ually situated a sh ort dis tance obtained wi th an appli ed anode potential of not outsi de each end of th e valve. If th e parallel mor e th an 400 volts . rods forming one si de of th e double li near It is not consi dered th at th e results obtained os ci llator ar e removed and another valve of th e fr om th e indirectly heated cathode valves same ki nd is connected to th e firs t valve wi th des cribed above repres ent th e limit of wh at rods wh os e length is twi ce th e dis tance from can be ef f ected wi th th is type of structure. th e envelope to a nodal poi nt, a two-valve linear Th e indi cations at present ar e th at all th es e os cillator is formed. Th e rods wh ich were valves have an upper fr equency limit wh ich is removed fr om th e firs t valve are of cours e deter mined by th e valve capacity and not by connected to th e second pair of leads of th e th e transi t ti me. Consequently it is hoped second valve. Su ch an os cillator operates at th at th e fr equency li mit may be extended by the same frequency as the single valve type changing the electrode dimensions. While and gives double th e output. Fi g. 12 sh ows th es e valves do not gi ve th e same perf ormance as an example. Th e coaxi al li nes for tuning th e th e Bell Laboratories ' valves , it sh ould be cathodes sh ould be noticed. Th us we have an remembered th at th ey have th e following os ci llator cons is ti ng of a trans miss ion line wi th advantages : valves si tuated at voltage anti -nodes and (l ) Indi rectly heated cathodes giving greater separated by one electrical half wavelength . simplicity in the circuits ; Owing to th e lumped capacities of th e valves (2) Lower cathode wattage ; th e ph ys ic al di stance between th em Is sh orter (3) Lower anode potentials (in ge neral) ; th an one half waveleE gth. (4) Simpler to manufacture.

www.americanradiohistory.com Ultra-Short Wave Police Radio Telephone Installations in Oslo and Stockholm

By G. WEIDER, M.N.I.F., Standard Telefon og Kabeljabrik A/S., Oslo, Norway

(5) Static from atmospheric disturbances. GENERAL Ultra-short waves, on the other hand, are ITH the extensive introduction of more sensitive to disturbances from car motor cars and vehicles in police ignition systems. W services, wire telephone and signal For two-way communication between cars box systems no longer aff ord the efficiency and rapidity required for communication purposes. and stations, ultra-short waves offer the best facilities within a local area. In view of the Radio, on the contrary, off ers an ideal medium possibility of immediate and positive acceptance for meeting the highly important requirements of a call, the two-way system is nearly always of a flexible and rapid communication system favoured. In the case of cities such as London between the cars and the police stations. Large or New York, where the number of cars calling areas thus can be controlled practically in­ simultaneously may be great, the introduction stantaneously and the cars directed to spots of the two-way system may present difficulties. where " something is happening." Since radio telegraphy necessitates the Two types of radio systems are available for employment of special operators, telephonic police services : working is generally preferred. The latter also Short wave . . 120-190 m permits police officers, who are not often expert Ultra-shm t wave . . 7- 10 m telegraphists, to communicate directly with the Both may be adapted to one- or two-way com­ cars without the intervention of a third person. munication, either telephonic or telegraphic. Because of the reliability and high quality of In cities and municipal or suburban areas the equipment to be described, the possibility covering maximum ranges of 15 to 20 km, the ultra-short wave system is preferable in nearly all cases. In rural areas, due to the restricted range of ultra-short waves, short wave working AK"ER MUNICI LITY. is usually more suitable. In cities and densely populated areas, the application of short waves in two-way police communication is not usually desirable for the following reasons : (1) The existence of dead spots when receiving. They are not so frequent with ultra-short waves due to their reflection from buildings and other structures along the streets. (2) Relatively high transmitter output, both for cars and headquarters required. (3) Difficulty in obtaining an efficient car transmitting antenna, especially for radia­ tion while the car is in motion. (In the case of ultra-short waves and a quarter­ wave vertical radiator, the length of the antenna is two to three metres. ) Fig. I-Map of Oslo and its Suburbs. 4 Interference with broadcasting services and ( ) with other police stations.

335

www.americanradiohistory.com 336 ELECTRICAL COMMUNICATION

designed and preferably obtained from the c:::r battery. A high degree of reliability is of vital import­ ance inasmuch as a breakdown may involve seri ous consequences. The equipment is operated mainly by personnel not expert in radio matters, and it should not, in fact, be necessary for them to know anything about radio. The characteristics of the apparatus, moreover, should be such as to engender confidence on the part of the user equal to that of the ordinary telephone subscriber in his subset.

THE OSLO POLICE INSTALLATION The Oslo Police have carried out trials with radio communication systems since 1931, but it was not until the end of 1936 and the begin­ ning of 1937, when tests were made with ultra­ short waves, that satisfactory results were obtained. Experiments confirmed that, with short waves, it was not possible to avoid the existence of several dead spots within the city. In April, 1937, Western Electric ultra-short wave equipment was demonstrated to the Oslo Poli ce and, for the first time in Scan- dinavia, two-way Fig. 2-Headquarters Transmitter and Receiver. ultra-short wave communication be­ tween cars and of a call " being lost " is reduced. Secrecy, if headquarters was required, can be obtained by the use of a simple carried out. After code, but its importance is considerably reduced the Police had by the speed and efficiency of the radio tested the equip­ system. ment thoroughly, Police radio equipment must be specially an order was placed designed, and contain high quality components with Standard in order to meet the exacting servi ce requi re­ Telefo n og Kabel­ ments. In addition to obtaining the best fabrik A/S., com- possible electrical characteristics, consideration prising : of the unfavourable working conditions imposed on the mobile equipment shows that great care For Headquarters : in mechanical construction is required. Rigidity of construction sufficientto withstand the effects '1 -No. 16-B of shock and vibration, ease of installation, transmitter, 50 adaptability of the apparatus to various types watts, of cars, accessibility of components, and simpli­ l--,- No. 19-A city of operation are all of major importance. Fig. 3-Headquarters su perhetero­ ]-typ e Antenna. Further, the power supply must be economically dyne receiver,

www.americanradiohistory.com POLICE RADIO TELEPHONE 337

Fig . 5.A.-Transport Car.

Fig. 4-Radio Telephone Switchboard Room at Headquarters.

Fig . 5.C.-Transmitter, Power Units and Public Address Equipment in Transport Fig . 5.B.-Receiver and Control Unit in Transport Car. Car.

aerial and control equipment. Subsequently, 211-A equipments for four For Four Patrol Cars : patrol car s were delivered. Wh en a new patrol 4-No. 18-E superheter odyne receivers. car is being provided by th e police, it is not now considered complete unless radio equip­ For Harbour Boat and Transport Car : ment has been installed. Following on th e 2-No. 211-A equipments including : successful results obtained with th e Oslo No. 18-A tr ansmitter, 5 watts, and system, seven No. 211-A car equipments also No. 18-E receiver. were furnished to th e Gover nment Police.

www.americanradiohistory.com 338 ELECTRICAL COMM UNICATION

Th e wavelength range of th e transmitters and Because of th ei r possible absorption of radiated receivers is 10 to 7.14 m (30 000 to 42 000 kc/s). energy, metal guys are not used. Th e mast is

Th e operating wavelength in Oslo is 8.086 m supported at th e base by two 5!in. x 2i in. x 6m (37 100 kc/s). Th e oscillator circuit of th e ch annel irons, passing th rough th e roof of th e

transmitters is crystal controlled, th e crystals building and resting on two 9 in. x 9 in. floor being cut for 1/6 or 1/4 of th e carrier frequency. timbers. Wh ile in th e horizontal position, th e Th e beating oscillator circuit of th e head­ antenna was mounted on th e mast and trans­ quarters' receiver is crystal controlled, th e mission line connections made. Th e mast was crystal oscillating on 11 083.33 kc/s. th en raised to th e vertical position by means of Th e headquarters building is situated as a sh aft fixed between th e ch annel irons. Th is sh own in Fig. 1. It is located on a low hill and process greatly simplifies inspection of th e its height is approximately 25 m to th e top of antenna system. th e roof. Th e transmitter and receiver, illus­ Th e transmission line, at th e base of th e trated in Fig. 2, are installed on th e top floor. mast, is connected by means of a special Th e output of th e transmitter and th e input of weatherproof demountable coupling to th e th e receiver are connected via 3/8 in. coaxial down lead to th e antenna relay mounted in th e transmission lines to a relay, wh ich connects th e transmitter-receiver room. Transmission line transmitter and th e connections must be receiver, respectively, made with great care to a 7 /8 in. coaxial in order th at th e transmission line insulation n:sistance leading to th e an­ between th e mner tenna, illustrated in and outer conductors Fig.3. can be maintained Th e antenna is a above 10Me goh ms. vertical J-type dipole Th e transmitter and is supported by and receiver are a 15 m steel tube operated fr om th e mast, 4! in. in dia­ telephone switchboard meter at th e base room (Fig. 4) located and 2 in. at th e top. on th e ground floor.

Fig . 6.A.-Patrol Car.

Fig . 6.B.-Transmitter in Patrol Car. Fig . 6.C.-Receiver, Control Unit and Power Units in Patrol Car.

www.americanradiohistory.com POL ICE RADIO TEL EPHONE 339

By th rowing another switch, plate vol tage is applied to th e transmitter valves, th e antenna relay disconnecting th e receiver from th e trans­ mission line and connecting th e latter to th e transmitter (the receiver input and output being sh ort-circuited). Th e previously mentioned ammeter reading is th en 6.5 amps., corresponding to a power consumption of 1.3 kW with a power factor of 0.9. Wh en modulating th e carrier, either with a 1 000-cycle tone produced by a microphone hummer or with speech, th e needle of th e ammeter follows th e modulation periods.

Th is arrange nt provides adequate means simplefor control of thmee equipment. Th e lay-out of th e apparatus in th e cars may vary, depending on th e type of car and space available. Th e No. 211-A automobile equip­ ment consists of : No. 18-A transmitter, Fig . 7-Transmitter and Power Units in a Government No. 18-E receiver with separate loudspeaker, Police Car. Control unit with microtelephone, Power unit for transmitter, Th e control equipment includes a control box Power unit for receiver, with switches, ammeter, microph one hummer, Antenna, microteleph one and amplifier with loudspeaker. Cables, sockets and plugs. On th e table beside the control apparatus is a The equipment meets all the specified map of th e c ity ; a wall panel with remove­ requirements. Sh ockproof mountings are used able numbered cards indicates th e cars in th roughout. Th e components are of small service and th e districts being patrolled. dimensions, th e transmitter being 18 cm high, A switch on th e control box puts th e equip­ 28 cm wide and 17 cm deep ; th e receiver is of ment in th e stand-by and receiving condition, th e same dimensions with exception of th e i.e., width, wh ich is 23 cm. Th e equipment is very (1) Th e receiver is made alive and connected flexible. All cables are connected to th e trans­ via th e antenna relay to th e transmission mitter, receiver and power units by means of line ; plu gs and sockets, allowing quick dismantling (2) Filament voltage is applied to th e trans­ of th e apparatus for inspection and replacement. mitter valves and, after about 30 sec., th e A car may be furnished initially with receiving operation of a time delay rel ay permits th e application of plate voltage and grid bias. An incoming call will th en be heard from th e loudspeaker, wh ich may be switched off and conversation carried on with the handset. By means of a key, th e " CODAN " circuit of th e receiver, wh ich will be referred to later, can be switched in or out. Th e equipment operates from a 220-volt, single ph ase, SO-cycle A.C. supply. In th e stand-by position th e reading of an ammeter on th e control panel is approximately 2.5 amps., corresponding to a power consumption of 500 W with a power factor of 0.9. Fig . 8-Po/ice Harbour Boat.

www.americanradiohistory.com 340 ELECTRICAL COMMUNICATION

car igmt10n system, suppressor resistances are connected between th e plugs and conductors, or special screened plugs are utilized. A sup­ pressor resistance also is connected to th e distributor and a c:mdenser is inserted between th e terminals of th e dynamo. [11-----1----'---._____.___.___tta== I 11 ==I I 11 Th e antenna consists of a flexible steel rod of

o I 5 10 50 100 1000 10,000 100,000 quarter wavelength, supported by a bracket INPUT IN MICROVOLTS and connected by means of a special cable or a Fig. 9-Receiver Characteristics with " CODAN " and Automatic Volume Control. coaxial transmission line to th e antenna transfer relay mounted in th e transmitter. To obtain correct matching and th us reduce losses, th e transmission line is cut to a length dependent equipment only, in wh ich case th e later addition on th e wavelength. Th e use of a vertical of transmitter and accessory equipment does antenna is desirable because of its high er not make any of th e equipment superfluous. radiation efficiency. On cars wh ere th e trans­ Th e transmitter and power units may be mitter is housed in th e trunk compartment, mounted wh ere most convenient, but th e th e antenna is mounted on th e trunk in order receiver and control unit with microteleph one to keep down th e distance between th e trans­ must, obviously, be located within th e range of mitter and th e antenna. th e operator. Th e power units are driven from Fig. 8 is a view of th e police harbour boat. th e car battery, th e total current drain being Th e antenna is mounted on th e top of th e mast 10 amps. in th e stand-by position and 20 amps. and th e radio equipment in th e pilot house. wh en transmitting. Th e operation of th e equipment is very Fig. 5 illustrates th e installation in a transport simple. By turning th e combined switch and car having a capacity of 20 patrolmen. Th is volume control on th e front panel, th e receiver car is also used as " mobile headquarters " in is alive within 30 sec. During patrol service connection with public meetings, demonstra­ th e receiver is in continuous operation. tions, etc. Loudspeaker and microtelephone switch on th e control unit starts th e transmitterA are duplicated, with one set in th e ch auffeur's and one in th e passengers' compartment. Th e car is also equipped with a Standard public address system for transmitting messages to large crowds. Fig. 6 sh ows an installation in one of th e new patrol cars. Both transmitter and receiver are mounted below th e dashboard. Fig. 7 gives details of th e installation in one of th e cars of th e Government Police. Th e transmitter with th e power units is mounted on a framework in th e trunk compartment wh ich also houses th e car battery. Th e control unit and microtelephone are placed on th e dash­ board, below wh ich th e receiver and loud­ speaker are arranged. All cabling between th e front and rear of th e car is run in a copper tube placed under th e car ch assis. With th is arrangement a practical cabling scheme is achieved without th e necessity of modifying th e body of th e car. In order to eliminate noise generated by th e Fig. IO-Stockholm Police District.

www.americanradiohistory.com POLICE RADIO TELEPHONE 34 1 power unit ; by me ans of a switch on th e othe r structures and re ach th e car antennae microtele ph one handle , plate and scree n grid from many directions. In some cases, th e voltages are applied to th e transmitter-an ph ase re lationship of th e waves is such th at arrangement wh ich re duces th e battery drain th e y will re inforce each othe r ; in othe rs, th ey to a mm1mum. Th e press-to-talk switch also te nd to ne utralize , re sulting in ve ry low fie ld controls th e antenna transfer re lay and in­ strengths. Signal strength th us will vary corporates a re ce ive r cut-off de vice. rapidly and widely while a car is moving along Th e circuits of th e transmitters and re ceive rs a stree t. Re ce ivers, th erefore , are equipped are of modern de sign with efficient type s of with a quick acting automatic volume control valves. Th e crystal controlled oscillators ensure (AVC). For an increase in th e signal stre ngth high carrier fre quency stability, and th e ch ar­ from 5 to 100 000 microvolts, th e ch ange in acteristics of th e equipment are above normal th e audio output will be le ss th an 3 db. for commercial radio equipment. Due to the Ordinarily, the AVC, during silent periods, high noise le vel, th e low antenna he ight on th e would cause amplification of th e ignition noise cars, and th e re stricted carrier power of th e car to a le ve l wh ich would be annoying to th e transmitters, high quality is esse ntial for operators and wh ich might le ad to false calls. establishing satisfactory two-way communica­ To avoid th is difficulty, a " CODAN " circuit tion. (" carrie r operated de vice anti noise ") is To de scribe de tails of th e electrical construc­ utilized. He nce , wh en no signals, or signals tion of th e apparatus, re garding wh ich informa­ be low a ce rtain le vel, are be ing re ce ived, a ne on tion has previously be e n publishe d, would be tube sh unts th e grid of th e output valve in th e be yond th e scope of th e present article . Me ntion re ce iver, th us silencing th e loudspeaker. Th e of some spe cial features of th e car re ce iver, how­ " CODAN " ge nerally is adjusted to function ever, may be of interest. on an input signal up to 5 microvolts. Th is Due to th e ir se mi-optical ch aracter, th e waves re pre se nts th e minimum use ful carrier le ve l and radiated from th e stationary transmitter are is be low th e ave rage noise le vel. Fig. 9 indicates subje ct to re fle ctions from building walls and th e combined working of th e AVC and th e

Fig. 11-Connection of Local Receiver and Two Remote Pick-up Recei•·ns.

www.americanradiohistory.com ELECTRICAL COMMUNICATION

" CODAN." By means of a potentiometer it instance, the harbour boat receiver with power is possible to adjust the operating level for the unit is in continuous operation, night and day. " CODAN " which, by means of a switch, may Maintenance work, notwithstanding, consists be disconnected. At great distances from essentially in the replacement of valves and headquarters the low field strength level may brushes. When a car transmitter or receiver necessitate switching off the " CODAN " becomes faulty, it is immediately replaced by device, but in the outskirts of the city the a spare, the replacement taking less than one noise is generally not disturbing. minute. The defective apparatus is then A noise suppression circuit, recently inspected by the police in their workshop, first developed, will increase the range of the by checking the valves with a valve tester. At receivers. This circuit will be introduced m regular intervals the aerial current of the car the present receivers in Oslo and also m transmitters is measured in order to determine Stockholm. the emission of the valves, and stationary At headquarters reception is disturbed by transmitter meter readings are taken weekly. ignition systems, electric motors, electromedical apparatus, etc. It appears, however, that THE STOCKHOLM POLICE INSTALLATION satisfactory reception with the " CODAN " in A commission from the Stockholm Police operation is possible from the entire area visited Oslo in March, 1938, to study its police served by the Police. From 5 p.m. to 7 a.m., radio system. Subsequently, Standard Telefon­ noise is not very disturbing with the "CODAN" og Kabelfabrik A/S received an order from switched off. All noise sources in the building Stockholm for a similar type of equipment, are compensated ; it was, however, rather comprising : difficult to trace the origin of a very annoying interference, the level of which increased with For Headquarters : the height above ground. By means of a noise­ l'-No. 16-B transmitter, 50 watts, detector, this noise was found to reach the 1-No. 19-A receiver, building over a pair of the telephone lines Antenna and remote control equipment. connecting headquarters with the telephone For Two Remote Pick-up Receiver Stations: signal boxes in the city and terminating at a 2-No. 19-A receivers. mast on the roof of the building. A choke coil For Two Patrol Cars : in series with the line, and a shunt condenser 2-No. 211-A equipments, including : inserted at the distant end, cured the trouble. No. 18-A transmitter, 5 watts, The radio system, which has been in service No. 18-E receiver. since October, 1937, has operated without a After the present system has been thoroughly single breakdown, thus proving the sturdiness tried out, it is the intention to furnish six or of its design, particularly in the case of the eight additional cars with radio equipment. mobile equipment. The service conditions The carrier frequency is 31.9 kc/s. The imposed obviously are rather severe ; for transmitters and stationary receivers are crystal controlled. Compared with the installation in Oslo, the Stockholm system differs principally with respect to : (1) Remote pick-up receivers, (2) Operation and control, (3) Connection of radio telephone subscribers, (4) Coaxial antenna at headquarters. The police district consists, as indicated in Fig. 10, of the city itself (600 000 inhabitants) and its suburbs (200 000). The main trans­ Fig . 12-Headquarters Control Equipment. mitter and receiver are housed on the top floor

www.americanradiohistory.com POLICE RADIO TELEPHONE 343

------· ------� -

-I I I I

I I I I I l I I t •rn I Fig. 13-Control Box Circuit Schematic.

of the police building, the antenna being about operator's room at headquarters, each receiver 70 m above the street level and the control may be connected and individually tested. The equipment on the ground floor. secondary side of the repeating coil is wired via Anticipating a maximum range for the car a relay contact in the remote control panel to transmitter of 5 km, two remote pick-up the loudspeaker. When transmitting, this relay receivers have been foreseen, located as shown contact disconnects the loudspeaker and another in Fig. 10. Since the southern section of the relay contact short-circuits the output of the district is rather rocky, a relay receiver would in local receiver. any case be required. These receivers are At the remote points quarter-wave vertical unattended and their output is connected to antennae are used, supported by 8 m steel headquarters through output transformers and tube masts mounted on the roofs of the buildings pads via telephone lines. housing the receivers : � in. coaxial transmission As will be seen from Fig. 11, each line lines connect the aerials to the receivers. terminates at headquarters at a double-pole The aim has been to simplify operation in double-throw switch by which the remote order to obtain the greatest possible conformity pick-up receivers may be linked to a common with usual telephone practice. In the cars bus-bar for connection through an impedance microphone hummers have been mounted, a matching repeating coil to an amplifier and 1 000-cycle tone-modulated signal in the loud­ loudspeaker. With this type of coil, a maximum speaker announcing an incoming call. On of six remote lines may be connected. starting a conversation, the loudspeaker may The local receiver is connected via an output be switched off, either by a separate switch on transformer in the remcte control panel of the the control desk at headquarters and on the car transmitter and a D.P.D.T. switch to the bus­ loudspeakers, or by means of contacts in the bars of the remote receivers. By means of switchhook of the operator's subset. switches mounted on a wall panel in the Control and operation at headquarters is

www.americanradiohistory.com 344 ELECTRICAL COMMUNICATION

usual C.B. subset, employing the same type of microtelephone as the operator's. Correspond­ ing to each subscriber, a key and a signal lamp UPPE"R ROD l SHORTING BAR. are included on the control box panel. To transfer an incoming call to one of the subscribers, the operator throws the respective key to the "local" position and presses a button

BRASS BUSHING on the panel, whereupon SO-cycle current operates the bell of the radio subset. The subscriber removes his microtelephone and may

INNER SURFACE be advised by the operator regarding the call. OF TUBE When the operator now throws the key of the subscriber in the "radio" position, the sub­ OUTER SURFACE I OF LINE I scriber receives directly from the car and may I I I answer by pressing the key on the micro­ J ...-i - t­ A A i ! telephone handle. The conversation may be B s heard by the operator through the loudspeaker, CONCE NTRIC LINE which is wire-connected to the operator's sub­ IsTRAY set when his key is in the middle position.

ZAB = The ammeter on the control panel for measur­ oo ing the current drain also gives an indication as Fig . 14-Coaxial Typ e Antenna. to whether or not a conversation is in progress. A subscriber desiring a radio connection depresses the microtelephone key momentarily accomplished from a control box (Figs. 12 and and his call is indicated on the control box by 13). On the right side of the control box panel, a ringing signal and by the flashing of a lamp the controls for the operation of the transmitter corresponding to each individual subscriber. and receiver are grouped. A main switch on The operator's throwing of the subscriber's key the panel serves to place the equipment in the into the position marked " radio " places the stand-by and receiving position. In this latter " on the carrier." position, reduced filament voltage is applied to At headquarters, a coaxial type antenna, the transmitter valves, thereby increasing the recently developed by the Bell Telephone life of the valves. By pressing a key on the Laboratories, Inc., is used. microtelephone handle, the antenna trans­ It will be appreciated that the most efficient mission line is transferred to the transmitter, antenna is one giving offno high angle radiation. the receiver output is short-circuited, the loud­ With the J-type antenna construction previously speaker is disconnected, and plate and full used in ultra-short wave police working, where filament voltages are applied to the transmitter the transmission line is mounted alongside the valves, resulting in the emission of carrier supporting pole, the system acts somewhat like frequency energy. The 1 000-cycle "attention" a long antenna due to excitation of the support­ signal is sent out by pressing a non-locking key ing pole and the outside surface of the trans­ on the control box panel ; by means of another mission line, resulting in partial high angle key, the "CODAN" circuit of the receiver may radiation. The coaxial type of antenna is free be connected. from such reactions. The left side of the control box contains Referring to Fig. 14, the coaxial antenna is apparatus required for th� connection of eight a centre-fed vertical dipole consisting of a rod radio telephone subscribers to the system in and the outer surface of a 3 in. tube, both of order that communication may be established quarter wavelength. A in. concentric trans­ from certain offices within the building (e.g., mission line running insidet a 2 in. supporting that of the police chief) to the cars. The radio tube connects the upper rod to the transmitter subscriber set in appearance resembles the output. Due to the high impedance across the

www.americanradiohistory.com POLICE RADIO TELEPHONE 345 lower end of the 3 in. tube section and the to mount on the top of a 45 m guyed steel tube transmission line, the stray pole current is mast placed on a balcony of the building. The reduced to a minimum. A maximum radiation length of the transmission line to the trans­ in the horizontal direction is thus obtained, and mitter is about 60 m. is of course of vital importance in its effect on The car equipments and remote receivers the transmission range. have been installed and tested with satisfactory This new antenna compared to the J-type is results. The car installations are similar to said to give a gain of about 6 db. in fieldstrength those of Fig. 7. for the same power input. In other words, the The installation of the equipment at head­ range of a SO-watt transmitter with the new quarters was completed during April, 1939. antenna is approximately equivalent to a 200- The ranges obtained during the first tests were watt transmitter with the J-type antenna. The better than had been expected. This result, no present J-type antenna in Oslo will shortly be doubt, is due to the satisfactory location of the replaced by the coaxial type. transmitter and the adoption of the coaxial For Stockholm the new antenna is arranged type of antenna placed at a great height.

View of one side of the Bell Telephone Mar.ufacturing Company 's stand at th� B1ussels Fa.ir, M_arch 12th to March 26th, 1939, showing the exhibit of the remcte control of street lzghtmg and multz-servzce system.

www.americanradiohistory.com R-6 Automatic System

By F. GOHOREL, Technical Manager, and R. LAFON, Engineer, Compagnie des Telephones Thomson-Houston, Paris, France

EDITOR'S NoTE.-Automatic telephone systems employing single motion switches or uni-selectors are now well-known. Such systems are characterized by the use of common control circuits, resulting in a minimum of equipment being held in use during the period of conversation. The R-6 system is a single motion switch system designed primarily for step-by-step areas and employs a single motion switch with a step-by-step drive. In this respect the R-6 sysfem is similar to the Bypath system.* The well-known 7-D Rotary system is also a single motion switch system but is designed on Rotary principles with power drive switches.

INTRODUCTION of the system in the provinces, and entered into HE R-6 automatic telephone system, an agreement with the Compagnie des developed and completed in the Telephones Thomson-Houston under which T laboratories and workshops of the the French Government reserved the right to Compagnie des Telephones Thomson-Houston, have R-6 automatic exchanges set up for its has made great strides since 1923, the date of its own needs by French manufacturers in accord­ origin. ance with the design requirements of C.T.T.-H. The first public network equipped with this There are at present 140 R-6 automatic urban system was the Neunkirchen (Sarre) system, exchanges equipped for from 50 to 10 000 lines, which consisted of a central exchange and two totalling 180 000 lines either in service or in sub-exchanges placed in operation at the end course of installation. By adding the rural semi­ of 1927. The importance of the R-6 system automatic and the private branch exchanges did not at that time escape the engineers of the (136 000 and 35 000 lines, respectively), it will French Postes Telegraphes et Telephones ; an be seen that, within ten years of its existence, automatic switchboard intended for the town the R-6 system has provided 350 000 lines of of Troyes had been ordered by way of the networks of France, Algeria and the French experiment and was cut over at the beginning Colonies. of 1928. The results obtained from the begin­ The maps, Figs. lA and show the large ning were remarkable in every way, in particular regional zones and centreslB , equipped with in so far as the quality of the service was R-6 automatic exchanges (excluding semi­ concerned. The P.T.T., moreover, considering automatic rural equipment, which is not the low cost of the new system in the establish­ considered in the present article). The reasons ment of telephone exchanges, modified its for this rapid development are due to the plans involving the installation of manual fundamental principle on which the system is exchanges in the towns of Nimes and Epinal and, based. in 1928, substituted two R-6 automatic exchanges. SELECTOR FUNDAMENTALS They were successful from the moment they A selector, in any automatic telephone system, were placed in operation. The P.T.T. con­ should fulfil two distinct functions : sequently decided on the generalized application (a) A "control selection " function, which

consists in selecting a group of lines " A Controlled Single Motion Switch System Operat­ * under control, directly or indirectly, ing in the London Area," by J. H. E. Baker and E. P. G. Wright, Electrical Communication, July, 1933. from the calling station ; 346

www.americanradiohistory.com R -6 A U T 0 M A T I C SYSTEM 347

(b) A function of " free selection," which consists in finding a free line in a group MEDITERRANEAN thus chosen. The first of these operations is accomplished by the calling station in conjunction with the connecting line to the exchange. The control from the calling station is effected by means of a dial resulting in electrical interruption of the connecting line in rapid sequence. These SCALE ,__ 0 JOO connecting lines may possess widely different ZOO ?-00 bit characteristics, depending on the quality of • Fig . l-B-Regional Zones and Centres ia North Afr ica equipp ed with the R-6 Automatic Sys tem. insulation and the distance which separates the subscriber from the exchange. Since the current impulses produced by the dial may be The function of free selection, on the contrary, considerably distorted when they reach the is purely local and depends solely on the actual exchange, it is necessary that they be received conditions at the telephone exchange. on devices which respond rapidly to these In accordance with the theory of probabilities, impulses ; that is, devices possessing minimum moreover, the number of components necessary inertia and, consequently, small dimensions.* at the exchange decreases as the extent of the groups in which they are distributed increases: The same reasoning applies to register systems when * Differently stated, the larger the number of the impulse transmission on the interconnecting lines between exchanges is considered. lines to which a selector has access in a single group, the smaller the number of necessary

• components. Taking CHANNEL :. _ .:rOURCOINr, �OUBAIS into consideration the LILLE '>-l

'' as possible. Accord­ rOuR� BESAN� ;-/ ingly, it follows that a selector should : v1CHY Jn ATLANTIC '· · \� ROANN� } (1) Be small, in OCEAN CLAR.MONT ®LYON order to fulfil rERR.A.ND ST. ETIENNE satisfactorily the function of con­

-, MENTO trolled selection; BEAULl�U BAYONNE TOUL�USE NICE CANNES (2) Be large, in order ---._ -""'"" RRl Z BEZIE�S sr. J�� : to fulfil satis­ · :�LUZ PAU TOULON factorily the · ____ ,-- ••• , •• ···· ··-- ···- ,.,_.-.,_,. Pl!:RPIC",NAN function of free MEDITERRANEAN selection. Combined on the LEI:;END SCALE. same mechanical mem­ S�PAR.a.TE CENTRES. 0 so 100 150 ic ... ber, these two functions, AUTOMATIC RE41 0NAL ZONES. ifl which impose contrary Fig. I-A-Regional Zones and Centres i11 France equipped with the R-6 Automatic SyHem. requirements, can pro· duce only a far from ideal

www.americanradiohistory.com 348 ·ELECTRICAL COMMUNICATION

of the control switch utilized in the R-6 system for establishing the communication is very low in relation to the non-operating holding time of the selector. The separation of the two members, involved in the operation of controlled selection and of free selection, has made it possible to employ a single control switch to obtain controlled selection of several selectors (from 6 to 20). In associating with the common control switch the complex components which are utilized only during the short period during which a connection is established, and restricting the selector itself to the two or three relays necessary for the maintenance of the established com­ munication and for the momentary connection of the selector to the control switch, it has been

Fig . 2-Eleven Poin t Rotary Switch .

. compromise. The use of two distinct members, each as far as practicable suitable to its particular functions, however, leads to a far more rational solution. This has been adopted in the R-6 system, in which each selector consists cf two distinct components : (a) A receiving switch controlled by the subscriber, termed the control switch, of low inertia (Fig. 2) and high velocity (the period of time for the attraction of the armature and that of its release is under 3 milliseconds) ; (b) A uni-directional line-finder of adequate dimensions to ensure reliable choosing of the wanted line from groups of 50, 100, 150 or 200 lines (Fig. 3). If the part played by a selector in a telephone connection be considered, it will be found that it is two-fold : The first, very complex but of short (a) duration, is to establish the communica­ tion ; (b) The second, which is much longer but also much simpler, is to maintain the connection until the communication is completed.

The operation of controlled selection taking Fig. 3-R-6 Automatic Switch-51 Point Rotary Switch. place entirely during (a), the operating period '------

www.americanradiohistory.com R-6 AUTOMATIC SYSTEM 349

possible to economize -- 0000 ...... T NSION 00 00 TO Vll.LERS LOCAL HUNDRED 00 700 considerably in com­ 0 �0 EX E N! 70 000 TO 70099 0 � 0 0 0 ponents without in any 0\ 0 \ VI R TO L LE 5 LOCAL HUNDRED manner degrading the "o 704 N� 70400 TO 70 499

100 LINES characteristics of the FINAL LOCA.L WlTH TO VI LLE:RS LOCAL HUNDRED LI NE.5 70)3 SELECTORS R-6 system. PER2 POSITION N<>70.300 TO 70399 ) AT VI LLER.S An R-6 automatic 0 0 0 TO VILLERS LOCAL HUNDRED l 0 0 N� 70200 TO 70 299 exchange, consequently, o 702 . 0 0 0 0 consists of an association 0 00 00 TO VILLERS LOCAL HUNDRED 000 701 N''70100 70199 of simple line-finders TO and some directive de­ TO BLONVILLE INCOMING 79 (NEIGHBOURING SATE LLITE) SELECTORS BLONVILLE vices, viz., the control N" 79000 TO 79 999 AT switches. An evident 0.1 . 2 .3. TO OEAUVILLE , TROUVILLE INCOMING 5 CIA SELECTORS. AT TROUVILLE '------4,5 ,6, SATE.LLITf"SANO PE L SERVICES 71 TO 78 (ALL NUMBERS EXCEPTTHOSE (TRANS!T CENTRE) analogy is presented by ABOVE) a well organized enter­ Fig. S--Lines Grouping on the First Selector Banks, prise in which a small " Villers " Satellite (Deauville Area).

NUMERICAL COMBI NATI ONS FOR DIRECTING THE SELECTOR BRU5HES number of expert in­ TO THE CORRE.SPDNOING LINE GROUP dividuals control a FA LSE CALL LINE.5

CIRCUITS number of workmen from whom only sim­ OE.AO LEVEL CIRCUITS ple, routine operations are required. TO ROUBALX SATELLITES

TOO LINES N'? 338,00o WITH 2 1..INES PER POSITl1.m TO ROUBAIX LOCAL THOUSAND PERFORMANCE N'? 337.000 The performance of

TO ROUSAIX LOCAL'f"HOUS.A ND 336 the R-6 system has N!' 336.ooo vindicated the concep­ TO ROUBAIX LOCAL THOUSAND 335 N!' 335.ooo tion which formed its basis. TO ROUBAIX LOCAL THOUSAND LOCAL 334 In the R-6 system with direct control (that TO ROUBAIX LOCAL THOUSAND 33' N!' 333.QOO is, selectors controlled directly by the sub­ TO ROUBAIX LOCAL THOUSAND scriber), operation for normal adjustment is TO ROUBAIX LOCAL THOUSAND N'? 331.000 satisfactory on lines with

TO ROUBAlX LOCAL THOU5ANO loop resistance varying N<:> 330.000 from 0 to 1 800 ohms

EXCHANGE TO ROUBAlX SECOND 2N.D and with insulation 32 EXCHANGE AND SATELLITES THOUSANDSS N!'320000 TO 32�.ooo S ELECTOR 100 UNES between wires ranging WITH 2 LINES TO TOURCOING INCOMING SELECTORS from infinity to 3 600 PER PO..:.ITION AND SATELLITES AT " TOURCOING H L N'?E 40.000 EXCHANGE. ohms, representing out­ TO LI L AND SATELLITES INCOM�NG SELECTORS " N!' 210000 - 2.30000 AT LILLE FA IOHERBE side limits met with in 25 26 250000 - 260000 TRAN51T CENTRE practice.

INCOMING SELECTORS AT "NODAL" In a network com­ CENTRE. prising a number of TO TOLL, TELEGRAPH SPECIAL. SERVICE INFORMATION , TE.ST. ETC ·· SELECTORS exchanges, the R-6 N�10JO I� system employs neither Fig . 4-Lines Grouping on the First Selector Banks, " Roubaix " Exchange. repeaters nor impulse

www.americanradiohistory.com ELECTRICAL COMMUNICATION 350

PDEO PD R

CCr-i

ccs

r� CN R ��s R A s RR

Fig. 6-SimplifiedJu nction Diagram in the R-6 System.

;IC·------

� WOl< A z 1- "-���������""""o� u WW B FB J: .J �---������-;��-----�:} I- w o lll FT I- h h'S: __- ______[;:���- ��, K�.� QJ>

TO OTHER SELECTORS ASSO CIATED WITH THE CONTROL. SWITCH rt

-i}llv a I z u I- 0 fi � :t .J'f' a 0 � l I- z 0 u ze D?

Fig . 7-R-6 Selector Simplified Circuit Schematic.

www.americanradiohistory.com R-6 AUTOMATIC SYSTEM 351

s s

Fig . 8 Fig. 9

Fig. 10 Figs. 8, 9, IO-Principles of Connections Between Selectors and Control Switches.

correctors on the junction lines between ex­ cable 94 km in length and with SO-cycle A.C. changes, even if these be of considerable dialling), has been in satisfactory operation for length. In the Lille network, for example, six years without any impulse corrector. the impulses pass up to five exchanges (20 km The use, for free selection, of a selector with of line) without repeaters and without attaining uni-directional movement, eliminates the dis­ the limit of operation. The automatic Casa­ advantage of the distribution of lines by levels blanca - Rabat connection, enabling a sub­ and makes it possible to arrange the groups of scriber of one sub-exchange of the Casablanca lines following on one another, whilst varying central exchange to call a subscriber of the their number and importance. It follows that a Rabat sub-exchange (linked by underground low traffic direction (towards a small capacity

www.americanradiohistory.com 352 ELECTRICAL COMMUNICATION sub-exchange, for example), may have available necessity of translating the called subscribers' only four or five lines on the selector bank, whilst numbers. a heavy traffic direction (towards In practice, arrangement in variable groups groups or public exchange) may be servedP.B. X.by has proved of great advantage in numerous groups of 20 or 30 lines. Similarly, a central cases, notably : exchange of 2 000 lines capacity may be (a) In networks with several central equipped with first selectors having access by exchanges, where it has been possible to 20 groups of lines to the final selectors, thus decrease the number of junction lines eliminating one selection stage without the between exchanges without recourse to any additional device (such as secondary line switches) or to avoid increasing the capacity of the selector bank (see Fig. 4, which represents the grouping of the lines on the first selector bank in the Roubaix exchange) ; (b) In sub- ex- changes, where a single selector is used to reach the central ex­ change, neigh­ bouring sub­ exchanges and local subscriber groups (see Fig. 5, which re­ presents the grouping of lines on the selector bank rn the " Villers " sub­ e x chan g e at Deauville). Finally, due to sim­ plification of the com­ ponents as a result of their specialized appli­ cation to each of the two functions of the selector, and also to the

Fig . 11-P.A.B.X. Unit Typ e 49-D. very delicate operations which the control switches are capable of

www.americanradiohistory.com R-6 AUTOMATIC SYSTEM 353

Fig. 12-P.A.B.X. Installation in the R-6 System.

Fig . 13-R-6 Automatic Telephone Exchange, La Baute-First Line-finders and Connectors Bays .

www.americanradiohistory.com 354 ELECTRICAL COMMUNICATION

finds the free first selector 8 associated with a disengaged control switch CC8. When this double finding has been completed, the calling subscriber is connected to the first selector 8 and receives the audible dialling tone. The sending of the first digit by means of the calling dial operates the switch CC8, which is advanced by a number of steps equal to the number sent (3, for example). The brushes of the selector 8, as will shortly be described, are directed to the first line of the called group (that is, a group of lines connected to the final selectors of the third hundred) ; and then, in this group, to a dis­ engaged final selector CN, associated with a free control circuit CCN. The calling subscriber is then connected to the final selector. The tens digit (2 for example), which is received on switch D, and the units digit (8 for example), which is received on switch are successively transmitted. The switch U,directs the brushes of the final selector CN to Dthe first line of the second tens digit, and the switch then directs them to the eighth unit of the Usecond tens digit, that is, to the dialled line 328. If the desired subscriber has several lines (as Fig. 14-R-6 Automatic Telephone Exchange-La indicated on the final selector CR) the finding Baule-Registers and First Selectors. of a free line is automatically effected by the performing, low maintenance expenditure and high grade service should be expected from the R-6 system. Experience has confirmed these ant1c1pations. In exchanges which have been in operation seven, eight and nine years and which have been maintained by a small staff, the percentages of faults vary from 0.1 % to 0.15%.

METHOD OF OPERATION AND CIRCUIT DESCRIPTION MEDITERRANEAN I The general arrangement of the components and their interconnection is shown in Fig. 6 for the simple case of an exchange capable of MANDE.LIEU dealing with 1 000 subscribers. LA NAPOULE THEOULE

The operation of an installation of this kind MtRAM.G..R is as follows :

The calling subscriber lifts his receiver LECi, END SCALE IZI CiROUP CENTRES. (PDR) and thereby places a calling-line finder o OTHE� 0 I Z 3 � Skm A in operation through the medium of the Fig . IS-Automatic Regional Network of the Cote calling relay RA. Simultaneously, the finder d'Azur. of the selector 8, associated with the finder A,

www.americanradiohistory.com R-6 AUTOMATIC SYSTEM 355

final selector, the brushes of which continue to rotate until they come to a disengaged line. It will be noted that the number of lines grouped ONESSE under the same numeral is restricted only by the capacityof the selector and not by level limita­ tions as in the case of selectors with contacts arranged by levels. For simplification, the switches D and have been shown separately ; in practice, however,U a single switch receives the tens and units digit impulses. The arrival of the final selector on the tens group of the lines (in which the wanted line is included) is effected in the interval of SCALE reception of the two digits. � 4 5 �km A circuit schematic of an R-6 selector 1s Fig . 16-Private Telephone Network of the " Societe indicated in Fig. 7. In general, it functions as des Transports en Commun de la Region Parisienne " with follows : Automatic R-6 Registers. When the selector is engaged for the establish­ ment of comm unication, " earth " potential is placed on the wire T of the engaged selector brushes of the selector. Relay A supplies and also on the wires T of the momentarily current to one of the windings of the low occupied selectors associated with the same resistance, differentially wound relay B, which is control switch (the point t being common to all normally energized. If the test potential is the associated selectors). The relay C is suitable and if two selectors do not arrive at energized and the current impulses produced by the same time on the same line, the currents the dial operate the relay which, in turn, acts in the two windings of relay B neutralize each on the electro-magnet R ofI the control switch. other. The relay B then releases its armature This latter advances the brushes and /2 by a and through its contact b causes the operation f 1 number of contacts equal to that of the impulses of the connecting relay H. The latter establishes received by the relay ; that is, equal to the the connection of the selector in question to the digits sent by the dial. As soon as the brushes called line, earths its test wire and opens the and/2 have left their rest position, the electro­ circuit of the relay C, which, in turn, disconnects f 1 magnet of the selector operates ; its movement the selector from the control switch. The latter S is controlled by the contact e which opens under thus becomes available for other calls, as do also the action of the relay when the brush FC the other associated selectors. makes a contact connectedE with the brush As will have been seen, it is through the brush f 1 to the relay ; that is, when the brushes of the and the contacts which it explores that the selector reachE the first line of the group marked FCorientation of the selector brushes takes place. by the control switch. Hence, by the grouping of these contacts, During the reception of the current impulses, arrangements on the selector bank can be the slow acting relay D remains in the operated obtained of groups of lines which are variable pos1t1on. When all the impulses have been in number and importance. received the relay D releases, and another Figs. 8, 9 and illustrate examples of the circuit operating the brushes of the selectors connection between10 the control switch and the is closed by the contact d and controlled by selector. the contact a, dependent on the test relay A. Fig. 8 shows a selector with ten equal groups The test brush FT of the selector explores the of lines and two sets of brushes ; one series group of lines required and when a free line is explores the groups of even lines and the other, found in this group (a line characterized by a the groups of odd lines. It should be noted that, " battery " potential on the wire T), the relay A in systems with direct control, the necessity of is energized and stops the movement of the obtaining an orientation of the selector before

www.americanradiohistory.com 356 ELECTRICAL COMMUNICATION beginning the succeeding operation of the dial are illustrated in Figs. 11 to 14 inclusive. means that, as a rule, two sets of brushes must be arranged on each selector with a view to R-6 REGISTER SYSTEM reducing the time of selection by half. From the above it is seen that the selector Fig. 9 1epresents a selector serving only three impulses are received on rotating low inertia groups of lines of different importance, and switches, which operate reliably even when the utilizing one or more sets of brushes. The impulses are much distorted. If the sole selection of a free line in the latter case takes purpose of registers were to transmit perfectly place on several lines simultaneously. correct impulses to the selectors, it would Fig. 10 illustrates a final selector with two be unneccessary to provide such devices in sets of brushes : one for even tens, the other for R-6 exchanges. Actually, in numerous cases odd tens. registers have not been included in the R-6 Equipment and installations of the R-6 system exchanges.

:,THHWEl'!CK

DUNKERQUE /+· +•+;c;'f---::='.':--:--�::::;:;::;::�� .

· · ...... + + . + ...... • . .� . +++•. .

...

SCALE

NODAL REGIONAL CENTRE. AUTOMATIC CENTRE: UR:BAN AUTOMATIC SATELLITE URBAN 0 INTE.RME.DIATE CENTRE RCGIONAL .. F"INAL REGIONAL CENT E. R 0 WITH OIALLl�G TRUNl<5 A.C. --- TRU NK'S WITH O.C. DIALLING --II- SE.Ml- AUTOMATIC U A R R L C.E.NTR:E. A

Fig. 17-Lille-Roubaix- Tourcoing Telephone Network.

www.americanradiohistory.com R-6 AUTOMATIC SYSTEM 357

As a result of the tendency to group in compnsmg a different number of digits-when increasingly extensive networks large numbers of associated with the additional possibilities exchanges, between which interconnections and afforded by the registers-provides great tariffarrangements are becoming more and more flexibility in the disposition of the selecting CJmplex, C.T.T.-H. engineers envisaged the stages and junction lines between exchanges. application of registers when the R-6 system was These advantages have led to the utilization originally developed. of registers in the majority of public networks Study of this subject has shown that, far from which have been installed since 1930. The very imposing any complication, the introduction complex network of the Cote d'Azur (Fig. 15) of registers in the R-6 system permits simplifica­ may be cited as an example. Despite its extent, tions of selectors and, in many cases, results in the calling numbers contain only 5 digits. nppreciable economy. Mention may also be made of the Lille-Roubaix­ It is interesting to note that, in a register Tourcoing network (Fig. 17). system, the time factor does not operate as In certain very large private installations the rigorously as in a direct control system. In the use of registers has been found especially latter case, the orientation period of a selector advantageous. Fig. 16 illustrates the private should as a rule be proportional to the number automatic network of the " Societe des Trans­ of impulses received, and selection should be ports en Commun de la Region Parisienne," sufficiently rapid to be completed before the comprising 30 R-6 automatic exchanges with sending of the following digit. capacities varying from 15 to 300 stations and In the R-6 register system these two restric­ extending over Paris and its suburbs. The same tions do not apply. It, therefore, becomes 4-digit calling numbers are used regardless of possible to employ selectors without a fixed the point of origin of a call. normal or home position and with only a single set of brushes. (In the R-6 direct control CONCLUSION system, the selectors, in general, should include several sets of brushes, functioning from a fixed Due to space limitations, the varied and normal or home position.) The introduction numerous applications of the R-6 system cannot of registers thus evidently makes it practicable be described. They embrace large urban considerably to simplify the selectors and the exchanges, extensive regional networks, rural associated control switches. exchanges, and long distance automatic inter­ Moreover, the facility of directing R-6 connections including P.A.B.X.'s. In every selectors to the same group of lines by case, the R-6 system has provided a simple numerically different combinations, and to solution to the increasingly complex problems other groups of lines by numerical combinations daily confronting communication engineers.

www.americanradiohistory.com J a1nes Lawrence McQuarrie

1867-1939

AMES LAWRENCE McQUARRIE, -who graph Corporation, appointed Chief Engineer advanced to the top of the technical phase and later General Technical Director. In this J of the telephone business in a career of position from 1926-1932 he supervised the fifty years, died on March 1st at Vineyard Haven, organizing of new research and development Massachusetts, at the age of 71. Mr. McQuarrie activities in Europe and established the technical was Vice-President and General Technical standards of I. T. T. manufacturing com­ Director of the International Telephone and panies and telephone& operating systems in many Telegraph Corporation and of International countries. Standard Electric Corporation when he retired He spent considerable time in Japan and for from active duty on July 1st, 1932, which was his very important part in the development of approximately his fiftieth anniversary in the telephony in Japan, he was awarded the Order telephone business. He had more than 100 of the Rising Sun by the Emperor. patents to his credit in the electrical field. He also covered many other parts of the Mr. McQuarrie started as a telephone world in his travels on behalf of telephone im­ operator at Bath, Maine, in 1882, with one of provement and wherever he went he won many the ancestor Bell System companies. He friends. He was a Fellow of the American demonstrated an outstanding aptitude for the Institute of Electrical Engineers, and was a technical end of the telephone business, and in great favourite in Bell System and I. T. T. 1894 the Western Electric Company engaged circles in the United States. His popularity& in him to work on common battery switchboard Europe is well known, and he had the affection de-v·elopment. He contributed substantially to as well as the respect of telephone leaders in the development and design of the common many countries. battery manual multiple switchboard and was At a meeting of the Board of Directors of the appointed Assistant Chief Engineer of the International Standard Electric Corporation, Western Electric Company in 1903. It is held on March 23rd, 1939, the following interesting to note that while with the Western resolution was passed : Electric Company Mr. McQuarrie had much That the Directors of this to do with the development of the automatic International" RESOLVED, Standard Electric Corporation central office switching system (panel type) adopt as their own the aboYe statement read which replaced the common battery manual by their Chairman outlining the career of system in many exchanges of the Bell System. their friend Mr. McQuarrie and that they As a result of outstanding successes in the record their deep sorrow for the death of one telephone development field in Europe and the whose great technical knowledge, wise business Far East, Mr. McQuarrie was appointed Chief judgment together with his upright character Engineer of the International Western Electric and keen sense of humour won for him the Company on January 1st, 1925, ar:d when the admiration and affection of his many friends properties of International Western Electric and associates to whom he has long been were purchased by International Telephone known as the 'Chief,' and they direct that a and Telegraph Corporation in October 1925, copy of these minutes be engrossed and and the International Standard Electric was handed to Mrs. McQuarrie as a mark of their organized, Mr. McQuarrie was elected a Vice­ affectionfor her husband and their sorrow for President of International Telephone and Tele- his passing."

358

www.americanradiohistory.com James Lawrence McQuarrie-An Appreciation

By F. B. JEWETT

LL of us have experienced the shock of intimately associated in a common undertaking finding our first judgment of men and while in later years our paths diverged some­ wrong. Sometimes those whom we what, the feeling of trust and security in his have rated highly on initial association have counsel and advice never altered. turned out to have feet of clay or only a polished His was a life grounded in inherent ability veneer masking an absence of ability. Some­ and high character schooled in the austerity and times those who have made a poor impression kindliness which is the hallmark of all that is disclose later and on closer acquaintanceship best in the tradition of New England. With hidden abilities and sterling traits of character. such qualities it is small wonder that he com­ Occasionally our first appraisal turns out to manded the loyal support of his associates, and be a correct one. When it has been an adverse this without any conscious effort on his part to one the thing is usually a mere incident of life, command. He did not know how to do a although sometimes fate decrees a long associa­ dishonourable thing. tion which is a continual tribulation. On rare Nor were his qualities and his influence con­ occasions, however, this first appraisal of ability fined to the sector of his professional and and character is both favourable and correct, business life. For many years now I have and in making it you have achieved one of the known him in his island home at Vineyard great satisfactions of life-the discovery of a Haven, Martha's Vineyard. To one raised in a dependable friend and associate. shipbuilding family on the coast of Maine in In my relations with James L. McQuarrie I the heyday of sailing ships it was foreordained had one of these rare satisfactions. that he should seek a seafaring community, When I firstmet him thirty-five years ago he first for vacations and later as a permanent had already made an international reputation abode in well-earned retirement. He knew and for creative ability in the telephone field despite loved those who had salt on their clothes-they the fact that he was still a comparatively young instinctively knew and valued his qualities as man. I shall never forget the impression which no others could. I suppose they took pleasure that first meeting made on me. It was the im­ in the credit for achievements in the busy places pression of an extraordinarily able and entirely of the world which he brought to his adopted honest man ; of a kindly thoughtful human island home. What they valued most, however, being who stated his beliefs modestly without was the simple sincerity of the man who, without bombast and maintained them against attack effort or any trace of affectation, fitted into the without rancour. It was an impression which daily life of the community. neither time nor circumstance has caused me In his death Vineyard Haven has lost one of to alter. its substantial citizens ; the world of electrical From the day of that first meeting until the communication one of its distinguished men ; day of his death I have cherished him as one of his family a beloved husband and father, and my close friends. For much of the time we were many of us a never-to-be-replaced friend.

359

www.americanradiohistory.com The Bucharest-Ploesti Toll Cable By A. C. NANO, Toll Lines and Transmission Engineer, Societatea Anonima Romana de Telefoane, Bucharest, Rumania

N December, 1938, the Societatea Anonima (a) Necessity for providing immediately Romana de Telefoane, a subsidiary of the general long-distance relief over nearly I International Telephone and Telegraph Cor­ the whole country ; poration and the holder of the concession for (b) Uncertainties regarding the possible operating the Rumanian telephone system, took long-distance demand during and follow­ the first step toward transferring its extensive ing the general conversion of the local long-distance service telephone net- Ill the work from open- INTERNAL OUTGO ING maJo r wire to under­ TOLL CALLS INTERNATIONAL TOLL CALLS cities to 200 8 auto ground cable. / - The firstsection matic ; 160 / of cable, which 7 (c) Advent has been in­ I I of the tJ) ti stalled, extends I 160 I new ear­ tJ) from Bucharest � 6 ::>� ner -on - :l I 0 I J: ::E / northward to I 1- cable art. , l40 I Ploesti, the �J 5 / / tJ) I An immed­ J < ..J u < iate cable pro­ junction point I u ... of the maJor 4 I � 120 v gramme cover­ z •· long- distance � z I ing the whole ead s serving I country was im - I 100 I 1the north-east 3 / practicable be­ and the north- cause of th� 0 :z west portions of 1931 1932 1933 1934 1935 1936 1937 1931 1932 1933 1934 1935 1936 1937 extent of the YEAR Rumania. As YEAR territories in­ explained later, Fig. I-Rumanian Toll Traffic Growth. volved (some this cable will 316 000 sq. km be extended to containing 1308 Brasov and to Buzau in 1939 and, eventually, telephone offices). On the other hand, by other open-wire routes probably will be replaced applying open-wire carrier systems to ex1stmg by cables. lines and by constructing new open-wire lines It has been possible, in the past, to care for specially transposed for complete carrier work­ the rapidly growing Rumanian long-distance ing, it was possible to obtain a large number telephone development by building open-wire of new circuits with minimum delay and to leads of modern construction with single- and distribute them over the whole country. three-channel "Standard" carrier systems super­ Simultaneously with these improvements on imposed. The use of open-wire and carrier to the long-distance lines, a programme of care for the initial growth of long-distance modernization was carried out in the local areas. demand in Rumania was dictated by numerous Experience in Rumania, as in many European economic and practical considerations, foremost and other countries, soon proved that a latent among which were : demand for telephone service existed and could 360

www.americanradiohistory.com BUCHAREST-PLOESTI TOLL CABLE 361 be developed by the prov1s10n of modern make possible the preparation of a logical cable facilities. The long-distance traffic demand, in programme. Carrier-on-cable, especially the fact, as indicated in Fig. 1, grew so rapidly that 12-channel type of system, moreover, had been accurate forecasts of future requirements became considerably clarified both as to its technical extremely difficult. A year or two after the and economic features. The extensive recon­ telephone system was taken over by the struction work done on these routes up to 1934, Societatea Anonima Romana de Telefoane, it furthermore, made it practicable to apply still became apparent, nevertheless, that a cable more carrier to the open-wire circuits and thus would shortly prove the most logical and postpone major reconstruction work until 1938- economical means of providing the necessary 1939, at the end of which period the newer circuits over the main route north from crystal filter 12-channel type system with its Bucharest to Ploesti and from thence to points broader band and improved performance was north-west and north-east, as indicated in Fig. 2. expected to be ready. All general open-wire By 1934 the necessity for placing cable over construction on these routes, except that the above-mentioned routes in the immediate incidental to the application of the carrier future was clearly evident ; and, from traffic necessary to cater for the 1935-1938 traffic statistics obtained and commercial surveys made growth, therefore, was cancelled and cables during the four years the company had been engineered for installation during 1938 and operating the telephone system, sufficiently 1939 in accordance with Fig. 2. accurate information had become available to Joint studies carried out by the Societatea

4. 1 � ,.

.... / ' 0 ! i <-

, .:;, f '

· Conslmlja Ir/

Jill -- O.W. Lead_

= Cable l9381'rogram

""""""' Calilel939 Program

Fig. 2-Rumanian Telephone Network.

www.americanradiohistory.com 362 ELECTRICAL COMMUNICATION

BUCURESTI SNAGOV PLOESTI CAMPINA SINAIA BRASO\/

r---- 33·5 km �-t--- 26·3 km-----33·4km----->;�- 33·7km --i---- 41·0 km --

36 SYSTEMS) ( 3

48 { 4 SYS TE.MS\ INTERNATIONAL

( SYSTEMS INTER- RE�fONAL 84 7 l ANO TOLL ENO LINKS.

35 I I

10 6 14

1- ______lg______I_ ____ ------�� �

CABLE A S AR QUADS 7 T 1·3mm

CABLE B CABLE CABLE B -7 STAROUA051 ·3nmr-I- 7 STAR QUADS8 STAR QUADS 1·3mm - +34 0·9mm +J4 M.T. QUADS O·::lmm1·3mm -r--- +177 M.T. QUADS 0·9mm MT. QUADS

BUZAU

t------70·8km------!

INTERNATIONAL

____ �------Z-�----�f------1�.ptf------'-7,,_5 _14------� l-- INTER-REGIONAL ------�"3'<------TOLL ENO LINKS

--l>------'-- -·------1.... - -

= DENOTES 12 CHANNEL C.ARRIER CIRCUITS. ------�------V. F'. CIRCUITS CJR U1TS INTERMEDIATE STA 1·3m111 - POINTS AND/ORVF RESERVEDC TO F"OR FUTURE � 7 CiROWTH THROUGH <;ROUPS �A��:o: IN

--- DENOTES BROADCAST CIRCUIT.

CHANNEL REPEATER 12 TERMINAL . 12 REPEATER V.F

BROADCAST REPEATER (REVERSIBLE) Fig . 3-Circuit Allocation over the Bucharest-Ploesti-Brasov Route.

Anonima Romana de Telefoane and the Inter­ at Snagov, Ploesti, Campina and Sinaia national Standard Electric Corporation resulted (Figs. 2 and 3). Seven star quads of the cable design of Fig. which shows mm conductors were required for the in 3 1.3 the circuits required over the Bucharest­ " Go " and seven for the " Return " Ploesti-Brasov route. They may be divided direction, providing a total of 168 channels into two main groups : between Bucharest and Brasov. (I) Circuits from Bucharest to Brasov and (2) Circuits for relatively short-distance traffic beyond, including a group of international between the various points on the cable circuits, for which it was found that the route, or for circuits to towns connected most economical construction would be to these points over open-wire routes. For provided by 12-channel carrier systems on this group, two-wire 0.9 mm loaded cable non-loaded cable circuits, with carrier circuits employing the well-known terminals at Bucharest and Brasov, and multiple-twin construction were chosen as intermediate carrier frequency repeaters the most economical, two-wire repeaters

www.americanradiohistory.com BUCHAREST-PLOESTI TOLL CABLE 363

being planned at Bucharest, Ploesti, Sinaia and Brasov. It was decided to lay-up the voice frequency two-wire quads around one of the groups of 7-star quads required for carrier working. Between Bucharest and Brasov there will therefore be two cables, one containing 7-star quads 1.3 mm, used exclusively for 12-channel carrier working, and the other comprising 7-star quads in

the centre with from one to three layers of 7 STARCA BLQUADSE: "/( 1· 3rnm. mm multiple twin quads around them. Over0.9 certain sections of the route, two similar cables might have been used, each containing 12-channel quads and voice frequency two-wire quads ; for example (between Bucharest and Ploesti), two cables each containing 7-star quads for carrier and 34 multiple twin quads for two­ wire voice frequency circuits. However, because of conditions existing at the time the cables were engineered, it appeared preferable, from a noise point of view, to use two different types of cables. Noise interference into the carrier circuits may arise from ringing or speech currents on the voice frequency circuits or from the power supply at the repeater stations ; also, where open-wire extensions are connected to the cable, the open-wire lines may pick up 7 STCABLEAR QUADS'S'. 1·3 11m carrier frequencynoise from various sources T 60 M.T. QUADS 0· 9mm. and transfer it via crosstalk paths to the Fig. 4-Target Diagrams of Cables. carrier circuits.

a: a: w w 1- � IL w IL jj 0 n. O A. w I- w I- IX SNAGOV . PLO BUCURESTI �a:i z a: ES Tl REPEATER AUXILIARY REPEATER - a: 2 MAIN REPEATER MAIN owo Owo STATION STAT ION a.-­ a.--1 STAT ION ' a: 1- a: 1- o a: u o a:u CABLE 0A' - wz w �:E ..J °'111 u t- � �o<{ �el1-1111!>----H-� u IX::>

wI- 5a )- � �W�lll{.... -4--�------f+ ---'--..::...---+t------+t---.....q------� �5�� ...,...__�------++------+t------+t---� 8 .---�------++------t-t------++----i'l"<� ------­ u N>g� " " CABLE 08" CABLE "S" CAElLE"S" e: CABLE B Fig. 5-Method of Transposing Cables.

www.americanradiohistory.com 364 ELECTRICAL COMMUNICA TION

Trenching with Tractor-drawn Plough. Pulling-in the Two Armoured Cables.

Noise is, of course, only serious if it occurs at of transposing the carrier quads from one cable a point of low power level on the carrier to the other at the carrier repeater stations. circuits. By reserving one cable solely for This transposition, in addition to improving carrier working, and placing all the voice the noise conditions, as already mentioned, frequency circuits in the other cable, it is breaks the indirect crosstalk path which would possible to separate the low level ends of the otherwise exist from output to input of the carrier quads from the voice frequency quads. earner repeaters via the voice frequency This is accomplished by crossing over the quads. carrier quads from the composite to the simple The general design and lay-ups selected are cable, and vice versa, at the mid-point of the indicated in Fig. 3. An interesting feature of carrier repeater section, as shown in Fig. 5. the cable design is illustrated by the Sinaia­ From this figure it is clear that, where the Brasov section where, in order to realize the carrier and the voice frequency circuits are in practical advantages of locating the 12-channel the same cable, the former are at a high power repeater stations in ex1strng central office level. The schematic also indicates the method buildings, it was necessary to cater for an

Loading Coil Case in Position and Jointed. The Placing Loading Coil Case in Position. The loading joints are protected by cast iron protection boxes. The coil case contains 60 units (i.e., 120 side circuit and 60 smaller cable by-passing the loading coil case is the 7-star phantom coils) for loading the 60 voice frequency multiple quad carrier cable. twin quads. It weighs approximately 700 kg (14 cwt.).

www.americanradiohistory.com BUCHARE ST-PLOESTI TOLL CABLE 365 abnormally long repeater section by the pro­ vision of a lower capacity cable. After the first section of the cable from Bucharest to Ploesti was put into service in 1938, it was possible not only to meet all demands resulting from near-term traffic growth via this most heavily loaded route in Rumania but, also, by temporarily utilizing voice frequency circuits ultimately reserved for short­ haul circuits, to provide all circuits, both long­ haul and short-haul, required in this section. Moreover, the carrier terminals originally located in Bucharest were transferred to Ploesti, thus making possible the abandonment of all open­ wire lines in this section. A similar procedure will be adopted in the cases of the two later sections, i.e., Ploesti-Buzau and Ploesti­ Brasov, which will be installed in 1939. Jointing Work in Progress. Furthermore, during the early part of 1940, when the Bucharest-Brasov cable section will have been completed, 12-channel equipment use of a tractor-drawn plough. Where soil will be installed and all existing open-wire and free from obstructions was encountered, it carrier circuits will be transferred to the cable, was possible by ploughing over a length three thus making it possible to abandon all open­ or four times to obtain a trench 50 cm wide and wire leads over these sections and to utilize 50 to 70 cm deep with practically no hand elsewhere the open-wire carrier equipment digging, the only hand operations necessary involved in order to provide for growth in being the cleaning out of loose dirt and levelling long-distance traffic in other parts of the off the bottom. Both cables were pulled into country. the trench simultaneously, as shown in the The installation of the Bucharest-Ploesti (unnumbered) photographic reproductions, portion of the cable was started on June 15th, which give a rather good indication of the 1938, and was completed on November 1st of methods and equipment used during installation. that year. Installation was done by the Details of the electrical characteristics of the Societatea Anonima Romana de Telefoane under cable have not been included in this article the supervision of the International Standard inasmuch as the 12-channel circuits, which are Electric Corporat ion. The cables were of most interest, will not be placed in service armoured and laid directly in the earth except prior to the end of 1939. After their completion, where duct routes were available in the towns. it is planned to publish information on their An interesting feature of the trenching was the characteristics.

www.americanradiohistory.com Some Industrial Applications of Selenium Rectifiers

By S. V. C. SCRUBY and H. E. GIROZ,

Le Materiel Tetephonique, Paris, France

URING the past few years the previously published.* The purpose of the technical characteristics of selenium present article is to present supplementary D rectifiers have resulted in the develop­ information concerning high power equipment ment of numerous applications in various for industrial applications and, particularly, branches of industry and improvements in the to describe equipments with which sufficient construction of complete equipments incorporat­ experience has been gained to permit a certain ing rectifying elements. degree of standardisation. The major advantages of selenium rectifiers AUTOMOBILE BATTERY CHARGERS over earlier types of dry rectifiers are as follows : In so far as single battery rectifiers (for private customers or small garages) are concerned, the (1) High permissible working temperature power output required from the charging (up to 85° C.), equipment is relatively small. Consrderably (2) High current density (up to 180 larger outputs are required for garages where mA/cm2 with cooling fins), it is necessary to charge several batteries (3) High permissible reverse voltage (up to simultaneously either in series or in parallel. 15 volts D.C.), The power ratings adopted by Le Materiel (4) Contact pressure not critical, Telephonique for different models of this type (5) Small size and weight compared to of equipment, shown on the following table, power output, correspond approximately to the requirements (6) High efficiency. of the automobile industry :

The technique of these rectifying elements Tvpe : Volts Amps. Watts ------is now definitely established, although further Model 3005 (Junior) 6 3 18 progress doubtless will be achieved in the 12 1.5 (Tourist) 6 5 30 future. At present, attention is mainly directed 12 2.5 to research in connection with supply and (Small Garage) 6 10 60 12 5 regulation circuits, and to the improved design (Truck) 6/12 10 120 of complete rectifying units containing not only 24 5 (Large Garage) 6/12 20 240 the rectifying elements themselves, but also 18/24 10 supply transformers, inductances (with or without saturation windings), filters,control, and The description given herein is limited to that automatic protection devices, etc. of the model, "Large Garage," since the other The experience of recent years shows that the models may be considered as simplifications selenium element characteristics are particularly or reductions thereof. suitable for industrial uses involving heavy "The Selenium Rectifier, " currents, for example, in electro-plating applica­ * by Dr. Erich Kipphan, Elec­ trical Communication, July, 1937. "Dry Rectijiersfor Repeater tions, where several thousand amperes are Station Power Supply, " by H. Jacot and M. Frey, Electrical required. Communication, July, 1937. "Der Selen Trockengleich­ richter," by W. Hofer, Schweizerische Technischen Descriptions of various applications have been Zeitschrift, Vol. XII, No. 35/36, 1937. 366

www.americanradiohistory.com SELENIUM RECTIFIERS 367

The equipment and its circuit diagram are shown in Figs. 1 and 2, respectively. The rectifier consists of the two bridge-connected units which can be coupled, by means of a shifting fuse system, either in series (for 24 or 18-volt battery charging) or in parallel (for 12 or 6-volt battery charging). Two groups of elements are mounted on cooling finsand fixed on the frame of the mains transformer. A robust and compact block is thus obtained, suitable for wiring before the block is housed in the case. This unit is shown 3. in OnFig. the front panel are mounted an ammeter and a volt-meter, both of the moving coil type, a multi-position fuse (on the primary of the transformer) to permit choice of the correct mains supply tap, two automatic fuses (used also for 6/12-volt voltage shifting) and a mains switch in the primary circuit of the transformer. The transformer has high leakage in order to limit the short-circuit current to a value which can be safely carried by the transformer and elements during the time required for the operation of the protective fuse. It is to be noted that in the case of automobile battery charging rectifiers,there is the possibility + of polarity reversal when the connections are Fig. 2-Circuit of "Large Garage" Selenium Rectifier. made by a customer. It is necessary, therefore, to provide a protective device in the D.C. if the equipment be disconnected from the circuit, since in case of reversed polarity, even A.C. supply, the battery is short-circuited through the elements and both may be damaged. This protective device consists of two units readily adaptable to the rectifier spindles and provided with a resetting knob such that, once operated, the circuit remains open as long as this knob is not depressed. The heat control element is ordinarily a bi-metallic plate. CINE ARC RECTIFIERS With the advent of copper-plated carbons and automatic carbon feed in modern cine projector arcs, the applied voltage between carbons is notably lower than that required in earlier projector arcs fitted with ordinary carbons. Furthermore, with automatic feeding, arc stability requirements are less stringent. Cine arc rectifier output depends on the carbons used. The following table indicates the normal powers required for various carbon Fig. 1-" Large Garage " Selenium Rectifier. sizes :

www.americanradiohistory.com 368 ELECTRICAL COMMUNICA TION

elements. The three-phase rectifier, which is Negative Positive carbon diameter carbon diameter Output the type most commonly used, provides current sufficiently rectified to make further D.C. 5 mrn 6mm 30 to 40 amps. 6mm 7mm 40 to 50 amps. filtering unnecessary. This unit has an average 7mm Smm 50 to 65 amps. I efficiency of about 70%, compared with an efficiency of 55% to 60% normally achieved The voltage between carbons is almost with rotary converters. independent of the arc current and in fact Cine arc rectifiers must fulfil the three depends chiefly upon the distance between the following major requirements : carbons. (1) Safely carry the short-circuit current The distance having a fixed value, based on during the spark over which occurs when the best optical performance, the voltage the arc is struck ; between carbons is therefore practically fixed (2) Be as compact as possible in floor space at an average value of about 35 volts. Neverthe­ requirements inasmuch as they must be less, it is advantageous to provide an adjustment installed near the projector and inside a capable of supplying the arc with voltages cabin of small dimensions ; ranging from 30 to 40 volts. (3) Work in a high ambient temperature Since the best working conditions of mm reaching, in some cases, 45° C. selenium discs with cooling fins occur112 at Figs. 4 and 5 show, respectively, front and 15 amps. output per element, three standard rear views of a 3-phase, 35 volts, 60 amps. units have been made available, delivering rectifier for projector supply. Fig. 4 shows the 30, 45 or 60 amps. at 30 to 40 volts, and con­ control wheel of the main commutator which sisting, respectively, of 2, 3 or 4 standard 1s connected to the primary taps and provides adjustment of the arc current. The design of the equip­ ment has been much simplified by the provision of a combined switch-fuse. The use of switches or contactors on an apparatus which must be short­ circuited to be put in service would be rather unsafe. The ability of the selenium element to oper­ ate efficiently under temperature conditions which would be dangerous to other types of dry rectifiers makes it par­ ticularly suitable for the above application. In fact, artificial or fan cooling is not required. It is merely necessary to design the housing with special care. A narrow high shape is recommended, without any Fig . 3-Selenium Rectifier "Unit" for "Large Garage" Rectifier. side ventilation and with

www.americanradiohistory.com SELENIUM RECTIFIERS 369

large apertures provided at the top and the bottom. The rectifying elements are superimposed to per­ mit the use of a housing of minimum cross-section. Under such conditions it has been found that the working temperature of the rectifying elements is notably less than that obtained when all the elements are fitted in the same horizontal plane inside a casing of wide section and reduced height. The selenium rectifiers for projector arc supply, in fact, are the only dry rectifiers ensuring entirely safe service inside the projection cabin without the use of artificial ventilation, which is indispensable with other types of rectifiers. Moreover, from the standpoint of reduced floor space require­ ments, the narrow high shape is ideal.

ELECTRIC VEHICLE BATTER Y CHARGERS Battery requirements for electric vehicles vary according to the type of vehicle and type of battery employed. Commoner specifica­ tions are : For small electric trolleys, (a) batteries with 15 to 18 cells, to 230 amps. hr. 165 (b) For trucks, tractors, etc., batteries with 24 to 44 cells, 200 to 500 amps. hr. The above characteristics apply to Fig . 4-Selenium Rectifier for Projector Supply (Front View) . lead batteries. For "nickel-iron" batteries, the most usual characteristics are : provided with an automatic cut-out device which ) For small electric trolleys, batteries with automatically switches off the charger as soon as (a 24 to 30 cells, 165 to 225 amps. hr. charging is finished. ( b) For trucks, tractors, etc., batteries with Electric vehicles are usually equipped with 38 to 70 cells, 200 to 500 amps. hr. an ampere-hour-meter, the needle of which Consequently, rectifiers designed for electric rotates in one direction during the charge and in vehicles or truck battery charging must be the opposite direction during the discharge. capable of delivering about 30 to 100 amperes In order to allow for battery loss, a correction at 30 to 90 volts, approximately. is applied in the following manner : the meter standard charging equipments are needle operates a contact (closing or opening, All

www.americanradiohistory.com 370 ELECTRI CAL COMMUNICATION according to construction) which in turn correspond to parts fitted on the vehicle, i.e., actuates the automatic cut-out device, as battery, ampere-hour-meter and polarized plug. explained below, as soon as the battery has been The latter consists of two main plugs and, in charged up to a predetermined number of addition, an auxiliary low current plug for ampere-hours, equal to the amount delivered connection to the ampere-hour-meter auxiliary during normal service plus the battery loss. contact. A rectifier wiring diagram of this type is To start charging, the sequence is as follows : illustrated in Fig. 6, the ampere-hour-meter The rotary switch designated "Manual having a closing contact. The dotted lines Charge," "Stop," and "Automatic Charge" is placed in position 3 corresponding to "automatic charge." The plug con­ nected to the charging leads terminat- ing at the truck is inserted in the corresponding rectifier jack. Under these conditions, if the ampere­ hour-meter has a closing contact (i.e., at the end of the charge, the ampere-hour-meter closes a contact), the coil circuit of the end-charge relay (b) is opened at the beginning of the charge and its contact closed. Consequently, the locking coil of the main contactor is connected to the battery and the contactor is switched on. Further, as soon as the plug is inserted in the main supply jack, the main contactor ( c) closes and connects the rectifier to the A.C. mains and the battery. On the main contactor, a com­ plementary opening contact is pro­ vided and designed to insert, after locking, a current limiting resistance in series with the contactor locking coil. When the charging is finished (i.e., after the ampere-hour-meter indicates that the necessary quantity has been delivered to the battery), the closure contact of the meter operates ; the end-charge relay coil (b) is then operated, its contact opened, and the contactor locking coil circuit cut out. The contactor opens and stops the charge. If, instead of automatic charging, manual charging is desired, the rotary switch is placed in position 1 ("Manual Charge "). Under these Fig . 5-Selenium Rectifier for Proj ector Supply with Cover Removed (Rear View) . conditions, the insertion of the charge leads plug starts the charge. The

www.americanradiohistory.com SELENIUM RECTIFIERS 371 charging can be stopped at any moment by chokes (assuming a sinusoidal A.C. current, turning the rotary switch to position 2 ("Stop"), which 1s only approximately true), 1s an thereby operating the end-charge relay. ellipse. Electric vehicle battery chargers must be Fig. 8 illustrates the volt-ampere character­ designed so as to satisfy the requirements of istic of the whole rectifier : the battery maker. For a given battery, current Curve 1-is the elliptic volt-ampere character­ and voltage at the end ( 11 , U1) and at the istic of the system, transformer + regulating beginning U of the charge are known. chokes. The co-ordinates are the D.C. current ( l 2, 2) Thus, assuming that the volt-ampere character­ and voltage values corresponding to the second­ istic is a straight line between the two points ary A.C. current and voltage, i.e.; the curve 11, U1 and U the slope of this characteristic represents the characteristic which would be l 2, 2, is determined. Generally, the voltage drop obtained if there were no voltage drop in the in the elements is not sufficient to obtain the rectifying elements ; desired slope, so it is necessary to increase it Curve 2-gives the voltage drop in the by the addition of a substantial inductive drop elements ; obtained by the insertion of self-inductances Curve 3-is obtained by subtracting the between the transformer secondary winding corresponding ordinates of 1 and 2 and gives and the elements. The volt-ampere character­ the resultant characteristic, passing through the points 11, U1 and U istic of the system, transformer + regulating l 2, 2•

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+ "'!'.....------�------"![.------' Fig. 6-Circuit of Electric Vehicle Battery Charger.

www.americanradiohistory.com 372 ELECTRICAL COMMUNICATION

secondary windings. The rectifier elements are connected in the 3-phase bridge arrange­ ment. Cases are frequently encountered in practice where the ampere-hour-meter has an opening instead of a closing contact. The circuit in this case is identical to that above described, with the exception that the end-charge relay is normally under current during the charging period ; its release causes the main switch to operate and stop the charge.

ARC WELDING RECTIFIERS There is some analogy between the working conditions of these rectifiers and those for cine projector supply rectifiers, since both types are designed to feed an arc between two conducting electrodes. In both cases short-circuit operation (arc­ striking) must be considered as normal rather than accidental ; this condition, however, occurs much more frequently in arc-welding than in projector supply. It is necessary, therefore, to devise supply and regulation in a manner such that the ratio, short-circuit current/normal current, is as low as possible. To attain this result, the rectifier has a high potential drop, the + natural drop of potential of the elements being j Fig. 7-Rectifier Circuit for Floating Battery Supply . increased by the addition of a substantial inductive drop obtained either by the insertion In addition to the regulating chokes and to the of self-inductance on the A.C. side, or by the apparatus for automatic or manual charging, presence of high leakage coils inserted between the following are provided :

3 fuses on the primary side for protection in case of failure of the maximum current (overload) relay provided on the D.C. side ; I three-pole seven-position switch connected to three groups of 7 taps on primary phases. This switch allows the rectifier to work with seven different and parallel characteristics. The requirements of battery manu­ facturers who prefer a choice of several charging rates, rather than a fixed charging rate, is thus met · I maximum current relay connected i the D.C. circuit designed to open the main switch if r:the charging current should reach a value dangerous to the selenium elements. In particular, it protects these elements against a short-circuit due to accidental polarity reversal of the leads connecting the rectifierto the vehicle battery. This operation cannot be effected by the maximum current relay connected in the A.C. side · I resistance for the tapered charge. uring normal battery charging this resistance is short-circuitedD by means of a switch. In order to obtain a tapered charge, . the switch. 1s opened enabling the rectifier to charge the battery at a low rate. l, The primary is usually "star" and the Fig. 8-Volt-Ampere Characteristic of Arc Welding secondary "delta" connected. This arrange­ Rectifier. ment reduces the current intensity in the

www.americanradiohistory.com SELENIUM RECTIFIERS 373 the mams transformer pnmary and secondary windings. The theory of the regulating chokes has been explained above in connection with electric vehicle battery chargers. But due to the necessity of a low value of the ratio, short­ circuit-current/welding current, these regulating self-inductances are of higher value. The volt-ampere characteristic must satisfy the following conditions : ( 1) Starting voltage (no load) : 55 volts ; (2) Working voltage (welding load) : 25 volts ; (3) Short-circuit-current/maximum welding

current :-1 : 10 to 1 : 12. Various welding current control devices have been proposed such as : transformers with variable leakage, regulating chokes with taps connected to a commutator and regulating chokes with saturation windings. The maximum current output (from 50 to 320 amps.) of an arc welding rectifier depends on the size of the electrodes (diameters from 1 to 12 mm).

RECTIFIERS FOR TELEPHONE EXCHANGE SYSTEMS One of the essential features of this type of rectifier, designed either for operation with floatingbattery or for direct supply, is the provi­ sion of a regulation device with saturation winding coils provided principally in order to give the rectifier a compound characteri stic. II

(a) Installation with Floating Battery These equipments must meet the follow­ ing conditions : under normal operation, the + rectifier must carry the major part of the load Fig. 9-RectifierCircuit for Direct Supply to Telephone required by the external circuit and provide Equipment. an additional small current (maintenance current) for continuously maintainingthe battery on floating charge. In case of main power with a filter designed to reduce the A.C. supply failure when the battery is called on to component in the output to the required carry the load, the rectifier must be capable of value. progressively restoring the battery to its initial Figs. 7 and 9 show the circuit diagrams for state of full charge after the power supply is the two types of telephone supply systems re-established. mentioned. The chief difficulty with regulating systems (b) Installation fo r Direct Supply using saturation coils lies in the fact that stable The circuit of such an equipment is different operation can be obtained only if the mains from that indicated above, in that it is provided power supply is sufficiently constant. Assuming

www.americanradiohistory.com 374 ELECTRICAL COMMUNICATION

the saturation winding Ls' in parallel with 1 the external circuit ; the current in this coil is l.a1 Ls ' LaJ controlled by means of a quick acting regulator Re, influenced by the rectified voltage. The compound coils Le1, Le 2 and Le 3 are used to maintain the rectified voltage constant in terms of the load, in accordance with the usual method already described. The pre-loading coils La1, La 2 and La3 enable the load variation compensa­ tion initiated by the com­ pound coils to be com­ Lf' II Re pleted, and also provide compensation for power supply voltage variation. ' This compensation is '

______._ J effected in the following manner : Assuming that the mains .B + voltage tends to increase, 13- Fig. IO-Schematic of Rectifier "Superregulation" Circuit. there results a rectified D.C. voltage increase, which must be kept at a minimum. The increase of that the mains power supply increases, the the rectified D.C. voltage actuates the regulator rectified voltage tends to rise, thereby causing Re, decreasing its variable resistance, the the output to increase. Further, any enlarged regulator being connected in series with the output, by increasing the compound coil saturation winding Ls' of the pre-loading coils. saturation, tends also to increase the alternating Under these conditions, the pre-loading coil voltage applied to the rectifier. In other words, saturation current increases and the current, the operation is unstable owing to mains voltage for the major part wattless, absorbed by these variations. coils, also increases. The term "superregulation" has been applied Since this current flows through the to devices designed to maintain at a constant compound coils, there is an increase in potential value the rectifier D.C. voltage, not only for drop in these coils compensating for the mains any load, but also for large mains supply voltage voltage increase and tending to maintain vanat10ns. The function of such a device will constant the voltage applied to the primary of be understood by reference to the circuit the rectifier supply transformer. schematic of Fig. 10, applying to three-phase operation. CONCLUSION Referring to the circuit, Le1, Le2 and Le3 are From the favourable reception accorded these the compound coils, the saturation winding Ls higher power selenium rectifiers in the field, being in series with the external circuit. La1, rapid development of additional industrial La 2 and La3 are termed pre-loading coils with applications may be confidently expected.

www.americanradiohistory.com A Long Distance Automatic Teleprinter Exchange with Manual Priority Services

London & North Eastern Railway Teleprinter Network

By G. A. M. HYDE, B.A., Standard Telephones and Cables, Limited, London, England

INTRODUCTION automatic system at Liverpool Street. The auto­ N automatic Teleprinter System matic network is connected to the point-to-point offeringunique facilities, designed and network by an extension to York, which is the manufactured by Standard Telephones Headquarters of the point-to-point system. and Cables, Limited, is now being installed Messages may, therefore, be exchanged between on the London North Eastern Railway, at the two areas via York Station. Liverpool Street Stat& ion, London. The system is designed to interconnect stations in the REQUIREMENTS AFFECTING DESIGN Southern Area of the Railway's network. A The problems encountered at the outset were point-to-point teleprinter system has been in the very high traffic and the limited line plant operation in available. the Northern Railway com- Area for munication, some ti me fl moreover, 1s p a s t ; i t s made up of successful urgent and performance non -urgent e d to the traffic ; u r- 1 d e cis io n to gent traffic, provide an such as dan- a u to matic ger messages exchange for /) and train con- the Southern trolmessages, Area, inas- must always much as it have immed- was felt that 'ill\... i at e p r e- such an auto- � ference over matic ex- all other change would forms of speed up the traffic. Some service still means of further and trunk offer- e f f e c t 1 n g, ther e- economies in fore, had to operation. be i n cor- Fig . I-L.N.E.R. Teleprinter Network shewing Long The map Distance Connections. porated in (Fig. l)shows the exchange the relation- to handle this ship of the exchange to the Railway's com- ty pe of traffic. While automatic schemes of munication network. The dotted lines are trunk offering were considered and are possible, those working on a point-to-point basis, and the it was felt that such a facility might be abused full lines represent stations connected to the by out-station operators. It was agreed, 375

www.americanradiohistory.com 376 ELECTRICAL COMMUNICATION

SUB. STAT ION L.IVE.QPOOL STl?E.ET E.XCHANGrE

AUTO TEL£X SE NO ER

PARTY L.INES SIN6LE. LJNE. /

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Fig . 2-Switching Scheme, Liver pool Street Teleprinter Exchange.

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a., N0 - tr Us ED !=OR �s.Ll�HT��6JNG-S PERMANE.NT tv\ARKIN� SIAS Fig . 3-Skeleton Connections for Switched-simp lex TN- Repeater-Liverpool Street Teleprinter Exchange. �Q���No �P�o:,�� J�f�cT

www.americanradiohistory.com AUTOMATIC TELEPRINTER EXCHANGE sn therefore, that all trunk offering of urgent messages should be carried out by a central supervisor who would have means for entering any existing communication. The system adopted ultimately may be compared with a Private Automatic Branch Telephone Exchange where local connections are obtained auto­ matically, and exchange traffic is handled by an attendant, the attendant having means of entering established automatic connections for the purpose of offering urgent calls. The line plant available for the initial installa­ Fig. 4-Dialling Unit. tion consisted of open wire earth return circuits, some of which were superposed on telephone channels. This required the development of line key associated with each subscriber. a switched-simplex repeater as repetition would Fig. 3 shows two elements of the repeating be required at Liverpool Street in order to keep circuit at the exchange when connected together. the overall distortion within reasonable limits. The orientation of the relays, when the circuit Switched-simplex operation was adopted be­ is the calling or called circuit, is performed by cause duplex operation was ruled out owing telephone switching relays associated with to the very large variation in line leakance. them. The system, as now designed, is capable of Subscribers may obtain direct access to one operation with li.ne insulation as low as 1 000 another by dialling the appropriate two-digit ohms. number. A group of teleprinters at Liverpool Owing to the very high traffic on all lines, it Street is required for the transmission and was decided to provide each extension on the reception of Liverpool Street traffic; this group system with a selector. The ultimate capacity is reached by dialling the single digit 9, the of the exchange is 80 lines, of which 34 are selector being arranged to hunt over the busy equipped initially. In order still further to machines and connect the calling party to the ease the busy hour peaks, arrangements are first free machine. included for reperforation and automatic re­ The supervisor at Liverpool Street is obtained transmission of messages from Liverpool Street. at all times by the transmission of a special signal from the teleprinter itself. This signal SWITCHING SCHEME is generated by a cam and springs driven by the Fig. 2 is a schematic of the switching scheme same mechanism as the "answer-back" device. at Liverpool Street. The party lines shown are Origination of the signal is accomplished by the arranged for selective calling and, when inter­ subscriber pressing a key on his dial box ; communicating with one another, the supervisor this trips the "answer-back" drum and switches at Liverpool Street may offerurgent connections over the line from the regular transmitting as in the case of single party circuits. contacts to the special supervisory springs. Subscribers' lines terminate at the exchange This special signal consists of two long spaces on a side-stable polarised relay. This relay of about 750 milliseconds each, separated by a repeats the impulses received from the line to short mark of 50 milliseconds, and concluded repeating relays associated with the line termina­ with a mark. It is, in fact, the signal used for tion and selector circuit. These repeating relays release repeated after 50 milliseconds. As this form a complete switched-simplex repeater signal may be used to call in the supervisor when connected through to a similar unit on the during a connection, special relays are provided wanted party's circuit. When not connected at the substation to erase it when received. through, they are used for dialling and for communication with the supervisor, who obtains OUTSTATION EQUIPMENT direct association with any line by means of a The equipment at an outstation (waystation)

www.americanradiohistory.com 378 ELECTRICAL COMMUNICATION

is illustrated by Figs. 4 to 6, inclusive, showing tion "UNOB" is printed on the calling party's a dialling unit and an apparatus rack containing machine. If the wanted party is free, the telex line relay and supervisory relays. The tele­ sender sends out the code required to trip the printer is started up automatically and is "answer-back" device on the distant party's stopped on receipt of the "clear" signal. In the machine, whereupon the number called is case of single line stations, the equipment is printed back on the calling party's machine as a decreased by the five telephone relaysotherwise check and indication that he has been connected required to count the pre-calling code required through. for selection. A machine of similar character has been used before for the generation of teleprinter signals ; AUTO TELEX SENDER but, in the present case, owing to the nature of Supervisory indications from the exchange, the lines and the absolute necessity of keeping such as "busy," "unobtainable," etc., are distortion to a minimum, special precautions generated by a special automatic telex sender. had to be taken in order that the telex sender If a subscriber dials a busy number, the word would transmit perfect signals. This result has "busy" is automatically printed back on his been achieved by the incorporation of a cleaning­ machine and his selector is re-set so that he may up device, a full description of which will be dial another party, should he so desire, without published later. first clearing the previous set-up. If the In addition to generating the teleprinter dialled number be unobtainable, the abbrevia- signals, the telex sender provides interrupted earth and timed im­ pulses for the operation of time delay alarms.

SUPERVISOR'S AND TESTING POSITION Fig. 7 shows a view of the supervisor's desk, which includes a test position to enable the speed and distortion of the remote teleprinters to be measured from Liverpool Street. Facilities are also pro­ vided, on the testing position, for checking the speed of the out­ station dials, and for making exhaustive rou­ tine tests on the auto­ matic equipment at Liverpool Street.

SUBSCRIBER TO SUBSCRIBER CONNECTION Connection between subscribers is effected by dialling the number Fig. 5-Apparatus Cabinet with Cover Open. of the wanted party.

www.americanradiohistory.com A U T 0 M A T I C T E L E P R I N T E R E X C H A N G E 379

No pre-dialling opera­ tion is required since, in this installation, each line has its own selector. If the wanted party is free , communication may commence as soon as his number has been automatically printed back on the calling party's machine. On originating a call, the red lamp on the dial box lights. On the in­ coming side, both the red and green lamps light in order to in­ dicate to the operators the type of call that has been set up. A centre- zero milliammeter is Fig . 6�Apparatus Cabinet, showing Accessibility of Components. incorporated in the dial box because of the type of operation, namely, switched-simplex, machine. The supervisor may then attract the and the fact that, if the line should become dis­ attention of the operator at the outstation by connected during communication, printing of pressing the bell key on the teleprinter, causing the home record would continue. The milli­ a buzzer in the dial box to operate until the ammeter, therefore, is provided as a visual in­ wanted party answers or the supervisor abandons dication of the line condition. the call. Operating instructions will provide for the originating subscriber transmitting the " Who CALLING IN OF SUPERVISOR are you " signal at the end of each message. On an established connection, either party This is desirable? as a check that the connected may call in the supervisor by pressing the teleprinter is still functioning correctly. OPK key on the dial box : the calling signal is sent out by the teleprinter and the calling SUBSCRIBER TO SUPERVISOR lamp flashes on the supervisor's position. The The subscriber calls the supervisor directly supervisor enters the connection by operating by pressing the OPK key on the dial box. This a line key associated with the calling lamp. starts up the teleprinter which sends out the In this condition he inserts a repeating relay in signal required for calling in the supervisor. series with the repeating relays associated with On the supervisor's position there is a "calling" the calling and called parties ; he may print and "engaged" lamp, together with a line key, simultaneously to both parties and he also associated with each subscriber. The calling receives a copy of a message transmitted by lamp will flash and the supervisor answers by either party. The supervisor, at his discretion, operating the line key and printing to the calling may withdraw from the connection. subscriber. Should the supervisor wish to communicate OFFERING OF URGENT CALLS with a subscriber, he operates the line key and Should a subscriber wish to send an urgent momentarily presses a calling key on the position message to an engaged party, he may call in the circuit : this sends out the code to trip the supervisor by operating the OPK key in the "answer back" drum on the wanted party's dial box. The supervisor, on ascertaining the

www.americanradiohistory.com 380 ELECTRICAL COMMUNICATION

requirements and at his discretion, may offer number is automatically printed back on the the call to the engaged party. He may do so by urgent calling party's machine as an indication operating the line key associated with the wanted that the circuit is available. party, whereupon he is connected in, and, at a suitable opportunity, may attract the attention REPERFORATORS AND AUTO SENDERS of both parties by operating the bell key. Facilities are provided on the exchange When the supervisor enters an established equipment for introducing a reperforator on a connection in this way, he does not mutilate the circuit adjacent to a "busy" subscriber. If this signals being transmitted. As simplex working subscriber be engaged when called by another is used, the supervisor, however, must await a party, the calling party's selector will automati­ suitable opportunity before transmitting as cally hunt on to a free reperforator and the word otherwise the communication in progress would "PERF" will be printed back on his machine. be interfered with. The supervisor then offers The calling party may then leave his message on the urgent call to the wanted party, who may the reperforator if he so desires. Subsequently, accept the new call immediately or ask the super­ the tape from the reperforator is passed through visor to wait until the existing communication an automatic sender. This automatic sender is concluded. is under the control of an operator at Liverpool In the first case, the supervisor may transfer Street, who may dial the sender on to any the wanted party to the urgent calling party by station desired, thus providing for the trans­ pressing the transfer key on his position circuit. mission of non-urgent routine messages from In the second case, he may leave the urgent Liverpool Street during the slack hours of the calling party "camped" on the wanted party's night. circuit, and the wanted party will be connected to the urgent calling party directly he releases PRINTING OF FALSE CHARACTERS from his existing connection. In this case the In teleprinter exchange systems where a long supervisor need not remain in circuit as the space signal is transmitted for supervisory switching is performed automatically. When the purposes, there is a possibility of false wanted party is connected to the calling party characters being printed on the connected in either of the above cases, the wanted party's teleprinters unless the teleprinter used is of a

Fig . 7-Supervisor's Desk with Test Position incorporated.

www.americanradiohistory.com AUTOMA TIC TELEPRINTER EXCHANGE 381 type in which five space signals stop subsequent character. Inasmuch as the printing of the release of the single revolution clutch. On the false character depends on the timing of the 7-A Creed teleprinter, used in the system mark signal in its relationship with the position described herein, the printing mechanism is not of the controlling cam in the teleprinter, the so arranged, and thus the transmission of the operation of a relay ensures that the mark signal release signal and the signal used for calling will not be fed to the teleprinter until the in the supervisor would, unless special pre­ teleprinter cam is in the "stop" position. cautions were taken, print false characters at Subsequent revolution of the clutch is prevented both ends of the circuit. and no character is printed. The Railway Administration considered this highly undesirable. An addition, therefore, was made to the Creed teleprinter and to the [The facilities and circuits incorporated in this substations circuit in order that the release and system will be described in greater detail in a supervising signals would not print a false subsequent article.]

SUEZ CANAL CABLE

This ioaded and armoured cable was supplied by Lignes TeUg_raphiques et Teliphoniques, France, . and Standard Telephones and Cables, Limited, London. It '.''as laid. alongside the Canal from Port Said to Suez, a distance of approximately 180 km, and was put into service in 1938.

www.americanradiohistory.com The Eiffel Tower Television Transmitter

By S. MALLEIN, lngenieur des Pastes et Telegraphes Charge du Service de la Television de l'Adminis tration Fran�aise des Pastes Telegraphes et Telephones

and

G. RABUTEAU, Le Materiel Telephonique, Paris, France

INTRODUCTION A building for housing the new equipment meet the requirements of modern was erected under the supervision of the P.T.T. television systems, the French Post Installation of the provisional equipment manu­ Office (P.T.T.), towards the end of factured by Le Materiel Telephonique was 1936, gave consideration to replacing the 10 kW started in July, 1937, and experimental trans­ equipment* used for broadcasting 180 line missions, with a 7.5 kW peak power and a television images by an equipment suitable 2 Mc/s bandwidth, were commenced m for transmitting images of high definition. September, 1937. During 1937, comparative tests of various The peak power was gradually raised to scanning systems were conducted, and an order in December, 1937. On April 8th, 1938, was placed with Le Materiel Telephonique for 25the kWtransmitter was inaugurated by the P.T.T.

Fig . I-Line and Image Signals as produced by the Studio Camera.

the realization of a 30 kW peak power television Minister, Mr. Lebas. A provisional antenna transmitter to be installed at the foot of the was used at the top of the Tower. Eiffel Tower. Regular transmissions, at 25 kW peak power, The programme adopted in March, 1937, for five days a week, were then started. The plans the erection of the new television station called for replacing the provisional by the final included an experimental period during which equipment, with a nominal power of 30 kW, the peak power of a temporary equipment towards the end of 1938. was to be progressively raised from 7.5 to Regular transmissions were discontinued dur­ 30 kW. ing December, 1938, to permit replacing the provisional equipment. During this period a "' In service since the latter part of 1935. temporary 1.5 kW peak power television trans- 382

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mitter, installed by Le Materiel Telephonique, was operated in the P.T.T. offices at Rue de Grenelle, Paris. The antenna used was installed at the top of a 70 metre mast supporting the antenna of the oldest French broadcasting (Paris P.T.T.) station. The new television transmitter has been in service since December 25th, 1938. Final adjustments were made during January and February, and official acceptance tests by the P.T.T. Commission were completed by March 15th, 1939. Studio and filmtransmissions are being made five days a week from the P. T. T. Studio at Rue de Grenelle, located 2.5 km from the trans­ mitter. The signals are conveyed to the transmitter by means of a coaxial cable and a terminal equipment furnished by Le Materiel Tel ephoni que.

RADIATED WA VE FORM The carrier frequency of the Eiffel Tower television transmitter is 46 Mc/s. The trans­ mitter radiates signals compnsmg both Fig. 3-Main Entrance to the Eiffel Tower Tele71ision sidebands, extending to 3 Mc/s each side of the Transmitter. carrier frequency.

The polarity of transmission is positive, frequency is comprised between 440 x 25 and i.e., a white image raises the transmitter power 455 x 25, i.e., 11 000 c/s and 11 375 c/s. to the peak value. The latter is actually 35 kW, The frame frequency is 50 per second, frame­ whilst the nominal peak power of the scanning being made from top to bottom of the transmitter is 30 kW. picture received. The French television standard, which is to The aspect ratio, i.e., the width versus height remain in force up to July, 1941, calls for 25 5 ratio of the image, is complete pictures per second, each picture 4 containing between 440 and 455 total lines. The line and frame synchronizing signals These lines are interlaced so that the frame and extend downwards so as to reduce the carrier flicker frequency is 50 per second. level to zero. The duration of the line syn­ The lines are scanned left to right when chronizing signal is 18% of the total scanning looking at the picture received. The line time of one line (a 2% tolerance is allowed). The shape of the ±frame synchronizing signals is not entirely specified in the French P.T.T.

RADIO standard. It is stated that suppression of the f"REQUENCY vision signals must occur during at least 15 EXCITERS MOOULATto lines per t image, i.e., about 7% of the scanning RA DIO FREQUENCY time of the complete image. MODULATION AMPLlflERS OUTPUT The maximum amplitude of the high fre­ quency signals capable of being radiated by the transmitter is taken as a reference level, i.e., 100%. Signals with an amplitude between 0 Fig. 2-Block Schematic of the Vision Transmitter. and 30% are used exclusively for synchroniza­ tion ; tolerances of 27% to 33% for the upper

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Fig . 4-The Transmitter Room of the Eiffel Tower Television Transmitter.

p;)rtion of the synchronizing pulses, and 5% for appreciably from those of the Compagnie the lower portion, are allowed. Signals of Fran\;'aise Thomson - Houston equipment. amplitude between 30% and 100% are used for During a period equivalent to 10 line impulses, the transmission of the vision signals proper. the signal amplitude is kept steady at 30%. Interlacing is performed by line impulses in­ VISION PICKUP EQUIPMENT stead of using impulses having a frequency Since the inauguration of the transmitter in twice that of the line as in the Marconi-E.M.I. April, 1938, an iconoscope and its associated wave form. equipment, supplied by Compagnie Frarn;aise The adoption of a common wave form for Thomson-Houston, has been used for the trans­ studio and film transmissions is under con­ mission of studio programmes. sideration by the French P.T.T. The equipment supplied by the Compagnie Frani;:aise Thomson-Houston, generally speak­ PRINCIPLE OF OPERATION OF THE VISION ing, is similar to that used in the London tele­ TRANSMITTER (FIG. 2) vision system and produces signals having the same wave form except that the number of lines The 46 Mc/s carrier frequency of the trans­ per image is 455 rather than 405 as in London. mitter is generated by a crystal-controlled master This wave form meets the requirements of the oscillator using screen grid valves. The master French P.T.T. television standard. Fig. is oscillator is followed a radio a reproduction of an oscillogram of the line 1and exciter delivering 5 kW driveby to the penultimatefrequency image signals produced by the Compagnie stage of the transmitter. The exciter units Franc,;aise Thomson-Houston equipment. employ triodes in push-pull. Film transmissions employ scanning equip­ The penultimate stage of the transmitter is ment furnished by "Radio Industrie." The wave an inverted amplifier working without balancing form of the signals produced by this equipment condensers and delivering a 20 kW drive into accords with the French standard, but the sig­ the transmitter output stage. The latter is of nals used for frame synchronization differ the inverted amplifiertype, also without balanc-

www.americanradiohistory.com EIFFEL TOWER TELEVISION TRANSMITTER 385 ing condensers-an essential feature for obtain­ formers and houses the compensating network ing the bandwidth required. used for flattening the antenna characteristic. The output stage is grid modulated from the The station is entirely A.C. operated. Rotat­ final stage of the modulator which is connected ing machinery is used only for the cooling directly to the grids of the output stage of the system. The filaments of the valves are either transmitter. The output stage of the modulator fed from raw A.C. (single or 3-phase) or from is arranged to maintain the modulation depth D.C. from an individual dry rectifier associated of the transmitter constant. with each stage. Grid bias and plate voltages The transmitter output is fed into a sym­ are obtained by means of dry rectifiers or from metrical output circuit. The latter is coupled hot cathode mercury vapour rectifiers. by two short lengths of coaxial line to a matching Provision. is made for the complete control transformer which adapts the impedance of the and monitoring of the wave form of the signals output circuit to that of the antenna feeder. at various points in the equipment, and also The antenna consists of eight vertical push­ for examining the incoming and the transmitted pull dipoles, each comprising two vertical, half­ images. wavelength frames. The radiating elements are equally spaced around the upper part of the TRANSMITTER BUILDING Eiffel Tower. The aerials are centre-fed from quarter-wave Fig. 3 shows a view of the main entrance to transmission line sections connected to four the Eiffel Tower television transmitter. The matching transformers projecting through the building houses the sound transmitter, the vision windows of the Tower beacon, which has been transmitter and the receiving end of the terminal dismantled to permit installation of the antenna equipment of the coaxial cable conveying the system. A junction box placed in the centre of vision signals from the studio. the Tower connects the coaxial cable coming The space available for the building was from the transmitter to the matching trans- greatly restricted due to the importance of not

MASTER OSCILLATOR

BUFFER !ST DOUBLER 2•0 DOUBLER STAGE

500 WAT TS 5 KW 20 KW FINAL STAGE AMPLIFIER AMPLIFIER AMPLIFIER 35 KW I I I I I I I I l I I I I iJ rnI I I I I I I I I I R4 I I I

FROM MODULATION RADIO FREQUENCY EXCITE.RS THE AMPLIFIER Fig . 5-Schematic of the Radio Frequency Amplifiers.

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lator includes a Y-cut crystal keeping the fre­ quency constant within 50 parts in a million. The fundamental fre±quency of the crystal is 3.83 Mc/s, but it operates on its third partial, i.e., it delivers directly a frequency of 11.5 Mc/s. The oscillator is followed by two doublers for raising the frequency to the carrier frequency of 46 Mc/s. A one-valve buffer-stage followed by a push­ pull amplifier increases the output power of the master oscillator to 50 watts. The next unit, designated as R.2, is a push­ pull amplifier with two air-cooled, type 3016-B, triodes, which deliver an output power of 500 watts. The drive from the master oscillator is applied on the grid of these two triodes by means of a parallel tuned circuit, balancing condensers being cross-connected between grid and plate of the two triodes. The output circuit

INPUT FROM PENULTIMATE AMPLIFIER

Fig. 6-View thro h the Window of the Pre-penultimate Radio�g Frequency Amplifier. \:.�

encroaching unduly on the gardens surrounding TO THE the Eiffel Tower. The vision transmitter and ANTENNA the terminal equipment occupy rooms of the following dimensions : A Television transmitter proper 120 sq. metres High tension room .. 20 " Water-cooling plant 30 " 20 Terminal and monitoring equipment " It will be evident that the space occupied is extremely small, particularly when it is con­ sidered that the vision transmitter equipment z z ' takes from the mains an input of 260 kVA. Equipment of unusually compact design was consequently necessary. Fig. 4 is a view of the vision transmitter room. B The high frequencyexciters and the modulation amplifier are on left and right, respectively. The control desk is in the centre. z z RADIO FREQUENCY UNITS

A schematic of the radio frequency portion c of the transmitter is shown in Fig. 5. The R.1 unit contains the master oscillator delivering an output power of 50 watts at Fig. 7-Fundamental Circuit of the Output Stage of the 46 Mc/s. The crystal-controlled master oscil- Vision Transmitter.

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is a parallel tuned circuit directly connected to the succeeding stage. The master oscillator and the first amplifier circuit employ air-cooled valves exclusively and include all necessary filament, grid bias and anode voltage supplies, obtained from dry rectifiers operating from 220-volt, 3-phase, SO-cycle mains. The following unit, the pre-penultimate stage of the transmitter, contains two water-cooled, type 3073-A valves connected in a push-pull circuit, similar to that of the preceding unit. Fig. 6 shows a view, through the window of the pre-penultimate unit, of the two water­ cooled triodes and of the balancing condensers surrounding the water jackets. These latter extend to the bottom of the bay and form the anode circuit of the unit. An adjustable short­ circuiting device is used for tuning the plate circuit. This unit, as well as the other units of

Fig. 9-Front View of the Output Stage (front panels removed) of the Vision Transmitter. the transmitter, is built in a standard steel cabinet. The penultimate amplifier also contains two water-cooled valves in push-pull. These are of the type 3081-A, a more powerful type than those in the pre-penultimate unit. In the penultimate amplifier the drive is applied to the filaments, rather than to the grids of the valves as in the preceding stages. The penultimate high frequency amplifier is coupled to the final stage of the vision trans­ mitter through two water-cooled resistances. This unusual method of coupling is due to the necessity of maintaining the load on the penultimate amplifier fairly constant over the band of modulation frequencies required, as well as to provide a sufficiently damped circuit in parallel with the input circuit of the final stage.

OUTPUT STAGE OF THE TRANSMITTER The output stage of the vision transmitter uses two water-cooled triodes, type 3084-A. Their characteristics are as follows : Fig. 8-Rear View of Output Stage (doors open) of the Filament voltage 3-phase A.C. Vision Transmitter. (between terminals). . 10.5 volts

www.americanradiohistory.com 388 ELECTRICAL COMMUNICATION

Filament current (per terminal) 123 amps. voltage at carrier or sideband frequencies applied Filament emission 18 amps. Amplification factor .. 25 between terminals 1 and 2 must not produce Slope .. 7.5 mA/V any voltage between terminals 3 and 4. Selec­ lVIaximum anode dissipation . . 30 kW Grid anode capacity .. 23.5 µ,t

VIS/01'1 TO THE /NP/IT-� OUTPUT STAGE

Vq; Fig . 10-Schematic of the Modulation Amplifiers. Vs

www.americanradiohistory.com EIFFEL TOWER TELEV ISION TRANSMITTER �9 mental bridge would not be negligible with upset the operation of the output stage at carrier respect to the wavelength. It would thus be and sideband frequencies if one were much difficult to maintain the balance of the bridge larger than the other. However, it has been over the whole of the sideband frequencies. found possible, by careful design of the filament, On the other hand, with a properly dimen­ grid and plate circuits, to make the resultant of sioned inverted am- these t w o e ff e c t s plifier, the reactions fairly constant over which result from the the band of frequen­ op era ti on of the cies required, and to valves tend to main­ utilize only a small tain the balance of amount of negative the fundamental cir­ feedback. This cuit of Fig. 7-C over renders the output the e n tire r a n g e stage perfectly stable of the sideband fre­ during modulation quencies. peaks, and also tends In the i n v e rte d to keep the harmonic amplifier, the grid­ distortion at a very filament portion of low value. the valves is com­ Neither a con- mon to both the in­ denser nor an in­ put and output ductance is connected circuits. Hence, directly between the electrons flowing be­ filaments, the circuit tween filaments and being tuned by means grids produce a vol­ of a condenser con­ tage in the filament nected at the end of circuit which opposes the q u a r t e r - w a v e the drive, i.e., a matching transformer negative feedback remote from the fila- is produced in oppo­ ments. sition to the drive. To balance the out­ As will be seen put stage, a capacity from Fig. 8, except is required between fora very small adjust­ the grid terminals of able condenser, no the valves. A con­ p ate condenser is Fig . 11-Back View of the Output Stage of the Modulator denser, if used, should used1 and nearly the (doors open). be capable of carry­ whole of the circu- ing the full plate lating current of the tank current, about plate circuit passes through the inter-elec­ 35 amps. RMS for 100% amplitude. For this trode grid-plate capacity of the valves and current, its overall dimensions and capacity to returns through the grid circuit. The grid­ earth necessarily would be rather large, repre­ to-grid impedance is adjusted to be equivalent senting an important load for the output stage to a positive reactance and the circulating plate of the modulation amplifier. To minimize the current, between the grids, produces a voltage capacity to earth of the grid circuit, an equivalent which adds to the effect of the drive ; in other network consisting of a quarter-wave transmission words, a positive feedback adds to the drive. line with its far end terminated by an adjustable These two reactions (negative feedback in the choke coil is used in place of a condenser. The filament circuit, and positive feedback due to mid-point of the inductance is connected to the the grid-to-grid inductance) would completely output stage of the modulation amplifier.

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pedance of the antenna feeder, i.e., 60 ohms, to that of the two coaxial lines to the transmitter, i.e., 175 ohms. This transformer can be con­ nected either to the outgoing feeder or to an artificial load for test purposes.

MODULATION AMPLIFIERS The modulation amplifier is illustrated schematically in Fig. 10. It is arranged to work from an input level, for white images, of 4 volts peak. The input impedance of the first amplifier is equal to the characteristic impedance of the coaxial cable feeding the vision signal into the modulation amplifier, i.e., 100 ohms. In the first two units of the modulation am­ plifier, air-cooled triodes are used ; the three last units contain water-cooled triodes, type 3053-A. The characteristics of the type 3053-A triode are as follows :

Filament voltage 19.5 volts Filament current 67 amps. Filament emission 7 amps. Amplification factor 6.5 Slope 7.8 mA/V Maximum anode dissipation . . 20 kW Grid anode capacity 40.5 µµF Anode filament capacity 3.5 Grid filament capacity .. 36.5 " Overall length .. 75 cm Maximum diameter 10.5 cm. The various valves used are operated as Class A resistance-capacity coupled amplifiers. Correction in the upper part of the video fre­ quency band is obtained by shunting the Fig. 12-0utline Sketch of Aerials : The sound antenna is cathode resistances, either wholly or partially, at the top of the flag pole ; the vision antenna surrounds the top part of the Tower a Jew metres below the bottom of the flag pole. REFL ECTION COEFFICIENT The output circuit is a parallel-tuned circuit 0.1 made with copper pipes of the same dimensions iI as the water jackets of the valves. The step­ 0.075 down ratio of the output circuit reduces the impedance to about 500 ohms. 0.05 The output circuit is connected through quarter wavelength transformers to the inner I 0.025 conductors of a pair of coaxial cables joining / the output stage to a junction box which term­ v inates the coaxial cable feeding the antenna. 0 2 3 Mc/s The junction box, placed on the roof of the transmitter building and about 15 metres away OFFCA RRIER Mc/.s from the output stage, consists of an adjustable FREQUENCY quarter-wave transformer matching the im- Fig . 13-Reflection Coefficient of the Vision Antenna.

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with correcting condensers, thus reducing the amount of negative feedback at the higher frequencies. The plate resistances in the low power stages are wound so as to be as non-inductive as possible. For the medium and high power stages, resistances of the mat type are used, wound on an asbestos support. As previously mentioned, the wave form of signals meeting French television standards is such that amplitudes below 30% are used ex­ clusively for synchronization, whilst amplitudes 300/o 100% missionbetween of the andvision signalsare proper.reserved for trans­ Another requirement of the French television standards calls for the amplitude of the high frequency signals radiated by the transmitter being less than 5% of the full amplitude during transmission of synchronization signals. To meet this condition with the various types of vision signals which might be obtained within the limits of the French television standard, it was found necessary to take as a reference the only factor common to all systems, i.e., sup­ pressions of the carrier during the transmission of the synchronization pulses. Consequently, the output stage of the modulation amplifier and Fig . 14-A Section of the Semi-flexible Coaxial Cable used the final stage of the transmitter were arranged to feed the Antenna. for invariable and complete modulation of the network opposes the detrimental effect of the transmitter during transmission of the syn­ rectifier impedance at low frequencies. chronization pulses. To permit the direct connection of the This constant depth of modulation is obtained modulation amplifier to the grids of the final (as also in broadcast transmitters operating on stage of the transmitter, the filament of the last the well-known " floating carrier " system) by modulation valve is insulated from earth and means of a diode connected between filament must withstand the full D.C. voltage of the and grid of the output valve in the modulation high tension rectifier, the positive terminal of amplifier(see Fig. 10). The circuit arrangement which is at earth potential. is such that the amplitude of the carrier of the Fig. 11 shows a rear view of the output stage transmitter is adjusted in terms of the vision of the modulation amplifier with doors open. signal to be transmitted. . At the upper part of the unit the filament and Suitable operation of the constant modulation plate resistances are supported by steati e ro�s. depth system is only possible if the output � . The lay-out of the unit is arranged to mimm1ze stages of the modulation amplifier and of the the capacity to earth of the various components. transmitter are directly coupled and arranged to The lower part of the bay contains porcelain pass correctly a frequency band e tending do:vn _x coils for the water-cooling of the valve. to zero. Since it is not possible to realize The operating conditions of the output stage rectifiers and associated smoothing circuits with of the modulation amplifier are as follows : an internal impedance sufficiently low for fre­ Plate impedance : 1 400 ohms, increasing to 2 600 ohms quencies down to zero, a special corre ting net­ for D.C. � . _ Plate current corresponding to white 1 amp . work is provided in the anode circmt of the : Plate current corresponding to the cut-off of the trans­ output stage of the modulation amplifier. This mitter : 2.85 amps.

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The filaments of the valves in the modulation ANTENNA SYSTEM amplifiers are D.C. fed from selenium rectifiers. Fig. 12 shows the disposition of the antenna The rectifier capacities to earth are kept to a at the top of the Eiffel Tower. The antenna minimum so as to reduce their effect on the consists of eight vertical push-pull dipoles, correcting condensers in parallel with the each formed by two vertical frames one-half cathode resistances. wavelength long. The aerials, as stated above, The control desk in the centre of the trans­ are centre fed by means of quarter-wave mitter room facilitates the operation of the transmission line sections connected to four equipment. It includes a meter panel for matching transformers projecting from the checking the high tension rectifier currents and antenna equalizer box through the windows voltages. of the Tower beacon. The distance of the In addition to the door contacts (providing eight antenna elements from the centre of electrical security), a mechanical interlocking the Tower is approximately one-half wave. system is used for preventing the doors of the To prevent an unbalancing effect due to the various cubicles from being opened unless the balcony at the top of the Tower, a screen of high tension busbars have been earthed. copper wires, equivalent to a conducting cylinder about one-half wave­ length in di a m ete r , covers the whole of the upper part of the struc­ ture. The coax i a cable coming fromthe 1bottom of the Tower ends in the antenna equalizer box, which is a cylinder one-half wave e n gth long. The cable1 from the transmitter is fed into the lower half of the box, whilst opposite it, projecting from the top of the box, is a q u arte r-w ave short­ circuited section of a coaxial line. The outer conductor of the cable from the transmitter is connected to the inner conductor of this compensating element, whilst the outer conductor of the com­ pensating e emen t is connected to1 the inner conductor of the coaxial cable from the trans­ mitter. The body of the box itself and the outer Fig. IS-Front View of the Monitoring Equipment. surface of the outer con­ ductor of the coaxial

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cable, as well as of the compensating section, also constitute quarter-wave short-circuited coaxial lines in parallel with the antenna. The characteristic impedance of these concentric lines is chosen so as to compensate the impedance variation of the antenna system over the range of frequencies required for the transmissions of the sidebands, and also to obtain a correct energy transfer into the antenna which, with respect to the frame of the Tower, is a symmetrical network, whilst the coaxial

Fig . 17-0ne of the Hot Cathode Mercury Vapour Rectifier Units supplying the High Tension to the Power Stages of the Transmitter.

the terminals of the matching transformers. Their characteristic impedance can be varied by inserting adjustable shields between con­ ductors. Fig. 13 shows the reflection coefficient of the antenna, i.e., the amplitude of the wave reflected into the cable feeding the antenna, due to mis­ matching of the antenna at the carrier or side­ band frequencies. Fig. 14 illustrates a section of the coaxial cable used to join the transmitter to the antenna. This cable, manufactured by the Allgemeine Elektricitlits-Gesellschaft, is of the semi-flexible type. Its characteristics are as follows :

Fig. 16-Jncoming Power Supply Cubicle. cable from the transmitter has its outer conductor grounded to the frame. The characteristic impedance of the four matching transformers (contained in the four arms extending from the antenna equalizer box through the windows of the upper part of the Tower), is adjustable by means of movable flanges fixed inside the arms. Outside the Tower, quarter-wave short­ circuited open wire lines are connected across Fig . 18-Water Cooling Plant.

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rectifiedoutgoing signal is obtained from a diode rectifier coupled to the antenna feeder, this detector being provided with two separate cathode-coupled output valves. A switching panel enables the incoming and outgoing signals to be applied to either of two cathode ray oscillographs or to either of two monitoring television receivers, thus providing means for comparing input and output wave forms at either line or frame frequency, or input and output images. Input potentiometers enable the level of both signals to be adjusted to the same value to facilitate comparison. Provision is made to modulate the transmitter with sine wave signals produced by a signal generator covering a frequency range from a few cycles up to 4 Mc/s. When using sine wave signals, switches on the monitoring cathode-ray oscillographs enable the modulation depth and the phase distortion of the transmitter to be measured directly by applying the input video frequency signal to the horizontal plates of the cathode ray tubes, and the modulated radio frequency signal or the Fig. 19-Power and Wa ter Control Board. detected radio f requency signal to the verti cal plates. Diameter of the inner conductor 28 mm Inner diameter of the outer con- POWER AND WATER EQUIPMENTS ductor 94 mm Spacing of insulators 304 mm Except for the pumps used in the water Outer diameter including armour- ing wires . . 128 mm circulation system no rotating machines are Weight 30.5 kg per m employed. The various power and water Characteristic impedance 60 ohms Attenuation at 40 Mc/s . . 0.36 db. per 100 m equipments are respectively assembled in two Attenuation at 50 Mc/s . . 0.42 db. pe r 100 m. separate rooms. The power room consists of The cable has been installed in six sections, concrete cubicles closed at the front by sliding each joined by elements similar to those doors, interlocked with earthed switches. Fig. constituting the cable. The total length of the 16 is a view of the incoming power supply cable between the transmitter and the antenna cubicle. The station is fed from 500-volt, is about 360 m which, for the carrier frequency 3-phase, SO-cycle mains. An induction regulator of 46 Mc/s, corresponds to an attenuation of controlled by a relay maintains the supply 1.41 db., i.e., an efficiency of 72%. voltage constant. The low power stages are fed by 220-volt, 3-phase A.C. through a step­ MONITORING EQUIPMENT down transformer. Filaments of the radio Extensive monitoring facilities are provided. frequency exciters and of the output stage are Fig. 15 shows the monitoring units, which are A.C. fed, using Scott-connected transformers installed in the same room as the terminal for the exciter valves and 3-phase A.C. for the equipment of the cable bringing the vision valves of the output stage of the transmitter. signals from the studio. The various valves of the modulation amplifiers The monitoring equipment receives incoming are fed by D.C. from individual dry rectifiers. and outgoing signals and also signals from a All the units using air-cooled valves include cathode-coupled valve picking up the signals their own high tension rectifiers, whilst all the at the output of the modulation amplifier. The units using water-cooled valves obtain their

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Two pumps, each capable of 600 litres per OJ f!S jJS 0, 1 minute flow, are used, one as a spare to the other. The water system is designed to handle fOO vs fOµs a 200 kW dissipation. Fig. 18 shows the water cooling plant. The incoming power supply and the water system are controlled from a Fig . 20-Square-wave Signal usedfor the Alignment of the Equipment. power and water control board (Fig. 19), whilst the various filament and high tension circuits are controlled from the control desk visible in high tension supplies from hot cathode mercury Fig. 4. vapour rectifiers. The several hot cathode mercury vapour rectifiers are enclosed in two ADJUSTMENT OF THE TRANSMITTER cubicles of the power room ; Fig. 17 shows a The adjustment of the modulation amplifiers view of the high tension rectifier of the output consists mainly in setting the correcting con­ stage of the modulation amplifier. Separate densers in parallel with the feedback resistances

LEVEL ABOVE: OR BEL OW JO KC/S LEVEL �:rn I I I I I I I I I I I I I I 1 i 2Utf.s SOCj.r IOOq/s 200C/s IKc/s 2Ktf's Stt('s IOKJ;ls 20Kr;/s SDKr;/s /OOKrf's 200.t'.o/s SlJDKq/s s\ SDOr;/,r !Mc/s 2M1/s SMcjs FPEQ UENCIES Fig. 21-0verall Frequency Response Curve of the Vision Transmitter. rectifiers are used for all units equipped with to their optimum value. With properly pro­ water-cooled valves in order to avoid undesir­ portioned components, this adjustment is able couplings. The hot cathode mercury relatively simple, but checking signals should vapour rectifiers are of the so-called tank type be available. in which the rectifier valves are mounted on Most of the alignment work was done with top of the transformer bushings, the trans­ the signal shown in Fig. 20. The most difficult former tank containing in addition to the problem connected with the modulation ampli­ high tension transformer, the filament trans­ fiers was the elimination of all irregularities formers and the smoothing choke coils. The resulting from the various high tension supplies, smoothing condensers are assembled above the wiring, cables and by-pass condensers. Any rectifier in concrete cubicles. Off-load taps spurious resonance up to 4 Mc/s must be and star-delta switches enable the output carefully avoided. It was, for example, neces­ voltage of the rectifiers to be varied while sary to terminate all lead-covered high tension testing the transmitter. Each hot cathode cables connecting the rectifier room to the mercury vapour rectifier has its individual con­ transmitter room by their characteristic tactor rack which, in addition to the contactors impedances. of the rectifier, contains the contactors control­ The determination of appropriate impedances ling the filaments of the water-cooled valves. Switching of the filament and of the high OVERALL TIME DELAY tension supplies is performed in two steps, the IN �ICRO SECONDS �- --i=====i===� first step inserting a resistance, whilst the o,s 'I ---,---,I 0 second step short-circuits this r�sistance. ,5 =---- 0,a. t==1 ==t==::::==-111 �1-1--- The water-cooling of the valves is effected by 2Mc/s IOOKcI /s 200Kc/s 500Kc/s IMc/s 5Mc/s distilled water in a closed circulation system, FREQUENCIES the distilled water being cooled by water-to­ Fig. 22-0verall Time Delay Curve of the Vision Transmitter. water cooling.

www.americanradiohistory.com 396 ELECTRICAL COMMUNICATION of filament, grid, and plate circuits of the provided between the penultimate and output output stage of the transmitter for obtaining stages, the setting of the final amplifier is almost the correct band-width presented a special completely independent of slight changes in problem. Experimental and theoretical work the filament and plate circuit tuning or in the was carried on simultaneously. When these valve characteristics. The substitution of valves impedances are determined, the adjustment of with characteristics within reasonable manu­ the output stage is extremely simple. facturing limits does not necessitate readjust­ Proper setting of the grid circuit is done ment of the penultimate or output stages. first with the filament cold, the correct setting being such as to prevent coupling between the PERFORMANCE filament and plate circuits with both the latter The measurements necessary for checking the tuned to resonance. When the filaments are operation of a television transmitter are farmore hot and the high tension is applied, a slight numerous and complex than those ordinarily modification in the setting of the grid circuit is required for the acceptance tests of broadcast required. The final setting is obtained when transmitters. The bandwidth, in the case of the high frequency drive from the penultimate the Eiffel Tower television transmitter, covers stage is prevented from passing into the output 6 Mc/s (3 Mc/s both sides of the carrier fre­ circuit, the filament and plate circuits being quency) and is 300 times greater than that of tuned to resonance and the output stage biassed broadcast transmitters. In broadcast trans­ to cut-off. Final settings of the filament and mitters, moreover, it is almost always possible plate circuits depart slightly from the resonance to connect measuring gear on each circuit ; in points ; they are arranged for obtaining both a television transmitter, it is nearly always a good frequency response curve and minimum impossible. Special coupling circuits must be phase distortion. provided or, alternatively, the input impedance Since the output stage works into a low plate of the measuring equipment must be high in impedance and very effective damping is comparison with that of the circuit to be checked. The use of measuring equipment of is, extremely difficulthigh input in theimpedance vicinity of however,a powerful U.S.W. RECTWIE.D transmitter. OUTPUT Up to now, it has not been normal practice to �.5 measure phase distortion in broadcast trans­ mitters, but such measurement is essential in television transmitters. For broadcast trans­ mitters, measurements are nearly always made with sine waves ; for television transmitters, the particular shape of the vision signal must be taken into consideration and, for some of the measurements, special signals are required. In broadcast transmitters the effect of sudden

0,5 variations of the power is relatively unimportant or notsupply transmitted voltage by the equipment. In television transmitters, on the contrary, any amplitude change in the power supply voltage is immediately visible in the 0 image, even if the level of the interference is 0,5 1,5 30 db. below the image level. For the alignment and acceptance tests of the INPUT Eiffel Tower television transmitter, most of the RMS VOLTS Fig. 23-Amplitude Response Curve at IO kc/s. necessary measuring equipment had to be developed. It includes :

www.americanradiohistory.com E I F F E L T 0 W E R T E L E V I S I 0 T R A M I T T E R 397 N N S

Wide-band video amplifier for television monitoring ; Modulation meter for television transmitter ; Square wave signal generator for television monitoring ; OUTPUT 1, 10, 100, 1 000 kc filters for harmonic content measure- AMPLITUDE ment ; ---j U.S.W. standing wave measuring set on open-wire line ; 100% 1----+------+----t----?'- U.S.W. standing wave measuring set on coaxial line ; Open-wire line parallel current measuring unit for U.S.W. ; 40 to 50 Mc/s variable frequency oscillator ; Screened U.S.W. transformer for measurements on coaxial cables. I-----+- For making measurements with sufficient 75% accuracy, the measuring equipment was developed with characteristics appreciably better than those of the transmitter ; in fact, most of it meets the following guarantee :

Frequency response curve within 0.5 db. for a frequency band extending up to 3 Mc/s ; Harmonic distortion less than 1 % ; Frequency response of monitoring receivers within 1 db. up to 3 Mc/s. The performance of the vision transmitter as a whole is such that a frequency band of 3 Mc/s is transmitted without appreciable D,2 D,4 0,6 0,8 distortion. INPUT The overall frequency fidelity of the trans­ AMPLITUDE mitter at 50% modulation is as follows : Fig . 24-0peration of the "Constant Modulation Depth" Modulation db. gain or loss Regulator. Frequencies over 10 kcfs level 50 c/s + 2 db. 1 Mc/s + 2.1 1.5 " + 1.2 response of the transmitter at kc/s. As will 2 + 0.5 be seen from this curve, practicallyIO no visible 2.5 1.7 3 4.5 amplitude distortion occurs at kc/s. 3.5 9� To meet the requirements IOof the French 4 - 12.5 . television standard the transmitter, as mentioned These results are reproduced in Fig. 21, which above, is operated under a "floating carrier shows the overall frequency response curve of system." The performance of the latter s�stem the transmitter. is indicated in Fig. 24, which gives the amplitude The overall time delay varies from0. 46 micro­ of the radio frequency output of the transmitter second at 100 kc/s to a maximum of 0.59 in terms of the amplitude of the square-wave microsecond at 2.7 Mc/s ; i.e., a maximum signal, shown in Fig. 20, applied to the input variation of 0.13 microsecond. Fig. 22 shows terminals of the modulation amplifier. the variation in time delay from 100 kc/s up to For an output of 35 kW, the overall power 4 Mc/s. For frequencies below kc/s the IO consumption of the transmitter is 233 kW "'.ith phase shift is not appreciable. a power factor of 0.92. When not transm1t. tmg The harmonic contents measured at 80% . signals, the output power of the tran�m1tter modulation are : falls to zero and the power consumpt10n to Madulation frequency Harmonic in kc/s Contents 140 kW. For an image of average brightness 1 1.8% which, according to the French television 10 2.1% 80 2.1% standard, corresponds to an amplitude of about 900 3.15%. 65% of the peak amplitude required for a white The curve of Fig. 23 gives the amplitude image, the power consumption is about 200 kW.

www.americanradiohistory.com Recent Telecomn1unication Developrnents of Interest

Athlone Short- Wave Broadcaster.-Standard mitters used by the British Broadcasting Telephones and Cables, Limited, London, Corporation at Daventry for the Empire Broad­ recently completed the installation at Athlone casting Services. High efficiency Class "B" of a central short-wave Broadcasting Transmitter modulation is used, giving maximum economy to the order of the Irish Post Office. This in power consumption, a distortion content transmitter has been installed initially for a less than 4 % at 90 % modulation, and an overall power of 1-1.5 kW, but the design is such as frequencyresponse characteristic level to within to facilitate future extension, as circumstances 1 db. between 30 and 10 000 p : s. warrant, up to the highest powers used in ± Although this type of equipment is normally short-wave broadcasting. designed for crystal controlled operation, the Basically the transmitter is similar in design special requirements for the Athlone station to the low power stages of the two 50 kW were met by a high stability variable frequency "Standard" short-wave Broadcasting Trans- master-oscillator. The transmitter is arranged to operate over the whole range from 15 to 80 metres. All power supplies are taken from A. C. mains through transformers and rectifiers, no rotating machinery whatsoever being used. The power supply apparatus is built into a cabinet of the same design as the transmitter proper, and is lined up with the transmitter cabinets. Reports received during the short time the trans­ mitter has been on the air show that the transmissions have been at times satis­ factorily received in places as far distant as Newfound­ land, South Africa, Italy, Portugal and many towns throughout the United States of America.

• • • High Power Broadcaster fo r Bangkok.-The new 100 kW medium wave broadcasting transmitter and studio equipment for the Siamese Administra- Athlone Short-Wave Broadcaster. tion, ordered from Stan­ dard Telephones and 398

www.americanradiohistory.com RECENT DEVELOPMENTS

Scale Model of proposed Control Room for the London Passenger Transport Board's Northern Extension.

Cables, Limited, London, will employ the high indication and telemetering equipment for ten efficiency Class "B" system of modulation which substations on the new extension of the London is used in the Empire Broadcasting Station at Passenger Transport Board's underground rail­ Daventry as well as in the four latest medium way from Highgate over the London North wave British stations at Stagshaw, Aberdeen, Eastern Railway Company's lines to& High Start Point and Bristol, and also at Kaunas, Barnet and Edgware. Lithuania, and Melnik, Czechoslovakia. In The equipment covers the remote operation order to increase the fading-free area of the and indication of upwards of 260 circuit transmitter, the station will be equipped w1th breakers, and telemetering of the load on a Blaw-Knox vertical radiator, 640 feet in 18 machines as well as of D.C. bus-bar voltages height. and air pressures at each substation. All of The new transmitter building will be located these functions are effected from the control 15 km from the new studios to which it will be point over one pair of telephone wires to each joined by a programme cable. The studio substation. building will house eight studios of various types. The studio amplifiers, employing the latest feed-back circuits, will be similar to those used for the new Copenhagen Broadcasting House and the Swiss Studios at Basie, Zurich and Lugano.

The whole system will be placed m service in the early part of 1940.

Remote Control of Power Stations.-The application of telephone technique and telephone type apparatus is making great advancement in the control circuits of heavy electrical engineer­ ing equipment in many countries. One recent instance is an order received by Standard Telephones and Cables, Limited, London, as sub-contractors to the English Electric Co., Radio-telephone Installation in the Douglas (Isle Stafford, for the supply of remote control, Man) Lifeboat. of

www.americanradiohistory.com 400 ELECTRICAL COMMUNICATION

I " (I ,,,,.. ' _- =.·, f

Portable Rectifier Unit.

Lifeboat Radio Telephone.-T he Royal apparatus installed in the fore-cabin of the National Lifeboat Institution's lifeboat Douglas lifeboat. The aerial runs between the Manchester and Salford, stationed at Douglas, main and mizzen masts, and is erected sim­ Isle of Man, is the latest of a number of these ultaneously with the hauling up of the masts boats to be fitted withradio telephone equipment after the boat takes the water. by the International Marine Radio Company, Limited, London. Although these equipments are only required to provide short distance Portable Rectifier Unit.-For starting air­ communication between the boats and their plane engines, a unit has been designed by shore stations, or with ships in distress, the Standard Telephones and Cables, Limited, Douglas boat, in sea trials to test the new London, to operate from a 400/440 volt 3-phase installation, successfully carried on a two-way A.C. supply and to give an output either of radio telephone conversation with the London 12 volts at 300 amps. or 24 volts at 150 amps. Daily Telegraph via the Post Office radio station on a short-time rating. Two banks of selenium at Seaforth, nearly 70 miles away, and 200 miles rectifiers are arranged to be connected in series of land line. It is understood that this was the or parallel according to the voltage required. first occasion on which a lifeboat at sea spoke A second unit rated at 24 volts, 300 amps. to an ordinary telephone subscriber. The continuously, or 700 amps. intermittently, is illustration on page 399 shows the I.M.R.C. available for starting Diesel omnibus engines.

ERRA TUM

Electrical Communication, 17, 3, 1939, Vol.1938" : No. January, Page"Electrical 215, first Communica paragraptionh, lines in seven and eight : "a few hundred of microseconds" should read "a few hundredths a microsecond."

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