US1578881A

US1578881A - Polyphase-carrier-current broadcasting system and generator

Info

Publication number: US1578881A
Application number: US1374A
Authority: US
Inventors: Jr Robert D Duncan
Original assignee: Wired Radio Inc
Current assignee: Wired Radio Inc
Priority date: 1925-01-09
Filing date: 1925-01-09
Publication date: 1926-03-30
Anticipated expiration: 1943-03-30
Also published as: DE484463C

Description

March 30-, 1926'. 1,578,881

R. D. DUNCAN, JR

POLYPHASE CARRIER CURRENT-BROADCASTING SYSTEM AND GENERATOR Filed Jan. 9, 1925 2 Sheets-Sheet 1 INVENTOR 1%602'1 2 30/250 J2;

ATTORNEYS.

PW-fb m w ai/vvr WM March 30,1926. '1 5 8,88.1

R. D. DUNCAN, JR 1 POLYPHASE CARRIER CURRENT BROADCASTING SYSTEM AND GENERATOR Filed Jan. 9, 1925 2 sneets-sfiee'r, '2 V INVENTOR Patented Mar. 30, 1926.

ROBERT :a. DUNCAN, 3a., or EAST ORANGE, NEW JERSEY, assrenon TO WIRED RADIO,

Inc, on NEW YORK, n. Y., A CORPO ATION OF DELAWARE.

IOLYPIiASE-CARRIER-CURRENT BROADCASTING SYSTEM AND GENERATOR.

Application filerl"Ja11uary 9, 1925. Serial No. 1,314.

'1 b all 10710??? i may concern: v

Be it kno'wnthat 1. ROBERT -D. DUNCAN,

J12, a citizen ofthe United States, residing at East- Orangc, in the county of Essex,- State of New Jersey-have invented certain new and useful Improvements in Polyphase- Carrier-Current Broadcasting Systems and Generators; andl do hereby. declare the following to be a full, clear, and exact description of the invention, such as will enable others skilled in the art to which appertains to make and use the same.

In high frequency carrier-current broadcasting systems superimposed on electric" carrier over a poly-phase system, but practical experlence has unheated that thls'can-' not be done consistentlyenough for com-f mercial broadcasting on a large scale.

Almost from the very beginning of the extensive research work which has been carried on in the wired radio broadcasting field it'has been realized that more even and "satisfactory carrier current distribution could be effected on poly-phase power lines byithe' use of poly-phase carriers, but in so far as,

it has been possible to ascertain, there has heretofore been noknown generator of poly-phase high frequency oscillations of The present invention practical character. is directed in part to such a generator and, in part, to a W1redrad1o broadcasting system of the poly-phase type inch-more specifically;

to a system wherein single phase high fre quency oscillations are converted nto poly-,

phase high frequency oscillations and superimposed upon the low frequency'p'ower currents on a poly phase power t *ansmission line. I

The poly-phase system in part, upon the method of producing phase displacement disclosed on pages 352 and of a publication entitled lVireless Telegraphy, by Dr. J. Zenueck, McGraw-Hill Book Company, Inc, 15))15, under! the caption, Production of any desired phase differences with undamped oscillations, wherein it is shown that between two loosely-coupled resdrawings, in; which i Fig-L531 is a schematic circuit diagrainfillus tinting-the underlying principles whereby "single phase'oscillations are converted into ,tially complete and generator herein dealt with are devolopments based,

onant circuits, the currents are 99 out of phase and that'a circular rotating magnetic field may be produced bytwo coils having equal magnetic fields with coincident magnetic centers and axes at right-angles and wherein the currents are out of phase.

In accordance with the preferred embodiment of this invention single phase high frequency oscillations. are produced by means of a master vacuum tube oscillator;

"and high frequency currents of, the master oscillator frequ'encyybut with a phase difference of. 90- are produced by loosely coupling two resonant circuits, one of whichis supfplied witlr high frequency current by the master oscillatoli ith the circular magnetic field thus produced in the manner hereiubeforereterred to from the single phase oscillationsgenerated by the master oscillator, a carrier current of any number of phases may be produced by arranging a corresponding number of coilsin the rotating magnetic lieldswith their axes at the proper angular relation toeach other, :In practise gthc three-phase or other poly-phase carrier thus. produced 'isamplified, modulated and impressed upon the power transmission lines at the central power station orsub-station as may be convenient, and-thus .over thepower network.

distributed The inveutio will be more clearly under-- stood;'from the following detailed description, in conyunction' with theaccompanying poly phase oscillations. p

Figs. .2 and are schematic circuit diagrams serving to illustrate alternative connections of the'coilsin which the poly-phase currents are, generated tothepower transmission lines, and r Fig. ris a circuit diagram of a substanthree-phase wired radio transm tter. v r

;In the schematic diagram of Fig. 1'l is'a. single phase high .frequencyoscillator of anyft-ype and ,niay conveniently be a vacuum tube oscillator This is referred to as the anaster oscillator and. is coupled.

througlra transformer 2, to a tunable circuit including the secondary=-w1nd1ng 6, an inductance 5,;coil e t aiid variable condenser 3. The

tunable circuit

3, 4, 5, 6 is loosely coupled to a secondary circuit comprising the variable condenser 7, coil 8 and inductance 9the coupling between the circuits being effected through the variably coupledinductances 5 and 9.

It is found that when the circuits 3, 4, 5, G and 7 8, 9 respectively are quite loosely coupled and. the latter tuned exactly or approximately to the frequency ofthe master oscillator, the currents in these two circuits are approximately or exactly 90 out of phase.

In some cases it is found that circuit 7-, 8, 9 must be tuned quite exactly to the master frequency while in other cases better results are obtained when this circuit is more or less detuned with respect to. the master frequency.

Circuit

3, 4, 5, 6 is not necessarily tuned to the master frequency but maybe so.

Coils

4 and 8 are so disposed with relation to each other that their axes are at right angles and their "centers of magnetic. flux are coincident. The center of magnetic flux is indicated on Fig. 1 asa point in each coil which is centrally located with respect to the circumference and the longitudinal extremities. It may be demonstrated that if the currents in the

coils

4 and 8 are 90 out ofphase with each other and the magnetic fields of the coils are equal, the combined magnetic field will rotate about the coincident centers of magnetic flux and the result will be the same as inthe case of a single coil rotating about its .own center of magnetic flux. In other words the resultant magnetic field is the same as in a dynamo-electric machine having a rotating field.

Three

co'ls

10, 11, 12 are shown having their planes intersecting at angles of 60 and their centers of magnetic flux coincident with that of the

coils

4 and 8. These coils being wound in the proper direction and being disposed in the rotating magnetic field will have generated in them currents which are .120 apart and if the terminals of each coil are connected together in star or delta:

as indicated in the circuits of Figs. ,2 and 3 and also'connected to a load circuit such as a three-phase power transmission

line comprising conductors

16, 1 and 18, three-phase high frequency currents are generated in these coils and impressed upon the three phase power transmission lines.

Condensers

13, 14, 15 are inserted in the power lines for the purpose of preventing the low frequency power currents being short circuited through the

coils

10, 11, 12 and furthermore, function to tune the power lines; 'The transmitter diagrammatically illustrated in Fig. 4 comprises a master oscillator 1, phase displacing circuits 19 and 20, a high frequency amplifier 21 and a modulator 22. The master oscillator 1 is one of the wellknown vacuum'tube oscillator circuits and needs no description. This master oscillator I is inductively coupled through windings 2 and 6, corresponding to those bearing the same reference numerals in Fig. 1, to the tunable phase displacing circuit 19, comprising

elements

3, 4, 5, 6, corresponding to the

circuit

3, 4, 5, 6 of Fig. 1, and in addition, varionieter 23 and ammeters 24 and 25 are included in this circuit. The secondary phase displacing circuit corresponding with

secondary circuit

7, 8, 9, of Fig. 1, includes in addition to

elements

7', 8, 9, a variometer 26 and an ammeter 27. The ammeter 25 is common to both circuits l9 and 20. Coils 421ml 3 of Fig. 4 are arranged with respect to each other in the same'way as coils 4 and rug-

Coils

10, 11, 12 of Fig. 4 correspond with the coils having the same reference numerals in Fig. 1. These coils should be physic'ally'disposed with respect to

coils

4 and 8 in the same manner as described in connection with Fig. 1,- that is to say they should be so arranged that three-,phase currents will be generated in them by the rotat-' 'ing magnetic field about .

coils

4 and 8.

Coils

10, 11, 12 are shown connected in star and are inc'luded in the input circuit of three-parallel vacuum 'tube amplifiers 28,

29, 30. It will be noted that the common I terminal of these three coils is connected to the grounded filaments while the remaining terminals are connected to the grids of

tubes

28, 29 and 30 respectively. The plate-film ment' or output circuits of

amplifier tubes

28, 29, 30 include

inductances

31, 32, 33,

respectively, each in series with a condenser, .34, 35, 36. These inductances are coupled threeparallel

amplifier tubes

43, 44 and 45.

The parallel input circuits of these tubes includes thesecondary winding-of a trans-- former 46 in the primary circuitof which is a microphone 47 and a battery 48. A grid biasing battery 49 may also be inserted in the input circuit of the modulator tubes.-

A generator 50 supplies direct current to the plate circuits of all the Vacuum tubes. A high inductance coil 51 functions in the well known manner to effect plate potential variations at the'ampli'fier tubes in accordance with the audio frequency variations impressed 'on microphone 47. Three-radio frequency choke coils 53 are inserted-respectively in the plate-current supply circuits of the

amplifier tubes

28, 39, 30. These coils serveto prevent the shunting of high frefrequency three-phase power supply and quency currents from the output side of the amplifier through the modulator tube.

In operation varior'neters 23 and 26 in circuits 19 and 20 respectively, and condenser 7 are ordinarily adjusted until the ammcters 24 and 27 show the same reading. If, under these conditions and with the proper degree of coupling between inductances 5 and 9 the reading of ammeter should be equal to times the reading of either of the other ammeters.

In the particular system of Fig. 4 modulation is effected at the amplifier tubes, rather than at the oscillator tube. Modulation is effected in this case through diversion of current from the plate circuit of the amplifier tube through the parallel plate circuit of the modulator tubes. It is to be understood that the three-

phase transmission line

16, 17, 18 is connected to a source of low that it extends to local distributing points where the phases are branched ofi.usually through stepdown transformersto the various power and lighting subscribers and that these subscribers or some of them are provided with receiving sets which are connected through lamp sockets or otherwise to .these respective branches. It will furthermore be understood that each. branch line, except in special cases, conducts only one of the three-phases of each frequency, that is,

the power frequency and carrier frequency.

It is apparent that the invention herein disclosed is applicable for the production of poly-phase high frequency carrier currents having any number of phases, at least within the limit of the number of phases employed in power transmission systems.

I claim: I

1. A broadcasting system comprising a poly-phase electric. power transmission line, a source of poly-phase high frequency carrier current connected to said power transmissiomline, means for modulating said carrier current in accordance with signals to be transmltted over said power transmission line, and receiving apparatus responsive to the modulated carrier current and operative to reproduce said signals, said receiving appar'atus being connected to said power transmission line.

2. A broadcasting system comprising a poly-phase electric power transmission line, a source of poly-phase hi h frequency carrier current, the phases-o said carrier current being the same in number as those of said line, said source of carrier current being so connected to said line that each power phase has superimposed upon it one of the phases of said p0 y-phase high carrier current, means for mo ulating said carrier current in accordance with signals to lbe transmitted, and a plurality of receivfrequency ing stations each of which is connected to one phase only of said transmission line, there being one or more of said receiving stations connected to each phase of said transmission line, said receiving stations each comprising apparatus responsive to modulated carrier currents to reproduce signals transmitted thereby over said transmission line. r 1

3. The combination with an electric power distribution system comprising a poly-phase power transmission line, of a poly-phase carrier current generator connected to said line, a plurality of receiving stations connected to said line, each of said receiving stations comprising means responsive to modulated hi h frequency carrier currents received from said line to reproduce sound waves corresponding to the modulations of said carrier currents, said generator comprising a singlephase master oscillator in combination with phase displacing circuit connections whereby high frequency currents having a phase difference of approximately are produced,

' circuit means utilizing said last mentioned power transmission line, of av three-phase high frequency carrier current generator comprising a source of single phase hi h frequency oscillations, a pair of tunable oosely coupled circuits at least one of which is tuned to the frequency of said single-phase oscillations and one of which is supplied with single-phase oscillations from said source, each of said tunable circuits including a coil, the centers of magneticflux of which are coincident and the axes of which are at right angles, the magnetic fields of said coils being substantially equal, three secondary coils having their axes angularly displaced by approximately 60, said secondary coils being situated in said magnetic field, the arrangement being such that threephase high frequency carrier currents are induced in said. secondary coils, means'for amplifying and impressing said three-phase transmitted.

In testimony whereof I atfix my signature.

ROBERT D. DUNCAN, J R.

' carrier currents on said power transmission line, and means for modulating said carrler currents in accordance With signals to be