US1548062A - Coupling arrangement for multiplex transmission - Google Patents

Description

Aug. 4, 1925. 1,548,062

P. H. PIERCE COUPLING ARRANGEMENT FOR MULTIPLEX TRANSMISSION Filed Sept, 4. 1919 2 Sheets-Sheet 1 fiwmmmt m Mu /Hven for: PM a/hfP/erce Aug. 4, 1925. 1,548,062

P. H. PIERCE COUPLING ARRANGEMENT FOR MULTIPLEX TRANSMISSION Filed Sept. 4. 1919 2 Sheets-Sheet 2 Pau/ H. P/e/ce Patented 'Aug. 4, 1925.

UNITED STATES PATENT OFFICE.

PAUL H. PIERCE, OF NEW N. Y., ASSIGNOR T0 WESTERN ELECTRIC COMPANY, INCORPORATED, OF NEW YORK, N. Y., A CORPORATION OF NEW YORK.

COUPLING ARRANGEMENT FOR MULTIPLEX TRANSMISSION.

Application filed September 4, 1918. Serial No. 321,604.

.To all whom, it may concern Be it known that I, PAUL H. PIERCE, a citizen of the United States, residing at New York, in the county of New York and State of New York, have invented certain newand useful Improvements in Coupling Arrangements for Multiplex Transmisslon, of which the following is a full, clear, conrise, and exact description.

The present invention relates to a coupling arrangement for transmitting currents covering a wide range of frequencies. A

feature of the invention relates to a repeater.

circuit for repeating currents of many frequencies at the same time, and particularly to a transformer for impressing 'currents of different frequencies upon the repeater proper.

The invention comprises as one feature a novel type of transformer which has a high cfliciency for currents of all frequencies embraced in the range of frequencies employed in composite Wire transmission, so that both modulated high frequency currents and currents of low frequency, such as ordinary telephone currents, may all be put through the same transformer for transmission from one circuit such as a line circuit, to another circuit such as a repeating or amplifying circuit. The invention is notrestricted in scope, however, to this particular use but may serve generally for the transmission of a range of frequencies whether for signaling or other purposes and either uniformly or non-uniformly as will-be described hereinafter.

In systems of multiplex telephony in which carrier currents and other currents covering a Wide range of frequencies are used, it has heretofore been found necessary, in repeaters for such systems, to separate the frequencies into different ranges to be repeated separately and then to recombine the frequencies in the outgoing line. For example, it has been the practice to provide separate repeaters for currents of speech frequency and for currents of carrier frequency. Repeaters are known which of themselves are capable of amplifying ourrents'of many, frequencies at the same time. If such a repeater is to be used. some means must be provided for impressing the currents of many frequencies upon the repeater proper, but the usual step-up transformer is not suitable for this purpose, since it is not capable of transmitting uniformly a wide range of frequencies. The present invention seeks to provide an efficient means for transmitting current waves of widely different frequencies by affording for the waves of different frequencies. a plurality of different transmission paths, so that either waves of all frequencies are uniformly transmitted or their transmission may be controlled to give a desired kind and degree of distortion to the Waves.

A better understanding of the invention may be had from the drawings, in which Fig. 1 is a schematic diagram of a two-way repeating circuit; Fig. 2 is a more detailed circuit diagram of one side of the two-Way repeater of Fig. 1 equipped with transformer circuits according to the invention; Fig. 2 is a fragmentary View showing a modification of part of the circuit arrange ment of Fig. 2; and Fig. 3' shows a further application of the invention to the same system. Like reference characters apply tolike parts throughout the drawings.

Referring first to Fig. 1, current waves on the line wires 1, 2 are impressed on the transformer windings 3, 4, and 5, 6. A not shown as an adjustable resistance 7 is provided to simulate the characteristics of the line 1, 2 and coils 5, 6 are designed to balance coils 3, 4. The purpose of this arrangement is to provide that energy from an output coil 8 will divide equally between the line and the coils 3, 4 on one side and the net 7 and coils 5, 6 on the other side without setting up a difference of potential between the bridging points 9 and 10, whereas current waves incoming over line 1, 2 will find a path through conductors 11, 12 to the input circuit of the repeater shown. This path may include a compensator as indicated to compensate for such distortion as the waves may have suffered in transmission so that in their restored form the waves reach the transformer 13 by means of whici they are impressed upon the input circuit of the repeater. The repeated and amplified Waves are now sent out over line 14, 15 through a transformer comprising coils 16, 17 18, 19 and 20 acting similarly to c'oils 8, 3, 4, 5 and 6 respectively, so that no potential difference is set up between the bridge taps 22, 23. Incoming waves from line 14, 15 will, however, find a path through conductors 24, 25 and through the lower comvent singing due to capacity between the impressed on the repeater.

windings.

The general layout of the repeater system having been given, a detailed descriptlon of the circuits to which the invention relates will now be given with particular reference to Fig. 2. This figure shows one side of the two'way repeater including the compensator together with the special transformer circuits forming the subject of the inventlon in place of the simple transformer 13 of Fig. 1 which is there indicated merely to show a coupling to the input side of the repeater. The other side of the two-way repeater being entirely similar is not shown in the detail diagram of Fig. 2. The input leads 11, 12 are shown connected to a compensator of the type disclosed in United States Patent No. 1,453,980, to R. S. Hoyt, issued May 1, 1923. This compensator is shown as comprising condensers 30, in series with inductances 31, 31 respectively, each condenser and inductance being shunted by the resistances 32 or 32 respectively. The combination of the series capacity and inductance with the shunt resistance may be so chosen relative to the rest of the circuit that a lower impedance is offered to the higher frequency waves than to the lower frequency waves, in such manner as to compensate for the greater attenuation of the higher frequency waves that may be assumed to have taken place in transmission. The compensator is connected to the pri mary series coils 33, 34 and 35 of a double input transformer, the secondaries of which are 36, 37 and 38 respectively. In the particular form used, the transformer 34, 37 had a high efficiency for the low frequencies, while the couplings 33, 36 and 35, 38 were designed to give I good transmission of higher frequencies. The latter coils being similar and being placed one on each side of the low frequency coil for symmetry may be regarded as one transformer forming the high frequency input path. The transformer ratios of the high and low frequency coils may be proportioned to give the proper potentials of the different frequency waves Thus, the high frequency coils may have a greater voltage transformation ratio to compensate partially, at least, for the line attenuation, or if a compensator is used as illustrated, the couplings may give uniform transmission for all frequencies. In the modification of Fig. 2 condensers 39' serve as shunt paths for the higher frequency waves around the low frequency coil. Since the low frequency coil itself may have a shunt capacity which is sufficient to serve as a by-pass for the higher frequencies, in which case the addition of the condensers would not be necessary, they are not shown in Fig. 2. The resistance 39 is provided to improve the impedance ratio of the low-frequency transformer. The secondary transformer coils are bridged by resistances 42 and 43 in series with inductances 40 and 41, the purpose of the inductances being to counteract, in part at least, the effect of the shunt capacity of the coils 36 and 38 for higher frequency waves. Resistances 42 and 43 are shown provided with suitable taps by which the voltages to be impressed on the repeater may be chosen. The repeater shown is of the thermionic type in which the impressed wave varies the potential of two grids oppositely at the same time, and is known as the push-pull type. The amplifiers 44, 45 of the first stage have their grids 46, 47 respectively connected to the potentiometer terminals 48, 49 of the double in ut transformer. The normal potential 0 grids 46, 47 is fixed by the battery 52, and filaments 50, 51 are supplied with heating current from filament battery 53 through regulating resistances 54 and 55 respectively. The negative side of the filament lead is shown grounded, and also connected through the plate battery 56 and impedances 57 and 58 respectively to the anodes or plates 59 and 60 of the respective amplifiers 44 and 45. The filaments 67 and 68 of the second-stage amplifiers and 66 respectively are supplied with heating current from battery 53 through suitable adjustable resistances, and the normal potential of each grid 63, 64 is fixed by polarizing battery 69 connected to the respective grids through high resistances 70 and 71 respectively, which resistances permit a potential to be applied to each grid 63, 64 but prevent the shunting of the output waves from the first-stage amplifiers. Plate potential is supplied to the plates 72, 73 of the respective amplifiers 65, 66 by the battery 56 through choke impedances 74 and 75. The current variations from the output of the first-stage amplifiers find a path through condensers 61 and 62, respectively, to the second stage amplifiers, causing corresponding variations of the potential upon grids 63 and 64 respectively. The impedances of the amplifiers 65, 66 are thus oppositely varied, causing corresponding current-flow in the path through the condensers 7 6 and 77 and the primary 16 of the output coil, from which current is impressed on the line 14, 15 as previously explained. Shield 26 is shown as both grounded directly and as connected to the grounded filaments, the

object of theshield being, as heretoforestated, to prevent singin due to capacity between the windings of t e transformer.

, The output coil shown at the right in Fig. 2 would ordinarily be a low impedance coil having a small transformer ratio, in which case experience shows that a single output coil may be designed to convey. the waves of different frequencies from the repeater to the line. In some cases, however, it might be desirable to provide a double output coil as well as a double input coil for the re mater, and such an output coil is shown in ig. 3;

In this figure the output circuit of the amplifiers 65, 66 is shown leading through condensers, 76, 77 to the primaries 80, 81 of the higher frequency coil and the primary 86 of the lower frequency coil in series. A condenser 88 may be used to afford a by-pass around coil 86 for the higher frequencies. From these coils the current waves are impressed upon the corresponding secondaries 82, 83, 84 and 85 for the higher frequencies and 87 and 91 for the lower frequencies. The bridging-taps 22 and 23 are tapped at the midpoints of the circuit and one half of the low frequency coil 87 is shunted by acondenser 89 and the other half by a con denser 90 between which tap 22 has connection, while coil 91 has its halves shunted respectively by condensers 92, 93, one on each side of the tap 23, so that the output energy of the waves of all the frequencies is divided between the line side and the net side of the bridged coils without setting up a difference of potential between the points 22 and 23 and without therefore disturbing the input of the other side of the two-way repeater.

From the foregoing description of the invention as embodied in the particular circuit illustrated, it will be seen that a means has been provided for conveying currents of many frequencies simultaneously from one circuit to another without suppressing some of the waves more than others. It is further evident that since a plurality of paths are provided, each of which accommodates a range of frequencies, these paths being independent in part at least, may have different characteristics such. as different voltage-transformation ratios, so that if the higher frequency waves, for instance, have become somewhat suppressed by the attenuation of the line over which they have passed, they may he stepped up by a higher ratio than the waves of lower frequency that have been less attenuated. Thus the transformer arrangement according to the invention may serve as a distortionless transformer, leaving the compensation for the line attenuation all to the compensator provided, or in the manner just now indicatedthe transformer may be made to distort the waves so as to aid in the compensation. Since the device is capable of functioning in either of the described ways according to the proportioning of the different parts, and since the particular function desired would depend upon the system in which it is to be used andthe conditionsof use, these different properties of the device are regarded as different aspects of the same invention and it is intended that the claims be interpreted broadly with this in View.

Although the invention has been described with reference to a composite multiplex telephone transmission system, it is not to be limited in its broad aspect either to signaling or to wire line transmission but is capable of general application.

lVhile the invention has been illustrated and described in connection with a specific circuit arrangement, it is to be understood that it is not to be limited either to the specific arrangement as a whole or to the particular details, but only by the scope of the appended claims.

What is claimed is:

1. In a multiplex signaling system, a line for simultaneously transmitting a plurality of separate current waves in separate frequency ranges, the frequencies in one of said ranges being higher than the highest essential voice frequency, an amplifier in said line for amplifying all ofsaid waves simultaneously, and a coupling between said line and said amplifier having means for transmitting all of said waves with substantially uniform attenuation.

2. In a signaling system in which current waves of different frequencies are transmitted simultaneously, a line the attenuation of which varies with the frequency of the transmitted waves, a compensating circuit for giving said vwaves an attenuation complemental to that produced in the line, an amplifier in said line for amplifying all said waves simultaneously, and a coupling between said compensating circuit and said amplifier having means for transmitting all of said waves with substantially uniform attenuation.

3. In a transmission system, a transmission line the attenuation of which varies with the frequency, a circuit associated with said line the attenuation of which as to the frequency is complemental to that of the line, a repeater for repeating currents of different frequencies, and a coupling between said line and said repeater having means for impressing currents of different frequencies upon said repeater with substantially uniform attenuation for all of said frequencies.

4. The combination with a line for transmitting waves in different frequency ranges, the frequencies in one of said ranges being higher than the highest essential voice frequency, and a repeater for said waves, of coupling circuits between said line and said repeater forming a path for the waves of higher frequencies, and a path for Waves of lower frequencies different in part at least from said path for higher frequencies.

5. In a signaling system, a repeater for repeating waves in different frequency ranges simultaneously, the frequencies in one of said ranges being higher than the highest essential voice frequency, and means for impressing waves in such different frequency ranges upon said repeater comprising a plurality of couplings having different high and low-frequency transmission properties respectively.

6. In a multiplex carrier-currerit repeat-,

er system, a line over which carrier currents of different frequencies may be transmitted, said carrier currents having -frequencies higher than the highest essential voice frequency, a repeater for said currents, and a coupling between said line and said repeater comprising a transmission path for low frequency currents and a different transmission path for higher frequency currents.

7. In a transmission system employing current waves in separate frequency ranges, {the frequencies in one of said ranges being higher than the highest essential voice frequency, a repeater, an inductive coupling for said repeater having primary series coils, a secondary series circuit containing secondary coils, and a plurality of inductive paths between said primary and secondary coils for current waves in the different frequency ranges, whereby Waves of all frequencies are transmitted through said inductive coupling with substantially uniform attenuation.

,8. In a transmission system for current waves of different frequencies, a transmission line the attenuation of which varies with the frequency, a repeater for repeating waves of all said frequencies, a plurality of inductive paths between said line and said repeater and a plurality of conductive paths in series with said inductive paths for compensating for the attenuation of said Waves and for impressing said waves upon said repeater.

9. In a transmission system in which current waves of different frequencies are employed, a line the attenuation of which is greater for waves of higher frequency than for waves of low frequency, means conductively associated with said line for compensating for said attenuation, a repeater for; repeating waves of both high and low frequencies and an inductive coupling associated with said means between said line and said repeater path for waves of the higher frequencies and a transmission path for waves of the lower frequencies.

10. A coupling circuit for transmitting currents of different frequencies comprising a pair of inductively related coils-having appreciable capacity impedance for high frequency currents and a pair of inductively related coils having appreciable inductive impedance for high frequency currents, said coils ofiering low impedance to low frequency currents, and means in said circult for counteracting said capacity impedance and a shunt path for said high frequency currents about said inductive impedance, whereby said coupling circuit transmits said currents of different frequencies in a substantially uniform manner.

lL An inductive coupling for transmit ting' current waves in separate frequency ranges, the frequencies in one of said ranges being higher than the highest essential voice frequency, comprising a primary low fre quency coil and a primary high frequency coil, secondary coils respectively inductively associated therewith, and a non-inductive shunt path around said low frequency coils for the high frequency currents.

12. An inductive coupling for transmitting current waves of different frequencies comprising a primary low frequency coil.

and a primary high frequency coil, secondary coils respectively inductively associated therewith, a non-inductive shunt path around the said low frequency coils for the high frequency currents, and means for lowering the impedance of said high frequency coil for the high frequency currents.

13. An inductive coupling circuit for transmitting currents in different frequency ranges, the frequencies in one of said ranges being higher than the highest essential voice frequency, comprising primary coils and secondary coils inductively related thereto, and shunt paths associated with said secondary coils and acting with said coils for rendering transmission through said coupling circuit substantially uniform for the currents in the different frequency ranges.

14'. In a transmission system, a line carry- .ing current waves in different frequency ranges, the frequencies in one of said ranges being higher than the highest essential voice frequency, a repeater for said waves and a step-up transformer-coupling between said line and said repeater having a plurality of pairs of inductively associated coils affording a plurality of inductive paths for said Waves between said line and said repeater, one said path being more eflicient in transmitting high frequencies than low, and another said path being more efficient in transmitting low frequencies than high.

15. In a repeating system for a line carrying current waves in different frequency ranges, the frequencies in one of said ranges being higher than the highest essential voice frequency, a thermionic repeater having inut terminals and an input circuit comprismg a resistance to which said input terminals are tapped, means for impressing said waves in the different frequency ranges upon said input terminals comprising coils conductively connected to the terminals of said resistance and coils connected to said line and inductively associated with said firstmentioned coils forming an inductive path for waves of low frequencies, and another inductive path for waves of higher frequencies for conveying said waves of different frequencies from said line to said repeater.

16. In a current wave transmission system, a line for transmitting waves of several frequencies simultaneously, primary coils in said line and secondary coils in series inductively associated therewith, an output connection across the terminals of said secondary series coils including a resistance and an inductance, a capacity shunt around one of said secondary coils serving as a by-pass for the higher frequency waves, and a repeater having its input terminals connected across said output connection.

17. An inductive coupling for. transmitting current waves in widely separated frequency ranges, the frequencies in one of said ranges being higher than the highest essential voice frequency, comprising inductively associated coils for transforming the higher frequency waves, inductively a'ssociated coils for transforming the others of said waves, the ratio of the transformation for the higher frequency waves being independent of the ratio of transformation for the other waves, and a path for the transformed high frequency waves around the second mentioned coils.

18. In combination, a transmission line for current waves of many frequencies, the attenuation of which line is greater for waves of some of said frequencies than for others,

a compensator in said line having attenuation properties complementar to those of said line, a coupling circuit aving means for transmitting all of said waves with sub stantially uniform attenuation, a second line, and a repeater for repeating all of said waves with substantially uniform attenuation to said second line.

19. In a transmission system for waves of many frequencies in which some of said waves are more distorted in transmission than others, means for restoring said waves by compensating for said distortion comprising a circuit for impeding the less distorted waves to a greater extent than the more distorted waves, and a transformer circuithaving a plurality of separate inductive paths for independently stepping-up the voltages of the less distorted waves and the more distorted waves.

20. A coupling for use between circuits carrying currents of many frequencies comprising a plurality'of transformers having their primary windings in series in one circuit and their secondary windings in series in the other circuit, one said transformer having high efficiency for the low frequency currents'and the other transformer having high cfiiciency for the high frequency currents of frequency above the highest essential speech frequency, a'low impedance path for said high frequency currents around the low frequency windings, and a non-inductive resistance connected in parallel with one of said low frequency windin s.

21. In combination, a first line section and a secondline section for transmitting current waves in separate frequency rangessimultaneously, the frequencies in one of said ranges being higher than the highest essential voice frequency, two-way repeating means for said Waves between said line sections comprising a repeater for simultaneously repeating said waves in each direction, each repeater having in its output side a winding, and each line section having a winding in each line limb conductively associated therewith and provided at its midpoint With a tap, a net for balancing each line section, a double input transformer for each repeater having primary coils connected to said taps and secondary coils connected respectively to the input sides of the repeaters, said primary and secondary coils forming an inductive path forv the higher frequency ones of said waves, and another path for the others of said waves.

22. In combination with a line for transmitting a plurality of currents of respective ly different frequency each modulated in accordance with signals and a repeater having a substantially straight line characteristic for simultaneously repeating all of said currents, a circuit for compensating for the unequal lineattenuation of the different frequencies and for impressing said currents upon said repeater including a transformer for transmitting currents of all of said frequencies substantially uniformly having coils for transmitting some frequencies and other coils for transmitting other frequencies. Y

23. In combination with a line for transmitting modulated currents having frequencies higher than the highest essential voice frequency and telephone currents and a repeater for amplifying all of said currents, a compensating circuit for correcting for the unequal attenuation of said currents of different frequencies including a transformer having a plurality of inductive paths for the currents of different frequencies for impressing the corrected currents of different frequencies upon said repeater.

24. In a signaling system, a combination of a main line for simultaneously transmit- IOU ting telephone currents and other signaling currents above the range of telephone frequencies, an amplifier adapted to amplify simultaneously both kinds of currents, and inductive connections between the line and the input and output circuits of the amplifier comprising means for transmitting both 4 kinds of signal currents.

25. In a signaling system, the combination of a main line for simultaneously transmitting telephone currents and other signaling currents above the range of voice frequencies, an amplifier adapted to amplify simul taneously both kinds of currents, composite transformers connecting the lines with the input and output circuits of the amplifier respectively, said transformers comprising separate windings for the telephone and other signaling currents, and means for bypassing the other signaling currents around the windings designed for the telephone currents.

26. The combination with two sections of line for transmitting waves in different frequency ranges, one of said ranges being above audibility, of coupling circuits between said line sections forming a path for the waves of higher frequencies, and a path for waves of lower frequencies different in part at least from said path for higher frequencies.

27. A coupling circuit for transmitting currents of different frequencies with substantially uniform attenuation comprising a pair of inductively related coils having appreciable capacity impedance for high frequency currents and a pair of inductively related coils having appreciable inductive impedance for high frequency currents, said coils offering low impedance to low frequency currents, and means in said circuit for counteractin said capacity impedance, and a shunt path for said high frequency currents about the coils which have appreciable inductive impedance for high frequency currents.

2.8. A repeater of the space current type having an electrostatic control element and an input circuit, and means including inductance in shunt to said input circuit having a substantially constant impedance for oscillations impressed upon said input circui't, said oscillations comprising frequencies both above and below the highest essential voice frequency.

29. An amplifier of the space current type having an electrostatic control element and an input circuit, and a network containing reactance connected in shunt to said input circuit, said network having substantially constant impedance for all frequencies'within the range including speech and a band of ultra-audible carrier frequencies.

30. In a signaling system, the combina-' tion of a main line for simultaneously transmitting telephone currents and other -currents having frequencies higher than the highest essential voice frequency employed in telephone transmission, a two-way repeater in said main line comprising a separate amplifier for transmitting current in each direction, three-winding transformers con necting the output circuits of the amplifiers with the line conductors leading in o posite directions, secondaries of said trans ormers including like windings in the opposite sides of the line, conductors leading from the central points of said secondary windings and a composite transformer connecting said conductors with the input circuits of said amplifiers and having separate windings adapted to transmit the telephone currents and said other higher frequency currents respectively.

31. In a signaling system, the combination of a main line for simultaneously transmitting telephone currents and other currents having frequencies higher. than the frequencies of said telephone currents, a two-way repeater in said main line comprising a separate amplifier ,for transmitting currents in each direction, three-winding transformers connecting the output circuits of the amplifiers with the line conductors leading in opposite directions, secondaries of said transformers including like windings in the opposite sides of the line, conductors leading from the central points of said secondary windings, a composite transformer connecting said, conductors with the input circuits of said amplifiers and having separate windings adapted to transmit the telephone and higher frequency currents respectively, said threewinding transformers comprising separate windings for transmitting the telephone and higher frequency currents respectively.

32. In a signaling system, the combination of a main line for simultaneously transmitting currents in different frequency ranges, a two-way repeater in said main line comprising a separate amplifier for transmitting currents in each direction, three-winding transformers connecting the output circuits of the amplifiers with .the line conductors leading in opposite directions, secondaries of said transformers including line windings in the opposite sides of the line, conductors leading from the central points of said secondary windings, a composite transformer connecting said conductors with the input circuits of said amplifiers and having separate windings adapted to transmit the different frequency ranges, said three-winding transformers comprising separate windings for transmitting said diflerent frequency ranges.

33. In a multiplex carrier current repeater system, a line over which carrier currents of different frequencies may be transmitted, a repeater for repeating currents to said line, a second repeater for repeating currents received from said line, and a coup-ling between said line and both said repeaters whereby currents repeated to said -line by said first mentioned repeater cannot afl'ect said second mentioned repeater, said coupling comprising a transmission path for low frequency currents and a different transmission path for higher frequency currents.

34. In a transmission system, a first circuit over which currents may be transmitted, a second circuit for transmitting currents to said first circuit, a third circuit for receiving currents from said first circuit, an output transformer for coupling said first circuit to both said second and third circuits comprising a primary winding to which said second circuit is connected, secondary windings connected to said first circuit, bridge taps from intermediate points of said secondary windings to which said third circuit is connected, condensers connected in shunt to portions of said secon dary windings in symmetrical relationship to said bridge taps and a net for fixing the impedance relationship between said several circuits whereby current from said second circuit has substantially no effect upon said third circuit.

35. In a transmission system, a first circuit over which currents in different frequency ranges may be transmitted, a second circuit for transmitting current to said first circuit, a third circuit for receiving current from said first circuit. an output transformer for coupling said first circuit to both said second and third circuits comprising a primary winding to which said second circuit is connected, secondary windings connected to said first circuit, bridge taps from an intermediate point of said secondary windings to.which said third circuit is connected, condensers connected in shunt to portions of said secondary windings in symmetrical relationship to said bridge taps and a net for fixing the impedance relationship between said several circuits whereby current from said second circuit has substantially no efi'ect upon said third circuit, and whereby currents in different frequency ranges are transmitted throu h said output transformer substantially in ependently.

36. In a transmission system, a first circuit over which currents may be transmitted, a second circuit for transmitting currents to said first circuit, a third circuit for receiving currents from said first circuit, an output transformer for coupling said first circuit to both said second and third circuits comprising a primary winding to which said second circuit is connected, secondary windings connected to said first circuit, bridge taps from the mid-points of said secondary windings to which said third circuit is connected, condensers connected in shunt to, portions of said secondary windings in symmetrical relationship to said bridge taps, and a net for balancing the impedance characteristics of said first circuit whereby current from said second circuit has substantially no effect upon said third circuit.

In witness whereof, I hereunto subscribe my name this 28th day of August A. 1)., 1919.

PAUL H. PIERCE.

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