US1582113A - Phantom carrier circuits - Google Patents

Description

April 27 1.926.

H. A. AFFEL PHANTOM CARRIER CIRCUITS Filed August 11. 1925 INVENTOR 44760 ATTORNEY Patented Apr. 27, 1926.

- UNITED. STATES PATENT OFFICE.

HERMAN A. AFFEL, or vrArLEwoon, Nnw'JERsR-Y, 'ASSIGNOR'TO AMRRIcAN- TELE- PHONE AND 'TELEGBAJEI COMPANY, A ooRPo-RA rIoN or NEW YORK.

PHANTOM cARRIER CIRCUITS.

Application filed August 11, 1925. Serial No. 49,608.

To all whom itmag concem:

Be it. known that I, 'H RMAN A. AFFEL, a citizen of the United States, residing at Maplewood, in the county of Essex and State of New. Jersey, have invented certain Improvements in Phantom Carrier Circuits, of which the followingis a specification.

This invention relates to transmission circuits and more particularly to arrangements for employing carrier transmission upon phantom ,conductiv'e systems. a

It has heretofore been the practice in ordinary telephone transmission to "Fphantom the telephone circuits so that each pair of conductors notonly acts as a seriesconvductive system or a side circuit, but also acts as one side ofa phantom circuit, 'the two conductors in parallel constituting one conductor of the phantom path while the two conductors of a similar side circuit operate in parallel as thereturn path for the phantom circuit. It ,has not, however, been the practice to utilize the phantom circuits thus formed for carrierqtransmission because-the requirements with respect tonnbalance and crosstalk-at-carrier frequencies have. been too great. .Thecarrier frequency unbalance and crosstalk ofthe phantom are gradually being reduced, however, and there is now presentedthe problem "of associating filters with each other so as to p'rop cr'ly separate the side voice circuits f and side carrier circuits from each otherand at the same time separate the phantom voice circuit and phantom carrier circuit from, each other and from the side circuit channels. I

It is one of the objects of the present invention to provide a suitable arrangement of filters for efiecting'the necessary separation between the various typesof circuits without introducing undesirable. transmission losses and without producing any undesirable efliect's upon the filters f due to the presence in. filters.

These objectsas wellasother objectsoi the invention may be attainedlby.meansof the arrangements set forth in the (following description and illustrated in the acCQInpanying drawing, the figure V of which: shows a ircuit diagram e bdt yi igtheinVntiQn 1n;ltspreferred-form. A

,to the voice side circuit channel-VL the same network ofotlier Referring to the drawing, HFL and I-IFLrepresent two telephonelines, each comprising a pair. of conductors which may be phantomed in a well known manner so that each pair of conductors acting in parallel operates as one side of a phantom circuit. The phantom connections are estab lished by means of transformers 10 and 10, from the middle points of whose windings taps 11 and 11 are led to form the phantom tern-finals. of the system; Con'ipositesets and OX are included inthei line HFL and HFL by means of which each olthc I fours conductors may be employed for Morse telegraph transmission. 'Thecomposite sets are. merely shownschematicallyin the drawmg, these sets being or" a type well known in the art so that detailed illustration is unnecessary. A v

In orclei'tliat thelineHFLrmay be em- .Jlo'yed foi ca 'rier transmission, a branch L is provided which leads to carrier equipment of any type Well known in the art. and, in thisbranch'a high pass filter .HF is included. This higlrpass filter is ofthe broad band type which freely transmits aband of frequencie within certain limits, while sharply attenuating andsuppressing the frequencieslying without the limits of the band. The filter is so designedasto pass the" various carrier frequencies employed in the system together with their associated'side bands, but it'will not permit ordinary voice currents transmittedover the line HFL to pass into the ,circuitCL Theordinary voice currents transmitted over the conductor HFL must be separated from the carrierfrequencies and transmitted through the transformer 10 In order to accomplish this result, a low pass .filter LF is connectedin the branch of the line circuitrHFL leading to the voice side circuit iVL The filter LF is of the broad band type and freely transmits all freouencies. lying Within the voice range while suppress ng all frequencies above the voicerange- .llhe carr er pfrequenclesare thereby ing through the loss pass filter LF to the voice side circuit VL The arrangement so far described is that ordinarily employed for superposing a plurality of carrier channels on an ordinary voice channel. It is possible to phantom a pair of circuits of this type for ordinary voice transmission by means of the phantom coils l0 and 10 with their phantom conductors 11 and 11. This follows at once from the fact that the unbalance between the phantom circuit and the side circuits at voice frequencies is no greater with the arrangement above described than in the case of circuits which are not arranged for mul tiplex carrier transmission, and the voice currents transmitted over the phantom, in so far as any unbalance occurs between the two conductors of the side circuit, are prevented from entering the carrier circuit, such as the circuit GL by the high pass filter. The effect upon the phantom of the filter LF -in the two conductors of the side circuit is to introduce impedance due to the series coils of the filter but this impedance is not serious at the ordinary voice frequencies. If, however, we attempt to transmit carrier frequencies over the phantom,

the inductance of the series elements of the filter L13 of LF, is relatively much greater, so that not only must this problem be overcome but the problem of selection between the carrier phantom and the voice phantom must also be overcome.

In accordance with the present invention, therefore, it is proposed to transmit the phantom carrier currents over the carrier branches including the filters HF and HR. For this purpose,phantom coils'20 and 20 are included in the circuits CL, and Chg as indicated, and phantom conductors 2i and 21 are led from the midpoints of .the phantom coils to form a carrier phantom terminal 011 With this arrangement, the phantom carrier currents need only be transmitted through the impedance of 'the filters HF, and H1 The shunt elements of these filters are inductance coils bridged across equal potential points (with respect to the phantom) of the two sides of the line forming one side of the phantom and consequently do not introduce an impedance to the currents transmitted over the phantom. The series condensers of the high pass filters, however, are included serially in the phantom circuits but these condensers readily pass thehigh frequency carrier currents so that the effect of the filters HF and HR uponthe carrier currents transmitted over the phantom is relatively smalh p in order to provide the necessary fre quency separation between the voice currents transmitted over the phantom and the carrier currents transmitted over the phantom,

a low pass filter LF is included in the voice phantom terminals VL and a high pass filter HF, is included in the carrier phantom terminal CL These filters are similar to the high and low pass filter combinations already described and operate in the same manner. The necessity for these filters arise from the fact that the conductors ol the voice phantom circuit are connected to the conductors of the carrier phantom cir cuit through the filters LR, and HF in series on the one hand. and the filters LF, and HR in series on the other hand.

It will be obvious that the general principles herein disclosed may be embodied in many other organizations widely different from those illustrated without departing from the spirit and scope of the invention as defined in the appendedclaims.

f-Jhat is claimed is:

1. In a transmission system, a pair of side circuits each adapted for the transmission of voice frequency currents and also for the transmission of carrier currents, a pair of terminal branches for each side circuit, a low pass filter in one branch of each pair to permit the transmission of voice currents over said branch while suppressing the transmission of carrier frequency currents transmitted over the conductors of the side circuits in series, a high pass filter in the other branch of each pair adapted to transmit carrier currents from carrier terminal equipment to and from the side circuit while preventing voice frequency currents from entering said branch, means to establisha phantom connection adjacent one end of said low pass filter associated with each side circuit to form a phantom circuit for the transmission of voice frequencies, means to establish a phantom connection adjacentoneend of said high pass filter associated wlth each side circuit to form a phantom connection for the transmission of carrier frequencies, a low pass filter in said first -mentioned phantom connection to permit the voice frequency currents to be transmitted thereover while suppressing carrier frequency currents, and a high pass filter in said second mentioned phantom connection to permit carrier frequency currents to be transmitted over said second mentioned phantom connection while suppressing voice frequency currents therefrom. i

2. In a transmission system, a pair of trans mission lines adapted to transmit either ordinary voice frequency currents or carrier frequency currents, a pair of branches for each line, one branch extending to a voice frequency terminal and the other branch extending to carrier equipment. alov: pass filter in ,said first mentioned branches of: each line and a high pass filter in said second mentioned branches or" eacnrline, means to connect a phantom conductor to the first mentioned branches of each line, a low pass filter included in the phantom conductors thus formed so that voice frequencycurrents may be transn'iitted over said phantom, means to connect a phantom conductor to the second mentioned branches of each line, and a high pass filter included in the phantom circuit formed by means of'sa-id second mentioned branches whereby carrier currents may be transmitted over said second mentioned phantom circuit to the exclusion of voice frequency currents.

'3. In a transmission system, a pair of transmission lines adapted to transmit either voice frequency currents or carrier frequency currents, a pair of branches for each line, one branch extending to a voice frequency terminal and the other branch extending to carrier equipment, a-low pass filter in said first mentioned branch of each line and a high pass filter in said second mentioned branch of each line, said low pass filter comprising a plurality of sections each of which consists of a series inductance and a shunt in'ipedance element, said high pass filter comprising a plurality of sections each of which consists of a series capacity and shunt impedance element, a phantom coil interposed between said low pass filter and said voice frequency terminals for each line, a phantom conductor connected to the midpoint of each phantom coil so that the two phantom conductors establish a Voice frequency phantom circuit, a low pass filter included in said phantom circuit, a phantom coil interposed between said high pass filter and said carrier terminal for each line, a phantom conductor connected to the mid point of each of said last mentioned phantom coils so that the two phantom conduc tors establish a carrier frequency phantom circuit and a high pass filter in said carrier frequency phantom circuit;

In testimony whereof, I have signed my name to this specification this 10th day of August,1925. I

HERMAN A. AFFEL.

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