US1973504A - Telecommunication system - Google Patents

Description

Sept. 11, 1934. A. PIERROT TELECOMMUNICATION SYSTEM 2 Sheets-Sheet 1 Filed April 24, 1933 Fig.1

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INVENTOIR ATTORNEYS Patented Sept. 11, 1934 UNITED STATES TELECOMMUNICATION SYSTEM Andr Pierrot, Paris, France, assignor to Lignes Telegraphiques et Telephoniques, Paris, France,

a corporation of France Application April 24, 1933, Serial No. 667,714 In France April 28, 1932 1 Claim.

In order to avoid reactions between the two one-way channels of the line repeaters connected in two-wire telecommunication circuits, it is the practice to arrange on the two sides of each one- 5 way repeater device a differential transformer which, together with the impedancesco-nnected to its different terminals, constitutes a balanced Wheatstone bridge. In order to increase the utilization of the circuits, the latter are grouped in pairs by means of coupling transformers to form phantom circuits.

However, the presence of all these transformers causes an appreciable weakening which is added to that of the line, as well as distortion of the speech currents.

Ihe present invention has for its object to reduce the disadvantages mentioned by so re-arranging the differential transformers and the impedances connected to their terminals that the transformers function also as coupling transformers and thus render especial provision of the latter unnecessary.

The invention will be better understood by reference to the accompanying drawings in which Fig. 1 illustrates diagrammatically in simplified form the repeater connections for a two-wire circuit, as at present known;

Fig. 2 illustrates the arrangement of Fig. 1 modified by the embodiment of a novel arrangement of differential transformers in accordance with the invention;

Fig. 3 illustrates the invention embodied in a repeater station for a quad and associated phantom circuit.

Like parts are referred to throughout by the same reference numerals or letters.

Referring to Fig. l, numerals l and 1 denote the two differential repeater-balancing transformers, the three windings of which are respec- 40 tively A, B, C and A, B, C. Numerals 2, 2 denote the two parts of the two-wire circuit which is connected to the repeater through coupling transformers 5, 5' respectively. The two oneway channels of the repeater are denoted by 3 and 3, the repeating devices of which transmit in opposite directions. The balancing networks are denoted by 4 and 4'.

For the purpose of explanation, it will be assumed that, for example, the winding C of the differential transformer 1 has 2 11. turns and that the two windings A, B each have 12 turns. Under these conditions, if Z is taken to represent the impedance of the line looking from the terminals a, a, it is known that in order to avoid interaction between the two channels 3, 3' of the repeater and in order to obtain maximum ef iciency, the impedance of the balancing network 4 must be equal to- Z, the impedance looking from c, 0 towards 3 must be 2Z, and the impedance of 3 looking from d, d must be Z/2.

However, I have found that it is possible in each differential transformer to interchange the members arranged according to one diagonal with those of the other diagonal (i. e., by an imaginary 90 anticlockwise rotation, as a whole, of e. g., the arrangement of apparatus comprising the terminals a, a and b, b; c, c and d, d; and the differential transformer 1)., provided that the impedances connected to the various terminals retain the same proportionate values as those above-indicated. By thus re-arranging the trans formers of Fig. 1, the arrangement of Fig. 2 is obtained. In the latter figure, if the impedance of the line 2 seen from c, c is denoted by Z, the balancing networks l, 4 will therefore each have an impedance Z/4 and the input and output of each repeating device 3, 3' each be of impedance Z/Z.

Stated in another way, therefore, my invention balancing transformers in the manner illustrated in Fig. 2, the transformers being modified to the extent that centre tappings m and m for the windings C and C respectively are provided, for effecting connection of the transformers of the phantom circuit. Fig. 3 represents the formation of the phantom circuit according to this method; the use of the usual coupling transformers is thus rendered unnecessary, which offers a great advantage in view of the fact that an improvement in transmission and appreciable economy results therefrom.

I claim:

In a two-way two-wire telecommunication circuit, a line repeater comprising two separate oneway channels and two one-way repeating devices, one in each of said channels, operating in opposite directions; differential transformers, each comprising line windings and repeater windings, for coupling said repeater with said circuit without the use of coupling transformers, centre-tap connections in said line windings for formation of a phantom circuit, centre-tap connections in repeater windings, balancing networks in said channels and connected to said centre-taps in said repeater windings, one to each, the respective impedances of the line, said two one-way channels, and said balancing network being so proportioned as to form, with the said line and repeater windings of the associated differential transformer, a balanced bridge.

ANDRE PIERROT.

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