GB430461A - Amplifying systems for electric waves - Google Patents

Abstract

430,461. Repeating systems. STANDARD TELEPHONES & CABLES, Ltd., Connaught House, Aldwych, London.-(Western Electric Co., Inc. ; 195, Broadway, New York, U.S.A.) Aug. 24, 1934, No. 24440. [Class 40 (iv)] Relates to the use, in repeater systems, of amplifiers having negative-phase feed-back circuits with transmission characteristics similar to those of the line so that line distortion is compensated as described in Specification 371,887, [Group XL]. According to the invention, the feed-back originates at a point distant from the amplifier, e.g. at another repeater station and is transmitted over the same or a similar line so that compensation is effected without the use of a network simulating the line. Variations of transmission characteristics, e.g. due to temperature are automatically compensated. In the system shown in Fig. 1, A, B and C are repeater stations although repeaters at B may be omitted. Energy is fed back from B to the input of A by balanced bridges and a transmission line b. Assuming B to be midway between A and C, the length of the feed-back loop from A to B and back equals the length of line from A to C, so that the distortion arising in line A to C is compensated. An application to two-way repeating systems is shown in Fig. 2, in which the usual balancing networks are replaced by lines 5, 5a to B and back. The lines 5, 5a function as balancing networks and also as a feed back circuit for both directions of transmission. In the modification shown in Fig. 3, network W4 is disposed on the output side of the repeater at B, while in the further modification shown in Fig. 4, the forward line a is used also as a feed-back circuit by the provision of additional bridges W2, W3. These bridges introduce additional loss into the feed back circuit and so increase the effective gain of the amplifiers ; this is compensated by bridges 14, 15 or other attenuators. The bridge connections render the gain and impedance of the section A B independent of the lines to which it is connected, but if this is not essential, the apparatus at B, Fig. 4, may be replaced by a reflecting point so that half the energy arriving at B is passed on and half reflected. The invention is also applied to two-way systems as shown in Fig. 6 which comprises a two-wire circuit developed from the fourwire circuit shown in Fig. 5. For W-E transmission, signals pass in the direction of the arrows pointing east while the feed-back path is indicated by arrows pointing west, while for E-W transmission, the reverse is the case. The overall gain of the circuit is zero. The two-wire circuit of Fig. 6 is derived from Fig. 5 by consolidating the bridges at each repeater station, the arrangement of a bridge being shown more clearly in Fig. 6a, wherein L1, L2 are the lines and A the feedback amplifier. Other bridge arrangements for two-way working are shown in Figs. 8a, 9a, in which the lines L1, L2 are connected in parallel and series respectively, the other arms excepting X being pure resistances. Irregularities in the cable circuits of systems employing the bridges of Figs. 6a, 8a, 9a lead to undesirable reflections and echoes in long systems and it may be desirable to break up the circuit into sections by interposing four wire circuits having each path arranged as in Fig. 6. The phase shift over the feed-back path may be controlled by additional networks such as Z, Fig. 4.