GB501915A - Telephone exchange systems - Google Patents

Abstract

501,915. Exchange systems; two-way transmission. BERRY, R. J. (Lorenz Akt.- Ges., C.) July 2, 1937, No. 18436. [Class 40 (iv)] Telephone substations are modified so that incoming traffic may be in the form of modulated carrier currents, no switching operations being necessary on the part of the subscriber to make the change from normal working. In one arrangement, Fig. 2, the microphone M and receiver T are separately bridged across the incoming line through high-frequency chokes, and the receiver is further connected to the line through a rectifier G and condensers C. In a further arrangement, Fig. 3 (not shown), the telephone receiver has two windings, one being associated with the line and microphone in an anti-side-tone circuit, and the other being fed with rectified high-frequency currents over a by-path. In a development of this circuit, Fig. 4, the use of two windings is avoided by arranging a relay A, which responds to a high-voltage impulse and locks up to the exchange battery, to switch the ordinary receiver over from its normal connection to the carrier by-path. Relay A also opens a part of the anti-side-tone circuit. The modulated carrier signals may be received over a junction or may be derived from low-frequency signals received over a junction. The latter arrangement eliminates a portion of the balancing arrangements which would otherwise be necessary. Fig. 6 shows an arrangement whereby low-frequency signals arriving over a two-wire junction D are converted by a modulator M<SP>1</SP> to high-frequency form. High- and low-pass filters M, N, H and amplifiers V, V are provided also.