GB522006A - Improvements in or relating to electrical signalling systems - Google Patents

Abstract

522,006. Automatic exchange systems. AUTOMATIC TELEPHONE & ELECTRIC CO., Ltd., and CORNER, A. C. Nov. 5, 1938, No. 32148. [Class 40 iv)] In a system in which a common source of carrier current supplies two communicating stations, the source OSC is connected through separate amplifiers Al, A2 to opposite sides of a high-pass filter or band - elimination filter HPFI designed to pass one or both sidebands but not the carrier. Combined modulator-demodulators of dry rectifier type are used. The two stations may be respectively a main and a rural telephone exchange connected together by a single junction. In this case dialling and supervisory signals for an audio and a carrier channel may be sent in various specified ways by sending currents of audible and sub-audible frequencies and direct current over the loop, the phantom circuit and the separate legs. Where the phantom is not used for signalling it can be used for telegraphy. Two separate carrier channels may be provided and may employ respectively 'the loop and the phantom circuit for signalling. In another suggested arrangement the automatic rural office is between two manual offices which communicate with each other by means of a carrier channel which may be carried by the rural office switches or by a permanent high-frequency bye-pass.