GB351070A - Switching arrangements for two-way telephone transmission systems - Google Patents

Abstract

351,070. Two - way repeaters. STANDARD TELEPHONES & CABLES, Ltd. and HODGSON, K. G., Columbia House, Aldwych, London. March 22, 1930, No. 9275. [Class 40 (iv).] A two-way repeating system comprises an echo-suppressor at each end adapted to be operated by signals from the opposite end to disable the return path, and an echo-suppressor control device at each end which disables the echosuppressor at the end at which signals originate. This arrangement prevents blocking of the system due to simultaneous signalling in both directions when it is a long one with finite transmission time, e.g. a long four-wire circuit or a number of circuits connected in tandem. In the system shown in Fig. 1, ES2, ES3 are suppressors for blocking the lines L1, L2 when currents arrive from W and E respectively. Simultaneous transmissions in both directions operate ES1, ES4 which disable both suppressors. The system shown in Fig. 2 consists of two four-line circuits connected in tandem and provided with normal echo-suppressing arrangements ES1 .. ES4 so that they can be used singly. This system is modified in Fig. 3 by providing control devices F1, F2 operable by direct or alternating pilot current from O to change the functions of ES1, ES4, when the circuits are connected in tandem, so that ES1, ES4 act solely as echo-suppressor control devices. The system then operates as described in Fig. 1. Detailed circuits for the tandem arrangement, and using direct pilot current, are shown in Fig. 4 which corresponds to circuit A, Fig. 3. Transformers T1 .. T4 are centre tapped to provide a path'for pilot current which is connected up over switch S4. Normally, signals incoming to amplifier A1 operate relay S1 over amplifier-detector AD2, thereby short-circuiting the output of amplifier A2 in the opposite path. When relay S2 is operated by pilot current, it short-circuits the output of amplifier D in a branch circuit leading from A2 to echo-suppressor AD1, S3 so that this echo-suppressor is disabled but the transmission path over A2 is still effective. When more than two circuits are connected in tandem, pilot current may be connected at the terminals. The pilot current may make preliminary changes in the suppressors to be controlled, the final change in function from echosuppressor to suppressor-disabler being effected by the actual signalling currents. The invention may be applied to radio and submarine cable links.