GB527099A - Improvements in or relating to wave transmission systems - Google Patents

Abstract

527,099. Valve amplifying circuits. STANDARD TELEPHONES & CABLES, Ltd., and MEERS, R. A. March 31, 1939, No. 10111. [Class 40 (v)] In a wave transmission system wherein signals are compressed before transmission and subsequently expanded, the compression and expansion are effected by varying the feedback ratio in negative feedback amplifiers by deriving the feedback voltages from networks including non-linear impedances. The Figure shows a compressing arrangement embodying amplifying valves V1, V2, and a metal rectifier bridge X1 forming the non-linear impedance in the feedback path to produce compression. The impedance of the bridge X1 is controlled by rectifier X2 over a smoothing circuit L3, C6, C7 and fed from the output through an amplifying valve V3. The sensitivity adjustment of the arrangement may be controlled by varying the feedback of the valve V3 by resistance P1 or by changing the secondary tapping on transformer T6. Relays AR, BR through contacts ar, br enable the control to be rendered inoperative or to be effected at a local point by resistance P1 or at a remote point over lines connected to terminals 12, 13 and to a remote resistance. The expansion amplifier at the receiving station is similar to the compression amplifier except that control voltages are derived from the input and the feedback voltage is taken across the non-linear impedance instead of across the series fixed impedence R2. The expansion amplifier is described in Specifications 503,083, 513,416 and 517,180. Specifications 475,310 and 479,388 also are referred to.