GB807780A - Improvements in or relating to circuit arrangements for automatic volume control - Google Patents

Abstract

807,780. Automatic gain control. SIEMENS & HALSKE A.G. Dec. 18, 1956 [Dec. 23, 1955], No. 38563/56. Class 40 (5). In a radio receiver automatic gain control (A.G.C.) is normally obtained from the load circuit 9, 10 of a rectifier 5 which is connected to one winding 4A of a transformer 4 in the carrierfrequency part of the receiver. A delay bias is obtained from the H.T. supply by means of a potentiometer comprising resistors 13, 14 and the load circuit 9, 10 is of short time-constant. A further winding 4B on the transformer feeds a second rectifier 6 having a load circuit 11, 12 of long time-constant; a delay bias is obtained from the potentiometer comprising resistors 15, 16. The voltage derived from the load circuit 11, 12 is also applied to the receiver, but via a third rectifier 8. The delay biases on the two rectifiers 4, 5 are so adjusted that in normal operation the third rectifier 8 is non-conductive, and the gain control voltage applied to the receiver is that across the load 9, 10; if, however, rapid fading occurs so that this voltage falls, the rectifier 8 becomes conductive and the voltage across the circuit 11, 12 of longer time-constant takes charge. A resistor 17 is provided in series with the rectifier 6 in order to prevent heavy loading of the transformer 4 by the rectifier circuit 6, 11, 12 on sudden considerable variations of the signal input level, e.g. during tuning. The arrangement is more particularly intended for use in single-sideband receivers, to combat the effects produced by selective fading, and in C.W. telegraphy receivers.