GB440494A - Improvements in and relating to automatic volume control in radio receiving apparatus - Google Patents

Abstract

440,494. Valve circuits for wireless reception. MURPHY RADIO, Ltd., and MOXON, L. A., 62, Brook Street, Hanover Square, London. July 2, 1934, No 19474. [Class 40 (v)] In order to facilitate aural tuning an automatic volume control bias is derived which is dependent both on the signal strength and on the difference between the carrier frequency and the frequency to which the receiver is tuned. As shown, the intermediate frequency output of a circuit 2 is fed to a coupled circuit 21 and signal detector 3 and also through a condenser 4 to the grid of a volume control valve 1. The output of valve 1 is fed through condenser 7 to an A.V.C. rectifier 9 with delay bias source 14 and load resistance 8, the D.C. output voltage of which controls the gain of preceding valves of the receiver through the filter 10, 11 and lead 12. The output circuit 16 of valve 1 is also coupled to a sharply tuned circuit 15 feeding a rectifier 17 whose load resistance 18 is in the grid circuit of valve 1. A delay bias proportional to signal strength is applied to the rectifier 17 from the load resistance 22 of a rectifier 20 fed from a tapping on the circuit 21, or a fixed delay bias which is also the steady grid bias of valve 1 may be used. When no signal is being received the amplification of valve 1 is high and an excessive degree of A.V.C. is produced by the rectifier 9 which is reduced to the normal degree only when the signal is exactly tuned, and the bias of valve 1 is therefore great. This action therefore gives interchannel noise suppression and accurate aural tuning.