GB643669A - Improvements in or relating to superheterodyne radio receiving sets - Google Patents

Abstract

643,669. Automatic volume control. STANDARD TELEPHONES & CABLES, Ltd. March 17, 1947, No. 7300. Convention date, Jan. 30, 1946. [Class 40 (v)] A C.W. receiver incorporating automatic volume control is provided with a variable biassing arrangement in the A.V.C. line to neutralize the change of A.V.C. voltage when the beat oscillation is brought into operation. As shown, a detector valve has the signal fed to its first anode D1 through a tuned transformer and produces the audio output at BF. The signal voltage is also fed to the second anode D2 through condenser C1 to produce an A.V.C. voltage across the load resistors R2, R3. When the beat oscillator valve V2 is switched by H.T. switch K1 on for C.W. reception, the A.V.C. voltage tends to rise due to the rectification of the beat frequency in the A.V.C. detector. This is compensated by passing the oscillator cathode current through resistor R3 to produce an opposing voltage when the oscillator is in operation, which varies in dependence upon the amplitude of the oscillation. In an alternative arrangement (Fig. 4, not shown), a common cathode double diode triode is used in a circuit similar to that of Fig. 2, and in a further alternative arrangement (Fig. 3, not shown) the opposing bias is obtained from the slider of a potentiometer supplying H.T. to the oscillator. Specification 518,437 is referred to.