GB612024A - Improvements in and relating to muting devices for signal receivers - Google Patents

Abstract

612,024. Radio signaling; receiving circuits. GENERAL ELECTRIC CO., Ltd., and STENNING, L. C. May 15, 1946, No. 14683. [Class 40 (v)] In a radio receiver provided with means for muting.in the absence of a signal carrier, the time-constant of the muting action is made greater than that for unmuting. Noise in a frequency band above that required for signalling is selected by a tuned circuit 13 in the receiver output and is applied to a rectifier 14 provided with a load circuit 15, 16 of short time-constant. The negative potential developed across the circuit 15, 16 is applied to a valve 17 via a circuit of long time-constant comprising a resistance 18 and condenser 20. With the condenser 20 charged, current in the valve 17 ceases, causing a relay S with contacts S1 to insert an attenuating network 21, 22 in the connections to the loud-speaker. Upon the cessation of noise, the condenser 20 is discharged rapidly over a rectifier 19, causing the valve 17 to become conductive and the network 21, 22 to be removed from circuit. A potentiometer 23 permits of adjustment of the muting conditions. The arrangement is particularly applicable to mobile receiving stations, in which the signal strength may vary greatly over short periods, and may be modified to permit of the selective unmuting of any of a number of receivers according to the transmission of appropriate identification signals. The identification signals take the form of a number of tone frequencies with the omission of those corresponding to, receivers it is desired to call. A further acceptor circuit in the receiver output applies the appropriate tone frequency, if present in the signal, to a rectifier and relay with contacts arranged in series with the anode circuit of the valve 17 so as to mute the receiver. The risk of a signal being missed by a receiver for which it is intended is thus minimized.