GB410549A - Improvements in muting devices for radio-receiving apparatus - Google Patents

Abstract

410,549. Valve circuits for wireless reception. GENERAL ELECTRIC CO., Ltd., Magnet House, Kingsway, London, and SMYTH, C. N., c/o General Electric Co., Wembley, Middlesex. Dec. 22, 1932, No. 36312. [Class 40 (v).] A muting device in a super-heterodyne receiver comprises a circuit so sharply tuned to the intermediate frequency that the set is inoperative unless the frequency about which the frequencies in the output of the first detector are centred differs by less than 1000 cycles from the intermediate frequency for which the set is designed. Preferably the tuned circuit comprises a piezo-electric crystal 5 tuned to the intermediate frequency, in series with a balancing condenser 6 shunting a tuned circuit 3, 4 fed from the first detector. When there is no output (from the first detector) having the intermediate frequency, the anode current of the triode section of the diode-triode 12 flows through the resistance 15 biassing the audiofrequency amplifier 17, fed from the second detector, to make it inoperative. When the intermediate frequency is fed to the circuit 3, 4, crystal 5 oscillates and current flows through the diode 7, 9 to set up a potential across resistance 8 which alters the bias on the grid 10 so that the anode current from the diodetriode ceases, thereby removing the prohibitive bias applied to valve 17. A resonance indicator of known kind may be included in the tuning control of the set. Specifications 379,608 and 395,569 are referred to.