GB812608A - Improvements in or relating to noise-controlled switching means for wireless receiving apparatus - Google Patents

Abstract

812,608. Noise-controlled switching means. PLESSEY CO. Ltd. July 22, 1957 [May 17, 1956], No. 15385/56. Class 40 (5). A switching device in which a D.C. voltage derived from the signal/noise ratio of an incoming waveform is applied to an electronic trigger which produces an output to drive a switching relay which in turn controls the muting of the receiver. The incoming waveform at 1, Fig. 1, passes via I.F. amplifier 2 and delay line 3 to the mixer 4 where it is mixed with the output signal f of the oscillator 5. The output of the mixer 4 is fed via filter 6, which selects signal f + I.F. = fl, for the second mixer 7 where it is mixed with the direct feed from the I.F. amplifier. The output of mixer 7 splits and one is taken via filter 8 which selects signal f whilst the other passes via filter 9. Both outputs are then rectified and used differentially to provide a D.C. input to the trigger circuit, Fig. 2, which will vary in accordance with the signal/noise ratio of the incoming waveform. When the signal/noise ratio is more positive than a predetermined figure the input to V7, Fig. 2, is more positive and V7 draws more current. Thus the voltage at the grid G1 of V8 becomes more negative, the left-hand triode draws less current and the voltage at G2 of V8 becomes more positive. This in turn increases the anode current of the right-hand triode and the voltage drop across the cathode resistor R40 is increased, effectively making the voltage at G1 more negative. The cycle is repeated until the valve reaches saturation and the grid of V9 becomes sufficiently less positive to release the relay RL which switches on the muted receiver. When the signal/noise ratio is such as to cause a negative swing in the input voltage the reverse action takes place and the relay is held operated to mute the receiver.