GB592274A - Gain-control arrangement for wave-signal receivers - Google Patents

Abstract

592,274. Wireless signalling; automatic gain control. HAZELTINE COR. PORATION. March 27, 1945, No. 7777. Convention date, April 19, 1944. [Class 40 (v)] A wireless receiver is arranged to have its output suppressed during predetermined intervals which are long compared with the time constant of the A.V.C. circuit, by means which also maintain the A.V.C. potential between predetermined limits during the said intervals. The invention is described in connection with a radio beacon of the kind described in Specification 592,269, adapted to transmit directionfinding information on receiving an interrogating pulse. This comprises a single transmitting and receiving aerial 46 which passes a received pulse to a super-regenerative receiving valve 60 having a quench oscillator 18, and thence to rectifier 21, pulse amplifier 40 and keying valve 43 to trigger an oscillator 30 to transmit a response pulse from aerial 46. The output from 40 is also fed to unit 50 which produces an A.V.C. potential from the quiescent noise output of receiver 10 and applies it through lead 68 to the grid of valve 10. When it is desired to use other radio equipment at substantially the same frequency it is necessary to suppress the receiver during the intervals when the other equipment is operative. This, however, allows the gain of the receiver to rise to such an extent that when the suppressor action is removed the receiver output is sufficient to trigger the transmitter even in the absence of a received pulse. This is overcome by a unit 70 which applies voltages to disable the receiver valve 10 and quench oscillator 18 and applies a third voltage to unit 50 to maintain the A.V.C. voltage within a satisfactory range of values. The suppressor signal, in the form of pulses, is applied to terminals 71, 72 of unit 70 and is fed to rectifier 74 and integrating circuit 76, 77 to give a saw-tooth waveform which is passed through valve 78 so as to provide at the anode a negative saw-tooth wave. This is applied through resistances 83, 85 to disable the receiver 10 and quench oscillator 18 and is applied through resistance 86 to the output side of A.V.C. rectifier 60 in unit 50 so as to maintain a satisfactory value of the A.V.C. potential during the blanking interval.