GB612627A - Automatic gain-control arrangement - Google Patents

Abstract

612,627. Automatic gain control. HAZELTINE CORPORATION. May 21, 1946, No. 15406. Convention date, June 1, 1945. [Class 40 (v)] To reduce the effect of interference pulses in a pulse modulated system, fast A.G.C. is employed, the control potential having a duration approximately equal to the desired pulse train, but being terminated rapidly thereafter. A super-regenerative receiver 12, Fig. 1, feeds a noise-gain stabilization circuit 15 of the type described'in Specification 592,271, having a long time constant circuit 16, 17. The receiver also feeds a peak rectifier 21 feeding amplifying valves 22, 23 which produce a control potential for application to the receiver 12. The received signal, Fig. 2, curve A, may comprise a pilot-pulse P1 and associated signal pulses P2, P3 and an interference pulse P4. Due to the peak rectifier 21 the pilot-pulse appears as a pulse P5, curve C, causing the gain of the receiver to fall, curve D. As the peak rectifier is only effective on pulses above a certain amplitude, only the early part of the pilot-pulse is used, the gain of the receiver decreasing the input to the peak rectifier 21 below the requisite level. The anode load of valve 23 includes a delay line 31 shorted at its further end and terminated by the characteristic impedance at the anode end. The pulse P5 is reflected at a pulse P6 after a time equal to the greatest length of the pulse signal, thus restoring the gain of the system, curve D. The signal fed to the limiter 13, curve E, is clipped at levels F, G to produce an output signal H. In a modification, Fig. 3 (not shown), a superheterodyne receiver is employed with A.G.C. units corresponding to units 15, 20. In order to dispense with the pilot-pulse, the signal is fed directly to an auxiliary channel and through a delay line to the main channel. Specification 612,371 also is referred to.