GB600166A - Improvements in or relating to gain-controlled electrical transmission systems - Google Patents

Abstract

600,166. Automatic gain control. SPERRY GYROSCOPE CO., Inc. Sept. 28, 1945, No. 25314. Convention date, Sept. 29, 1944. [Class 40 (v)] In a signal transmission system, an automatic gain control voltage is derived in such a way that its magnitude is dependent upon the frequency at which the signal level exceeds a predetermined level. The invention is shown in a gated pulse receiver comprising a frequency changer 12, I.F. stages 13, 24, detector 24<1>, wide band amplifier 26 and utilization circuit 31. A gating circuit 27 renders amplifier inoperative except for the short periods during which pulses may be received. The output from amplifier 26 in the form of negative pulses is fed to a triggered multivibrator 34, 35 arranged so that in the absence of a signal, valve 34 is conducting and valve 35 is cut off. Any of the negative pulses that have an amplitude greater than a predetermined threshold cause valve 34 to cut off and valve 35 to conduct. Thus, the potential of anode 37 of valve 35 varies between the fixed potential of H.T. source 40 when the valve is cut off, and a lower fixed potential when the valve is conducting. This varying potential is fed to an integrating network 58, 59 to produce a control potential, the value of which depends on the frequency with which the pulses from 26 exceed the predetermined amplitude threshold. The average voltage across condenser 59 is fed through a cathode follower 65 to provide an A.V.C. voltage which is applied to the screen grids of the I.F. stages 13 and 24.