GB377307A - Improvements in or relating to automatic gain control devices for use in high frequency receivers - Google Patents

Abstract

377,307. Valve amplifying and detecting circuits. MARCONI'S WIRELESS TELEGRAPH CO., Ltd., Marconi House, Strand, MATHIEU, G. A., 3, Mayfield Gardens, Shirehall Park, both in London, and STED, G. A., Terling, Essex. March 28, 1931, No. 9493. [Class 40 (v).] In a high frequency receiver comprising a plurality of amplifier members in cascade means are provided to vary the gain, operated by the detector output, first of one of the cascade amplifier members and then successively the gain of the other amplifier members if the output exceeds a pre-determined value. Fig. 1 shows a gain unit AGC operated from the second detector D of a superhet receiver in which the control is applied first to vary the output of the detector D, and then the output of the intermediate frequency amplifier IFA and next the output of the frequency changing valve FC and finally the output of the high frequency amplifier HFA. The control may be effected by a diode detector arranged in parallel with the signal detector D Fig. 2 (not shown) and may be operated from the first detector, Fig. 3 (not shown). Fig. 4 shows a push-pull frequency changer in which the local oscillator LOV is coupled through a coupling valve CV to the mid-point of the grid inductance of the valves VM<1>, VM<2>. The grid bias 2 of the coupling valve is controlled by the gain unit and the circuit II is tuned to a harmonic of the oscillator circuit I. The control may be applied to both signal and oscillator valves by connecting lead 2<1> to the gain unit.