GB392230A - Improvements in or relating to thermionic modulation systems - Google Patents

Abstract

392,230. Valve amplifying circuits. MARCONI'S WIRELESS TELEGRAPH CO., Ltd., Marconi House, Strand, London, and RUST, N. M., 109, London Road, Chelmsford, Essex. Nov. 18, 1931, No. 32043. [Class 40 (v).] The low-frequency modulating current applied to a carrier transmitter is maintained approximately constant by the use of a variable Á valve despite variations in signal intensity, whereby the modulation level is maintained at a " deep " value and overloading of the transmitter when the signal intensity is high is prevented. The Figure shows an amplifying system in which signals from the microphone amplifier 1 are passed through a variable attenuator 2 and potentiometer level adjustment 4 and are applied to the push-pull variable Á valves 10, 11, the output from which is passed to the modulating system through a further variable attenuator 31. Part of the output from the microphone amplifier is passed to a full-wave rectifier 14, the rectified current traversing a condenser-resistance combination 20, 21 which provides grid bias for the valves 10, 11. As the grid bias of the valves is varied in accordance with input level, the output will be substantially constant at a level determined by the adjustments of attenuators 2, 4, 31. The systems may be applied to the prevention of fading on short waves and tends to compensate for excessive variations in the microphone input.