GB410668A - Improvements in or relating to radio and like modulated carrier wave transmitters - Google Patents

Abstract

410,668. Valve modulating and amplifying circuits. MARCONI'S WIRELESS TELEGRAPH CO., Ltd., Electra House, Victoria Embankment, London.-(Assignees of Hansell, C. W. ; Port Jefferson, Long Island, New York, U.S.A.) Sept. 25, 1933, No. 26400. Convention date, Oct. 31, 1932. [Class 40 (v).] Undesired amplitude modulation in the output of an amplifier in a phase or frequency modulated transmitter, due, for example, to the use of an alternating or fluctuating supply for the operating voltages, is balanced out by rectifying a portion of the output to obtain a wave copy of the undesired modulation and applying this wave to an input electrode of the amplifier in the proper phase and magnitude to .effect compensation. The compensating wave may be applied to the screen grid of the amplifier valve or valves. In the arrangement shown in Fig. 1, the output of phase or frequency modulator 2 is amplified by a cross-neutralized push-pull amplifier 8, 10, to the output of which is coupled a coil 32 in circuit with rectifier 30, a copy of the undesired amplitude modulation being thus taken to a suitable tapping point on resistance 22 in the grid biassing circuit of the amplifier. As shown, anode, grid biassing and filament potentials are supplied by rectified A.C. The grids may be biassed by a battery or the valves may be self biassed. A cascade amplifier is described in which the first stage is biassed by a battery, the compensating voltages being applied at this stage. Specification 383,412 is referred to.