GB376154A - Improvements in or relating to radio and other high frequency transmitters - Google Patents

Abstract

376,154. Valve modulating circuits. MARCONI'S WIRELESS TELEGRAPH CO., Ltd., Marconi House, Strand, London. -(Assignees of Pray, G. E. ; Wading River, Long Island, New York, U.S.A.) Nov. 14, 1931, No. 31585. Convention date, Nov. 19, 1930. [Class 40 (v).] In a radio or other high-frequency transmitter improved circuit arrangements are employed to enable the keying to give comparatively gradual changes in the high-frequency amplitude, with the object of reducing key-click interference at adjacent receiving stations. As shown in Fig. 1, the key or relay K is arranged to apply either positive or negative voltage to the grid 11 of the keying-valve 9, the plate of which is connected to the screen-grid of the high-frequency valve 1. The screen-grid is given a positive voltage by connection to the HT supply B through a resistance R2 which is also in the plate supply circuit of the keying- valve 9. The keying changes are rendered gradual by the provision of a resistance R1 and condenser C1 in the grid circuit of the valve 9, and also by the resistance R2 and condenser C2 in its plate circuit. The resistance R may be in the plate circuit of the valve 1 instead of the screen-grid circuit. As shown in Fig. 3, the keying-valve 9 is in the grid direct-current circuit of the valve 1, and is shunted by a condenser C4. Positive and negative bias voltages for the keying-valve 9 are supplied by tappings on a potentiometer R4 from which also plate voltage is supplied to the valve 9. Plate voltage for the main valve 1 may be supplied from a separate source HV, or from the same potentiometer. A condenser and resistance in series may be connected across a section of the potentiometer R4, and the key K may be arranged to short-circuit this section.