GB715353A - Improvements in or relating to apparatus for amplitude modulating electric signals - Google Patents

Abstract

715,353. Valve modulation circuits. GENERAL ELECTRIC CO., Ltd., and KIRKNESS, R. H. Feb. 16, 1953 [Feb. 14, 1952], No. 4012/52. Class 40 (5) A carrier voltage is applied to the control grid of a valve 10, and a modulating signal to the grid of a valve 6 connected in series with the valve 10 across the H.T. supply 4, 5, a resistor 8 being interposed between the valves; and an output load resistor 1 develops at the anode of the valve 6 an amplitude-modulated carrier. In order that the modulation may be linear, a rectifier 23 with its anode earthed is connected to the anode of the valve 10. The valve 10 is so biased that current passes only during the positive half-cycles of its carrier input. Whilst the valve 10 is blocked its anode voltage is positive and the rectifier 23 is non-conducting; but when the valve 10 is passing current, its anode voltage falls, and the rectifier 23 gives a low-resistance path to earth. The H.T. supply is so arranged that the positive lead 4 is, e.g. at +200 volts, and the negative lead 5 at, e.g. -100 volts, relative to earth. As shown, a pair of such modulating circuits is used, with a common output load resistor 1. The carrier voltage is applied in pushpull to the grids of the carrier valves 10, 11, and is balanced out in the output circuit. The modulating voltage may be applied to the grids of either or both of the modulating valves 6, 7. When applied to both valves, the modulating voltage may be in parallel or in push-pull; m the latter case this voltage is balanced out in the output circuit. Pulse signals of positive polarity may be supplied to both the valves 10, 11 in place of an oscillatory carrier, and amplitudemodulated pulses taken from the output load 1.