GB447888A - Improvements in or relating to modulated carrier wave transmitters - Google Patents

Abstract

447,888. Wireless systems. MARCONI'S WIRELESS TELEGRAPH CO., Ltd., Electra House, Victoria Embankment, London.-(Assignees of Hansell, C. W.; Rocky Point, Long Island, New York, U.S.A.) Dec. 12, 1935, No. 34540. Convention date, Dec. 12, 1934. [Classes 40 (iii) and 40 (v)] A phase-modulated carrier wave transmitter comprises means for reducing the energy of undesired side frequencies by automatically increasing the energy of the modulated wave as the phase thereof deviates ahead of or behind the phase of the carrier. As shown the phase modulator 4, Fig. 4, supplied with carrier frequency from source 2 and modulating currents from source 6 feeds the pushpull amplifiers 8 feeding a radiating system. Some of the modulating energy from source 6 is fed to a double-wave rectifier 22 the load resistance R of which is in series with a resistance R1 in the lead supplying screengrid current to the paralleled valves 20. These valves act as amplitude modulators of the energy in valves 8, there being a common supply circuit to the valves 8, 20 including a modulating choke MC. In a modification, Fig. 5 (not shown), the valves 20 are triodes and the choke MC is replaced by a modulation transformer. In order more accurately to compensate for the defects in the phasemodulated output, automatically variable resistances such as the substance known as " Thyrite" (Registered Trade Mark) which have resistances varying with the potential applied thereto may be substituted for the resistances R, R1 for example or a variable resistance network, Fig. 7, containing such a resistance B may be connected between the modulator 4 and source 6. Alternatively, valves may be used in the modulator 4 having the desired characteristics. Specification 416,396 is referred to.