GB299316A - Improvements in high frequency electric signalling systems - Google Patents

Abstract

299,316. British Thomson-Houston Co., Ltd., (Assignees of Bird. L. F.). Oct. 21, 1927, [Convention date]. Thermionic modulating systems ; combined transmitting and receiving arrangements.-The parent Specification describes a combined transmitting and receiving wireless telephone station in which the oscillations of the transmitter are inhibited, except when the operator is speaking, by a control valve which has a negatively biassed grid and is located in the anode circuit of the oscillator. According to the present invention the speech circuits are rectified before being used to neutralize the negative grid bias of the control valve. The control valve is thus prevented from momentarily acting as a modulator when speech begins; initial distortion of words is therefor avoided and smaller condensers can be used for smoothing the positive potential applied to the control grid. The oscillation generator 1 acts through a high frequency amplifier 4 and transformer 5 on a line or aerial system 7, and the outgoing oscillations are modulated through the modulator 19 by speech currents coming through the transformer 18 from the microphone 16. A receiving apparatus 28 is connected through the hybrid transformers 5, 17. Inhibition of the outgoing radiation is effected as follows :-The plate circuit of the oscillator 1 extends via the high tension battery 9 through the filament and plate F10 , P10 of the control valve 10 to the filament F1 of the oscillator via the conductor 11. The grid G10 of the control valve is negatively biassed by the battery 23, so as to block the above circuit except when the battery 23 is opposed by a potential drop, due to speech currents, in the resistance 24. Such currents pass from the microphone 16 through the transformer 18 to the amplifier 20, the output of which is rectified at 22 so as to produce the required potential drop in the resistance 24. Smoothing condensers 25, 26 are provided, and these may be of smaller capacity than those shown at 23 in the drawing accompanying the parent invention.