GB239309A - Improvements in radiotelephonic and other radio-frequency signalling systems - Google Patents

Abstract

239,309. Hale, G. W., and Radio Engineering Co., Ltd. June 18, 1924. Thermionic modulating systems. - Relates to modulating systems of the type in which a power oscillation and control valve are placed in series as regards the high tension supply, the cathode of the power valve operating at a high-frequency potential relative to earth. The invention consists in an arrangement wherein the high-tension supply c, Fig. 1, is connected directly to the plate of the power valve a, this plate being maintained substantially at high-frequency earth potential. The output from the oscillator a is modulated in accordance with micraphonic variations applied to the grid of the series control valve b. A condenser m prevents the high-tension voltage from shorting across the filaments of the two valves, and forces the direct-current component to flow via the plate of the control valve b. A radiofrequency choke n prevents undesirable damping of the main oscillating circuits through the varying impedance of the control-valve shunt, whilst admitting the necessary low-frequency modulating effect. The plate of the control valve may also include part of the aerial winding d as well as the choke coil n. Also the filament supply to the main valve a may pass through a part of the aerial inductance d, a balancing choke being introduced on the other side of the filament battery. As shown in Fig. 4 the potential of the plate of valve b is the same as that of the filament of valve a, the choke n being dispensed with. The filament supply from the battery t passes through the portion o of the main inductance, and a choke q is introduced for balancing purposes. A radio-frequency choke r is included in the grid circuit of the valve b to prevent high-frequency grid currents. The leak resistance h in the grid of the main valve may also be supplemented by a choke coil k.