GB399616A - Improvements in modulating systems for carrier-wave signalling - Google Patents

Abstract

399,616. Valve-modulating circuits. GENERAL ELECTRIC CO., Ltd., Magnet House, Kingsway, London, NOBLE, H. R. and WESTELL, E. P. L., c/o General Electric Co., Stoke, Coventry. June 20, 1932, No. 17433. [Class 40 (v).] A modulating-circuit comprises a wheatstone bridge with the carrier applied to one diagonal and the modulated output taken from the other diagonal, the signal being employed to vary the resistance of one or more arms of the bridge, preferably constituted by triode valves, and so to vary the degree of unbalance of the bridge. As shown in Fig. 2, the carrier source O is coupled by a transformer T3 to two circuits which are coupled respectively by transformers T4, T5 to two of the bridge arms, thus applying the carrier wave across the diagonal A, B. Valves V1, V2 constituting the other bridge arms have their grids excited in opposite phase from a microphone transformer T6 and potentiometer P. The valves are differently biassed so as to unbalance the bridge and to transmit a carrier even though no modulation is present. The modulated carrier is taken from the diagonal C, D and applied to an amplifier M. The voice-frequency impedance of the arms AC, CB should be low. In a modification, the coils T4, T5 form a divided secondary coil to a primary coil in the circuit of the source O.