GB424470A - Improvements in or relating to modulating and keying systems for radio and like transmitters - Google Patents

Abstract

424,470. Valve modulating circuits. MARCONI'S WIRELESS TELEGRAPH CO., Ltd., Electra House, Victoria Embankment, London.-(Assignees of Plebanski, J. ; 32, Wapolna, Warsaw) July 12, 1934, No. 20468. Convention date, Aug. 17, 1933. [Class 40 (v)] The modulating and high frequency stages of a thermionic modulation system have their cathodes connected together, the common cathode point being connected to earth through a resistive impedance permeable to direct current. In Fig. 1 the common portion of the anode circuits of the modulating valve V1 and the high frequency valve V2 comprises a resistance R shunted by a condenser C1. By this means it is found that the anode current of V1 falls as that of V2 rises so that economy of high tension current is effected; also the characteristic of the oscillatory output from OC has a straight slope from the origin, so that 100 per cent modulation may be obtained with small distortion. Automatic volume control may be employed to keep the operating point at its optimum position. Modulation is effected by varying the grid bias of V2, and may be by modulation or keying potentials; in the latter case the output energy is reduced substantially to zero during spacing. A pair of modulating valves in parallel may be similarly associated with a push-pull high frequency pair ; or the valve V2 may be made self-oscillating by back-coupling, Figs. 3 and 5, (not shown). Fig. 4 shows a push-pull arrangement of the modulator and high frequency valve anode circuits, suitable chokes and condensers being provided in the input of the high frequency valve as shown; the valve V2 may be provided with back-coupling for self-oscillation. Fig. 6, (not shown).