GB471128A - Improvements in or relating to modulated carrier wave transmitters - Google Patents

Abstract

471,128. Valve modulating circuits. MARCONI'S WIRELESS TELEGRAPH CO., Ltd., GREEN, E., and CLOUGH, N. H. Feb. 27, 1936, No. 5933. [Class 40 (v)] .In a modulated carrier wave transmitter the fmal modulator is preceded by a coupling valve stage giving no voltage amplification but serving solely as a generator of low impedance so that the final modulator may run into grid current without causing serious distortion. Fig. 2 shows a choke modulator V1 fed by an auxiliary amplifier V<1>1 of low internal resistance having a choke L2 in the cathode lead. In a modification the source to be modulated is in series in the anode circuit of the modulating valve V1, Fig. 3 (not shown). The amplifier preceding the modulator may be directly coupled. Fig. 4 shows a series modulating arrangement in which the modulated source R is in the cathode circuit of the modulating valve. The auxiliary amplifier V<1>1 has an additional anode supply HT2 and is coupled to the modulating valve by the cathode resistance R5. An additional valve V<11>1 is provided to give coupling to the auxiliary valve V<1>1 to which variable grid bias may be applied to give "floating carrier" action. Fig. 7 shows a valve VF rectifying the audio frequency which is byepassed by condenser CF and varies the bias of the modulator V1. Instead of the tapped choke CH a transformer may be employed in the input to the modulating valve V1 or alternatively a tapped resistance may be employed. A quiescent or other push-pull system may be used the circuit being duplicated and the output fed through a transformer the secondary of which is in parallel with the modulated source. The output transformer in the case of a push-ull system may be in the anode circuits of the modulating valves, Fig. 8 (not shown), or in the cathode circuits of these valves, Fig. 9 (not shown).