GB451237A - Improvements in or relating to carrier wave transmitting apparatus - Google Patents

Abstract

451,237. Valve modulating systems. STANDARD TELEPHONES & CABLES, Ltd., STRONG, C. E., and McLEAN, F. C., 63, Aldwych, London. Feb. 1, 1935, No. 3391. [Class 40 (v)] In a modulating system of the kind in which the carrier wave amplitude is varied in accordance with changes in signal volume, this is effected by influencing the plate circuit of the modulated carrier amplifier by voltages varying with the signal volume and at syllable frequency. As shown in Fig. 2, speech is amplified by a push-pull pair of valves V3, V4 biassed to operate as a Class B amplifier, and the speech output voltage is applied through a transformer T2 and blocking-condenser C3 across the plates and cathodes of the carrier amplifiers V1, V2, thus producing a modulated carrier in the output circuit and aerial. The direct current through the valves is varied by including the plate-cathode paths of the carrier amplifiers V1, V2 in series with the plate-cathode paths of the speech amplifiers V3, V4 and with a choke L1. Owing to the biassing of the grids of the valves V3, V4 the direct current therethrough varies according to signal volume and at syllable frequency, and the series connection of the valves causes these variations to be imposed on the carrier amplitude. Rectified signal voltages may also be applied to the grids of the valves V3, V4. In a modification shown in Fig. 3, the speech is plate-modulated on the carrier by the valves 2, and is rectified at 5 and applied at 4 to vary the voltage of the D.C. source 3 for the modulated amplifiers 1. When the source 3 is a mercuryvapour rectifier, the voltage derived at 5 may be used to vary the phase of a grid control element. Alternatively this control voltage may be derived from the plate current of the amplifier 2 if this is of Class B type. Specification 283,264, [Class 40 (v)], is referred to.