GB515047A - Improvements in or relating to modulator circuit arrangements for high-frequency electrical signalling - Google Patents

Abstract

515,047. Modulation systems. MARCONI'S WIRELESS TELEGRAPH CO., Ltd., and CLOUGH, N. H. April 22, 1938, No. 12156. [Class 40 (v)] A modulator system comprises two class-C high-frequency stages in series, with four class-B modulator valves so connected as to constitute alternative paths from the D.C. source to each stage, two of the modulator valves operating to secure modulation for positive half-waves, and the other two operating for negative half-waves: The two highfrequency stages HF1, HF2 are connected in series with the modulation frequency choke CH across the high-tension supply. The modulator valves V1, V2 are each connected across the choke CH, and one high-frequency stage and the modulator valves V1<1> V2<1>, are each connected across one high-frequency stage. Valves V1 and V2 are arranged to be simultaneously conducting on one modulation halfcycle and valves V1<1> and V2<1> on the other halfcycle. The grids of V1 and V2<1> are fed in phase-opposition from points IT1, IT2 on the secondary S of the modulation input-transformer T. The grids of V1<1> and V2 are fed with layeramplitude voltages from the extremities of secondary S due to the fact that their cathodeearth potentials are varying at modulation frequency. In a modification, Fig. 3 (not shown) the grids of VI and V2<1> are driven from a modulation transformer, while the modulation voltages for the grids of V1<1> and V2 are obtained from tappings on the choke CH. In a modification of this, Fig. 4 (not shown) the voltages supplied to the grids of V1<1> and V2 from the choke CH are adjustable by means of potentiometers. In a preferred modification, Fig. 5 (not shown), the modulation input is applied to sub-sub-modulator valves which feed valves V1 and V2<1>, and also sub-modulator valves which feed the grids of V1<1> and V2. The outputs of the two high-frequency stages may be combined in a single circuit; or, where the same modulation is required to be transmitted on two different wavelengths simultaneously, two high-frequency stages may operate on different wavelengths with individual output circuits.