GB563205A - Frequency modulator - Google Patents

Abstract

563,205. Frequency modulation. MARCONI'S WIRELESS TELEGRAPH CO., Ltd. April 23, 1943, No. 6571. Convention date, April 27, 1942. [Class 40 (v)] In a frequencymodulated transmitter, the oscillation generator comprises a pair of thermionic valves V1, V2 with their anodes connected in common to a tuned circuit L1, C1 and with their control grids connected to opposite sides of a similarly-tuned circuit L2, C2, the two circuits being loosely coupled by inductive relation between the coils L1, L2 and being also coupled by a direct connection between a point on the coil LI and the mid-point of the coil L2. The voltages fed back to the grids by the direct connection are in phase opposition to the anode voltage and are sufficient to maintain selfoscillation. The voltages fed back by the inductive coupling are in opposite phase to each other and in quadrature with the anode voltage. The signal voltage is applied in pushpull through a transformer T to screens or other grids in the valves, and causes a modulation of the frequency of the generated oscillations which are taken off by the coupling coil L3. In a modification, a condenser is interposed between the tappings on the coils L1, L2, Fig. 2 (not shown).