GB575159A - Improvements in frequency modulation - Google Patents

Abstract

575,159. Frequency modulation; copying telegraphy. DEHN, F. B. (Press Wireless, Inc.). Sept. 16, 1943, No. 15196. [Classes 40 (iii) and 40 (v)] An audio-frequency oscillator, comprising reciprocally-coupled valves with a resistancecapacity phasing-network between them, is frequency modulated by variation of the network resistances, which take the form of variable-resistance electronic valves. As shown, the coupling network between the reciprocallycoupled triode valves 6, 13 comprises a series electronic resistance 2 and capacity 4 connected between the plate of valve 6 and the grid of valve 13, and an electronic resistance 3 shunted by a capacity 5 connected between that grid and earth. The signal, which may arise from a facsimile telegraph transmitter, is used to vary the oscillation frequency by varying one or both of the electronic resistances 2, 3. The electronic resistances 2, 3 may take the form of double-triode valves which have their grids connected to the signal source and their plate circuits transformer-coupled to the circuit of the oscillator. The signal voltages applied to one of the control valves may be less than that applied to the other with a view to avoiding amplitude modulation of the generated oscillations,(Fig. 2, not shown). Specification 537,689 is referred to.