GB641543A - Improvements in or relating to frequency-modulation circuits - Google Patents

Abstract

641,543. Frequency modulation. PHILIPS LAMPS, Ltd. July 4, 1946, No. 20021. Convention date, June 30, 1942. [Class 40 (v)] Frequency modulation is produced by feeding back from a modulator comprising one or more valves to the anode circuit of an oscillator valve 1, Fig. 1, an amplitude modulated signal derived from but differing in phase by about 90 degrees from the anode voltage of the valve in such a way that no coupling exists between the anode of the oscillator and the modulating oscillations except that due to the electron stream of a valve. A condenser 5, Fig. 1, of high reactance and resistance 7 feed to a modulator valve 6, having in its anode circuit a modulator 10, a grid voltage in phase quadrature with the anode voltage of the oscillator valve 1 to produce a modulator valve anode voltage also in quadrature which is impressed by a condenser and inductively coupled coils 9, 2, on a tuned anode circuit of the oscillator 1, additional coupled coils 8, 11 negativing any in-phase coupling between the anode circuits of the valves. Alternatively, Fig. 2, the modulator valve 6 is connected by resistance capacity coupling with a reactance valve 12 with anode connected to the oscillator valve and to a phase quadrature condenser 5 and resistance 7 input of the modulator valve 6. Alternatively, Fig. 3, amplitude modulation of the quadrature volate fed from the oscillator valve 1 to the grid of the reactance valve 12 by a condenser 5, resistances 7 and 19, and a circuit 17 tuned to the mean oscillator frequency"damped by a resistance 18, is effected by a diode 14, battery 15 and modulation source 16 across the grid. The diode limits the modulating carrier wave amplitude to the difference between the battery and modulation voltages. Valves in push-pull may alternatively be used.