GB625268A - Improvements in circuits for modulating the frequency or the phase of electrical oscillations - Google Patents

Abstract

625,268. Frequency and phase modulation. PHILIPS LAMPS, Ltd. July 18, 1946, No. 21540. Convention date, Feb. 25, 1943. [Class 40 (v)] In a circuit for modulating the frequency or phase of oscillations by means of a modulator tube which functions as a reactance, feed-back of the modulating oscillations, but not of the carrier, is provided for the tube so that the instantaneous value of the frequency or phase displacement produced by the modulation is proportional to the instantaneous value of the modulations and distortion thereby eliminated. As shown in Fig. 1, the oscillator generator 1 is connected to an oscillatory circuit 2, 3, which feeds a pentode 4 arranged to act as a reactance for the oscillations to be modulated by the provision of a network 6, 7. To secure frequency modulation without distortion, negative or positive feed-back of the modulating oscillations only is provided for the tube 4 so as to obtain a square function characteristic for anode current-control grid voltage. The correct negative feed-back is obtained in the circuit shown by a resistance 13 included in the cathode circuit which is shunted in respect of the carrier oscillations by a condenser 14. The desired negative feed-back may however be obtained from a resistance in the screen grid circuit or when a triode is used by a resistance in the anode circuit. When positive feed-back is required, the control grid circuit may be coupled to the circuit of one of the current carrying electrodes by a transformer. In a modification employing a hexode as the modulator and wherein the anode current/ control grid voltage is linear, the feed-back resistance 13 is connected in the screen grid circuit.