GB564504A - Improvements in and relating to electron discharge circuits - Google Patents

Abstract

564,504. Frequency modulation. BRITISH THOMSON-HOUSTON CO., Ltd. July 9, 1943, No. 11151. Convention date, July 11, 1942. [Class 40 (v)] In order to'permit a large frequency deviation without loss of linearity in a frequency modulation transmitter, the anode circuit of a reactance control valve has an auto-transformer connection to the inductance of the oscillator tank circuit. Oscillations are maintained in the tuned circuit 21 by three-point connection to the electrodes of the generator valve 12, and are fed through an amplifier 13 to a line or other load 14. The reactance control valve 11 has its anode connected to the outer end of an inductance coil 20, part of which is included in the tuned circuit 21. The cathode is earthed through a bias resistance 32 shunted by a condenser 33. The control grid receives a quadrature voltage from the junction of a resistance 35 and condenser 40 connected across the tuned circuit 21 in series with a blocking condenser 41. As the cathode is in effect connected to the earthed tapping 26 on the inductance 20, the phasing circuit 35, 40 can be arranged to supply an accurate quadrature voltage to the grid of valve 11. A microphone 10 shunted by a condenser 42 is connected in the grid leak circuit of the valve 11 for modulating the frequency of the generated oscillations.