GB488111A - Improvements in or relating to radio and like receivers - Google Patents

Abstract

488,111. Valve circuits. MARCONI'S WIRELESS TELEGRAPH CO., Ltd., and KEALL, O. E. Dec. 31, 1936, No. 35885. [Class 40 (v)] In an automatic frequency control system of the kind in which the anode-cathode space of a control valve acts as a variable reactance in a resonant circuit, the quadrature voltage for application to the grids of the control valve 4 is obtained from a portion of a phasesplitting network of constant impedance, energized from the resonant circuit. The local oscillator 1 of a superheterodyne receiver has coupled to its tuned circuit 2, 3, by means of a coil 8 a valve 9 in whose anode circuit is connected the phase-splitting circuit, cornprising between points 14, 16, two parallel paths consisting of inductance 10 and resistance 11, and condenser 12 and resistance 13, the junction points 22, 23 being connected by screened transformer 5, 21 to the grid circuit of valve 4. Resistances 11, 13 are each equal to the square root of the quotient obtained by dividing the inductance by the capacity, and under these conditions valve 4 acts as a pure reactance whose sign depends upon the sense of coupling with the local oscillator, and whose magnitude is controlled by the bias of valves 9 and /or 4. By departing from the quadrature relation of voltage on the control valve grid a positive, or negative resistance which latter may be advantageous in the case of short wave frequency changers, may be thrown across the tuned circuit, the value of which may be controlled by the condenser 12. Interlinking of the condenser 12 with the tuning-condenser may be employed to control the oscillator amplitude over the tuning range. In modifications the valve 9 is not employed and the phase-splitting circuit, with a series condenser and resistance, is connected across the tuned circuit, the quadrature voltage being taken from points 22, 23, or across inductance 10 only by means of an auto-transformer.