GB570392A - Improvements in control circuits for radio and like oscillation generators - Google Patents

Abstract

570,392. Valve generating circuits. FEWINGS, D. J. Feb. 4, 1942, No. 1500. [Class 40 (v)] The phase-quadrature voltage required for the grid of a thermionic reactance is derived from a choke coil acting as a capacity in the anode circuit of the oscillator valve. The oscillator comprises a pentode valve A with the control grid and screen grid back-coupled to produce oscillations in the tuned coil L<11>. A choke coil L<1> resonant below the frequency range of the oscillator is connected in its anode circuit, and voltage in quadrature with the anode current is taken from the anode through a large condenser C<1> and a potentiometer PR<1> to the grid of the reactance valve B, the anode of which is connected to the control grid of the oscillator valve A. The anode circuit of the valve B comprises a load resistance R<11>. Adjustable bias is applied trom potentiometer PR<11> to the cathode of valve B ; and the negative inductance represented by the reactance valve may be varied by applying a control voltage to one of its grids to vary its mutual conductance. In a modification suitable for higher ranges of frequency, the grid circuit of the valve B includes an inductance which resonates with the grid-earth and associated capacities at a frequency which may be either below or above the oscillator frequency. In the first case, the control valve acts as a negative inductance, and in the second, as a negative capacity. The system is designed to give a considerable range of frequency such as is required in a panoramic receiver. Specifications 474,682 and 484,701 are referred to.