GB575156A - Improvements in frequency-controlled electric oscillators - Google Patents

Abstract

575,156. Frequency measurement. GENERAL ELECTRIC CO., Ltd., and FOOT, J. B. LOVELL-. June 18, 1943, No. 9834. [Class 37] [Also in Group XXXV] Automatic frequency control of an electric oscillation generator is effected by beating the oscillations with those from a standard oscillator, and passing the beat currents to a rectifier through a filter which has a characteristic of the form shown in Fig. 2 or 3, the rectified output being applied as a variable bias always of the same sign to the grid of a reactor valve associated with the variable oscillation generator. The latter is initially tuned to generate a frequency which always lies on one side of the standard frequency, the reactor valve grid being initially biassed to increase the difference. The unidirectional control bias derived from the filter and rectifier opposed this initial bias. In Fig. 6, the standard and the variable oscillations are applied as 8, 9 respectively to the control grids of a mixer valve 7, from the anode of which the beat frequency is led through a filter 17 to an amplifier 16. The output from this amplifier is rectified by the diode 27 and positive control bias is led from the terminal 31 to the reactor valve grid. The filter 17 may be designed to give a characteristic as shown in Fig. 2 in which abscissae represent the beat frequency and ordinates the rectified filter output. The characteristic has a sloping portion O, Q for beat frequencies below a low value FM and a level or rising portion for higher beat frequencies up to a limit FN which may be infinite. Alternatively, and as shown in Fig. 3, the filter may have an upper cut-off limit at a frequency which is less than the difference between successive standard frequencies, where a plurality of standards are employed. The filter may have a transmission showing more than one minimum. The reactor valve may have a relay in its anode circuit which operates, when the reactance control bias attains a value greater than a predetermined limit to reduce the said bias substantially to zero.