GB692003A - Improvements in or relating to frequency-stabilizing circuits for frequency-modulated oscillators - Google Patents

Abstract

692,003. Automatic frequency control systems. PHILIPS ELECTRICAL INDUSTRIES, Ltd. Aug. 3, 1951 [Aug. 8, 1950]. No. 18402/51. Class 38 (iv). [Also in Group XL (c)] Relates to circuits for frequency modulation of a carrier source, of the kind in which the source 1, Fig. 1, is synchronized with a frequency derived from a stage 3 at which a stable oscillator 4 is phase-modulated by the signal voltage 5 after integration at 6. Synchronization has been effected by applying the output from the stage 3 through a frequencymultiplier 7 to a mixer 2 where its phase is compared with that of the carrier source 1 to derive a control voltage a which is applied to a frequency-control device 8 associated with the carrier source 1. The invention consists in simultaneously applying the signal voltage 5 direct to the frequency control device 8, so that the control voltage a can be confined to D.C. and slowly-changing voltages, thus diminishing the tendency to self-oscillation due to back coupling round the loop 1, 2, 8. The frequency-control device 8 may comprise two valves 8<SP>1</SP>, 8<SP>11</SP>, Fig. 2, with their anodes connected jointly to control the frequency of the source by means of a valve reactance, a saturable-core inductance, or other device. The control grid of the valve 8<SP>1</SP> receives the D.C. and low A.C. output from the phase-comparer 2, and gives control over a wide frequency range; and the control grid of the valve 8<SP>11</SP> receives the modulating signal b and through the capacity 10 the remainder of the phasecomparer output a. If the phase-modulated output from 3 is converted into pulses of short duration, the phase-comparing stage may take the form of a gated mixing stage. A seriestuned circuit may be connected across the output of the phase-comparing stage 2.