GB979861A - Improvements in or relating to frequency synthesisers - Google Patents

Abstract

979,861. Automatic frequency control systems; frequency changing circuits. RACAL ELECTRONICS Ltd. Aug. 28, 1961 [Sept. 6, 1960], No. 30654/60. Drawings to Specification. Headings H3A and H3F. In a frequency spectrum generator a plurality of oscillators tunable over ranges 3.3-4.2 mc/s., 2.7-3.6 mc/s. and 3.1-4 mc/s., i.e. of overlapping and comparable frequency ranges, are frequency and phase locked with harmonics of a 100 kc/s. pulse train from a 100 kc/s. crystal oscillator, by closed loop circuits using phase detectors and reactance valves. The second and third oscillator frequencies are then divided by 10 and 100 respectively by a phaselocking loop, and a pair in sequence of such loops, controlling tunable oscillators of frequency ranges 270-360 kc/s. and 31-40 kc/s. respectively, giving selectable frequency steps of 10 kc/s. and 1 kc/s. respectively. The latter oscillators are used to control on a phaselocking control loop a local oscillator of range 301-400 kc/s., ganged with the selected 10 kc/s. frequency step, the higher frequency tunable oscillator (of range 270-360 kc/s.) first reducing it to a range 31-40 kc/s. which is phase compared with the lower frequency tunable oscillator in a phase detector of the control loop. This local oscillator is then compared in the phase detector of a further phase-locking loop with a difference frequency produced by beating a final output oscillator of range 3.6-4.6 mc/s. with the first tunable oscillator, ganged with it, (of range 3.3-4.2 mc/s.), this phase detector controlling the frequency of the final output oscillator to the 1 kc/s. step selected. The frequency dividing circuits are ganged together and may each include circuits producing pulses from the divided frequency oscillators, preceding their inputs to the phase detectors. The phaselocked oscillators may all include capture circuits. A phase-locked loop controlling an oscillator to a reference frequency 1 mcs/s. (10 times the reference pulse repetition frequency of 100 kc/s), may also be used.