GB973421A - Improvements in or relating to variable frequency oscillators - Google Patents

Abstract

973,421. Automatic frequency control systems. MARCONI CO. Ltd. Sept. 11, 1961 [Feb. 7, 1961], No. 4537/61. Addition to 839,656. Heading H3A. A variable frequency channelized oscillator 10 is stabilized at intervals of 1 kc./s. by (1) beating it with a selected harmonic of a stable 1 mc./s. source in a mixer 9 to derive an output from filter 111 of frequency less than 1 mc./s., then (2) dividing the filter output by an integer factor selectable between 500 and 1000 in a frequency divider 13 to derive a 1 kc./s. output which is then compared in a phase discriminator 114 with a 1 kc./s. oscillation obtained by frequency division at 15 from the 1 mc./s. stable oscillator. The phase discriminator output then stabilizes the oscillator 10, through a reactance tube 16, at 1 kc./s. intervals according to the selected division factor. The frequency division range 500-1000 alone suffices (instead of 1-1000) provided a ganged control means GC is used to reverse by a changeover switch S the polarity of the output of the phase discriminator and, in the case of additional frequency fractions selected for the oscillator of less than ¢ mc./s., to conjointly select the next higher of the 1 mc./s. harmonics from which the channelized oscillator frequency is subtracted in the filter 111. The gang control GC may operate a pair of indicator scales, one indicating the actual range of frequency divided, the other the complement to 1 mc./s. of the actual range of frequencies divided to 1 kc./s.