GB888587A - Improvements in or relating to high-stability variable-frequency generators - Google Patents

Abstract

888,587. Frequency synthesisers; automatic frequency control systems. SIEMENS & HALSKE A.G. June 30, 1959 [June 30, 1958], No. 22422/59. Classes 40(5) and 40(6). A beat oscillator comprises a first oscillator variable in frequency stepwise over a relatively wide frequency band and a second oscillator variable over a band corresponding to a step, the output of the two oscillations being mixed to provide a difference frequency output and the second oscillator being manually variable by virtue of means for converting its output to a low intermediate frequency and means for automatically adjusting the frequency of the oscillator so as to reduce the difference between the intermediate frequency and the frequency of a manually adjustable low frequency oscillator. The Figure comprises a first oscillator 1 adjustable over the wide frequency band and a second oscillator 9 adjustable over a narrower band, the two oscillations being mixed in a mixer 8 to produce a difference frequency which is filtered at 10 and amplified at 17 to produce an output at 19. The first oscillator is maintained in operation at a selectable one of the harmonic frequencies of a crystal controlled oscillator 2 by means of a variable reactor 5 controlled by a discriminator 3. The output of an oscillator 9 is combined with the output of a crystal oscillator 12 in a mixer 11 and the resulting intermediate frequency is selected at 13 and applied to a phase comparator 15 together with the output of a interpolating oscillator 14, the phase comparator controlling a reactor 16 so that the intermediate frequency output the mixer 11 corresponds with that of the interpolating oscillator. Thus by varying the frequency of the interpolation oscillator the frequency of the output from terminal 19 may be, varied over a range equal to the difference between the harmonics of oscillator 2. The oscillator 12 may be replaced by an oscillation supply derived from the crystal oscillator 2. Frequency "wobbling" of the beat frequency oscillation output may be effected by disconnecting the automatic frequency control from oscillator 1 and varying the adjustment of a tuning member of the oscillator.