GB913364A - Improvements in or relating to tunable electric oscillators employing frequency stabilisation - Google Patents

Abstract

913,364. Automatic frequency-control systems. GENERAL ELECTRIC CO. Ltd. July 6, 1960 [July 6, 1959], No. 23126/59. Class 40 (5). An oscillator 1 continuously tunable, e.g. over 3-20 mc/s., is stabilized relative to harmonics of a 100 kc/s. crystal oscillator 4 and an interpolation frequency set by a tunable A.F.C. frequency discriminator 7 ganged with the tuning of the oscillator 1. Crystal harmonics, generated at 3, pass through a filter 5 (cutting-off any harmonics of higher frequency than oscillator 1) and beat with the oscillator 1 in a mixer 2 before passing to a filter 6 of pass-band just over 100 kc/s. and A.F.C. discriminator 7. The latter comprises two frequency discriminators 8, 9 in parallel, one 8 being tunable by a capacitor over a range 150 kc/s. centred on the mean frequency of the pass-band of filter 6 during three-quarters of its rotation but during a final quarter rotation of the capacitor (returning it to its initial value), the discriminator output being reduced to zero by a switch; another 9 having a tuning capacitor and frequency sweep over the same frequency range as but 180 degrees out of phase with the capacitor variation of discriminator 8 and its output likewise rendered zero by a switch during a final quarter rotation. If one only of the 100 kc/s. harmonies is passed by filter 6 (therefore lying around its centre frequency), only discriminator 8 is operative, but if two harmonics pass (at the ends of the pass range of filter 6), both of discriminators 8, 9 pass outputs, being then tuned apart by 100 kc/s. Preferably the discriminator conjoint outputs are equal to what would be obtained if one signal only was passed by filter 6.