GB782878A - Improvements in or relating to automatically controlled variable frequency oscillators - Google Patents

Abstract

782,878. Automatic frequency-control systems. SOC. FRANCAISE RADIO-ELECTRIQUE. Oct. 12, 1955 [Nov. 12, 1954], No. 29057/55. Class 38 (4). A frequency sweep oscillator 1 has its frequency sweep stabilized by a control loop, including a frequency discriminator 3 whose output is additively combined with the sweep voltage in a comparator circuit 4 as negative feed-back. Also, during intervals when the frequency sweep is inoperative, the discriminator output is corrected for each of two different voltages alternately applied at the control voltage input 15 so that the discriminator zero output and characteristic slop are both corrected as necessary. The oscillator output may first be transposed down in frequency by a stable heterodyne oscillator 7 and applied to each of two circuits having frequency discriminators 11, 20 tuned to centre frequencies fn, fm alternately with reference frequencies of these values fn, fm, from stable oscillators 10, 19, the change-over for each circuit being controlled by an electronic or other switch 26 at a frequency, e.g. 50 c/s. The outputs of discriminators 11, 20 will thus be rectangular pulses of amplitude and polarity depending on drift of the transposed frequency from the values fn, fm. The pulses are applied through gated amplifiers 12, 21 opened alternately by a gating control circuit 27 only during constant reference voltages Un, Um being applied at 15 (while the frequency sweep of oscillator 1 is inoperative), to one phase of two phase motors 13, 22 whose other phase inputs are the switching frequencies (50 c/s) of switch 26. The motor 13 opertaes a potentiometer slider 24 to vary a bias additively combined with the output of discriminator 3 to correct this output to the required value producing frequency fn at the output 16. Moreover, motor 22 drives the tapping point of the output potentiometer 28 fed by discriminator 3 so that the characteristic slope is controlled to give an output of correct value also at the frequency fm.