GB718722A - Improvements in or relating to automatic frequency control of electric oscillation generators - Google Patents

Abstract

718,722. Automatic freauency control systems. MINISTER OF SUPPLY. Oct. 9. 1952 [Oct. 15, 1951], No. 24036/51. Class 38À(4) In the automatic frequency control of a reflex klystron oscillator for which a reference frequency is available only for short periods separated by longer periods, a freauency comparison supplies the correcting voltage to the reflector electrode during the shorter periods, and the resonantcavity of the klystron is adjusted during the longer intervening periods towards that resonance value which results in maximum power output. The system is particularly applicable to the control of the local oscillator in a pulse radar apparatus the reference frequency being provided by the transmitter oscillator which Generates trains of pulses extending over short periods separated by longer periods of quiescence. Fig. 1 shows the general circuit arrangement, and Fig. 5 the means for controlling the cavity-adjusting motor. Oscillations from the klystron are fed at terminal 3 to a mixer 1 which also receives the reference oscillations at terminal 2. The mixer output is fed to a frequency discriminator 4 centred on the desired difference frequency, and during the shorter periods of transmitter activity, the discriminator output passes via contacts RA, RNA2 to the klystron reflector electrode to adjust its frequency. The mean value of the electrode voltage is sustained, during the longer periods of transmitter inactivity, by a condenser C. During these intervening periods the contacts RA and RNA2 are open, and a contact RNA1 is closed to connect a lowfrequency source G to a transformer T whose secondary coil is then in effective control of the reflector voltage. A frequency modulation is thus imparted to the klystron and results - in an amplitude modulation of the klystron output unless the cavity is accurately tuned. The amplitude modulation appears at the output of the mixer 1 as an alternating current of the same low frequency as 'the source G and in phase agreement or opposition therewith according to the direction of mistune of the cavity. A phase-sensitive rectifier 5 of any suitable form converts this A.C. to D.C. which is applied to an input terminal of a pair of cathode-coupled valves 7, 9, Fig. 5. If the D.C. input is positive, valve 7 allows current to pass through a field coil 10 of a motor m to cause it to run in one direction. With negative input, valve 7 is blocked, and valve 9 energizes the field coil 11 to run the motor in the opposite direction. The motor m drives a generator g to feed back to the grid of the valve 7 in the manner described in Specification 606,673. The motor m effects the adjustment of the klystron cavity in the direction to give maximum oscillatory output by driving a threaded shaft controlling a plunger system within the cavity, Fig. 4 (not shown). In an alternative form of motor control, the low frequency A.C. output from the mixer is applied through an amplifier 31, Fig. 6, to one field coil 32 of a two-phase motor M, the other coil 33 being fed through a 90 degrees phase shifter from the source G. The direction of rotation of the motor is dependent on whether the current in coil 32 is in phase or anti-phase with that of the source G. Specifications 670,238 and 718,721 also are referred to.