GB718705A - Improvements in or relating to automatic frequency control - Google Patents

Abstract

718,705. Automatic frequency control systems. MINISTER OF SUPPLY. June 1, 1953 [June 20, 1952], No. 15630/52. Class 38(4) In an AFC system for control of a klystron oscillator by joint adjustment of the resonator cavity and the reflector voltage, the error-detecting circuit is connected to the reflector by an A.C. coupling having a time constant larger than the response time of the cavity adjustment, whereby slow increase in the degree of mistune is counteracted by cavity adjustment, and faster increase by reflector bias control. The reference frequency may be continuous or pulsed. At starting, or when the klystron frequency is outside the lock-in range the motor driving the cavity adjustment may search over wider limits until a lock-in frequency is attained. In Fig. 1 the output of the klystron 5 is mixed at 2 with a reference oscillation 4 to provide a beat frequency which is amplified at 3 and fed to a frequency discriminator 1. The detected error voltage through a circuit 6 controls a motor 7 and gearing 10, from which a shaft 9 adjusts the klystron cavity, and a shaft 12 drives a potentiometer slider 11 to adjust the reflector bias. Correction is thus provided for slow changes of the degree of mistune. More rapid changes are provided for by applying the error voltage from the discriminator 1 through a condenser 14 (or a transformer) to the reflector electrode which gives a rapid though transitory adjustment of the frequency until the slower-acting motor adjustment becomes effective. When the reference oscillation is discontinuous or pulsed, the output of the discriminator comprising positive (or negative) pulses is fed at 16, 17, Fig. 3, through a pair of diodes V1 to an integrator valve V2. The integrated output passes to the grid of a valve V3 forming a cathode-coupled pair with a valve V4. The anodes of valves V3, V4 are connected to field coils reversibly controlling a motor M for adjusting the cavity of the klystron. Quick changes of the degree of mistune are corrected by connecting the anode of the valve V2 through a condenser 14 to the reflector electrode. The motor M also drives a generator G whose output is connected to the grid of the valve V3 as described in Specification 606,673. When the tuning error is too great to permit direct locking- in, a frequency-sensitive test member 15, Fig. 1, connected to the mixer output 2 releases a relay and throws the contact SI to connect the grid of the valve V3 to a limit switch T. This causes the motor M to drive the klystron tuning through a wide range and to reverse its direction at each limit of the range by throwing the switch T. As the klystron tuning reaches the lock-in range, the test member 15 operates its relay SI to bring the AFC into action. The motor may control the cavity adjustment by screw-and-nut mechanism, Fig. 4 (not shown), operating a plunger within the cavity as in Specification 718,721. Specification 670,238 also is referred to.