Patent GB-738160-A (GB)
Title: Improvements in or relating to the automatic frequency control of electric oscillation generators
Inventor: BRYDEN JOSEPH EASTO
IPC: H03L7/04
Filed: 1952-03-26
Abstract: 738,160. Automatic frequency control systems. GENERAL ELECTRIC CO., Ltd. June 19, 1953 [March 26, 1952], No. 7771/52. Class 38 (4). [Also in Groups XL (b) and XL (c)] The frequency of an electric oscillation generator is stabilized at the natural frequency of an electric resonator by providing a rotary member within the resonator to impart an alternating wobble to its resonant frequency the oscillatory output of varying amplitude being detected to provide an alternating output whose phase is dependent on the direction of mis-tuning, which detected output is used to correct the generator frequency. Fig. 2 shows the lay-out of the system, Fig. 1 the oscillation generator, and Fig. 4 the electric resonator. The output of the generator 31 is fed by a probe 32 through an attenuator 33 to the cavity resonator 34. A disc, ring, or loop 45 of metal, or dielectric material, is rotated within the resonator by a synchronous motor 46 connected to supply mains 53, so as to wobble the resonance frequency of the resonator at, say, 50 c/s. The resonator output, picked up at loop 43, thus acquires an amplitude modulation which is detected at 44, and passed through amplifier 49, and filter 51 and a phaseadjuster, if necessary, to a two-phase motor 52, the other phase winding of which is fed from the mains. The detected modulation is at 50 c/s. and its phase sense is dependent on whether the generator 31 is operating above or below the natural frequency of the cavity 34. The motor 52 is thus started in the direction necessary to correct the generator frequency, it being geared to adjust an associated tuning- stub 54. In order, on starting up, to bring the oscillator frequency within the pull-in range of the A.F.C. system, the two-phase tuning motor 52 may be supplied with both phases from the mains, this supply being interrupted as soon as modulation components are supplied by the crystal detector 44. The generator, Fig. 1, comprises a triode tube 1 with its cathode connected to an axial rod 5, its grid to a coaxial tube 6, and its anode coupled to an outer tube 7. Pistons 8, 9 provide for tuning adjustment. The automatic tuning control operates on a length of coaxial line 4 loosely coupled to the generator by a flexible line 4 and a probe 12. The effective length of the coaxial line 4 is varied by axial movement of a shorting-bridge 19 of the non-contact-making type, comprising two lowimpedance sections 21 separated by a section 23 of higher impedance. The bridge 19 is supported by a ring 24 of lossy dielectric material, and by six buttons 25 of insulating material. Movement of the bridge is effected by a member 26 projecting through a slot in the outer conductor 18, and coupled by rack-and-pinion mechanism to the motor 52, Fig. 2. The resonator 34, Fig. 4, comprises a metal cylinder 36 and an axial metal rod 37, accurately located by three insulating studs 40, and with a micrometer head 39 for controlling axial adjustment of the rod 37. The exciting probe 42 enters at one side of the cylinder, and energy is conveyed to the crystal detector 44 by a pickup loop 43. The motor 46, Fig. 2, for driving the modulating member within the resonator, may be of the kind described in Specification 738,159, and is mounted on the outside of the cylinder 36 with its axis horizontal and at rightangles to the axis of the probe 42.