Patent GB-656124-A (GB)
Title: Improvements in or relating to phase controlling circuits
IPC: G01S1/30
Filed: 1948-10-08
Abstract: 656,124. Automatic phase control systems. DECCA RECORD CO., Ltd., O'BRIEN, W. J., BRIDGES, D. E., HENDLEY, D. A., EASY, M. H., and VICKERS, J. Oct. 8, 1948, No. 25731/49. Divided out of 656,108. [Class 38 (iv)] [Also in Group XL (c)] A phase control circuit for adjusting the phase of an output signal relative to an input signal in accordance with the amplitude of a control signal comprises, a valve circuit deriving from the input signal first and second signals differing from phase opposition by a small angle and combining them to produce a third signal which varies in amplitude and phase in accordance with the relative amplitude of the first and second signals as controlled by the control signal, a tuned circuit to which the third signal is applied and means for varying the resonant frequency of the tuned circuit in accordance with the control signal so that the variation in amplitude caused by the change in resonant frequency of the tuned circuit substantially counterbalances the variation in amplitude of the third signal and so that the tuned circuit is in resonance at the input signal frequency when the second and third signal are in phase quadrature. The invention thus provides a circuit in which phase can be varied whilst the signal amplitude remains constant. In an embodiment of the invention a reactance valve is used to vary the resonant frequency of the tuned circuit. The input signal is applied to V1 and V2 in phases differing slightly from phase opposition and a resonant circuit T4 is provided in their common anode circuit. Potentiometer 12 is adjusted so that with no control voltage applied over line 11 to the grid of V2 the combined output of V1 and V2 is in phase quadrature with that of V2 operated alone. Control is normally applied both to V2 to vary the magnitude and phase of the combined output and also to reactor valve V3 to vary the resonant frequency of circuit T4, which also varies the magnitude and phase of the output. The phase shift due to the variation in amplitude of the output of V2, which causes an amplitude variation proportional to sec # (# being the phase shift) is made equal to the phase-shift due to the variation in the resonant frequency of T4 which causes an amplitude variation proportional to cos #. The amplitude variation is thus propoitional to sec # X cos #, that is to say, it is independent of #. It is stated that phase variations of Œ 120 degrees with substantially constant amplitude are possible in practice and two circuits may be used in series to cover more than a whole cycle. The invention is described as being of particular use in maintaining the radiated signal of a station such as is used in the radio navigation system described in Specification 656,108, in phase with the master oscillator at the station. For this purpose the radiated signal is received and compared with the master oscillator in a phase discriminator whose output is applied to a phase control circuit between the oscillator and power stages of the station in such a way as to reduce any error. Specification 630,698 also is referred to.