Patent GB-518480-A (GB)
Title: Improvements in or relating to electrical frequency-dependent control means, primarily for radio apparatus
IPC: H03J7/04
Filed: 1938-07-23
Abstract: 518,480. Wireless receiving apparatus ; directive wireless signalling. JONES, J. E. RHYS-, BARRETT, J. O. G., and PLESSEY CO., Ltd. July 23, 1938, No. 21912. [Class 40 (v)] [Also in Groups XXXV and XXXVI] In a receiver means are provided for effecting a continual variation in the tuning so as, with the incoming signal, to produce a control voltage or current for correcting deviations. In a direction finder a continual oscillatory movement may be given to the search coil to produce with the incoming signal a voltage or current for controlling the mean setting of the search coil. The Figure shows a superheterodyne receiver comprising a frequency changer 11 followed by a selective LF. amplifier 13, detector 14, and low frequency amplifier 15. The local oscillator 12 is frequency modulated over a narrow range by the mains frequency from transformer 16 acting through the electromagnet 23 on the iron core of the inductance 22. When the receiver is correctly in tune the intermediate frequency does not shift on to the sloping portions of the resonance curve of amplifier 13 and the output of detector 14 does not contain the mains frequency. When however the mean intermediate frequency occurs on the flank of the resonance curve, detection of the frequency modulation occurs and mains frequency, whose phase and amplitude depends upon the direction and amount of error in the receiver tuning, is passed by filter 24 to the magnet 25 of motor 26 controlling the local oscillator frequency by means of condenser 21. A second magnet 27 on the motor is energized directly from the transformer 16 and phasing resistances 19 are inserted in the supply to magnet 23 so that the magnet 25 is energized with phase lag or lead with respect to magnet 27, causing the motor to rotate in one or other direction to correct an error in the tuning of the receiver. The amplitude of the detected control frequency may be employed to remove a muting bias from a valve or apply a brake to tuning mechanism when the receiver is correctly in tune. Alternatively, a phase-controlled relay operated by the control frequency output may be employed, to control a reversible motor employed to correct tuning, or to control the bias of a thermionic reactance in the oscillator circuit. In the application of the invention to " straight " receivers the resonant frequency of one or more of the tuned circuits may be periodically varied. The principal may be employed to correct the setting of a radiogoniometer by causing the rotor to move through a small angle, at a suitable frequency with respect to its mean position. A corresponding frequency is obtained in the output of a detector fed from the goniometer, the phase and magnitude of which depends upon the difference between the mean setting and the setting for maximum output. This output is then utilized to correct the goniometer setting. Instead of swinging the rotor, two windings displaced by a small angle may be used and connected alternately in circuit. The windings may comprise either the stator or the rotor of the goniometer. Specification 445,350 is referred to.