Automatic tuning for radio receivers

Abstract

Abstract 445,350. Valve circuits for wireless reception. COLE, Ltd., E. K., Priory Crescent, Southend-on-Sea, and BRADFIELD, G., 34, St. Benets Road, Prittlewell, Essex. Oct. 5, 1934, No. 28497. [Class 40 (v)] A radio receiver is automatically brought into exact tune with a desired signal by deriving from the receiver a control current whose magnitude depends on departure from exact tune and combining therewith separately generated low frequency oscillations, the rectified resultant being applied to a grid of a valve constituting or associated with the local oscillator of the receiver. In the Figure, V1 is an I.F. amplifier, V2 the local oscillator, V3 the mixing valve, and D1 the signal rectifier of a superheterodyne receiver. A further diode D2 provides a rectified voltage which increases as exact tuning is approached, this voltage being applied to the primary 4 of a transformer, audio frequency variations are byepassed by condenser C. Low (sub-audible) frequency oscillations, generated for example by a neon tube-condenser combination (Fig. 2, not shown), are applied at 7 to the secondary of 4 and are rectified by rectifiers 5, 6, producing pulsating potentials on the grid of V2 over resistance 8. The resulting pulses rectified by D2 aid or oppose the pulses from 7 in circuit 4, 5, 6 ; when the pulses aid, the change of frequency of V2 is cumulative towards the in-tune position ; when they oppose, there is no substantial change in frequency. The normal frequency of the oscillator V2 is arranged to be slightly displaced from the true required oscillator frequency. In a modification, a hexode frequency changer is employed, the oscillator frequency being varied by a thermionic valve acting as a shunt capacity across the oscillator circuit, Fig. 3 (not shown). Reference has been directed by the Comptroller to Specification 437,442.

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