GB541393A - Automatic control system for a carrier-wave signal receiver - Google Patents

Abstract

541,393. Automatic tuning correction. HAZELTINE CORPORATION. Aug. 16, 1940, No. 13112. Convention date, Sept. 13, 1939. [Class 40 (v)] In a superheterodyne receiver having an automatic frequency control of the kind comprising a discriminator network for applying a frequency control bias to an oscillator control tube, means are provided for applying a low-frequency voltage to the control tube for varying periodically the oscillator frequency to tune the receiver to signals which initially are out of the frequency response range of the discriminator, and means for removing the low-frequency voltage from the control tube when the signal frequency has a value within the frequency-response range of the discriminator. As shown in Fig. 1, the intermediate frequency output is applied to a discriminator network 23, 24, 25, 26 which feeds a double diode 27, 28 having load resistors 29, 30 from which a negative bias is taken and fed through lead 20 to the control grid of an oscillator control tube 21. An A.C. voltage 38 of, say, 60 cycles is fed through valve 36 and transformer 34, 35 to vary the oscillator frequency over a wider range than that of the discriminator. When a signal is received in this range, the discriminator functions to lock it in. Also the negative bias developed across resistor 30 biases valve 36 to cut-off and so removes the effect of voltage 38. In a modification, Fig. 2 (not shown), the diodes are reversed so that the bias for removing the lowfrequency voltage is a positive one and acts by energizing a gas discharge tube arranged to short circuit the transformer 34, 35. In a further medification, Fig. 3 (not shown), ,the auxiliary lowfrequency voltage is rectified and used to mute the audio-frequency stage between stations. Specification 532,081, [Group XXXV], is referred to.