GB414769A - Improvements in or relating to supersonic heterodyne receivers for wireless and like reception - Google Patents

Abstract

414,769. Valve circuits for wireless reception. ELECTRICAL & MUSICAL INDUSTRIES, Ltd., Blyth Road, Hayes, and CHARMAN, F. J. H., The Cottage, Parkway, Hillingdon, both in Middlesex. Feb. 13, 1933, No. 4436. [Class 40 (v).] In a superheterodyne receiver, a plurality of intermediate frequencies are generated which are close to one another without the side bands of adjacent intermediate frequencies overlapping, all the intermediate frequencies being fed to a single channel having a band-pass filter whose frequency range is less than that of all the intermediate frequencies and their sidebands. The first detector 3, Fig. 1, has local oscillations supplied from an oscillator 4 modulated by an oscillator 5 generating an auxiliary frequency of e.g. 30 kilocycles. The frequency of oscillator 4, together with the sum and difference frequencies of oscillators 4, 5, beat with the signal frequency to give three intermediate frequencies 9, 10, 11, Fig. 2, which are fed to the intermediate frequency amplifier 6 and second detector 7. The intermediate frequency amplifier comprises a bandpass filter whose frequency range is indicated by rectangles 12, Figs. 2, 3, and is preferably twice the frequency of oscillator 5, Fig. 1. Should the frequency of oscillator 4 drift, the intermediate frequencies 9, 10, 11, are shifted laterally with respect to the rectangle 12, and the second detector will receive portions of the intermediate frequencies 9, 11, to compensate for the loss due to this shift. In modifications, the oscillator 4 may be modulated with more than one auxiliary oscillation, e.g. a series of harmonic oscillations of frequencies f, 2f, 3f &c. such as would be produced by a saw-tooth wave form generator ; the oscillator 4 may produce the auxiliary oscillations and may be a saw-tooth wave form oscillator; the signal frequency may be modulated with the auxiliary frequency before being heterodyned; and the auxiliary frequency may be produced mechanically when the side bands of the signal frequency have a small frequency range.