GB434902A - Improvements in or relating to radio and like receivers - Google Patents

Abstract

434,902. Valve circuits for wireless reception. MARCONI'S WIRELESS TELEGRAPH CO., Ltd., Electra House, Victoria Embankment, London.-(Assignees of Hansell, C. W. ; Port Jefferson, Long Island, New York, U.S.A.) Aug. 1, 1934, No. 22461. Convention date, Aug. 1, 1933. [Class 40 (v)] To eliminate image frequency interference in a heterodyne receiver, a mixture of incoming signal energy, and local oscillation is applied to each portion of a double detector system, the phase relation between the signal and local oscillation applied to one portion differing from that applied to the second portion,while an additional relative phase shift is produced between the output energies from the two detectors before they are combined and passed to the next stage. The phase relations are so chosen that the outputs from the detectors effectively cancel in respect of image frequencies. Fig. 2 shows a superheterodyne receiver in which the output from the radio frequency amplifier 8 is applied to a pair of first detectors 1, 2, into the input circuits 12, 13, of which'are injected oscillations from a phase splitting circuit 10 associated with a separate oscillator 4. The injected oscillations in circuits 12, 13 are thus 90‹ out of phase. The output currents, in circuits 17, 18 are given a further relative phase displacement of 90‹, preferably by tuning one circuit above and the other below the intermediate frequency, so that the detector outputs transferred to the intermediate frequency amplifiers 20, 21 are in phase opposition for one band of high frequencies which includes the image frequency, and in phase agreement for the other band. Instead of the local oscillations being displaced in phase, the received signals applied to the two detectors may be so treated, Fig. 1B (not shown) ; any known phase shifting device may be utilized. The receiver may be made suitable for reception of continuous wave signals by providing a locally generated beating frequency input to the second detector from a further oscillator, Fig. 3 (not shown). The local oscillators may be dispensed with by arranging the valves 1, 2, and for C.W. the second detector 22 as self oscillating detectors, the necessary phase displacement being obtained by mistuning the input and output circuits of the first detectors above and below the carrier frequency concerned, as previously described for circuits 17, 18 of Fig. 2, (Figs. 5 and 6, not shown). A further modification provides the phase shift of the output circuits of the detectors by a second oscillator operating at the intermediate frequency and injecting 90‹ phase - displaced oscillations into the inputs of a second pair of detectors, the output from which is passed to an audio frequency amplifier or filter, Fig. 7 (not shown). Fig. 8 shows a receiver for ultra high frequencies the first detectors 1" 2<11> operating as Barkhausen oscillators locked in step with a phase difference between the oscillations ; the output circuits 171 181 are arranged as previously described. Fig. 9 shows a circuit for use as a beating oscillator wherein a pair of oscillators 40, 41 are held in synchronism with phase displacement of 90<0> irrespective of variations in frequency. The circuit 2LC tuned to the second harmonic of the frequency is in the cathode side of the common anode circuit of the oscillators and exerts a degenerative effect at the second harmonic frequency on each oscillator alone ; when both valves are active the second harmonic currents balance out in the circuit 2LC, and are thus held in phase opposition, which corresponds to 90‹ phase displacement of the fundamental frequency of the two oscillators. A similar arrangement employs two screen-grid valves as dynatron oscillators with the circuit 2LC in the positive anode lead, Fig. 10 (not shown) ; an alternative arrangement comprises two normal screen grid oscillators with the second harmonic circuit connected in push-pull to the two - anodes, Fig. 11 (not shown). Relaxation oscillators having their frequency controlled by a doublefrequency oscillator may also be used. Further modifications of the oscillator arrangements comprise a pair of back-coupled screen-grid oscillator detectors with the circuit 2LC in series with the screen grid potential lead, Fig. 12, (not shown) ; or two back-coupled pentodes similarly arranged, the input being applied to the control grids and back-coupling to the suppressor grid circuit, Fig. 13 (not shown). In certain cases, resistances may be employed in place of the second harmonic circuit 2LC of Figs. 10, 12 and 13. The invention is also applicable to wired wireless and photophone systems.