GB998028A - Improvements in or relating to plural channel superheterodyne receivers - Google Patents

Abstract

998,028. Superheterodyne radio receiving systems. COMPAGNIE GENERALE DE TELEGRAPHIE SAN FIL. Feb. 23, 1962 [Feb. 24, 1961], No. 7149/62. Headings H3Q and H4L. In a multi-channel receiving system of the superheterodyne type more particularly for direction-finding receivers of the kind wherein the amplitudes of signals received on a number of receiving channels are compared to ascertain an incoming signal direction, signals of the same carrier frequencies from the same source are converted into the respective channels of the receiver to the same I.F. by mixing them with a heterodyning signal produced by combining signals of the said carrier frequency from the said source received on a further channel with a fixed frequency equal to the I.F. As shown in Fig. 1 in a multi-channel D.F. receiver, V.H.F. signals of frequency F from directional aerials Gl, G 2 , G n are supplied to respective mixers M 1 , M 2 , M n and signals of frequency F from an omni-directional aerial Go are supplied via an amplifier 10 to a modulator 13. An oscillator 14 provides a signal / of much lower frequency than that from 10 to the modulator 13 and the sum or difference frequency (as described, F +f) is supplied via a divider 16 providing frequencychanging signals of equal amplitude to the respective mixers M 1 to M n which feed IF. amplifiers A 1 to An. After detection at D 1 to D n and amplification at B 1 to B n , the information contained in the relative amplitudes of the signals is utilized in known manner. In a modification to reduce the effect of noise, Fig. 2, the signal from the auxiliary aerial Go is combined in modulator 13 as before with a signal from oscillator 14, the output F +f being amplified at 15 before application to the device 16. The outputs S 1 to S n of the device 16 are coupled through isolators T n &c. to the respective mixers M n &c., and an additional output S n is coupled via an isolator Ta to a further mixer Ma, like the mixer M n , but having a matched load 18 coupled to one input. It is stated that this causes the intermodulation of parasitic signals resulting from noise applied to the other input of Ma, the output of Ma being fed into a device 19 providing outputs on leads U 1 to U n of adjustable amplitudes. The signals on the leads U 1 to U n are of opposite phase to the signals applied to the I.F. amplifier A 1 to An and are also applied to the I.F. amplifiers to balance out the noise signals in each channel. The incoming signal at G 0 may be pulse modulated by a device M so that the output amplifiers do not pass a continuous D.C. component. A further output S 0 from 16 is detected at D 0 , amplified at B o and may be used for triggering a cathode-ray tube or providing a.g.c. for amplifiers 10 and A 1 to An.