GB845847A - Radio diversity receiving system - Google Patents

Abstract

845,847. Radio recording systems. STANDARD TELEPHONES & CABLES Ltd. Feb. 20, 1959 [Feb. 21, 1958], No. 5934/59. Addition to 810,698. Class 40(5). A diversity system of the kind described in the parent Specification in which the signals of the same frequency are received by two spaced diversity aerials and combined in the same phase before demodulation, is modified to provide for signals of different radio frequency, by having two tuned frequency selective channels and means to change the signal frequencies to the same frequency before combining. In addition, each selective means directs the selected signal to the corresponding frequency changer. In the embodiment described two frequencies fA fB received by aerials 14, 15 (Fig. 1) are applied to selective tuned circuits 20, 23, and frequency changes 21, 22, 24, 25, the signals applied to transmission lines 3, 4 having the same frequency f The remainder of the circuit is the same as disclosed in the parent Specification. The signals f A f B at the outputs of the tuned circuits vary continuously in phase due to fading and since one of the minor outputs is amplitude modulated at the frequency of source 6, then after combination in circuit 7 a phase modulated combined signal will be produced except when the phase difference between the two signals has been adjusted to 0 or 180 degrees. If the receiver is to be used in a time diversity system, a delay circuit 26 is switchedwith circuit to make signals f A f B time coincident in a second embodiment (not shown) a phase or frequency modulator is employed instead of an amplitude modulation, as described in the parent Specification. A third embodiment (not shown) employs a phase adjustable, local oscillator in the frequency change circuit of one channel in place of the local oscillator 25 Fig. 1. A fourth embodiment is the same except for the generating means which is described in the parent Specification.