GB668913A - Improvements in or relating to radio diversity receiving systems - Google Patents

Abstract

668,913. Diversity receivers. STANDARD TELEPHONES & CABLES, Ltd. April 6, 1950, No. 8664/50. Class 40 (v). In a spaced diversity receiving system comprising a plurality of aerials, and a single radio receiver, the output from each of the aerials is continuously and automatically connected in turn to a sampling receiver unit and means dependent on the output from said unit automatically couple the radio receiver at all times to the aerial providing the strongest signal. As shown, the aerial 1 is connected to gating units 12, 13, and the aerials 2 and 3 are respectively connected to gating units 18, 19 and 20, 21. A continuously-running commutator 22 gates the units 12, 18, 20 in turn and passes the successive outputs from the respective aerials via a sampling unit 30 comprising R.F. stages, frequency changer and I.F. stages, to a shaping circuit 32 which gives preferential accentuation to the strongest signal. The outputs from unit 32 are fed to gating circuits 37, 38, 39 which are also fed from the commutator 22 so that they are opened in turn and synchronously with the aerial commutation, and the respective outputs of the gating circuits are rectified at 46, 47 and 48, and fed through filters 52, 53, 54, which suppress the switching frequency, to a non- running commutator 58 which provides one output which is of zero or positive potential, the remaining two being negative, the zero or positive potential always corresponding to the strongest input voltage. Gate circuits 13, 19, 21 are connected to the commutator 58 so that only the gate corresponding to the aerial providing the strongest signal is opened at any one time, and the output from the selected gate circuit is supplied to the receiver 66. The unit 22, Fig. 2 (not shown), comprises a Hartley oscillator generating at, say, 1000 cycles per second whose output is fed through a limiter to a differentiating circuit, the negative-going pulses in the output being removed by a diode to leave a train of positive-going pulses having a recurrence frequency of 1000 cycles per second. The train of pulses is fed to the control grids of three reciprocally coupled valves so that the valves are alternately non-conducting, the respective outputs from the three valves being applied to successively gate the circuits 12, 18, 20. The unit 58, Fig. 3 (not shown), comprises three reciprocally-coupled valves, having three stable positions, whose control grids are supplied with negative potentials from the respective rectifiers 46, 47, 48, Fig. 1, and whose anodes are connected through capacitors to the corresponding anodes of three similar reciprocally coupled valves, each of the output terminals having two possible potential settings, and when any one terminal is at its most positive potential to open one of the gates 13, 19, 21, the remaining two being at their negative potential settings. In a modification a diode is connected between each output terminal and earth so that when the output goes positive, the output terminal is kept at earth potential to open the gate valve. Specification 579,507 is referred to.