Patent GB-1137498-A (GB)
Title: Improvements in or relating to communications systems
IPC: H04B7/02
Filed: 1966-05-11
Abstract: 1,137,498. Radio signalling. RUCKER CO. 11 May, 1966 [13 Sept., 1965], No. 20799/66. Heading H4L. A diversity reception system comprises a  detector in each of the receiver channels which is coupled to a corresponding integrator, a comparator for comparing the integrated signals and providing a selector signal indicative of the " best " integrated signal, and means responsive to the selector signal to apply the signal on the channel corresponding to the " best " integrated signal to a utilization means. The selection is dependent on the signal having a periodically recurring characteristic, for example, in speech, the pauses, which are stated to occur at a frequency of 2 cycles per second, the speech impulses and the speech pauses being of approximately equal duration. General description.-A transmitter-receiver 10, Fig. 1, which may be located in one of a fleet of taxi-cabs, communicates in both directions on a frequency f 0 , via relay stations A, B, C situated along the route, with a transmit-receive station 14. Relay stations A, B, C retransmit on frequencies f 1 , f 2 , f 3  respectively and co-operate with receivers A, B and C at the station 14. The most satisfactory signal in accordance with the immediate past history of the received signals is selected at 28 and supplied to a utilization device 30. A transmit switch controls transmitter 23 via leads 36 and 42. The received signal selected at 28 also generates a code peculiar to the relay station responsible which is passed via OR gate 40 to transmitter 23 to ensure that transmission is on the carrier frequency appropriate to that relay station. Channel selector, Fig. 2.-Three identical channels A, B, C are included, one for each receiver. The signals from each receiver are supplied via switches 59A, 59B, 59C to the utilization circuit, all these switches initially being closed so that none of the signal will be lost at the start. Considering channel A, the output from receiver A is also supplied via a band-pass filter 50A and amplifier 51A to a speech envelope detector 52A having a time constant such that the output voltage will decay to almost zero level before the end of a speech pause interval. The output of the demodulator is integrated at 53A, the integrator having a short rise time and a decay time which is very long compared with the speech envelope period so that its output increases in amplitude when the input is due to successive speech impulses. This decay time is selected so that a given number (e.g. three) of consecutively received speech impulses and speech pause intervals will raise the output of the integrator to a level which exceeds a D.C. reference level supplied from 65 to a comparator 54A. The first channel which satisfies this condition is selected as the best channel taking into account (due to the integrator) the immediate past history of the signal. For an abnormally long impulse, e.g. a signal other than speech, the output of the integrator will rise initially and then continue to decay exponentially so that there will be no output from the integrator. Initially there will be no output from OR gate 66 and the inverter 67 will enable AND gates 55A, 55B, 55C. Assuming that comparator 54A provides a channel selection signal this signal sets bi-stable device 56A via gate 55A to supply a signal via OR gate 66 which enables AND gates 57A, 57B, 57C and thus opens switches 59B, 59C. AND gates 55A, 55B, 55C are disabled by inverter 67 and a signal via lead 80 inhibits the integrators so that their outputs are zero until another selection is required. A monostable device 70 is also set and provides the required delay between selection and reselection. After the desired interval the output of device 70 is supplied via AND gate 68 to reset bi-stable device 56A via a pulse generator 90 so that a fresh selection is initiated. When the switch 72 is in the " transmit " position, and assuming that channel A has been selected, a signal is supplied via AND gate 60A to energize transmitter select code generator A which supplies a signal to transmitter 23, Fig. 1, selecting the relay station A. When the switch 72 is returned to the " receive " position a signal is supplied via AND gate 68 to initiate a new selection.