GB1291743A - Single channel duplex space linked pulse communications system - Google Patents

Abstract

1291743 Radio communications BENDIX CORP 16 Oct 1970 [4 Nov 1969] 49292/70 Heading H4L In a common channel, duplex pulse communication system having a plurality of like stations, each station includes: a receiver 7 Fig. 1 and a transmitter 6, the receiver being continuously operative to receive its transmissions as well as the transmission of the other stations; pulse repetition period modulating means 3, 4, 5 fed with the source of intelligence 1, 2 to be transmitted; synchronizing means, 8, 9 exerting intermittent control on the modulating means in response to the total pulses received by 7, such that, whereby each station, if operating alone unmodulated, would emit pulses of a certain p.r.p, which could be different for each station, the combined effect of this synchronizing results in all the stations emitting pulses at the same p.r.p which is the average of the separate station p.r.p's and demodulating means 10, 11 providing an intelligence signal carrying the combined intelligence of all the stations. Such a system needs no "press to talk" facilities and is particularly useful for intercommunication by groups of workers. In Fig. 2 the relaxation oscillator 3 of Fig. 1 comprises capacitor 14 and charging circuits, together with discharge unijunction transistor 13. The discharge through 13 feeds a negative trigger pulse to monostable trigger circuit 15, 16, 17 acting as the delay of 4 to give a 6 Ás pulse, the trailing edge of which triggers a further circuit 18, 19, 20 to give two opposite polarity 8 Ás pulses for feeding the transmitter 6. The capacitor is normally fed with a contact charging current via current limiter 25 and one of the diodes 24, 27, 28. When a received pulse is not synchronous with the transmitted pulse or comprises a mixture of pulses spread over to partly start before and partly finish after the transmitted pulse e.g. D, Fig. 3 (the output of amplifier 8) the enabling of transistor 22 and shutting off of transistor 23 switches on diode 29, such that an additional pulse of current is fed to the capacitor 14 via limiter 26 until transistor 16 switches back at the trailing edge of pulse B and switches off diode 29. The extra charge J(E) causes a jump K in the capacitor voltage A which would cause a reduction in the period of the transmitted pulses. The lagging part of the received pulse(s) switches off all the operating diodes however and a reduction L in the charging current brings the voltage A back to its original path, indicating that the average p.r.p.'s of the received pulses is equal to the transmitter's p.r.p. Discriminator 9 (items 21-28) may be omitted, the output of amplifier 8 giving the charging current directly.