Patent GB-766430-A (GB)
Title: Improvements in or relating to electric multiplex communication systems
Inventor: DUKES JOHN MARCUS CUTHBERT
IPC: H04J1/16
Filed: 1955-03-31
Abstract: 766,430. Multiplex pulse signalling STANDARD TELEPHONES & CABLES, Ltd. March 31, 1955, No. 9370/55. Class 40(5) In a multiple pulse-amplitude or pulse-code modulation communication system (for either radio or cable link) with several repeater stations interposed; the effect of failures at repeater stations is minimized by providing 5 (or 7) terminal transmitters and 5 (or 7) terminal receivers with corresponding quintuplication (or septuplication) of the receiving amplifying and re-transmitting equipment at each repeater station, distributing the signal pulses among the 5 (or 7) "arteries" so obtained, and providing automatic switching at each repeater station to subtitute artery 5 (or 7) equipment for any that fails; and subsequently substituting artery 4 (or 6) equipment for a second failure at the same repeater. In one embodiment, Fig. 5, pulse amplitude modulated time-division multiplex signals are derived from five input channels 110...114 by means of gating circuits 115. 119 and progressively increased timedelay networks 121...124. A synchronizing pulse from generator 125 is also added in sixth place by a delay network 126. The amplitude of the synchronizing pulse is made greater than that of any signal pulse so that it will remain distinguishable if certain code-pulse digits are subsequently discarded in transmission. The multiplex pulse train is encoded at 120 into a 7 digit binary code and there are provided 7 radio transmitters 129-135 (each operating on its own distinct carrier frequency), one transmitter for each code digit. Thus transmitter 129 handles number one digit of the code in respect of the five signal channels, transmitter 130 handles code digit two, and so forth. A number of repeater stations (not shown in Fig. 5) are interposed between the 7 transmitters 129...135 and the corresponding 7 receivers 136...142, each repeater station including 7 receivers and 7 transmitters, signals, on each of the 7 arteries being received on a first carrier and re-transmitted on a second and vice versa, with or without intermediate demodulation and pulse regeneration. The outputs of all the receivers 136...142 are recombined to form the 7 digit code pulse groups which are decoded at 143, and the five original signal channels are separated by delay networks and gating circuits similar to, and synchronized with, those at the transmitter. The seventh artery carries the seventh digit of the code and hence is of the least significance for message intelligibility. The equipment of this artery is therefore selected to act as substitute if any other artery fails, and artery 6 which is the next in order of insignificance is selected as substitute for a second failure. It is stated that the mathematical probability of a third failure is negligible. Since each artery operates on its individual radio frequencies, substitution has to be effected at a standard intermediate frequency by linking the repeater stations in pairs, Fig. 7, by means of a separate control circuit 187 whereby the replacement of the receiver frenquency changer 177 and I.F. amplifier 178 corresponding to a particular artery by those of artery 7 (not shown) over contacts 180, is accompanied by corresponding replacement of the transmitter frequency changer 176 at the previous repeater station. The particular artery to be replaced is determined by using six different tone frequency signals over the circuit 187-a seventh signal is unnecessary, as failure of artery 7 can be ignored. Substitution of equipment is effected, Figs. 8 and 9 (not shown) by signal detectors in the outputs of the first 6 arteries which control the tone signal generators and also control self-holding change-over relays which not only substitute artery 7 equipment for the defective equipment upon the first occurrence of a fault, but also prepare a second set of relays which will substitute artery 6 equipment for a defective section upon the occurrence of a second fault. At the preceding repeater station, the tone signals are distinguished and control a similar relay system. The relays are re-set manually by a trip circuit when the faults have been repaired. The action of the relays for successive repeater station pairs is time-delayed so that a temporary interruption whilst equipment is being switched does not cause unnecessary substitutions all down the line. The removal of part of artery 6 due to a "second fault" substitution, would normally appear to subsequent repeater stations as a fault on that artery, so to prevent further unnecessary switches a local carrier source is injected by the change-over relays at the affected repeater station. In a second embodiment. Fig. 1 (not shown), the inputs from 5 different sources are sampled periodically by a distributer which consists either of five linked 5-target cathode ray tubes, Fig. 2 (not shown), or of a rotary contact distributer, Fig. 3 (not shown), and the sample pulses are applied in turn to five transmitters which are linked to five receivers with their corresponding demodulating distributer by a number of " five artery" relay stations. As above, the equipment corresponding to artery 5 is automatically substituted at any repeater station, Fig. 4 (not shown) for any defective artery equipment, and artery 4 is automatically substituted on the occurrence of a second failure. Specification 673,354 is referred to.