Multiplex transmission systems

Abstract

Abstract 814,158. Multiplex transmission systems. STANDARD TELEPHONES & CABLES Ltd. July 12, 1957 [April 8, 1957] No. 22155/57. Class 40 (4). In a system in which sections of several signals are time compressed and interleaved a time gap is allowed between successive sections to accommodate transients. In the transmission of one embodiment eight channels 2, Fig. 1, modulate pulses A ... H in a multiplexing device 1 to produce interleaved pulse trains on lead 3 as illustrated in Fig. 2 (1), the space between successive pulses being t1 and the space between channel pulses being t2 = 8t 1. The pulses are fed to a delay line 6 having five taps a ... e whose outputs are passed to a common lead 8 via gates 7 opened by pulses from a delay line 13. If the intervals between the outputs from the tappings of line 13 are t3 and the corresponding intervals for delay line 6 are t2-t3 then the gates 7 will open in succession to pass five consecutive pulses of a particular channel, e.g. A. If the delay line 13 is fed with pulses at intervals t5=5t1 then the next set of outputs from delay line 13 will gate out five pulses of another channel (e.g. F) and so on so that (since 5 is prime to 8) pulses of all the channels are gated on to the common lead 8 in groups of five, as shown in Fig. 2 (2). The pulses are then passed to line via a low-pass filter 10 which passes the modulation envelopes of the various groups of pulses, modified by transients at the beginning and end of each group. As shown in Fig. 2 (2) t3 and t5 can be chosen so as to leave a gap t4 between successive groups, for accommodation of transients. At the receiver, Fig. 3, the incoming signal is sampled by circuit 16 at intervals t3, the resulting pulses being passed to a delay line 18 having tappings at time intervals t2-t3. The outputs from these tappings are passed to a common line 22 by gates 19 opened by pulses from tappings of delay line 20 which have a time interval of t2. This restores the interleaved pattern of the channel pulses, but the presence of additional gates corresponding to additional tappings causes the presence of additional pulses corresponding to the transients. The interleaved pulses are then fed to a distributor 24 for separation into the various channels. As shown in Fig. 4, which illustrates one set of channel pulses, the transients at the end of one section of signal and at the beginning of the next may thus be caused to combine to restore the original signal accurately. Synchronization may be effected by sending a 50-cycle synchronizing signal over the eighth channel, the signal being extracted at the receiver to synchronize the master pulse generator 17. In a second embodiment, Fig. 5, at the transmitter n channels feed recording heads I1 ... In which record their signals on a magnetic tape moving at m revs./sec., the signals being picked up by a reproducing head A moving in the opposite direction at N revs./sec., reciprocal arrangements being provided at the receiver. It is shown that time intervals of seconds between adjacent sections which may be made long enough to accommodate the transients. A plurality of parallel connected reproducing heads A and recording heads I may be used. A storage device consisting of an electric charge storing medium may also be used. Specification 656,151, [Group XL (c)], is referred to.

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