Patent GB-638345-A (GB)
Title: Multi-channel communicating systems
IPC: H04J3/04
Filed: 1945-08-03
Abstract: 638,345. Multiplex radio signalling. STANDARD TELEPHONES & CABLES, Ltd. Aug. 3, 1945, No. 20074. Convention date, Aug. 7, 1944. [Class 40 (v)] A two-way channel pulse communication system wherein signals are conveyed by means of a plurality of interleaved modulated pulse trains, comprises at each station, a single delay device for controlling the interleaving of transmitted pulse trains and also the separation of received pulse trains. Fig. 1 shows a system comprising two terminals, West and East. The West terminal comprises a basic wave source 15 and generator 16 for generating pulses which are applied to a delay network 17 having a number of output points to provide a plurality of trains of pulses. The pulses of one channel are specially widened or otherwise modified, by pulse shaper 21 to provide a train of synchronizing pulses. Each pulse channel is time modulated by modulators 19, and then applied, together with the synchronizing pulse train, to mixer amplifier 25 which provides a single train of interleaved pulses. The output from amplifier 25 is applied either to carrier transmitter 11, or amplifier 10 for transmission over a cable or other direct link. The East terminal comprises a clipper amplifier 28, which eliminates interference included in the output from receiver 13, and a pulse selector and shaper circuit 32 which selects the synchronizing pulse train and applies this to delay network 35. Delay network 35 has a number of output points providing, channels of pulse energy at intervals corresponding to the separate pulse channel intervals, which are applied to shaper circuits 39, 41, 42 to provide a wide selector or pedestal pulse for each channel. These selector pulses, together with the interleaved single pulse train from amplifier 28, are applied to channel selectors 45, 46, 47 which by mixing and threshhold clipping arrangements separate and may also amplify the pulses of each channel. For demodulating purposes, each channel is provided with a demodulator 50, to which is applied the output from one of the selectors 45, 46 or 47, and also a harmonic of a base wave produced by a generator 51 from the synchronizing, pulse from selector circuit 32 and which is selected by harmonic selector 52. The harmonic wave is applied through phase shifter 53 so that a linear portion of the wave may be put in time relation with the pulses of the channel. The demodulator 50 mixes the pulse and harmonic waveforms, (Fig. 3f, not shown), and is provided with a threshold clipping level whereby the time displacement of the pulse train is translated into pulse amplitude variation. The output from demodulator 50 is applied to a reproducer or utilization circuit. Return multichannel communication from East to West also utilizes the delay networks 17 and 35. The East terminal transmitting system comprises pulse modulators 56, 57, 58, fed with signals from sources 59, and also pulses from appropriate output points of delay network 35. As a synchronizing channel is not required for the return trains, the pulses from selector 32 may be used to provide an additional coramunication -channel. Mixer 61 supplies a single train of interleaved pulses for transmission by transmitter 14. At the West terminal, the pulses are applied from receiver 12 to a clipper amplifier and selector circuits as before. The selector circuits 65, 66, 67 are deblocked by pulse energy from delay network 17 at appropriate time intervals. Demodulators 70 are supplied through phase shifters 72 with waveforms from harmonic selector 71 which selects harmonics from the base wave source 15. Specifications 509,820, 592,584, 592,789, 600,291 and 635,472, [Group XL (b)], are referred to.