Patent GB-592779-A (GB)
Title: Improvements in or relating to multichannel electric pulse communication receivers
IPC: H04J3/00
Filed: 1945-06-01
Abstract: 592,779. Multiplex pulse signalling. STANDARD TELEPHONES & CABLES, Ltd. June 1, 1945, No. 13869. Convention date; July 29, 1944. [Class 40 (v)] In a multichannel pulse communication system in which the pulses of each channel have a characteristic duration, the channels are separated at the receiver by translating said pulses into pulses of amplitude determined by the durations of the received pulses, by means of a resonant 'circuit, and thereafter effecting an amplitude selection. In one embodiment an adjustable pulse width-to-amplitude translator 1, Fig. 1A, feeds in parallel the circuits for the first and second channels. The clipper circuit 2 in the first channel selects the pulses of channel one only, which are those in the output of translator 1 having the greatest amplitude. The mixer 3 in channel two, supplied with pulses from translator 1 and clipper 2 has an output in which the channel one pulses are reduced in amplitude so that clipper 4 selects the channel two pulses which are now those of maximum amplitude. Mixer 5 and clipper 6 operate in a similar manner to produce an output of channel three pulses only and so on. In a modification, Fig. 1B (not shown), all the channel mixer circuits are fed with the pulses of all the channels from translator 1 and also with a composite signal consisting of the sum of the pulses from the clippers of the preceding channels which are thus reduced in the mixer output. The circuits of the width-to-amplitude translator and clipper, 1, 2, are shown in Fig. 2. A received pulse train, Fig. 3a, which in this example comprises three channels having pulse width, W1, W2, W3 respectively is fed to an amplitude limiter stage 7 the output from which, Fig. 3b, is applied to a resonant circuit 8. The natural period of circuit 8 is twice the duration of pulses of width W1. Connected across it is a valve 9 which is blocked by the pulses applied to its grid but at other times damps undulations in circuit 8 which would drive point 12 positive. The leading edge of a pulse W1, for example, shock-excites circuit 8 to produce a negative undulation 29, Fig. 3 (c), the valve 9 being blocked. The succeeding positive undulation 30 is reinforced by undulation 32 produced by the trailing edge of pulse W1 to produce a resultant undulation 33. The succeeding negative undulation 34 is damped out by valve 9 which is now unblocked. The positive undulations 35, 36 due to pulses W3, W2, respectively, have amplitudes depending on the pulse widths but will always be smaller than those due to pulses W1. The following clipper valve 18 has grid circuit components 16, 19 of such a value that it is automatically biassed back to a level, for example 39, Fig. 3 (c), such that the output is confined to impulses 40, Fig. 3 (d), corresponding to the undulations of maximum amplitude applied to its grid. Thus the clipper 2 of. channel one, Fig. 1A, passes impulses corresponding to the received pulses of width W1 of channel one only. The mixer 3 of channel two is supplied with the wave c, Fig. 3, and wave e derived from pulses d, the resultant output being wave f in which the undulations 33 of channel one are suppressed. The following clipper circuit 4, therefore selects undulations 36 of channel two which are now those of maximum amplitude, the biasing level being indicated at 41 and the resultant output being impulses 42, curve g. A similar process. in mixer 5 and clipper 6 selects channel three pulses only. Specification 554,456 and 592,789 are referred to.