GB624514A - Improvements in or relating to receivers for multichannel electric pulse communication systems - Google Patents

Abstract

624,514. Multiplex pulse signalling. STANDARD TELEPHONES & CABLES, Ltd. Aug. 23, 1946, No. 25227. Convention date, Sept. 1, 1945. [Class 40 (v)] In a demodulator for multiplexed pulse time modulated signals, the various channels are distributed to a number of interlaced cathode-ray demodulator tubes by means of synchronizing pulses and phaseshifters. In any tube, adjacent electrodes handle non-adjacent channels. Twelve channel signals received at 16 are passed via shaper 37 to the control grid 33 of the demodulator tube 13 and similarly to the grids of tubes 14 and 15. These signals are also passed to a synchronizing pulse selector 17 which selects the pulses of channel one, which are wider than those of other channels, and serve as synchronizing pulses to produce at 18 a base wave having a frequency equal to the repetition rate of the pulses. Said base wave is applied through a phase splitter 19 to the tube 13 and, through phase-shifters and similar phase splitters to tubes 14 and 15 to provide the rotating sweep for the electron beams. Of the signals applied to the grid of tube 13, those of channels 1, 4, 7 and 10 will be demodulated during each full sweep of the beam, since the remaining channel pulses occur whilst the beam is between electrodes. The other tubes being displaced in phase, demodulate the appropriate remaining channels. Each collector electrode produces pulses having an amplitude proportional to the time during which the beam coincides with a collector electrode, and since the beam is swept at a constant speed, this time is proportional to the modulation time displacement of the signal pulses which are keying the beam. In each tube, signal pulses of the desired channels are admitted by gating pulses that are derived from the base wave and are synchronized to coincide only with the four desired channels of the demodulator tube. These gating pulses are obtained by passing the base wave through phase-shifter 43, frequency multiplier 44, full-wave rectifier 45, to a shaper 46 that selects the peaked output of the rectifier. Undesired pulses may also be blocked by mixing the output pulses of a given tube and feeding them back inverted to the control grid.