Patent GB-604817-A (GB)
Title: Improvements relating to multi-channel pulse communication systems
IPC: H04J3/04
Filed: 1945-12-28
Abstract: 604,817. Multiplex pulse signalling. STANDARD TELEPHONES & CABLES, Ltd., and LEVY, M. M. Dec. 28, 1945, No. 35067. [Classes 40 (v) and 40 (vi)] In a receiver for a multi-channel timemodulated pulse communication system, a channel pulse train is separated by generating a train of boundary pulses of the same periodicity as the channel pulses to render the pulse translating means responsive only to those pulses which respectively follow next after the boundary pulses. In one embodiment, the train of mixed channel pulses A ... J, Fig. 2a, and synchronizing pulses 7, is applied to a saw-tooth generator 2, Fig. 4, which is synchronized by pulses 7. The saw-tooth output, Fig. 2b, of generator 2 is applied to control a pulse generator 3, biassed to generate a short " boundary " pulse 9, Fig. 2c, at the beginning of each period allotted to the particular channel pulse which it is desired to isolate. The channel selector 4 receives the boundary pulses from generator 3 and all the received signal .pulses over lead 5. Circuit 4 is unresponsive to signal pulses until sensitized by a boundary pulse 9, after which it responds to the next following signal pulse H and becomes insensitive again until the next boundary pulse arrives. It may be arranged to produce durationmodulated rectangular pulses 11, Fig. 2d, of which the leading edges coincide with the boundary pulses and the trailing edges coincide with the next following time-phase modulated signal pulse. If it is not desired to demodulate the selected channel pulses, short pulses 12, Fig. 2e, may be obtained from the trailing edges of the rectangular pulses by differentiation, and transmitted, for example, to a terminal different from that of the remaining channels. By providing the generator 3 with an adjustable bias, the pulses of any channel may be picked out for monitoring or broadcast reception &c. In order that the boundary pulses may be accurately timed without critical adjustment of generator 3, the sawtooth wave from generator 2 may be modified by the addition of pulses 31, Fig. 2f, provided by a generator 30, the repetition frequency of which is the product of that of the synchronizing pulses and the number of channels. The generator may select the required harmonic component from a band-pass filter fed with the synchronizing pulses, and convert it to rectangular pulses by amplification and amplitude limitation. The generator 3 is triggered when the leading edge 33 crosses the critical voltage value indicated by line 32, which may vary between limits 34, 35 without varying the boundary pulse timing. The lower limit may be extended to 36 if the rectangular pulses 13 are differentiated before superposition on the saw-tooth wave. A common saw-tooth generator and harmonic pulse producer may control a plurality of boundary pulse generators associated with channel selectors to separate all the incoming channels, Fig. 5 (not shown). A circuit for the channel selector 4 is described in which the boundary pulses are applied from terminal 24, Fig. 3, to the grid of a gas-discharge triode 13 and all the signal pulses are applied to the grid of a second gas-discharge triode 14. Anode voltage for valve 14 is derived from the cathode resistor 17 of valve 13 across which the output pulses are developed and fed to terminal 29. In the quiescent state both valves are non-conducting and condenser 19, between the anode of valve 13 and earth, is charged to full H.T. potential from terminal 16. The boundary pulse causes valve 13 to conduct, partially discharging condenser 19 and providing H.T. voltage for valve 14 across resistor 17. The next signal pulse renders valve 14 conducting and condenser 19 discharges through valves 13 and 14, to extinguish valve 13 and remove H.T. voltage from the anode of valve 14 which is also therefore extinguished. The circuit is then quiescent again until reenergized by the next boundary pulse.