Patent GB-685216-A (GB)
Title: Improvements in or relating to multi-channel pulse communication systems
IPC: H04B7/17
Filed: 1949-11-24
Abstract: 685,216. Multiplex pulse signalling. GENERAL ELECTRIC CO., Ltd., HARLING, D. W., and HEAD, N. E. Nov. 24, 1950 [Nov. 24, 1949], No. 30163/49. Class 40 (v). [Also in Group XXXV] At an intermediate station in a multi-channel pulse communication system, a synchronizing pulse signal is injected into the multiplex signal if the synchronizing pulses are absent from the incoming signal. A complete two-way 32-channel system is described in which, in normal operation, all the equipment is controlled by synchronizing pulses originating at one of the terminal stations. Facilities are provided for the removal and insertion of selected channels at an intermediate station. The intermediate station comprises a synchronizing signal separator 16, Fig. 2, fed from the " go " line 2, which controls waveform generators 15, 21, and an oscillator 22 which feeds a generator 23 supplying the scanning waveforms for cathode-ray tube modulators and demodulators, which may be of the type described in Specification 652,357. The waveform generator 15 controls gate circuits 12, 13, 14 of which circuit 13 passes selected channels to a demodulator, circuit 12 prevents said channels from reaching the output of line 2 and circuit 14 inserts corresponding channels from a modulator. Waveform generator 21 controls similar gate circuits 17, 18, 19 in line 4. Where a block of adjacent channels is to be extracted and replaced, the generator 15 comprises a discriminator 121, Fig. 4, to which is fed the synchronizing pulse train. The discriminator controls the frequency of a channel recurrence frequency oscillator 123 through a reactance valve 122. The oscillator output is fed to a circuit 124 which feeds back to the discriminator two anti-phase sawtooth voltages 125, 126, which are applied respectively to the control grids of valves 129, 130. Positive-going synchronizing pulses are fed in parallel to their suppressor grids to produce pulses of anode voltage, the amplitude of which is determined by the phase of the sawtooth waves, and the synchronizing pulses are arranged to occur on the steep portion 133 of the waveforms. The rectified outputs of the valves, in the networks 153, 154, balance out when the oscillator 123 is correctly phased, but phase deviations produce a resultant voltage for correction through the controlling reactance valve 122. The oscillator output is also fed to two square wave generators 135, 136 through phase-adjusting networks 133, 134 respectively so that the period of overlap of the square waves may be adjusted. The outputs of generators 135, 136 are mixed in circuit 137 to provide a waveform, consisting of rectangular pulses of duration equal to said period of overlap, which are applied to the gate circuits 13, 14, Fig. 2, to select the desired number of adjacent channels. An inverse waveform is fed to gate circuit 12. If it is desired to remove and replace a block of alternate channels, a similar gate wave generator is used in which waveforms C ... H are produced by the frequency division of square waves A, B derived from a synchronized oscillator operating at a frequency equal to the channel pulse recurrence frequency multiplied by half the number of channels, Fig. 5 (not shown). Thus a gating wave K, Fig. 6, which selects channels 1, 3, 5, 7 and 17, 19, 21, 23, is derived by mixing waves A and D. If no synchronizing pulses are received over the path 2, Fig. 2, a monitor device operates switches 24, 25, 28 so that the input to line 2 is disconnected, and the local channel signals and synchronizing pulses from the modulator are fed to the synchronizing signal separator 16 and to the gate circuit 26 which is opened to pass the synchronizing pulses only to the outgoing line 2. The removed channels may be transmitted to a remote station without demodulation in which case a further gate circuit 27 is provided to pass the received synchronizing signal to the remote station.