Patent GB-634452-A (GB)
Title: Improvements in or relating to multi-channel pulse communication systems
IPC: H04J3/04
Filed: 1947-09-24
Abstract: 634,452. Multiplex pulse signalling; pulse generating circuits. STANDARD TELEPHONES & CABLES, Ltd., and ROBERTS, W. L. Sept. 24, 1947, No. 25929. [Classes 40 (v) and 40 (vi)] A multi-channel pulse system for two-way communication over a common medium uses different channel pulse recurrence frequencies in the two directions, their difference being greater than the highest frequency of the signal frequency band. In one embodiment, using three channels in each direction, at the master station eight pulses are transmitted during each signalling period T, Fig. 3 (a), the first pair being used for synchronizing and the remaining three pairs being used as channel pulses, each pair being modulated in amplitude, duration or timing by the corresponding channel signal. At the slave station four single pulses are transmitted during each period T, Fig. 3 (c), the first being used for synchronizing the receiver at the master station, the others being the three channel pulses and all of them being of twice the duration of those of the master station. At each station the receiver is blocked for the duration of each pulse emitted by the adjacent transmitter. This may result, at the slave station, in the elimination of alternate received pulses, but' the remaining pulses carry the channel signals. Overlapping at the master station can remove only part of the received pulses, Fig. 3 (e), as shown at Fig. 3 (f) for example, and the signal is satisfactorily conveyed by what remains of the pulses. The master pulse generator 1, Fig. 1, at the master station supplies pulses through eight parallel circuits to a radio transmitter 2. The first and second circuits provide the two synchronizing pulses, the second being delayed by a time T/8 in device 5. The next pair of circuits include delay devices 7, 8 and pulse modulators 11, 12 fed by the first channel signal from source 13. The second and third pairs of channel pulses are produced in the other four circuits. All the delay devices, which may be of the kind described in Specification 587,364, are automatically controlled to the appropriate delay times, by a voltage derived from a frequency monitor 16 connected to the pulse generator 1. The radio receiver 19 is blocked, over lead 34, for the duration of each transmitted pulse and feeds the synchronizing pulse separator 20 and the channel pulse demodulators 27, 28, 29. The synchronizing pulses, which are of greater amplitude than channel pulses, provide gating pulses for the demodulators after delays of T/4, T/2 and 3T/4 in circuits 21, 22, 23 and shaping in circuits 24, 25, 26. These delay circuits are also controlled by the monitor 16. At the slave station, Fig. 2, pulses from the radio receiver 36, which is blocked over lead 54 for the duration of all the pulses emitted by transmitter 40, synchronize a gating pulse generator 37 adapted to produce pulses having a recurrence period of T/4. These gating pulses eliminate, in circuit 38, every alternate received pulse, and the resulting pulse train, Fig. 3 (b), is fed to the synchronizing pulse separator 39 and the three channel pulse demodulators such as 46. Gating pulses for the demodulators and input pulses for the modulators such as 45, are produced from the synchronizing pulses by delay devices 43, 50, 51 and pulse shapers such as 44. The outputs from the modulators, and synchronizing pulses, shaped by circuit 42, are applied to the transmitter 40 through a delay device 41 which may be adjusted so that transmitted and received pulses do not overlap. All the delay devices are controlled by the frequency monitor 52. In a second embodiment, Fig. 4 (not shown) the, recurrence frequencies, f1, f2, in the two directions, are different and have no particular relation therebetween; the two stations are otherwise identical. All receiving channels have an output at the difference frequency f1-f2, which is above the signal frequency band and is removed by a low-pass filter. As some of the synchronizing pulses are blocked out at the receiver, a synchronizing pulse generator is provided which is controlled by the incoming synchronizing pulses and is capable of maintaining its supply of pulses-substantially unaltered during the suppression of the control pulses. The pulse generator 96, Fig. 5, has its recurrence frequency controlled by the voltage developed across the cathode resistance 116 of triode 115. Pulses from the generator 96 and control pulses from terminal 92 are applied to the control and suppressor grids respectively of pentode 95. When these pulses overlap, an output pulse at the anode charges condenser 107 through diode 106 to a potential proportional to the time of overlap. The condenser 107 is shunted by a normally non-conducting triode 109, which is rendered conducting to discharge the condenser shortly before each control pulse is applied to valve 95. For this purpose a delay device 93 is connected between terminal 92 and valve 95 and the undelayed control pulses are differentiated in circuit 110 to provide a sharp leading-edge positive pulse for application to triode 109. The potential variations of condenser 107 are applied through a low-pass filter 113 to control the anode current of triode 115 and hence the recurrence frequency of generator 96 in a direction to synchronize it with that of the control pulses. Specifications 611,986 and 626,136 also are referred to.