Patent GB-470495-A (GB)
Title: Improvements in or relating to multiplex signalling systems
IPC: H04J3/10
Filed: 1935-11-14
Abstract: 470,495. Multiplex transmission. BLUMLEIN. A. D. Nov. 14, 1935, No. 31591. [Class 40 (iv)] [Also in Group XL] In a multiplex system using non-contact making distributers such as thermionic tubes, cathode-ray tubes or metal rectifiers, the synchronising signals, which are transmitted between trains of elementary signals and have a greater amplitude, are used to control a transmitting distributer in which each of the channels is connected in turn to the multiplex line or in which all the channels are connected simultaneously at periodic intervals to different points along a delay network connected to the multiplex line. By this means signals from a number of telephone or other voice-frequency circuits may be given a form resembling that of television signals for transmission over cable such as that described in Specification 455,492, The synchronizing signals may be used as described in Specification 422,906, [Group XL], for the reinsertion of direct and low-frequency components which are not transmitted directly. Arrangements of thermionic distributers. In one arrangement, Fig. 3 (not shown), the telephone circuits are associated with the common circuit through triode valves having their cathodes connected to different points along a delay network. The valves are normally inoperative but are brought into action in turn by a synchronizing pulse which travels along the network. In another arrangement, Fig. 4, in which hexodes 12 are used for connecting the telephone circuits to the common line 10, the output circuits are connected to different points of a delay network D and the valves are all rendered operative together by a signal applied to the points 13. The righthand valve is not associated with a telephone circuit and simply relays the control impulse. A further transmitting arrangement, Fig. 6 (not shown), combines these methods, the distributer valves being rendered operative in succession by a control pulse in one delay network, and their outputs being connected to different points along a second delay network. The same may be done in a receiving arrangement. Fig. 5 shows a receiving distributer for working with the transmitting distributer shown in Fig. 4. The valves 17, 18 operating as described in Specification 422,906 respond to synchronizing impulses only and periodically render the coupling valves operative simultaneously. The point 19 at which the synchronizing impulses should be taken from the delay network D is found experimentally. Filters may be inserted in the telephone circuits to cut out the carrier frequency. Where the number of the telephone &c. circuits is very large, they are divided into sub-groups, the train of signals corresponding to each subgroup being preceded or followed by a syn-. chronizing signal and the whole group of signals being preceded or followed by a synchronizing signal of another kind. The two synchronizing signals may differ in duration or amplitude or both, and one of the train signals may be replaced by the edge of a group signal. Fig. 7 shows the receiving end of such a system, the group synchronizing signals being separated by apparatus GS and passed along a delay network GD so that they render the blocking valves B conductive in succession, the train synchronizing signals and the intellgence signals controlling a separator S and distributer valves H as in Fig. 5. Correcting and minimizing interference between channels, Fig. 8. The hexodes form part of a receiving distributer similar to that shown in Fig. 5 and each has an associated triode 21 which produces amplified signal voltages across potentiometer resistances in its own anode and cathode circuits. By this means, with the help of a switch 23, correcting currents of suitable amplitude and phase may be fed to subsequent channels. As an alternative, the anode of each hexode in Fig. 5 may be coupled by a small transformer to the grid of the next. Cross-talk may be minimized by giving a very short synchronizing signal so that only the middle of each elementary signal is used or by transmitting elementary signals alternately with dead intervals. Cathode-ray distributers. At the transmitter, Fig. 9, the cathode beam in known manner under the control of saw-tooth oscillators 28, 29 scans a plate 26 which is held slightly negative and carries a munber of positively charged targets 25, each of which is associated with one of the telephone circuits. A positively charged mesh screen 37 is arranged close to the targets and receives back from each of them a number of electrons depending on the telephone currents in the associated circuit. The screen currents are amplified and passed to the common line 40. The screen may be omitted, the line being fed from the plate 26 in virtue of its capacity to the targets. Synchronizing signals may be produced by shutting the beam off. At the receiving end, Fig. 10, saw-tooth scanning oscillators 28, 29 are controlled by the synchronizing impulses and control the cathode beam to connect up telephone circuits 45 coupled to targets 25. Distant control and signalling. The invention may be used for transferring meter readings or controlling switches or rheostats. Minimizing noise. The transmission circuit can be designed to pass only moderately highfrequency components thus discriminating against noise. Necessary L.F. components are reinserted at the receiving end in the way described in Specification 422,906. Construction of cathode-ray distributer, Fig. 11. The targets 25 are stuck in a metal plate 26 which may be the end of the tube by means of glass heads having a suitable coefficient of expansion.