Patent GB-621613-A (GB)
Title: Multiplex signalling system
IPC: H04J3/18
Filed: 1945-09-17
Abstract: 621,613. Cathode-ray tubes. MARCONI'S WIRELESS TELEGRAPH CO., Ltd. Sept. 17, 1945, No. 24016. Convention date, July 31, 1943. [Class 39 (i)] [Also in Groups XXXIX and XL(b)] In a multiplex signalling system (.see Group XXXIX) use is made of a thermionic distributor comprising a plurality of cathode-ray tubes, one per channel, in each of which signals corresponding to the channel concerned are stored in the form of capacitative charges on a target electrode by a signal-modulated onput cathode-ray beam and are removed from the same target electrode by an offtake unmodulated cathode - ray beam. Transmitter. (Figs. 1a, 1b). In the case of the three-channel system described, a clipped saw-tooth wave is applied to the deflecting coils 7a of the cathode-ray tube 8a of channel 1, and serves to deflect the low velocity offtake beam thereof. An unclipped saw-tooth wave lagging on the first by 60 degrees is fed to plate 13a and deflects the high velocity onput beam, plate 14a being grounded. Similar waves, each lagging 60 degrees on the wave preceding it, feed tubes 8b and 8c corresponding to channels 2 and 3 respectively. The target of each tube is scanned by an onput and an offtake beam at the same frequency, but the clipping of the wave controlling the offtake beam increases its scanning speed to three times that of the onput beam, two-thirds of each scanning cycle being a rest period for each offtake beam and the three beams scanning their respective targets successively during each cycle. The onput beams are of high velocity so that the targets acquire positive charges corresponding with the signal, whereas the low velocity offtake beams remove these charges, the signal units produced being applied via the diode 21 to the amplifier 22, the output of which is applied to a modulator. Synchronizing signals are obtained from the deflecting coils 7a of tube 8a and are applied to the control grid of the pentode 27. The elements 3, 4, 5, 6, 10, 11 and 12 are conventional in design (Figs. 2, 3, not shown). Receiver. (Figs. 4, 5a, 5b). The apparatus for each channel comprises two chains of elements and a two-gun cathode-ray tube, the upper chain controlling the deflection of the onput beam, and the lower, the offtake beam. The demodulated input is applied to a detector 91a which separates the synchronizing signals and passes them to a phase inverter and sawtooth wave generator 92a and a multivibrator 96a in the second chain. Saw-toofh waves from 92a pass via a clipper 93a and an amplifier 94a to the deflection plate 13 for the onput beam of tube 8a (Fig. 5a), a portion of the clipper output also feeding a blanking signal generator 95a which produces blanking pulses for application to the cathode 42. The output of the multivibrator, delayed by 60 degrees, is fed to a phase inverter and saw-tooth wave generator 97a and thence via an amplifier 98a to the deflecting coils 7 of the tube 8a. The multivibrator 96a also feeds another multivibrator 99a in the second channel which replaces 91a in the first channel. The elements 91 to 99 are all conventional (Fig. 5a, 5b). As a result of the inclusion of the clipper in the upper chain of each channel, the 60 degrees lag between chains, and the provision of the blanking signals the onput beams scan in succession at three times the speed of the offtake beams, which scan simultaneously, the signal currents from. each flowing in a load resistor such as 53 (Fig. 5a) whence they may be applied to amplifiers (not shown).