Patent GB-652397-A (GB)
Title: Improvements in and relating to multi-channel pulse signalling systems
IPC: H04J3/04
Filed: 1948-03-16
Abstract: 652,397. Cathode-ray tubes. GENERAL ELECTRIC CO., Ltd., and LEVY, M. M. March 16, 1948, No. 7882. [Class 39 (i)] [Also in Group XL (c)]  In a multi-channel cathode-ray tube pulse duration or time modulator, in which the beam sweeps over a plurality of slotted or strip electrodes to generate pulses, the time of occurrence of the leading and/or trailing edge of which is determined by the edges of the slots or strips, beam-deflecting means reduce, preferably to zero, the component of beam movement parallel to the line joining the strip or slot centres when the beam is in their neighbourhood. In one embodiment, Figs. 1 and 2, pulses are produced when the beam traverses slots S 1  ... S 6'  in a plate P behind which is a common target electrode C. The voltage wave (c), Fig. 3, is applied to the vertical deflecting electrode M and the wave (f), which is the sum of waves (b) and (c) is fed to the horizontal deflecting electrodes E 1'  E 2 . The beam thus traces out the broken line track T. The tube is arranged to handle the odd-numbered channels of a 12-channel system and the signals from these channels are applied to the individual vertical deflecting electrodes M1 ... M6. The effect of the channel signals is to modulate the time at which the beam crosses the related slot S1 ... S6 and to produce time-modulated interleaved negative channel pulses at the target C. The first channel may be reserved for a synchronizing pulse group provided by three slots S1, S1<SP>1</SP>, S1<SP>11</SP>', and unmodulated. The beam is suppressed during the return strokes b, c, by a voltage wave (a) applied to the control grid or (e) applied to the cathode. The working strokes of the beam may be lengthened by replacing wave (f) by one produced by the addition of wave (b) and the unsymmetrical saw-tooth wave (d). The wave (c) on electrode M may be modified to the form (h) by the addition thereto of the pulses (g), in order to ensure the production of pulses if over-modulation occurs. Screens G may be provided between the modulating electrodes M1 ... M6 to prevent cross-talk between channels. In a modification two inclined slots are provided for each channel and the signals deflect the beam horizontally so that pairs of pulses modulated in spacing are produced, Fig. 5 (not shown). In another embodiment, Fig. 6, the slots S1 ... S4 are arranged with their lengths perpendicular to the line joining their centres. The voltage wave (f) is applied to electrodes El, E2 as before, but the wave (c) is applied in parallel to horizontally-deflecting electrodes K1 and the channel signals to horizontally deflecting electrodes M1 ... M4. Thus the beam reverses direction in the vicinity of each slot and produces channel pulse pairs modulated in spacing, but single time-modulated pulses may be produced by suppressing the beam during one traversal of each slot. A further embodiment is described, Figs. 7 and 8 (not shown), in which each slot acts as a modulator for a plurality of different channels in succession as in Specification 652,357. In all the arrangements the slots may be replaced by strip electrodes. For generating durationmodulated pulses, the slots or strips may be of greater width, the leading or trailing edge of the pulse being determined by their edges and the other edge being determined by switching off the beam at regularly recurring instants by black-out pulses.