Patent GB-603614-A (GB)
Title: Improvements in or relating to receiver systems for multi-channel electric pulse communication systems
IPC: H04J3/04
Filed: 1945-10-26
Abstract: 603,614. Thermionic distributers. STANDARD TELEPHONES & CABLES, Ltd. Oct. 26, 1945, No. 28360. Convention date, Nov. 25, 1944. [Class 40 (iii)] [Also in Groups XL (a) and XL (c)] Means are provided, in a receiver for a multichannel train of time-modulated pulses, for separating the pulses of individual channels and for so controlling the separating means by the pulses as simultaneously to demodulate the latter by conversion into amplitude modulated pulses. The means described is a cathoderay tube having a cyclically swept electron beam, under the control of incoming synchronizing signals, and electron responsive means disposed in the sweep path of the beam, and energized for periods depending on the time modulation of the received pulses. In one embodiment, incoming pulses from a radio receiver 10, Fig. 1, are applied to a pulse shaper 35, where their amplitude and duration are made uniform, and then fed to the grid 32 of cathode-ray tube 13, to release the beam during each pulse. Synchronizing pulses of greater width than the channel pulses are selected by pulse-width discriminator 11 and applied to synchronize a sine-wave generator 12 whose output feeds a phase-splitter 14 providing quadrature voltages for application to the deflecting electrodes 18, 19. The circular sweep of the electron beam is arranged to traverse collector electrodes 21 ... 28, and unmodulated pulses switch the beam on so that it overlaps 50 per cent the electrode provided for the appropriate channel. Time modulation varies the overlap period and hence in a proportional manner the amplitude of the resulting pulses in the circuits of the output electrodes. An eight-channel system is illustrated, channel 8 being the synchronizing channel. In the output circuit of each electrode is a low-pass filter 29, for example, and a signal reproducer 30 which are shown fed from electrode 21 corresponding to channel 1. In a second embodiment, Fig. 3 (not shown), the cathode-ray tube is provided with annular deflecting electrodes to which the pulses are applied. In this case, the electron beam is not suppressed between the pulses and is deflected thereby on to the collector electrodes. The synchronizing signal is a tone modulation of one of the channels, the pulses of which are of normal width. A filter tuned to the tone frequency selects the syn. chronizing signal which is used to control a multivibrator which provides a gating pulse for the amplifier feeding the filter and synchronizes the beam-scanning sine wave generator. In a further embodiment, Fig. 4 (not shown), the electron beam falls on a fluorescent screen coated with an opaque mask provided with apertures behind which are arranged selenium cells, energized by light from the screen. The collecting electrodes may be replaced by secondary emitting electrodes 64, Fig. 5, arranged behind apertures 63 in a positively biassed barrier plate 62, the signal output being derived from circuits 65 connected to the secondary-emitting electrodes. Alternatively, the secondary-emitting electrodes may be biassed to cut-off the pulse signals being applied through lead 69 to the barrier plate 62 and the beam being maintained at constant intensity and radius. In this case secondary emission from electrodes 64 occurs for the periods when the beam is in the aperture and the pulse potential is simultaneously applied to electrode 62.