Patent GB-711577-A (GB)
Title: Improvements in or relating to arrangements for coding electric signals
IPC: H03M1/00
Filed: 1952-05-12
Abstract: 711,577. Cathode-ray tubes. BJORKMAN, S. J. May 12, 1952 [May 10, 1951], No. 2026/52. Class 39(1) [Also in Groups XXXVIII and XL(c)] Relates to pulse code modulating systems (see Group XL(c)) some of the embodiments of which comprise specially-designed cathode-ray tubes. In a cathode-ray tube binary coder, Fig. 5, the flattened electron beam 56 from cathode 69 passes the grid 58 and slotted anode 70, is focused by electrode 71, deflected by electrodes 55, 97 over the grid 57 and may pass therethrough to a subtraction plate 61. A sample signal amplitude is passed by generator 60 from source 51 through rectifier 84 to the storage condenser 73 shunted by resistance 74. The discharge circuit also comprises the damped resonant circuit 75, 76, 77. The voltage across condensers 73, 75 is applied to the deflecting electrodes 55, 97 to sweep the beam across the grid 57. At marking instants, the beam is switched on by generator 59 at the grid 58, and if it passes through the grid 57, it impinges on the subtraction plate 61 to discharge the condensers until the beam again strikes a bar of the grid 57. In a ternary coder, Fig. 8, the cathode-ray beam 56 is deflected by the magnetic field of a coil 55 supplied, through amplifier 114, with the putput of the division circuit 73 ... 77. A "scale" is provided by two interlaced code grids 571, 572 and a catcher electrode 610. When, at a marking instant the beam passes through both grids to the plate 610, the deflection corresponds to a level divisible by three and no code pulse is generated. If however it falls on a bar of grid 571 or grid 572, secondary electrons are emitted which are collected by the electrode 61 to extract charge from the code condensers 73, 75 and thereby deflect the beam to the plate 610. At the same time code pulses are generated at terminals al and/or a2 across impedances 631, 632. In another embodiment of binary coder, Fig. 9, a trochoidal-shaped electron beam 57 forms a "scale" and an end plate 56 apertured at 98 forms a "contact". Electrons from the cathode 69 are accelerated by the anode 70 and guided by the transverse field from coil 99 into the space between a positive upper plate 55 and a lower plate 97 at cathode potential or lower. The position and number of the nodal points 95 and arcs 96 in the trochoidal beam thus set up, is determined inter alia by the potential of plate 55 which is connected to a division circuit 54. At marking instants generator 59 applies a suitable voltage to the end plate 56 so that the beam can pass through the aperture 98 if the level of the output of the division circuit is not divisible by two. The beam then falls on the subtraction plate 61 connected to the division circuit 54. In a similar embodiment, Fig. 10, the electrons in thebeam 57 describe helicoidal paths and become focused on the axis of the tube at spaced points 95. The position of these foci is controlled by the current in an axial coil 55 which surrounds the tube and forms an element of the division circuit 110 ... 113. At odd output levels a focus occurs at the aperture 98 of the end plate 56 and the subtraction plate 61 is energized as before. The other tube electrodes comprise cathode 69, cylindrical grid 58, apertured anode 70 and the positively biased cylinder 93 screening the electron path.