GB577280A - Improvements in electron discharge apparatus - Google Patents

Abstract

577,280. Electron discharge apparatus. BRITISH THOMSON-HOUSTON CO., Ltd. Dec. 23, 1940, No. 18048. Convention date, Dec. 22, 1939. [Class 39 (i)] Electron discharge apparatus comprises a magnetic structure for producing a static magnetic field which gives a wave-like form to an electron beam passing through it, means for varying between limits any or all of the conditions of the beam as regards its velocity, position, and direction under which it enters the magnetic field, thereby varying the wave-form taken by it in the magnetic field, and an output system the effect of the beam on which varies with the wave-form of the beam, whereby the variation of the entry conditions of the beam excites oscillations in the output system. The form shown, with the parts separated, comprises a cathode 12 and an apertured accelerating electrode 13 producing an electron beam which passes through an off-centre aperture 17 in a plate 16 closing the end of a hollow conductive structure 15 of rectangular cross-section. In passing through this structure the beam is acted upon by transverse static magnetic fields produced by elongated electromagnets 19, 20, between the poles of which the structure 15 is situated. Owing to the fact that the beam enters the structure 15 to one side it is deflected by the field of the magnet 20 towards the other side, then back by the field of the magnet 19, and so on, the beam being thus given a waveform path as shown by A, Fig. 4., and finally reaching collector electrodes 29, 30 connected in push-pull across a tuned circuit. By varying the potential of the accelerating electrode 13 the velocity of the beam is altered, and hence the number of reversals of transverse movement which it undergoes before reaching the collector electrodes, so that the beam may be transferred from one to the other of the electrodes 29, 30, as illustrated by the paths A,B respectively, by suitable variation of the potential of the electrode 13. By cyclic variation of this potential a cyclic variation in voltage across the electrodes 29, 30 is produced by the transfer of the beam from one to the other, and by making the range of variation of potential of the electrode 13 sufficient to cause a change greater than. one in the number of beam reversals a corresponding number of reversals of potential across the output electrodes occur for each cycle of the potential applied to the electrode 13, producing frequency multiplication. In a modification, the same results are obtained by varying the direction in which the beam enters the magnetic field, instead of its velocity, for which purpose a pair of electrostatic deflecting plates are arranged between the electrode 13 and the end of the structure 15. The device may be used in the system of frequency modulation described in Specification 534,757.