GB493751A - Improvements in or relating to electron discharge devices - Google Patents

Abstract

493,751. Cathode-ray tubes and circuits therefor. FERNSEH AKT.-GES. April 8, 1938, No. 10799. Convention date, April 8, 1937. [Classes 39 (i) and 40 (v)] In an electron-discharge device the proportion of electron current of a single electron beam passing through an apertured control electrode or falling on a collecting electrode is varied by deflecting fields acting independently in two directions at right-angles. The electron stream from a thermionic cathode 2 is concentrated by a Wehnelt electrode 3 on an aperture in a diaphragm 4; the aperture is preferably rectangular but has at least two mutually rectangular sides. The image of the aperture is focused by a lens 5, 6, 7 on an electrode 8, which may have an aperture similar to that in the diaphragms and with its mutually perpendicular edges parallel to those of the image of the diaphragm, or may be solid with a corresponding boundary. The image is deflected by the two sets of plates 9, 10 or by magnetic means, so that differing electron currents pass through the aperture in the electrode or fall on it in the two forms described. The current may then be amplified by secondary emission and collected by an anode. The variation in the current is proportional to the product of the deflections produced by the two pairs of plates, so that a carrier may be modulated by applying the carrier signal to one pair and the modulation to the other, or an intermediate frequency signal provided in a superheterodyne circuit by applying the incoming signal to one pair, and the local oscillation to the other. Alternatively, if the same signal is applied to both, an output proportional to the square of the signal is obtained. The device may be used for rectification or amplitude limitation, since its output characteristic has a sharp lower bend, and the diaphragm aperture and control electrode may be shaped to give it a sharp upper bend also. By applying a steady potential to one of each of the pairs of plates the undeflected position of the beam may be adjusted, so that by varying a steady potential on one of the plates carrying the modulant the degree of modulation may be altered. For certain purposes this control may be mechanically coupled with one which alters the carrier amplitude, so that a definite relationship between carrier amplitude and degree of modulation may be preserved.