GB318331A - Improvements in television and telephotographic apparatus - Google Patents

Abstract

318,331. Roberts, C. E. C. June 22, 1928. Vacuum tubes.-In a television transmitter an optical image is projected by a lens L on to the photo-electric surface of a cathode K. The density of the electrons in the elementary pencils which form the stream E varies according to the intensity of illumination of the surface elements from which the pencils originate. The stream E is caused to oscillate in two dimensions by electromagnetic or electrostatic means so that the elementary pencils pass successively through the aperture a in the anode A, which thus constitutes the scanning aperture for the picture. The pencil emerging from the aperture falls upon an electrode C which is connected to the grid of a thermionic valve or other means for controlling the outgoing signals. In modifications, a wire passing through the aperture a may be substituted for the electrode C, (Fig. 3, not shown); or the apertured screen A may extend across the valve, a separate anode being provided either in front of, or behind it, (Fig. 4, not shown); or the incident light F may pass through a further aperture in the screen A, so as to fall on the cathode in a more nearly perpendicular direction (Fig. 5, not shown). The cathode may be rotatable so that the effective part of its surface is subject to continuous change (Fig. 7, not shown). In a further modification, Fig. 6, the pencil of electrons emerging from the aperture a may pass through an aluminium or other window g into an ionization chamber G. More than one simultaneous projection of the image may be made on photo-electric surfaces of the same or different materials and these projections may be used for the production of coloured images. According to the Provisional Specification the cathode stream from the picture may be encased in a more powerful stream which serves to generate synchronizing signals.