GB644047A - Improvements in or relating to systems for reproducing television images - Google Patents

Abstract

644,047. Television. STANDARD TELEPHONES & CABLES, Ltd. July 18,1947, No. 19277. Convention date, April 24, 1946. [Class 40 (iii)] [Also in Group XL (a)] In a television receiving system the image is initially reproduced in ultra-violet light and then converted into a visible image. The ultra-violet light image is produced by scanning a screen 3 of material which emits ultra-violet light (e.g. calcium tungstate) under electron bombardment the successive image lines, which are produced in substantially the same position on the screen 3 by means of a modulated cathode-ray beam, being converted into visible radiation by transmission through transparent curved fluorescent screens 5 arranged on a rotatable drum 6 which is driven at such speed that a complete screen 5 is caused to fluoresce by the successive lines of one picture frame, the motion of the screen imparting the necessary component of scanning in the frame direction. The visible images thus produced are projected on to a viewing screen 13 by means of an optical system comprising a projection lens 12 and an octagonal glass drum 11, rotation of which neutralizes the motion of the image on the screens 5. The screens 5 may have a long persistence characteristic since the images thereon need not disappear until the drum 6 has nearly accomplished a complete revolution. Instead of producing the successive image lines in the same position on the cathode-ray tube screen 3, the life of the latter may be increased by applying a vertical deflection to the scanning cathode-ray beam and arranging the motion of the drum 6 to compensate for the resulting line displacement. For colour television the screens 5 may comprise materials which fluoresce in the required colours.