GB926182A - Index signal generating device - Google Patents

Abstract

926,182. Colour television tubes. D. E. SUNSTEIN. May 22, 1959, No. 1759/59. Class 39 (1). [Also in Group XL (b)] In a colour television receiver employing a cathode-ray tube with a screen, Fig. 1, made up of repeating groups 26 of red, green and blue colour-reproducing strips and which incorporates indexing strips 30 to indicate the instantaneous beam position during scanning the indexing strips repeat at a rate which is a non- integral number greater than 1 times the rate at which the colour groups repeat. The rate may, for example, be 1¢, 2¢, 3¢ &c. times the colour group rate, the preferred rate, which is illustrated in Fig. 1, being 2¢ times. The Specification shows, with reference to Figs. 2-5 (not shown), that the resulting indexing signal obtained from strips 30 is not subject to phase errors in accordance with the modulation of the scanning beam to reproduce different colours. In order to produce an indexing signal at the frequency of scanning the colour groups it becomes necessary to divide down the frequency of the original indexing signal. This will produce in the derived signal an ambiguous phase relationship with the colour groups. To avoid this, an edge portion of the tube screen, Fig. 6, which is scanned before the main part of the screen, is provided with further indexing strips 10 which are positioned to form a continuous series with strips 30 but which are spaced so as to produce an indexing signal at a frequency equal to or a subharmonic of the frequency of scanning the colour groups. As illustrated in Fig. 6, strips 60 occur at onehalf the rate of the colour groups. The signal from strips 60 is in unambiguous phase relationship with the colour groups and may be employed to establish the correct phase relationship in the frequency division operation performed on the signal from strips 30 (see Group XL (b)). Specifications 926,183 and 926,184 are referred to.