GB954941A - Improvements in colour television receivers - Google Patents

Abstract

954,941. Colour television. SYLVANIATHORN COLOUR TELEVISION LABORATORIES Ltd. Feb. 21, 1963 [Dec. 15, 1961], No. 45094/61. Heading H4F. In a colour television receiver utilizing a beam indexing tube 10, Fig. 1, having indexing stripes of such a spacing as to yield a signal of m frequency (-)#, from which the beam modun lating signal of frequency # is derived by means including a 1/m dividing circuit 14, and " runin " indexing stripes of a different spacing for producing a signal at the frequency # or a submultiple thereof which is applied through a gate 18 to start the divider in operation in the correct phase, the beam current applied to the electrode 24 is increased during the interval in which the "run-in " indexing stripes are scanned to ensure that the signal produced when these stripes are scanned is of sufficient magnitude to unambiguously determine the phase of the divider 14. As shown applied to a conventional system where m=3, n=2 and the " run-in " signal is of frequency #, an output from the divider 14 comprising bursts of a frequency #/2 (Fig. 2a) is converted to a square wave P (Fig. 2b) at 20 and restored to be at a datum level in the amplifier 21. Blanking pulses B (Fig. 2c) having an amplitude equal to their normal value plus that of pulses P are added to the square wave P to produce the signal of increased amplitude Q (Fig. 2d) which is applied to the electrode 24. The Specification also disclosed that a monostable multivibrator triggered by the trailing edge of the blanking pulses could be used to increase the beam current.