Improvements in and relating to colour television

摘要

780,814. Television. SYLVANIA-THORN COLOUR TELEVISION LABORATORIES, Ltd. Nov. 18, 1955 [Jan. 13, 1955], No. 1130/55. Class 40 (3). In a colour television system comprising a single-gun beam-index C.R.T. with repeated groups of red, blue and green phosphor stripes scanned perpendicularly thereto, the line scan is velocity modulated at the stripe recurrence frequency by means of a signal derived from the beam indexing pulses generated during the scan so that the dwell of the scanning spot on the stripes is increased, Fig. 3 (not shown), thereby increasing the colour purity and intensity. The invention is applicable to the transmitter and the receiver but it is described as applied to a receiver in which red, blue and green signals are applied sequentially to the cathode of the C.R.T. 15 by means of gates in a " modulator " 21 controlled by indexing pulses of frequency F (the stripe-group recurrence frequency) produced by modulating the grid of the C.R.T. at a frequency Fc (Fc > Fo) from an oscillator 22 so that the output from a blue-responsive photo-cell 24 comprises a carrier Fc and sidebands Fc ΠFo, the upper sideband Fc + Fo being selected by an amplifier 25 and heterodyned in a mixer 25 with an output from the oscillator 22, the resultant signal of frequency Fo being shaped in an amplifier 26 and applied as the indexing signal to the " modulator " 21 or to a frequency multiplier 27 to give a signal of frequency 3Fo which is shaped in an amplifier 28 and applied to auxiliary deflection members 29 to modulate the velocity of the linear horizontal timebase produced by the horizontal deflection member 17 energized from the line sweep generator 16; alternatively the oscillations from 28 and 16 may be combined and applied to a common deflecting means. In order to increase the indexing discrimination, the decay time of the blue phosphor is less than that of the red and green phosphors and the frequency Fo is of the order of the reciprocal of the decay time of the blue phosphor. Alternatively the indexing signal may be derived from a grid or other beam-obstructing structure.