GB912312A - Improvements in and relating to colour television and like apparatus - Google Patents

Abstract

912,312. Television. PHILCO CORPORATION. Nov. 23, 1960 [Nov. 23, 1959], No. 40268/60. Class 40 (3). In a colour television receiver utilizing a beam indexing tube 10 (Fig. 1) having auxiliary (run-in) indexing stripes 40 (Figs. 1 and 2) of pitch n outside the picture area and conventional indexing stripes 44 of pitch m associated with the colour phosphor stripes 30, 32, 34, the beam of the tube is modulated by a signal of frequency (m/n - 1) fw (where fw is the "writing- frequency " and m and n are integers greater m than unity and - is also greater than unity) n from an oscillator 52 which is pulsed " on " only during the scanning of the " run-in " stripes 40 so that the effective indexing signals produced by scanning the stripes 40 have the same frequency m/n #w, as the indexing signals produced by scanning the stripes 44 during which period the beam is not modulated by oscillator 52. A single amplifier 50 tuned to the frequency m/n #w then suffices for both sets of indexing signals. During the scanning of the " run-in " stripes the phase and frequency of the " writing-frequency " oscillator 56 is controlled by the output of mixer 54 which derives the difference between the outputs of amplifiers 50 and oscillator 52. During the picture area scanning period oscillator 56 is controlled by the output of mixer 64 (gated " on " during this period by a pulse from generator 58), which derives the difference between the multiplied outputs of oscillator 56 itself and amplifier 50. The phase of the " writing-frequency " oscillator 56 is thus initially established absolutely by the stripes 40 during the " run-in " period and then subsequently controlled during the picture area scanning period by the rate of scanning the indexing stripes 44. The output of oscillator 56 is then employed to control the application of chrominance information in the form of a phase and amplitude modulated sub-carrier wave to the modulator electrode 14 of the tube. This is brought about by combining in mixer 70 the outputs of the further mixers 66, 68 to which are respectively supplied the output of multiplier 60 together with the chrominance subcarrier wave and the output of multiplier 62 together with a reference wave of sub-carrier frequency. The output of mixer 70 then comprises a wave at the " writing-frequency " modulated by the chrominance information such that the " colour phase " thereof corresponds at any instant with the position of the scanning beam relative to the colour phosphor stripes 32 ... 34. This wave is supplied to the modulator electrode 14 together with the separately derived luminance information.