GB823981A - Improvements in or relating to colour television apparatus including frequency changing apparatus - Google Patents

Abstract

823,981. Colour television. FERNSEH G.m.b.H. Oct. 5, 1956, No. 30404/56. Class 40 (3). [Also in Group XL (c)] In a colour television system, the frequency separation of sound and vision carriers and twice the line frequency (h) are both derived from the colour sub-carrier by means comprising only frequency dividers with integral ratios and frequency converters having conversion factors between 0.5 and 1.5. The colour sub-carrier frequency (7x7x11 h/2) is generated by a crystal oscillator 1 and is passed by a buffer stage 2 to a socket A from which it may be fed to a colour modulator. The voltage at the cathode of valve 2 is fed via a second buffer stage 5 to a locked oscillator frequency divider 7, the division ratio of which (7 : 1) is governed by the time constant of the transformer 8 and the resistor 9. The divided frequency is added to the sub-carrier frequency in the ring modulator 11 and the sum (8 Î 7 Î 11 h/2) is selected by the tuned circuit B. A similar frequency changer 12, 13, 18 provides 8 X 8 X 11 h/2 which is fed via buffer stages 19, 20 to control the separation between sound and vision carriers. As described, this frequency is 5.5 Mc/s. A frequency of 8 X 11 h/2 obtained from the second frequency divider 13 and is reduced to twice the line frequency (i.e. 31.25 kc/s.) by a similar divider having a ratio of 11 : 1, followed by a bistable multivibrator 16. Another embodiment (Fig. 2, not shown) is described wherein the crystal oscillator 1 operates at 3 X 17 x 11 h/2 and the same output frequencies are obtained by using the difference from one of the frequency changers.