GB1107548A - Improvements in and relating to colour television reception - Google Patents

Abstract

1,107,548. Colour television. BRITISH BROADCASTING CORPORATION. 8 Feb., 1967 [17 March, 1966], No. 11816/66. Heading H4F. The Specification describes a circuit for decoding the colour burst signals in a received signal of the PAL type, wherein the colour burst signal undergoes a 90 degrees phase change on alternate lines. The colour burst signals are separated from the video by a filter 10 and are applied to one input of a synchronous detector 11 and to a one line period 64 Ás delay 12. If the colour burst signal from the nth line is E cos wt, that from the next (n + 1)th line is E cos (wt + #/2) and so on. The outputs of the delay for corresponding lines are E cos (wt + #/2) and E cos wt. A 90 degrees phase shifter converts these output signals to E cos (wt + #) and E cos (wt + #/2) &c. which converted signals are applied, via a gate 14, opened during the line blanking periods, to the other input of synchronous detector 11. Thus, for odd lines, the two inputs to the detector are in antiphase, and for even lines, are in phase. The output 17 of the detector thus has a polarity indicating the phase of the colour burst signal, and can be used for synchronizing &c. purposes.