Improvements in colour television receivers

摘要

985,108. Colour television receivers. SYLVANIA - THORN COLOUR TELEVISION LABORATORIES Ltd. April 4, 1963 [Jan. 5, 1962], No. 558/62. Heading H4F. In a beam-indexing colour television, cathoderay tube display system, indexing signals of angular frequency 3#/2 are obtained through tuned amplifier 12 from photo-multiplier 11 and applied to a frequency divider 15, whilst " runin " signals of angular frequency #/2 for resolving phase ambiguity in the divider operation are obtained through tuned amplifier 13, the circuit including gates 14 and 19 which are controlled by divider 15 such that gate 19 is open and gate 14 is closed during the scanning of the " run-in " stripes and their conditions are reversed once the divider starts operating. The characteristic feature of the invention is the use of a frequency multiplier 20 to derive a signal of angular frequency 3#/2 during the scanning of the " run-in " stripes. Furthermore, a multiplier 21 is used for deriving a signal of angular frequency # for starting divider 15 into operation in the correct phase. If the " run-in " strips are arranged to produce a signal of angular frequency #, multiplication by multiplier 21 is not necessary. The signal of angular frequency #/2 at the output of divider 15 is applied to remodulation circuit 17, which also receives the colour signals to be reproduced, and the resulting signal is combined in mixer 16 with the 3#/2 signal from gate 14 to obtain finally a colour modulated signal of frequency # for application to the tube gun 18. The Specification discusses the desirable occupancy of the " run-in " stripe (i.e. the ratio of stripe width to pitch) and in accordance with a further feature of the invention a value in the range 0À25 to 0À50 is chosen. Specification 895,772 is referred to.