GB1425341A - Wired broadcasting systems - Google Patents

Abstract

1425341 Wired television COMMUNICATIONS PATENTS Ltd 28 Feb 1973 [28 Jan 1972] 4034/72 Addition to 1043232 Heading H4R In a wired distribution system for two colour television signals, each comprising a modulated carrier wave brightness information component and a suppressed carrier wave colour information component, a frequency control system is provided to ensure that the frequencies of the carrier waves of at least the colour components of the two signals, which initially are of different frequency, are identical on transmission after frequency changing first to an intermediate frequency then to the transmission frequency. As described, for each programme, a frequency converter 3 or 4 is provided, each comprising a first frequency changer 7 which brings the received signal to a standard IF in the 30 to 40 MHz range for application to the IF amplifier 9. The brightness component from IF amplifier 9 is frequency changed to a lower frequency range having a carrier of 509 MHz using mixer 10 and a selection filter 13 while the colour component is similarly changed to have a carrier of 10À33 MHz using mixer 11 and filter 18. The two components, after suitable time delay equalization in delays 24, 25 are combined in 26 for application to the line 29. The oscillators 15 feeding mixers 10 in both converters 3 and 4 are synchronized by a common oscillator 34, and the oscillators 20, feeding mixers 11, synchronized by the common oscillator 34. In each ease the carrier at the output of the mixer is compared with the reference oscillator in the a.f.c. units 16 or 21 to provide adjusting signals for the oscillators 15 or 20, a gate 22 being provided in the case of the colour component signal so that the colour burst signal is picked out to synchronize the oscillator 20.