| 摘要 |
<p>1,149,003. Wired broadcasting system. COMMUNICATIONS PATENTS Ltd. 30 March, 1967 [30 March, 1966], No. 13991/66. Heading H4R. In a system for distributing a colour television transmission comprising a brightness signal and two colour information components, the signals are transmitted over the network in the following form: (i) a modulated carrier wave brightness information signal having a bandwidth 9 on a carrier (10À5 MHz) 8; (ii) a suppressed carrier wave colour information signal 10, 11 in respect of both colour components; and (iii) a pilot carrier wave signal 12, 13 in respect of the frequency of the suppressed carrier wave and of one of the colour components ; and a receiver 6, 7 includes a synchronous detector 54 for demodulating the signal (ii) to recover the colour component not indicated by signal (iii) with the aid of a re-insertion wave the frequency of which is determined by the pilot signal (iii). The colour television signal received by aerial 14 produces signals (i) and (ii) through a modulator 21 and a vestigial sideband filter 24, and signal (iii) by causing colour bursts on line 19 to produce a carrier corresponding in frequency and phase to the suppressed carrier, and applying it chopped in bursts by a line scan frequency on 20, to a unit 33 where it is added to information concerning the frequency of the colour signal before modulating the pilot from oscillator 26. The signals are combined in an output stage 25. In a receiver a video frequency brightness signal is produced on line 41 by a filter 38 which passes band 9 to an envelope detector 40, and a colour information signal selected by a filter 42 passing band 11 is applied to a colour recognition device 44 and a subtraction circuit 43. In the colour recognition device a phase comparison with the pilot modulation is effected, and its output is applied to reverse in switch 52 the phase of a re-insertion oscillator 50 energized by colour burst signals separated in unit 47, for application to the synchronous detector 54 producing a colour information signal. The other colour information signal is produced in an envelope detector 48 and made available on line 49. When the frequencies of oscillators 26 and 29 are chosen to be identical, envelope detector 48 may be replaced by a synchronous detector.</p> |
