GB1155622A - Improvements in Wired Broadcasting Systems and apparatus therefor - Google Patents

Abstract

1,155,622. Wired broadcasting; colour television. COMMUNICATIONS PATENTS Ltd. 30 March, 1967 [30 March, 1966], No. 13993/66. Headings H4F and H4R. In a colour television wired distribution system the signal fed to the system comprises a modulated carrier brightness information signal, a suppressed carrier colour information signal in respect of a first and second colour information components in quadrature, and a pilot signal which has a frequency equal to a sub-multiple of the suppressed carrier and which is amplitude modulated by the first colour information component. At the receiver the first colour component is derived from the pilot signal by an envelope detector while the second colour component is derived from the supressed carrier colour information signal using a reinserted carrier derived from the pilot signal. The figure shows an embodiment for PAL system signals which are received from a conventional broadcast system by aerial 15 and applied to a receiver 16 from which the brightness information and supressed carrier colour information signals are applied to a modulator 20 fed with a 5.4 Mc/s. carrier from oscillator 21. The resulting signals are applied to the line via a vestigial sideband filter 23, a gate circuit 24 and a mixture circuit 25. In addition gate 24 is enabled by signals from the receiver on line 19 to pass colour burst signals, of a frequency of 9.83 Mc/s. equal to the suppressed carrier frequency, from gate 24 to a comparator 27, where they are compared with the output of a frequency tripler 28 fed with the output of pilot oscillator 29, to derive a.f.c. signals used to control the pilot frequency to be one third the suppressed carrier frequency, i.e. 3.28 Mc/s. The pilot signal is also fed to a modulator 31 where it is amplitude modulated with one colour information component from receiver 16 and applied to the line via mixer 25. At the receiver 6 the brightness component is derived via filter 33 amplifier 34 and detector 35. One colour component is derived by filter 39 amplifier 40 and detector 41 from the pilot signal, while the other colour component is derived from the suppressed carrier colour signal which is filtered at 37 and synchronously detected in 38 using a reinserted carrier derived from the pilot signal via a narrow pass band filter 45, which eliminates the modulation sidebands, amplifier 46, and frequency tripler 47. The level of the detected pilot signal may be used to apply a.v.c. to the system.