GB745322A - Improvements in or relating to colour television systems - Google Patents

Abstract

745,322. Colour television. MARCONI'S WIRELESS TELEGRAPH CO., Ltd. Oct. 15, 1954 [Nov. 26, 1953], No. 32913/53. Class 40 (3). In a colour television system in which luminance and chrominance signals are transmitted as modulations of different carrier frequencies Fy, Fc, the two signals occupying bands of frequencies adjacent to, but spaced from, one another, a pilot frequency Fp is transmitted midway between the luminance and chrominance carriers and serves at the receiver to provide a signal of reference frequency and phase for demodulating the chrominance signal. Accompanying sound signals are transmitted on a carrier Fs and the pilot Fp is also employed for demodulating this signal. The invention is described as applied to a system in which the chrominance signal is in the form of quadrature modulations of carrier Fc by " I " and " Q " signals in accordance with the American M.T.S.C. standards. At the receiver, Fig. 7 (not shown), after conversion to an intermediate frequency, the received signals are applied to two channels. In the first of these, which has a pass-band including Fs, Fy and Fp, the luminance signal component is selected and applied to a detector to derive the luminance signal. The sound component is also separated in a timed detector as the 4.8 Mc/s. beat frequency between the sound and pilot carriers. Thereafter a detector recovers the sound signal. In the second channel, which has a pass-band including Fy, Fp and Fs, the received signal is detected and the chrominance component extracted and applied to a synchronous detector. The signal is also applied through an amplifier having a response peaked at Fy and Fp to a detector from which the 1.3 Mc/s. beat signal between Fy and Fp is separated. This signal then provides the reference signal for the synchronous detector and is either doubled in frequency and employed directly to effect demodulation or is employed to control a local 2.6 Mc/s. source.