GB1456502A - Television apparatus - Google Patents

Abstract

1456502 Television INDEPENDENT BROADCASTING AUTHORITY 14 Nov 1973 [15 Aug 1972] 38076/72 Heading H4F An input video signal M, Fig. 4A, modulated on a 6À65 MHz vision carrier PC is sampled at 26À6 MHz (4 x 6À64) in an A/D converter, Fig. 1, and the digitized signal is passed via a digital vestigial side band filter VSBF to a selector depicted as a two bank four pole rotary switch rotating at 6À65 MHz, the video output being taken from bank B 1 and comprising only alternate digital samples P 1 , P 2 as shown in Fig. 4C at a rate of 13À3 MHz (i.e. three times the colour subcarrier frequency) all the samples having the same polarity (samples such as P 2 are inverted). The signals from bank B 2 (which are in quadrature with those from bank B 1 ) are used to control a local oscillator LO to thereby ensure that the 6À65 MHz carrier is phase locked to the clock pulse generator CPG that controls the A/D converter. The digital filter VSBF is described with reference to Fig. 3 (not shown), and includes a plurality of digital shift register-type delays and multipliers. In modulator, Fig. 2, the video signal M, Fig. 4C, is fed via a low pass filter LPF to an A/D converter operated at a sampling rate of 13À3 MHz derived from a 4À43 MHz source, and the resulting digital signals are passed to a selecter shown as a four pole bank rotary switch B operated at 26À6 MHz which changes the sign of alternate samples and introduces zero samples between those from the A/D converter to derive the output shown in Fig. 4B. This output is fed via a VSBF, a group delay corrector GDC, a D/A converter and a low pass filter LPF to derive a modulated 6À65 MHz carrier, Fig. 4A.