GB1031246A - Improvements relating to colour television systems - Google Patents

Abstract

1,031,246. Colour television. TELEFUNKEN PATENTVERWERTUNGS G.m.b.H. Dec. 24, 1962 [Dec. 22, 1961], No. 48562/62. Heading H4F. In a colour television system there is transmitted continuously a brightness signal as modulation of a main carrier wave and two or more colour or colour difference signals one after the other line-by-line as amplitude modulation of a sub-carrier wave with suppressed carrier. In the specific embodiment described the signals employed are red and blue colour difference signals. A synchronizing " burst " at subcarrier frequency is transmitted every other line to identify which of the two signals is being transmitted and also to provide a reference frequency whereby the suppressed carrier may be restored at a receiver. The subcarrier is transmitted within the band of the brightness signal with a full lower side-band and vestigial upper side-band, Figs. 8 and 9 (not shown). At a receiver, Fig. 5 (not shown), the carrier is restored to the subcarrier signal from an oscillator synchronized by the subcarrier " bursts " and is then amplitude detected in the customary manner. The derived line sequential red and blue colour difference signals are translated into simultaneous signals with the aid of circuit including a one-line duration delay line and a double-pole, changeover switch. The switch is actuated by linescan pulses and established in the correct phase by the subcarrier synchronizing " bursts." A green colour difference signal is derived by matrixing. The signal together with the red and blue colour difference signals and luminance signal is then applied to a three-gun cathoderay display tube. Colour killing is effected by switching-off the sub-carrier channel in the absence of synchronizing bursts. In a modified receiver, Fig. 6 (not shown), the subcarrier signal after restoration of the carrier is passed directly to the delay line so that the signal delay is effected at carrier frequency. This permits the use of a supersonic or magnetostrictive delay line. The delayed signals are converted to simultaneous form and are then amplitude detected by separate detectors in the red and blue channels. This receiver forms the subject of Specification 1,031,247. The signal employed for restoring the suppressed carrier need not be of precise phase since phase errors introduce saturation errors without altering hue. Reference is made to the use of signal which is adjustable in phase over a range of 90 degrees to permit control of saturation. Automatic control of saturation may be effected in response to the amplitude of the " burst " at the output of a detector.