GB1005696A - Improvements in or relating to colour television transmitters - Google Patents

Abstract

1,005,696. Colour television transmitters. MULLARD Ltd. April 28, 1964 [Aug. 9, 1963], No. 31584/63. Heading H4F. A colour television transmitter has means for modulating first and second colour information components in quadrature on a sub-carrier and means for reversing the phase of the second of said components on succession transmitted lines of the televised picture, the first of the components comprising substantially equal proportions of two colour signals of either sign and the second of the components comprising substantially equal proportions of the same two colour signals, the sign of one of the two colour signals in the second component being reversed with respect to the sign of that signal in the first component. Thus, when the two signals are R - Y and B - Y, the first component may be a (R - Y) + a (B - Y) and the second component may be b (R - Y) - b (B - Y). It is not necessary that a equals b. Fig. 1 illustrates an arrangement in which a=b. ÁN denotes the first component and # the second component which alternates between the phase positions #N and #R. The components are shown in relation to the normal I and Q components. It is not necessary that the component # should be the component which is periodically reversed. Other arrangements are possible. For example component #R may be transmitted in each line and component Á reversed in successive lines between positions Á N and Á R . The invention is said to be of particular value with the receiver demodulator circuit described in Specification 1,005,290. When the particular arrangement shown in Fig. 1 is employed the two synchronous detectors of the demodulator circuit may operate at the R - Y and B - Y phase angles to produce these signals directly. A simple matrix may thus be used to obtain the third colour signal G - Y. The components may be transmitted with different bandwidth, that for Á N being narrower than that for #N. A suitable circuit for the transmitter is illustrated in Fig. 2 where the first and second components are formed by matrix circuits 1 and 2 and applied to modulators 1 and 2. The phase reversal of the second component is brought about either by reversing the phase of the subcarrier signal by a phase reverser 1 or by reversing the phase of the modulating signal by a phase reverser 2. The subcarrier signal from modulators 1 and 2 are combined and modulated in a modulator 3 on a main carrier wave which carries luminance and sub-carrier synchronizing " bursts."