GB1092455A - Improvements relating to colour television systems and receivers therefor - Google Patents

Abstract

1,092,455. Colour television. TELEFUNKEN PATENTVERWERTUNGS G.m.b.H. Nov. 26, 1964 [March 13, 1964, No. 32114/67. Divided out of 1,092,454. Heading H4F. In a P.A.L. system the colour synchronizing " burst " which is transmitted in the intervals between lines consists of two quadraturephase components, one of which assumes the same fixed phase in all lines and the other of which alternates in sign in successive lines. The two components 103, 104 may be transmitted in succession, Fig. 1, or may be transmitted simultaneously, Fig. 2, whereby the resultant signal 7, 7<SP>1</SP> alternates in phase Œ45 degrees with reference to the fixed phase 103. In a receiver for use in the system, Fig. 5, a transittime demodulator 3, 4, 16 is used to separate the I<SP>1</SP> and Q<SP>1</SP> components of the chrominance subcarrier signals and also functions to separate the components of the " burst " signal such that the fixed phase components 103 alone appear in the Q<SP>1</SP> signal channel and the alternating phase components 104 alone appear in the I<SP>1</SP> signal channel. The subcarrier and " burst " components are separated by appropriately timed gates 5, 6, 115, 122, the subcarrier components passing to demodulators 20, 24 and the " burst " components being applied to synchronize oscillators 9, 117 which supply reference signals to the corresponding demodulators. Oscillator 9 is synchronized at the fixed phase of component 103, but oscillator 117 is caused to alternate in phase in agreement with component 104 so that demodulator 24 is operated in the appropriate phase in successive lines to cause the output to be + I<SP>1</SP> despite the alternation of the subcarrier input in accordance with P.A.L. method of operation. The " burst " components function to establish the oscillators in the correct phase at the beginning of a line whilst synchronism during a line is maintained by the I<SP>1</SP> and Q<SP>1</SP> subcarrier components which are applied to control the oscillators via a frequency doubling circuit as described in Specification 1,070,193. The successive components of Fig. 1 may be separated without a delay line system (as in Fig. 5) by the use of appropriately timed gate circuits. The fixed phase component 103 may then be used to synchronize a quartz crystal oscillator which synchronizes a second oscillator via a phase shifter which is switched at line frequency in response to the alternating phase component 104. Reference is also made to the use of the " bursts " of Figs. 1 or 2 to synchronize a quartz crystal oscillator so that it is established at a phase midway between the " burst " phases of two successive line intervals. The production of a synchronizing signal as shown in Fig. 5, by adding components in successive lines with aid of a delay line, forms the subject of Specification 1,092,454.