GB1250096A - - Google Patents

Abstract

1,250,096. Television. BRITISH BROADCASTING CORP. 13 Feb., 1970 [9 April 1969], No. 18198/69. Heading H4F. Before mixing PAL or NTSC signals e.g. from a remote source, the chrominance information must be provided on a subcarrier sychronized in phase and frequency with a master subcarrier of frequency W R . This is accomplished without first demodulating the chrominance signal cos w 0 t from a filter 12, by passing the signal through a 90 degree phase change network 17, multiplying 16, 18, the chrominance signal and the output of the network 17 respectively by signals sin w D t and cos w D t from a generator 20 and adding 21, 13, the multiplied signals to the luminance signal Y from a filter 11, whereupon Y + sin w D t. cos w 0 t + cos w D t sin w 0 t = Y + cos w R t, where w R =(w D +w 0 ). In the generator 20, Fig. 3 (not shown), signals cos w 0 t and sin w 0 t are derived from an oscillator locked to the colour bursts of the input signal and are composed in phase with the master subcarrier signal cos w R t to develop the signals cos w D t and sin w D t. In a modification, Fig. 2 (not shown), the generator produces a signal (sin w D t - 1) rather than sin w D t, and the entire input signal Y + cos w 0 t is added to the outputs of the multipliers 16, 18 to give an output signal Y + sin w R t.