Automatic On-Line Correction of Differential Phase in NTSC Signals

This paper describes the design, development and testing of a new type of coder/ decoder called 'The Double Burst Codec' for colour television signals. This has the simplicity of the NTSC system and the differential phase correcting property of the PAL system. It is realized by modifying the horizontal blanking interval of the video signal to incorporate two subcarrier bursts, one at the blanking level and the other at the maximum luminance level. The first burst is used to regenerate the subcarrier in the decoder while the second is used for phase comparison with the regenerated subcarrier. Any phase error between the two is available as a d.c voltage for correction purposes. The error voltage and the luminance level together are fed to a level dependent phase shifting network for automatic on-line correction of the differential phase in the chrominance signal.