English NTSC TV's.

[Penthode]

Originally Posted by ppppenguin

... The idea of colour phase alternation as a solution to this was first raised at Hazeltine labs (c1955?) but was judged impractical then. CPA could be done on dot, line or field basis. The latter 2 were totally out of reach back then. Bruch picked up the CPA idea, did on a line by line basis and invented PAL.

Actually CPA predated I/Q with no CPA (in the final NTSC standard). The benefit of CPA was realized early in 1951 and Hazeltine was initially indecisive whether to pursue Phase Alternate Line or Phase Alternate Field. At the last moment they opted to proceed with Phase Alternate Field because of the lack of a line delay for line averaging and field averaging by the human eye was preferred.

The NTSC originally pursued CPA because of limited bandwidth available for the interleaved chroma channel and CPA would facilitate R-Y/ B-Y full vestigial sideband operation with quadrature crosstalk cancellation. Unfortunately the electronic technology still had a long way to go to effectively use CPA and ultimately the vestigial sideband I and double sideband Q was adopted. The picture would have reduced chroma bandwidth but produced superior pictures at the time. The NTSC made the right decision when forty years later the electronic technology could more effectively use the standard and hue errors had become a thing of the past.

It is interesting to consider that 50's designed NTSC sets today display pictures consistently much better today than they did when they were new simply because the signal source now is consistently much better.