[ppppenguin]

Strictly that's John Watkinson's paper, published by S&W. JW is a very well respected engineer here in the UK. His books include "The art of digital audio" and "The art of digital video". Both of these books are always to hand by my desk.

He covers historic practice as stated in the SMPTE docs and then correctly states that modern NTSC coders often use 1.3MHz chroma. This too is correct, my own designs do, as do many others. I don't bother to switch filters when changing between PAL and NTSC. This is fine in the studio. However the upper sideband of a 1.3MHz chroma signal will be heavily mauled by a system M transmitter. Strictly the coders maintain 1.3MHz for U and V, not I and Q. Though if U and V are both 1.3MHz, I and Q will be too.

Poynton, in "A Technical introduction to Digital Video" pp187-190, takes a similar view to Watkinson. He notes that SMPTE170M encourages the use of wideband (1.3MHz) chroma in the studio but also says that the practical broadcast chroma BW is only about 600kHz.

The subtleties of I/Q coding have been largely ignored in practice. Most broadcast coders simply encode on the U/V axes and bandwidth limit before the TX. Hence even a receiver with full chroma BW and I/Q demod will not find any benefit on virtually all material. Any claims like this are markting puff.