Vertical interval signals on 405

[ppppenguin]

Indeed from the POV of a TV repairer diff gain and phase are really only of academic interest. Absolute (as well as differential) phase errors can cause big colour problems in NTSC but PAL converts these into saturation errors. The swinging aspect of the burst is merely to ensure that the PAL sequence is correct. ACC looks after colour saturation, on the assumption the burst and chroma are equally affected by amplitude errors. This is true for NTSC as well as PAL.

Diff gain and phase were very much problems for the broadcasters. VTRs, transmitters, and to some extent the national distribution system were the big offenders. As digits and YUV components (analogue or digital) found their way into broadcasting so diff phase and gain problems went away for all but the actual transmitters.