In message , Terry Casey writes
With System B , I think it's the closer proximity of the TV adjacent sound traps that create the horrendous group delay curve. In System I, they are 0.5MHz further away, and that seems to make all the difference.
So you've never had the ecstatic pleasure of tuning up the group delay pre-distortion circuit in a System B/G modulator? ;o)))))
Of course, Norway realised the SAW filters for TV set IFs could be made with a flat group delay response (rather than slavishly mimicking the traditional L/C horrendous "-90, +140 microsecond" curve). For reasons unknown to me, they decided to change the pre-distortion curve of their transmitters to something like "flat to 4MHz, and -100us at 5MHz". Heaven knows what your average Norwegian TV set made of this!
I've never actually come across it. Is it actually used? I guess it's simply a relaxation of the unnecessarily-tight VSB roll-off of System G. However, as the TV set IFs will all be B/G, they will hardly know the difference.
Ah! You could well be right. I only recently became aware that the Irish launched their 625-line broadcasts in 1962, and of course, at the time, the BBC were still only making experimental transmissions (albeit at UHF). It's therefore unlikely that UK cable systems had any 625-line programmes to put out until 1964 - and that would only have been BBC2. It therefore makes sense that they adopted the Irish VHF TV frequency plan, instead of vice versa!