Ian Jackson wrote:

I recall that certain systems insisted that the four set-top
bypass channels had to be close to the standard off-air broadcast
channels, because some TV sets would not tune to anything but these.


They would have to be very unusual TV sets!
They existed. We used to have problems with a system that had crappy
modulators that drifted. Some of the tellys just wouldn't tune the
signals unless they were exactly on the channel. Just skipped over them.


A comb of 7.988636364MHz would allow E25, E27, E29 and E31 to be used
with +/-34kHz error (off-airs being 23, 26, 30 & 33)
When I worked at CBC (near BH) about 20 years ago the cable input was on
channels 29 and 31.

On the subject of adjacent channel working we have several systems that
use almost every UHF channel and the tellys tolerate it perfectly well.
And they mostly cheap Vestels.

Bill