On Fri, 09 Mar 2018 10:52:20 +0000, Dave Plowman (News) wrote:

In article ,
Johnny B Good wrote:
Presumably, this change was implemented early on in readiness for
colour transmissions, perhaps to ease the final transition to a system
that could no longer be locked to the mains frequency.

It may have been to do with the increasing use of outside broadcasts
and
so on as inserts to programmes. Think things like Nationwide. Where
those might use their own generator or battery supply. You could lock
the studio to a pulse generator anywhere, allowing pictures to be mixed
between the two. Terms like genlock and natlock were bandied about at
the time. And of course a VTR needs a stable 50 Hz reference too. Which
mains simply isn't.

If a VTR is locked to mains, its playing time will vary with that mains
frequency. Not exactly ideal.

Aha! An excellent reason to bow to the inevitable then. :-)


--
Johnny B Good