I didn't work in the video industry, John, but I
did work with computers all
the while. Monitors of the time, at least of the NTSC-compatible type, were
typically equipped with PL-259 connectors on the rear. The only video
monitors I encountered with BNC connectors on them were the high-frequency,
then-mono, types, from Motorola, intended for use as "page" monitors.
I think it might have had more to do with what kind of single was being
sent. (at least in the video industry)
My old UMatic decks from the 70s have either "UHF" connectors (PL-259),
or F connectors (depending on age) for all the modulated signals
(connects to a TV shows on either channel 3/4 or 6), but all the ones
that have composite signals (non-modulated, needs a "line in") have
either BNC or RCA (depending on quality, doesn't seem to have bearing on
age... higher quality decks have the BNC for video, RCA for audio, and
lower quality have the RCA for video and audio).
I don't think I have ever seen a "UHF" (PL-259) or F connector on a non
modulated composite signal (not saying they don't exist, just I have
never seen them), same with I don't think I have ever seen a BNC or RCA
on a modulated signal.
-chris
<http://www.mythtech.net>