Southern Television - 26/11/1977

In the very early (analogue only) days of the BBC Cambridge opt, there would occasionally be random opt-backs at Sandy Heath (the opt-out switch was actually at the transmitter, not at BBC Cambridge). The opt-switch was controlled by VBI data on the vision feed (fibre) from BBC Cambridge to the Sandy Heath transmitter - and if the VBI reader was confused, or thought the VBI data had changed, it would default to "safe" (i.e. not opted out) mode...

Because Cambridge's gallery was genlocked to the "Norwich dirty" feed incoming (on a reverse microwave feed from the transmitter - also used to backhaul the microwave FRV receiver at Sandy Heath - via another VBI controlled switch...), if Norwich had any dodgy sources on their mixer, they caused Cambridge to "bump" and the opt-switch could be triggered. Even subcarrier/horizontal issues could be a problem... And the output of one Beta SP deck in Cambridge could also semi-randomly trigger it for some reason.

Does that mean it'd go back to network? Trying understand the routing path here.

Yes, there was something about the ITS signal from Bristol (by the time it had travelled from there and been mangled by Rowridge) that Hannington didn't like. It was always a very temperamental transmitter, and had no end of issues, would drop to RBS CP at the drop of a hat.

I had a tour of the ex BBC (and ex IBA) transmitter buildings a short while before DSO. The BBC Tx analogue hall was just a pile of lashed up kit, much of it held together with 'luck'. !

Wasn't there a system in place during the late 1990s/early 2000s whereby there were two separate systems for both BBC One and Two analogue and digital?

The network playout was separate yes, (or at least for much of the day)

Tx paths were always separate, and in the English regional studio centres analogue took priority, with digital switching of the digital paths being controlled by GPIs derived from tallies etc

Yes when digital started it came from a new playout area which was only on air for a few hours a day - initially noonish to midnightish. Outside of those times digital viewers got converted PAL and of course no widescreen.

In late 99 it switched over so the digital area was 24/7 and the older analogue one 12-12 ish. Then the hours reduced to just evenings until the analogue area closed. There was still the ability to put different things on analogue and digital if needed though it wouldn't have been used much.

Not quite. It switched away from the output of BBC Cambridge to the incoming feed of BBC One - which wasn't network, but instead was the BBC One Norwich feed (which was the other input to the remotely controlled opt-out switch at the Sandy Heath transmitter) There was no clean feed of network available at BBC Cambridge (or at Sandy Heath)

Yes. There were two playout areas - NTA for analogue and DTA for digital. The analogue network feeds and digital network feeds were distributed separately (140Mbs for PAL "analogue" and 9Mbs MPEG2 for the digital feeds).

Because there was less delay on the analogue distribution, the analogue network feed was "master" and for most of the regions that soft-opted, analogue network was the "network" that was routed to the gallery vision and sound mixers. The output of the gallery sound and vision mixers was then fed to the analogue transmitters. Network talkback was tied to analogue network.

HOWEVER the digital network arrived late (due to MPEG2 encoding), so the opt-out of digital network was done using a clever video delay system (to delay the studio vision mixer output to match the relative delay between the incoming analogue and digital network feeds) and the digital opt-out switch between digital network incoming and the delayed studio mixer output was slaved and triggered, again after a delay, by the tally for the (analogue) network source on the studio vision mixer going low. (i.e. when network has been cut away from)

The opt-switch and vision delays had to be carefully timed (and in some cases some ARCs or masks used) to avoid a flash of analogue network appearing on the digital transmissions (which would appear to be a flash frame of soft, PAL-artefacty, cropped network) - though not all regions quite cracked this.

And that was the time that TV Centre studios also stopped getting their on-air lights flashed remotely by Pres. Until then, the Pres director had remote control of the studio red lights and could flash them at 2'00" to TX. Sad to see that go.

How did BBC2W work? Didn't that split analogue ans digital BBC2 on Friday nights or something?

IIRC BBC 2W was on from 8.30pm - 10pm on the weekdays...

The Nations initially, like London, had separate analogue and digital presentation areas, which allowed BBC Two Wales to be broadcast on analogue and 2W on digital. Separate channel directors (who both directed and sound/vision mixed AND announced) for each.