[Stooky Bill]

wondering what that EU 16:9 slide was about. I know Ch4 was using PALplus in the 90s and that was one of its tricks, but when would the slide have been used?

I assume it wasn't anything to do with the preceding film - doubt the EU paid for it to be rescanned!

It was an initiative to encourage the transition to 16:9. Details here:
eur-lex.europa.eu 

Television in the 16:9 screen format
Television in the 16:9 screen format 1) OBJECTIVE To ensure the accelerated deve…
  Source: eur-lex.europa.eu

The caption was shown after 16:9 content, going by the way there was an incorrect caption immediately before it I assume that was a mistake too. Looks like it was meant to go straight to the caption for the back anno about the film

Mod edit - snipped out content meant for another thread.

[Transmission]

As well as all that, there's also an example of something that used to occasionally happen from time to time - the chief exec of a company introducing their all the ads from their new campaign.

[Si-Co]

But yes those are (or were) generated by the transmitter when it lost its signal, although according to the comments a continuity announcer said it was more widespread than just one transmitter.

That being said, I would have thought there would have been a visual roll on the snapback to transmission once the transmitter gets its signal back, bearing in mind those are exaggerated on home recordings.

I think the fault evidently lasted much longer than the footage we see here, so that’s not the actual cut back to the programme. It definitely looks like a break in the recording as you can see the clues that old footage has been recorded over. (ah, nostalgic in itself!)

I assume there must be a way to avoid that “blue screen of death” appearing during scheduled periods of black (eg. straight after closedown before the testcard, caption or 4-Tel appeared, and the minute of black and silence between the testcard and start-up or schools roto). Something to to do with whether pulses are present?

[Neil Jones]

I think I asked the question before, did the system know the difference between black as in "oh crap everything's gone off" and black as in "we're transmitting but we're deliberately not showing anything". And the answer was yes.

I think it was whether the feed itself was present was the test, as the transmitter would only show the blue screen if it had lost said feed - otherwise you'd just have static.

[Stooky Bill]

Yes I think it was loss of signal that triggered it, that is a loss of sync pulses. As you say there's no way of it knowing if it's an intentional black image or not.

Very different in the digital world. That sort of thing can't be done at a transmitter as all the services arrive together as a single stream of data. But at a baseband video level, things like loss of audio, and frozen image are standard in equipment along with loss of signal.

Frozen video also catches out a full frame of black of course, and it will have a hold off so it doesn't go off until it lasts x number of seconds and not repeat until a certain amount of time after.

What the broadcaster does with that alarm is up to them, however I don't think there's many auto captions in use except for the 'Signal Loss' type alarms on decoders

[Steve in Pudsey]

Presumably there was some means of differentiating a loss of syncs because of a fault and a deliberate closedown during which the TX should shut down? Was the latter done manually by the IBA ROCs or on a time switch?

[agemame]

I seem to remember someone saying there was a specific code of tones and sync pulses that could be used to mark a signal as shutdown so that the detector wouldn't kick in, but I forget the precise details. Presumably a similar setup turns things back on, but that implies even when shut down, there's something monitoring somewhere.

[James2001]

When the ITV transmitters came on air, it wasn't the ITV companies broadcasting anyway, as the test cards were generated at either the transmitter, or later, the ROC, the signal only switching to the ITV companies (or TV-am post-83) themselves later, so whatever the process to fire up the transmitters was, it would have been triggered by the ITA/IBA themselves at the transmitters and ROCs rather than from the ITV companies.

Unlike the BBC where it was triggered by a piece of equipment at TV Centre being unplugged and plugged back in.

Not sure about Channel 4... but I think in the early days at least, that also came on air with the locally generated ETP-1 before switching to Charlotte Street's a bit later (the lines above and below the IBA:CH4 being an indication of where it was coming from). I've seen later videos from 1991/92 where the transmitters open up to 4-tel, so clearly linked to Charlotte Street right from power up, though whether anything was actually done there to turn on the transmitters, or the transmitters were triggered to turn by a timer or similar, I can't say (and post-93 they were just left on all night anyway).

[Stooky Bill]

Loss of transmission (seemingly planned) during an episode of Woof on Yorkshire TV
youtu.be 

[James2001]

I remember there used to be a page in the 600s on ITV teletext telling you about such planned outages or periods of low power, though I doubt many people looked at it.