[Bluecortina]

IBA transmitters had ‘silence’ detectors - if they detected no audio for a period (2 minutes from memory) they would automatically transmit a locally generated apology caption. So to prevent this, as the transmission staff were putting on their hats and coats before leaving the building they would output black/bars/test card and tone to the transmitter as they rushed out to their cars.

This example from late-1981 shows the blue caption kicking in less than 30 seconds after loss of video.

www.youtube.com 

Interesting example. Again from memory the apology card would kick in for continuous loss of video too. Again I thought is was around 2 mins but your example seems to confirm it was shorter. If you were transmitting anything with a long section of black or silence you advised the transmitter in advance of the tx so that the automatic detection system could be bypassed. I vaguely recall playing out the war film ‘The Longest day’ and the opening scene consisted of a fair bit of black with the somewhat famous V for Victory sound track only (there are different opening versions of the film so don’t bother to Google). When I was showing it to Pres a short while before transmission I advised them of the long section of black and it wasn’t a fault on my vt machine!

The YouTube clip pointed to captures a somewhat infamous night at LWT transmission. The complete presentation and networking ‘desks’ failed for a period and there was frantic over-patching going on to try and keep the show on the road - networking bring a primary task. I would presume the other ITV companies taking these network transmissions would have put out local apology captions. Two completely local separate tx paths from Kent House to Crystal Palace but neither any good if the common sending point has fallen over, both the local Pres desk and network equipment shared common CDL frames and had gone faulty. Very, very cool heads prevailed.