Andy Quested, the BBC's chief technologist for HD and 3D, had this to say on his blog:
The last transmission of the BBC HD Channel promo is actually the morning of the 25 March through to the start of programming later that day. However, after the last programme at around 1.30am on the morning of the 26 (still to be confirmed) and the start of BBC Two HD programmes at 6.30am there is a gap and I made what would be called a 'land grab' for the time!
To say goodbye to the test signals we will be transmitting them continuously overnight!
To make it more interesting I have worked with BBC R&D colleagues to recreate some of the older test cards from a 30 line version through the 405 line era, on to 625, colour, widescreen and finally high definition.
I must thank all the current and past BBC R&D engineers who put so much expertise into creating many of these industry standard test cards.
The loop is 10 minutes long so set your PVRs for about a 30 minute recording any time after the last programme (please check the EPGs just in case there are last minute schedule changes) until around 6.00am.
Please remember that the majority of these cards are recreations adapted for the HD Channel and not the originals and also that the HD version is still the modified version which means the grey scale is not exactly correct, but I hope that doesn't distract from the event.
If anyone has screenshots of vintage test cards used in their own region or country - we'd love to see them. If we get some nice ones, we'll publish them. Just send them to firstname.lastname@example.org