BBC Re-Broadcasting (RBS)

How come only the BBC do a re-broadcasting test every year? I Have never seen ITV, Channel 4 or five ever do one is there a reason for this?

Also if there was a need to rebroadcast the sytem and not all of the country had switched to digital yet what would happen? would they just keep the digital feed and only select the analouge feed?

It is only necessary to do it once a year.

ITV never did it because of the regional nature of it - rebroadcasting another region's transmitter just wouldn't have happenned.

Not sure why C4 never did, but for C5 it might not work anyway because I guess many transmitters might not be able to receive a usable signal and besides they're all fed from satellite, so duplicating the satellite receiver would be a better way to provide redundancy.

What happens mid-DSO is an interesting question.

C4 originally had different advertising run by the regions, and now has it's own ad regions, which makes rebroadcasting difficult still. As for Five, as said, it uses satellite anyways, and the transmitters are too weak to easily rebroadcast.

I don't know if it still happens, but ITV London often do a test in the middle of the night (usually during Nightscreen) where they switch the feed from Crystal Palace to their backup at Croydon (Channel 4 also share the same system), which would kick in if Crystal Palace failed... The screen would go fuzzy for a brief second when they started and ended the test and Teletext would be being received from the Meridian transmission of Rowridge.

I don't know whether you'd count this as a sort "rebroadcast test" or not. As far as I know it's the only ITV transmitter that does it.

Perhaps only the BBC has put the investment (or can afford to put the investment) into having such a system in the first place? Or sees their network as being so vital that it has to have such uptime?

Rebroadcasting another transmitter really is a worst-case scenario; each transmitter already has two feeds to it coming by diverse paths. You've got to be really unlucky for both of those to fail at once.

okay then another question. What would cause the BBC to rebroadcast the system? It Must be something Really Major for it to do it surley

It happens automatically - if both feeds to a transmitter should fail (due to a misplaced JCB or two or something like that), it goes "'ang on a minute, I'm supposed to have a picture and stuff! Ooh, er, that transmitter over there's still broadcasting, I'll just do what he's doing".

The annual tests are a really really worst case scenario: what would happen if all the feeds to all the transmitters failed? It's very unlikely to happen in normal operation.

It's hardly necessary for ITV, Four and Five to carry out RBS tests, as, should the ultimate ever happen, they would be simply put off air for the duration by the Emergency Powers Act.

Only the BBC would be turned into the NBS (National Broadcasting Service) by the Act and be required to keep a service going.