Presentation

It is easy to think of your programme in isolation, and to forget that we are all just a small part of the bigger picture – the network.

In the centre of any network is the presentation department, sometimes known as Transmission. They physically transmit programmes, trails, adverts etc. from a network control room that looks similar to a small studio control room, except that instead of having cameras on preview monitors there are studios.

Computers often control much of the transmission, but there still needs to be a network director (or transmission controller) to make decisions and to check details.

How networks function

Most television channels have a system of a central transmission point or network centre. Their signal (or ‘feed’) is sent out to other parts of the country where there are local studio and transmission facilities. For large chunks of the day the output will be the network centre feed, but these regional transmission sites can switch to local studios to broadcast their own programmes or ‘opt-outs’.

Regional opt-outs

Typically these are local news summaries, evening news programmes and local sports shows.

For regional opt-outs to work smoothly the regional centre must be able to make a clean switch away from, and back to, the network transmission. This means every regional centre producing programmes of exactly the same fixed length, starting and finishing to within a split second.

The central network offers suitable points during the day for regional transmission suites to switch to local studios. At the end of the agreed duration, the network director counts the regions back into the main network. The switch can either be done manually at the regional centre, or controlled by the network centre, sending out control pulses hidden at the top of the screen.

Note that even if every regional centre in a country is switching away from the network centre, there must still be a usable picture on the network feed. Very occasionally there will be a problem with one of the switches. If a region fails to switch away you don’t want any old rubbish accidentally going to air.

Simplified transmission system with ‘opt-out’ capability
Presentation control rooms in the north and south areas have the option of taking the network centre feed, or switching to a local studio.

In practice it is a little more complex, as the switch to local studios is often controlled by the network centre, which sends switching codes hidden in part of their broadcast picture.