The main components of the DTT Pilot Network

The multiplex (mux) and transmission services were provided by BT (Ireland) under contract. Multiplexing is the key new activity that makes DTT different from analogue transmission. Multiplexing comprises a multiplex head-end (like an IT centre) which for the DTT trial was located in Citywest. The head-end received the TV, radio and data services taking part in the trial and encodes, combines and converts these services to put them in the right digital format for transmission. The head-end was also used to process the service information and subtitling.

There were 4 multiplexes on the DTT trial.  MUX 1 carried the national Irish TV and radio stations, MUX 2 and MUX 3 carried stations supplied by commercial broadcasters and MUX 4 carried the trial HD test channel.

Distribution involves the provision of the broadcasting streams from the broadcaster to the multiplex head-end and the provision of the multiplexed signal to the transmission sites. For the DTT trial TV and radio content was provided by both national and commercial broadcasters and their content was delivered to the multiplex (mux) centre either by fibre, satellite or was fed directly from a play out server housed at the mux centre. Once the content had been multiplexed, it was transmitted over fibre and radio links to the broadcasting stations at 3 Rock near Dundrum in Co Dublin and Clermont Carn near Dundalk in Co Louth.

The broadcasting stations use high power transmitters connected to high gain aerials to transmit or broadcast the signals over a wide area. For the DTT trial the transmitters provided coverage of County Dublin and North Leinster. Content on the trial was received by the DTT triallists using a conventional UHF aerial and a set top box (STB) specifically designed for the DTT trial. The STB processes the received signal so that it can be displayed on a conventional analogue TV.