Digital switchover policy

Between now and 2012, analogue channels and the existing digital terrestrial multiplexes, will be switched off transmitter group by transmitter group and replaced with new switchover multiplexes. Turning off the analogue signals will make it possible to boost the strength and coverage of digital terrestrial services. Before digital switchover, 73% of UK households could receive digital TV through an aerial. After switchover, 98.5% of UK households will be able to receive digital terrestrial TV, the same proportion of households as can currently receive analogue signals.

Switchover will also enable the release of spectrum for new services, which might include additional television services, wireless broadband and mobile television. Ofcom is in the process of awarding the spectrum freed up by switchover through the Digital Dividend Review process.

International perspective 

The Council of Ministers has agreed that all EU member states should aim to switch to digital by 2012. Countries including France, the Netherlands, Finland and Sweden have already done so. Outside the EU, many other leading countries, including the USA, Japan and Australia, have published plans to turn off their analogue terrestrial TV services.

Digital switchover planning and preparations

The timetable for switchover was confirmed in September 2005 following planning by the public service broadcasters, the multiplex operators, the transmission companies, Digital UK and Ofcom.

The technology used to broadcast digital terrestrial television signals is tried and tested, having been used in the UK and other countries around the world for more than a decade. However, in order to avoid interference with the existing analogue system, digital terrestrial services can currently only be broadcast at low power and from a limited number of sites. After switchover, when analogue services are turned off, the digital terrestrial signal will be extended from the current 80 main sites to more than 1,100 transmission sites and the signal power will be boosted to universally cover the UK.

In order to achieve the transition from analogue to digital television major re-engineering work on transmitters is necessary in advance of the actual switchover dates in each area. This work to upgrade the UK’s network of more than 1,100 transmitters is now well underway. It is being carried out gradually to minimise disruption to viewers and is coordinated by Digital UK. The engineering work may result in temporary disruption and degradation to reception of both television and radio services in addition to that caused by routine maintenance activity. Digital UK publishes switchover related planned work on its website. This can be found on digitaluk.co.uk/engineering_works which also provides links to the broadcasters’ sites for information on other planned engineering works.

The digital terrestrial television (DTT) spectrum plan

The new digital switchover spectrum plan is based on, a "universal" roll out of three public service broadcaster (PSB) multiplexes to give analogue equivalent coverage and keeping PSB multiplexes within the analogue aerial group wherever possible. In addition spectrum planners have incorporated the Ofcom relicensing requirements for the clearance of 14 channels of conventional broadcasting and the conversion of existing analogue channels to digital wherever possible.

This spectrum plan has also been based on the transmisson of the three commercial multiplexes from 80 sites, and placing these muxes within the analogue aerial group if possible.

The UK television coverage model

The UK planning organisations (BBC, Arqiva and Ofcom) have to use a statistical model that is based on a set of assumptions.  The prediction model has been agreed by the UK planners and is most probably the most advanced broadcast prediction tool in the world.

The model has improved greatly in resolution and prediction accuracy over the years as computing power and terrain data availability has increased the analogue reception prediction, which used to be predicted to 1km squares, today the current model predicts to a resolution of 100m. It is this planning model that sits behind the Digital UK postcode checker.

It must be noted that the model cannot take into account factors such as - buildings, other than a general allowance for "clutter"; trees or individual recieving circumstances.

What is DTT 'coverage'?

For a location to be within DTT coverage, there must be enough signal from the wanted transmitter at 10m above ground level in order for the representative installation to work.

In addition there must be little or no signal from more distant unwanted transmitters on the same frequency to cause interference.