Guidelines

UK television - The situation in 2008

The majority of television viewing (over 50%) in the UK is done via some 1100 terrestrial (ground based) transmitter sites, currently using a mixture of analogue and digital services, but satellite transmission (digital) has a substantial share (some 36%) and digital cable holds about 13% of the market. The ‘new’ IPTV (Internet Protocol) television services, where TV signals are delivered via broadband internet services using radio frequency signals over standard telephone wires (ADSL – Asymmetric Digital Subscriber Line) have so far had little impact on the market.

The period from 2008 to 2012 is a time of significant change and innovation in UK television.

For many years UK broadcasters have been providing four analogue television programme channels: BBC1, BBC2, ITV, and Channel 4 to around 98.5% of the population, with a fifth analogue programme channel, Five, which was introduced later, available to just under 80%.  Terrestrial TV transmissions in the UK are broadcast in the UHF (Ultra High Frequency) band between about 470 and 850 Mhz, a spectrum range that is broken up into channels 21 – 68, with each channel able to carry just one analogue programme in a given area. Other transmission bands, including VHF Band III (174 -225 MHz) are also used in Europe.

Digital terrestrial transmissions were introduced in 1998, in parallel with the analogue transmissions, and now provide coverage of some 73% of the population. Digital technology allows for more efficient use of the transmission channels than analogue, so any given frequency channel can now carry far more than one programme – each channel carries a ‘multiplex’ of perhaps six TV programmes plus several radio channels.

As one example, Multiplex B, operated by the BBC, carries the following collection of programme material on a single radio frequency channel in any particular area:

Six multiplexes have been provided from most of the main transmitters, so those who can receive the digital signals can receive up to around 40 different TV programmes plus dozens of digital radio services as well as text and interactive services. The digital services also bring with them subtitling and signing for deaf viewers, and audio description to help blind and partially sighted viewers to better understand what is happening on screen.

The coverage of the digital terrestrial signals is currently restricted to 73% of the population because the digital transmissions have to share the UHF frequency band with the existing analogue transmissions – they have effectively been squeezed into the gaps between the analogue services, as the diagram below shows.

The six broad vertically placed lines across the centre of the scale represent the six digital multiplexes carrying dozens of programme channels in total, whilst the larger ‘peakier’ signals are the analogue channels each carrying one programme vision signal, with a lower powered sound channel to its right. The greater efficiency of the digital transmission system means that digital transmitter powers can be much lower than analogue powers to achieve the same coverage area.

The bar diagram below shows a similar situation in graphical form, these being the frequency channels used by the Crystal Palace transmitter that serves the London area.

 

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