Digital TV – broadcasting with one hand tied behind its back

Puny transmitters shove pictures of digital cliff

UK Culture Secretary Chris Smith pledged today that conventional analogue TV broadcasts will only cease when 95 per cent of homes have a digital receiver. He said the switch could take place sometime between 2006 and 2010, but told broadcasters at the Royal Television Society Convention in Cambridge that viewers' interests must come first. Broadcasters are keen to junk the old analogue system because it will free up valuable bandwidth which can be sold to mobile phone providers for megabucks. Each digital channel, although it is broadcast on the same UHF wavelengths as conventional TV signals, can carry six separate TV channels today and many more in the future as the technology is developed. But what Smith failed to mention is that fewer people can receive digital terrestrial TV today than the technology allows. This is due to the new digital broadcasts causing interference on the analogue channels which share the same transmitters. In the light of viewer complaints, the signal strength of digital channels has been severely reduced, thus reducing the area covered by each transmitter, A quick check on BBC and ITC websites reveals that for two main transmitters – Sutton Coldfield in the Midlands and Sandy Heath in East Anglia – analogue signals for all five main channels are rated at a stonking MegaWatt while the strongest digital channel is broadcast at just 10KW, with some being dribbled out at a puny 2KW. This means that it is far more difficult to receive a reliable digital broadcast, even in areas with excellent analogue coverage. Weather conditions can have a severe effect on reception and in digital terms, that doesn’t mean a fuzzy picture – it means no picture at all. One of the key benefits of digital is greatly enhanced picture and sound quality. Near perfect reception continues until the signal strength drops below a critical level – dubbed the digital cliff – when the picture simply vanishes. And the end result of keeping analogue users happy, of course, is that viewers will move to digital TVs much slower than is necessary, pushing that magical 95 percent market penetration figure further into the future. ®

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