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Science: Tuning in to confusion: When the Government determines the destiny of Channel 5, writes Steve Homer, it will also be deciding the future of British television

A big question mark hangs over the future of British television. In a month or so, the Government will make a decision on the fifth terrestrial channel. If it chooses the soft option, it may saddle Britain with outdated broadcasting technology which could handicap our electronics and telecommunications manufacturing companies.

Britain could have a fifth terrestrial channel reaching most of the country on the air in a couple of years. Alternatively, these frequencies could be reserved for up to 16 new digital services - but digital television will take longer, and consumers will have to buy new equipment.

Digital television has matured amazingly rapidly. It allows signals to be squeezed into a piece of radio frequency much more effectively than today's analogue system. Technical experts generally agree that, in the long term, terrestrial television will be delivered by digital means. This could bring many more services and free frequencies for mobile phones and other technology.

Today's PAL transmission system produces a good picture under the right circumstances. But it is horrendously inefficient. Fifty-one high-powered transmitters reach around 90 per cent of the population and nearly 1,000 relay transmitters bring the total coverage to 99.4 per cent. But each transmitter can interfere with others nearby. The only way to avoid this is for individual stations to be transmitted on different channels on nearby transmitters. So while 44 channels are available on our UHF TV frequencies, we can only squeeze in four stations.

If the PAL system were switched off today and replaced with a digital system, instead of four stations we could have 100 or even more. But the transition is the nightmare.

The most likely scenario is to offer the existing four or five terrestrial channels in digital alongside the analogue services, with extra services and/or benefits. Initially viewers will have to buy a separate box of electronics, like a satellite box, to watch the digital transmissions, but eventually the electronics will be built into television sets.

The recent upsurge of interest in digital television has focused attention on the frequencies due to be allocated to Channel 5. Using two channels that have only recently been cleared - UHF channels 35 and 37 - it was advertised last year but the sole bid, from a consortium led by Thames, was rejected. The problem is that not only will Channel 5 be unavailable to 20- 30 per cent of the population, but about half of those who can get Channel 5 will need to instal a new aerial, and millions of video recorders and satellite receivers will suffer interference. This last point will cost the winner of a Channel 5 franchise up to pounds 350m in retuning VCRs and satellite receivers, according to a report published recently by Dermot Nolan, director of the Convergent Decisions Group.

Quite separately from studying the technical feasibility of Channel 5, the Independent Television Commission (ITC) has been working on a digital project called Spectre. This aims to use so-called 'taboo' frequencies to transmit digital television in the UK. The taboo frequencies are those where analogue signals would interfere with adjacent analogue transmitters. Research carried out by NTL for the ITC has proved that, at medium power, digital signals will not interfere with nearby analogue transmitters. The problem with this approach is that it cannot give coverage to the whole of the UK.

The BBC has a different vision. It proposes using channels 35 and 37 for a national digital service. Each channel would be able to transmit between four and eight programmes, in a quality similar to today's PAL transmissions, to 97 per cent of the population. If high-definition television (HDTV) were introduced, each channel would be able to transmit one signal of HDTV quality, which it is claimed gives a crystal-clear picture.

The BBC proposes a single frequency network, to take advantage of the ability of digital systems not to interfere with each other. But the ITC believes that this a complicated technological trick and is many years away.

The Department of National Heritage expects to tell the ITC whether channels 35 and 37 are available for Channel 5 by June. However, while a fifth channel available to most of us in about two years' time at almost no extra cost looks attractive, it is likely that longer-term forces will prevail. No other European country has the luxury of two clear UHF channels. Phil Laven, the BBC's controller of engineering policy, says: 'We have a one-off opportunity. If we do not hold on to these frequencies for the introduction of digital services, I believe in the year 2000 we will look back and say: 'My God, what a short-sighted decision that was.' '

Change in television takes a long time. The move from 405-line VHF to 625-line UHF began in 1964 with the advent of BBC 2, which was only ever available via UHF. The 405-line services were not withdrawn until 1984. Terrestrial digital television is not likely to start before 1997. But while your current set looks fine for now, difficult decisions have to be taken in the next few months.

(Photograph omitted)