Network: A DAB hand at transmitting clear signals: Fed up with crackly radios? Maggie Brown tunes in to digital sounds

DIGITAL sound, in the shape of the compact disc, was one of the most successful products of the Eighties. But while the consumer boom was going on, research engineers in various countries were investigating how to apply the technology to radio.

A major attraction for broadcasters, including the BBC, was that digital audio sound would provide improved reception on mobile sets, car radios and home sets, where reception frequently suffers from interference, distortion or inadequate signal levels. This is possible because a digital system broadcasts sound (as the term implies) in numbers.

A team based in Germany cracked the problem of transmitting music digitally in a manner that used the radio spectrum economically: only one-sixth of the information stored on a compact disc was needed. A parallel team collaborating in France, meanwhile, worked on ways of transmitting the signal to ensure it was resistant to all interference. Its findings have now been thrown open to all wishing to exploit the new technology.

Scroll forward to 1994: the research is complete, what is needed is a drive to get the sluggish radio equipment market moving. It was this imperative that led Phil Laven, controller of engineering at the BBC, to confirm that the corporation plans large-scale network radio transmissions in digital formats next September.

He outlined the BBC's intentions to the first plenary session of the UK DAB (Digital Audio Broadcasting) Forum in September, set up last year by Michael Heseltine, President of the Board of Trade, who is anxious to encourage new broadcasting technology. The BBC, as a public service broadcaster, has decided to start the broadcasts to stimulate the market for new radio sets.

The first models are likely to be car radios for executive cars. The microchips which control them also require comparatively large amounts of energy, meaning that plug-in home sets are likely to be launched next, until the problems of power and size are solved.

Mr Laven's remarks caused a flurry at the BBC, where programme heads are still busily working out the programming implications of the onset of the technology. Next year's launch is also likely to be co-ordinated with other European broadcasters.

Howard Farmer, director of advanced projects for the consumer electronics division of Philips, says that next year's broadcasts will take the form of large-scale trials, rather than a long-term commitment to services, with reception in cars being a key test. He says that at present there are probably less than 100 test receivers in Europe, but companies, including Philips, plan to supply the thousands of sets that will be required for the trials next year.

He says that a proper launch of sets is unlikely to come before 1997, and that one obvious approach will be through car manufacturers. Mr Farmer believes that people like new products to resemble the ones they already have, so a digital car radio would have to fit in the dashboard place currently occupied by a conventional set.

Although the DAB radios will be able to carry all sorts of extra data, and will have a liquid crystal display information screen, they are unlikely to have keyboards to allow listeners to get the set, for example, to seek out music by Bach that is currently being broadcast.

The consumer electronics industry is rife with examples of new technologies and applications that have failed to translate into sales. Nobody knows whether digital radio will take off, but there is dissatisfaction with poor reception. One key point is that unlike FM radio signals, which spread their transmissions over a range of frequencies (Radio 4 transmits its broadcasts between 92.4MHz to 94.6MHz), a DAB channel will broadcast on an exact frequency, so it will not interfere with another channel. A single DAB signal can also carry up to six stereo channels.

'It is amazingly efficient. This is why the Government is so keen. In one fell swoop, you greatly expand capacity,' Henry Price, a spokesman for BBC engineering, says.

The BBC is already putting out digital test transmissions from Crystal Palace and Alexandra Palace in London, Wrotham in Kent, and Reigate in Surrey. The BBC says that it is the first digital radio channel capable of delivering to portable radios, though in the United States there are satellite digital transmissions.

The transmissions in Britain follow a Government decision last January to release comparatively high frequency bands (217.5MHz- 230MHz) for DAB. These wavelengths were previously used for black and white ITV pictures and defence communications.

Because DAB is so flexible, the services can be varied during the day, Mr Price says, switching from six stereo radio services to 12 mono-services within seconds. This means, for example, that Test Match Special, now on Radio 4 long wave, or services modelled on it, are obvious DAB converts.

World Service radio is another output area of the BBC that could have a use for the service.

Mr Price says: 'The big question is how to use it.' And it is that ability to vary output which is likely to pose a challenge to commercial radio regulators.