Aerial nightmare


By Barry Fox TV VIEWERS in the US may have to start using aerials again, after decades of relying on cable reception. Digital terrestrial TV is due to be launched in the US on 1 November but the channels won’t be available on cable for some time. About 70 per cent of homes in the US get their TV by cable, but the digital terrestrial signals cannot be squeezed into the existing cable system because each channel uses roughly four times the frequency capacity—or bandwidth—of a conventional analogue channel. No agreement has yet been reached on how to upgrade the system to make digital channels available on cable. What’s more, even those homes that already have an outdoor aerial are unlikely to be able to receive all the channels allocated for digital TV, as most aerials can’t pick up signals over the wide range of frequencies—both VHF or UHF—used. Electronics companies in the US are now hurrying to develop wide-range indoor aerials for digital reception, but such aerials will not work in homes effectively shielded by a metal framework—or metallised-glass windows. As a result, the US’s Consumer Electronics Manufacturing Association is to distribute maps that show precisely where digital TV can be received—and, along with television makers, is advising dealers not to sell equipment to customers in areas with poor reception. This is not the only problem facing digital TV. In the US, as in Britain, digital terrestrial channels will use frequency bands previously left empty to stop neighbouring analogue channels interfering with each other. The trouble is that manufacturers have unofficially taken advantage of these empty bands for wireless systems such as microphones, connecting VCRs to TV sets, and even patient monitoring in hospitals. No one yet knows what interference will be caused as more high-power digital TV transmitters are switched on. But a test in April gave a preview: at the Baylor University Medical Center in Dallas, a digital test transmission from WFAA-TV in Dallas interfered with 60 wireless heart monitors, corrupting the data received by nurses’ stations. Similar problems could occur in Britain as digital broadcasts begin. With both US and British services starting up around the same time, observers are waiting to see which country has opted for the right technology. US broadcasters will use their bandwidth to deliver a handful of extra terrestrial channels with high-definition picture quality, while Britain will get many more terrestrial channels than the existing five—up to 30—but with standard picture resolution. The downside is the expense: HDTV set prices range from $7000 to $12 000. Set-top decoders costing under $1000 are promised but they need a special display,
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