WHEN digital television takes off in Britain next year it will cause
widespread interference to other television services. Some homes may lose their
TV programmes altogether, while some viewers in Wales will have to watch English
instead of Welsh programmes. An internal survey for the Independent Television
Commission, which is licensing the new digital services, estimates that more
than 60 per cent of the digital transmitters will cause interference to existing
services.
Engineers at Channel 5 have become experts at the logistics of retuning,
because of interference to videos caused by the channel鈥檚 trial broadcasts.
They are sure that the problem of digital interference is 鈥渟ignificant鈥� and
has been downplayed in the rush to get digital services up and running. Channel
5鈥檚 chief executive, David Elstein, has warned that 鈥渢ens of thousands鈥� of homes
will be affected by digital TV.
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Technical documents published by the ITC show that although the number of
affected homes should be fewer than the number affected by Channel 5, the
effects will be more serious, and the remedial work more extensive and more
expensive. Broadcasting engineers are currently touring the country trying to
work out exactly how many homes will suffer interference.
NTL, the company that runs Britain鈥檚 commercial transmitters, says that 鈥渙nly
a very small proportion of the UK population will be affected鈥�. But NTL鈥檚
research was based on computer predictions and the company admits it is 鈥渢oo
early to say鈥� what the practical effects will be.
Television retailers feel they have been kept in the dark. Fred Round, the
chief executive of the Radio, Electrical and Television Retailers鈥� Association,
says: 鈥淲e have only just received information that digital terrestrial TV can
create interference problems. This has come as a surprise. No reference has been
made to this issue in any of the consultations the association has been involved
in. We need to find out exactly what the facts are.鈥�
Digital TV will use channels which cannot be used for analogue TV because
they are too close to existing transmissions, or would clash with frequencies
used by stations in other parts of the country. Because digital services will be
transmitted using around one-hundredth the power of analogue TV, it should be
safer to use these frequencies. But NTL鈥檚 research shows that there will
nevertheless be interference in many parts of the country.
Last October, the ITC published a draft code of practice on 鈥渃hanges to
existing transmission and reception arrangements鈥�. The document is a shortened
version of a tome produced by NTL for internal use. The draft code, a highly
technical document, has so far attracted little attention. But it predicts that
51 of the 81 digital TV transmitters will cause interference to analogue
transmitters. Broadcasters in these areas will have to make changes to their
analogue services.
In some areas, broadcasters will have to switch existing analogue
transmissions to a different frequency. Viewers will no longer be able to see
these stations until their TV and videos have been retuned. In some cases,
viewers will have to point their aerials at completely different transmitters,
as well as retune all their equipment to a different frequency.
In each case, if the new frequency is out of the range for which the existing
aerial was designed, the viewer will need a new aerial which can cover a broader
frequency band. All this work will involve time-consuming and expensive home
visits and the ITC will require the digital broadcaster to foot the bill.
The predicted effects and remedies vary widely. The ITC鈥檚 draft code warns of
鈥渓oss of gross coverage鈥� in some areas, including Bradford, Welwyn Garden City
and Sutton Coldfield. In Cefn-mawr, Wales, viewers will have to turn to a
different transmitter and watch their favourite programmes in English instead of
Welsh.
In its bid to the ITC for a licence to transmit new digital TV services, the
NTL company, Digital Television Network, talks optimistically of only 鈥渟everal
thousand homes鈥� affected and a retuning bill of just 拢3.3 million.
NTL fears that publicity may blow the problem out of proportion. Bruce
Randall of NTL says: 鈥淭here are bound to be some isolated pockets of
interference. Our predictive work shows potential areas which need to be looked
at. We are already doing field surveys to determine the actual situation.鈥�
