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FEATURE
TELEVISION INTERFERENCE , CAUSES AND CURES
Television interference, or
TVI as it’s known in the trade can be a major problem, and according to BBC
engineers, it is one of the biggest causes of dissatisfaction amongst TV viewers,
generating more complaints than the quality of the programmes themselves.
TVI can be caused by almost
anything, from a next-door neighbour’s badly suppressed vacuum cleaner to the
cab firm over the road. Even the weather can
have an effect and foreign TV stations can interfere with UK broadcasts
in a phenomena called ducting, which happens during a weather condition known
as thermal inversion. Interference comes in many forms, varying in severity
from mildly irritating speckles and flashes on the picture, to wiping it out
altogether.
In fact most TVI is caused
by the householders own electrical
appliances, which produce very characteristic crackles and flashing.
It’s normally quite easy to track down; make a note when the interference
occurs, you may well find it coincides with a refrigerator switching on and
off, or a central heating boiler firing up. Be very suspicious about the boiler
if the interference only happens in the winter, when the heating is on. In both
cases have them checked out by a competent electrician.
TV aerials are the next
biggest source of interference, especially cheap set-top aerials which often
have very poor directional characteristics, or are badly screened. If you’ve
got one of those chuck it away and have a proper loft or roof-top aerial installed
and chances are it will get rid of the interference. Even properly installed
rooftop aerials can cause trouble if they’re fitted with an amplifier or
booster. If it goes off-tune it can produce ‘venetian blind’ patterning --
clearly visible as coloured stripes across the picture. The cure is to have the
offending device adjusted or replaced. Living too close or too far from the
transmitter is another potential problem, in both cases a competent aerial
installation engineer should be able to come up with an appropriate solution.
If the interference is
man-made but coming from a long way away, or cannot be identified there are two
alternatives. The simplest DIY answer is to try a TVI or ‘high-pass’ filter,
which connects between the TV and the aerial lead. These are designed to
prevent radio frequencies lower than those used by TV broadcasters, from
getting into the TV. These include transmissions emanating from CB and ham
radios, police and taxi operators. They’re widely available from aerial
installers, or your local Tandy store, for around £3.50.
The final recourse is to
report the interference to the authorities. The organisation responsible is the
Radio Interference Service, they are part of the Radio Communications Agency,
who in turn are a division of the Department of Trade and Industry. Complaint
forms and a very helpful leaflet called ‘Advice on Radio Reception and
Interference’ used to be available from local Post Offices, but they have since
been withdrawn, presumably as a cost-saving measure. Now they have to be
obtained direct from the DTI library, who can be reached on 071-215 2072. Both
the BBC and ITC will obligingly send you the relevant forms as well; you should
be able to find their numbers in your local telephone directory. Be warned that
the RIS may make a call-out charge of £35 if they feel it necessary to visit
your home, though that may include the fitting of filters and relevant advice.
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1994 1907
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