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FEATURE
INSTALLING A SATELLITE TV SYSTEM
INTRO
It’s a wonder satellite
television works at all! By the time signals broadcast from TV satellites have
travelled through 36,000km of space, and fought their way through the Earth’s
dense, soggy atmosphere they are unimaginably weak, just a few billionths of a
watt. A heavy thundercloud can be enough to wipe them out altogether.
Most satellite dish
antennas function like concave mirrors, except they work by collecting and
concentrating high-frequency microwaves, rather than light. The incoming
signals are focused onto a highly sensitive microwave receiver and amplifier,
which converts the signals to a lower frequency, before sending them by cable,
to the set-top tuner/decoder.
For all this to work properly
the dish or antenna has to be very carefully aligned, so that it points
directly at the satellite. Accuracy is critical, half a degree either way and
the signals will be lost, or corrupted by transmissions from adjacent
satellites. It sounds straightforward enough, but the point is nothing must be
allowed to get in between the satellite, and the receiving dish; in other words
that dish on the side of your house must have clear line-of-sight to an object, not much larger than a family car, several
thousand kilometres away, out in space, and that takes some doing.
All TV satellites are in an
equatorial geosynchronous orbits, which means that from the UK, and much of
Northern Europe, they appear to be at fixed positions in the sky, strung out
along a narrow arc, low in the southern sky, stretching from the Eastern to the
Western horizon. Fortunately the three Astra satellites (a fourth is due be
launched in the next few weeks) are fairly close to the centre of the arc -- as
viewed from the UK -- at a position that is defined as 19.2 degrees, East of
due South, at an elevation of between 20 to 30 degrees (depending how far North
you live).
1. CAN EVERY HOME HAVE A DISH?
The simple answer is no,
research carried out by British Telecom in the early 1980s for a direct to home
satellite TV service, suggested that as many as 15% of UK homes would not have
a suitable site for a dish, though they didn’t reckon with the ingenuity (and
avarice) of dish installation engineers. However, if there is a physical
barrier between your home and the satellite there’s simply nothing you can do,
apart from subscribe to a cable TV service, providing there’s one in your area.
The best way to find out if
you can receive satellite television is to carry out a site survey of your home,
there are three basic methods. The first is the one preferred by unscrupulous
dish installers, and that’s to look at neighbouring properties, see if there’s
any dishes and take note of which way they’re pointing. The second, slightly
more scientific method is to look and see where the sun is at noon, throughout
October, (great timing huh....). At that time the sun is in pretty much the
same spot in the sky as the Astra satellites, so it follows if any part of your
property is in sunlight at that time you’re probably okay for Astra.
The most accurate method
though, is to use a compass, to work out the bearing of the satellite. Find South
then count back 20 degrees to the East and you should have it. You’re looking
for a clear expanse of sky; don’t despair if there’s something in the way, try
it from an upstairs window, or up a ladder, you may get lucky. If you don’t you
can always call on the experts.
2. WHAT SIZE DISH DO I NEED?
Satellite dishes come in an
amazing variety of shapes and sizes but the simple rule of thumb is the bigger
the better. Along the South coast it’s possible to get away with quite small
dishes, 40 cm or less in diameter, and under ideal conditions picture quality is
comparable with a standard 60cm dish, (the smallest size recommended by the
operators of the Astra satellites). However, such small dishes have very little
in reserve, any slight reduction in signal strength -- caused by heavy cloud
cover for example -- and the picture will deteriorate very quickly indeed, more
so than it would on a larger dish.
60cm dishes are suitable
for most locations in England and Wales, South of Nottingham, say, though other
factors have to be taken into account, including the efficiency of the LNB (low
noise block converter -- the device stuck out in front of the dish). The
easiest way to determine LNB performance is to look at the noise figure stamped
on the LNB serial number plate, it’s quoted in decibels (dB). Most standard
Astra LNBs have a noise figure of between 1 and 1.2dB, noise figures below 1dB
are considered good, less than 0.8dB and you’re into the specialist (and that means
expensive) end of the market, for multi-satellite operation.
North of Nottingham it is
wise to start thinking about a slightly larger dish, the next step up in size
is 80cm, and providing it’s fitted with a reasonably sensitive LNB it should
produce a good picture up to the Highlands of Scotland. Beyond that dish sizes
for Astra reception increase at an alarming rate, as the satellite sinks
further towards the Southern horizon and the signal has to struggle through
progressively more of the Earth’s atmosphere. Beyond the Shetlands it’s
probably best to find something else to do in the evenings...
3. CAN I INSTALL IT MYSELF?
DIY dish installation is
possible but inadvisable for most people. The first problem is to find a
suitable position for the dish. It’s not that difficult to do from the ground,
but if the only place you can mount your dish is twenty feet off the ground, it
means clambering up a ladder. Even if you’re comfortable working at heights it’s
worth bearing in mind that a satellite dish is a heavy and unwieldy lump of
metal, they’re difficult enough to carry with both feet on the ground...
A satellite dish has to be
rigidly bolted to a wall or other similarly unyielding and secure surface, that
means drilling deep holes and tightening big heavy-duty bolts. Putting your
weight behind a power drill at the top
of a ladder, and not falling off the ladder is no mean feat, and it’s the sort
of thing you only get wrong once....
Professional dish
installers have the skills, tools and insurance cover needed to do this sort of
job safely, so it really is a good idea to leave it to them, if it involves
working off the ground. By all means consider the possibility of a ground-based
installation, but this is usually only possible on a small number of sites,
which have a clear unobstructed view of the southern sky. Moreover ground-mounted
dishes tend to look untidy, and are prey to a variety of problems, including
unwelcome attentions from animals and small children, any of whom can knock the
dish off beam.
4. HOW DO I INSTALL IT?
Okay, so we haven’t managed
to talk you out of it, how do you go about putting up a dish yourself? The first
thing to do is to get hold of a very helpful booklet published by the
Department of the Environment. It goes under the snappy title ‘A Householder’s
Planning Guide for the Installation of Satellite Television Dishes’. It’s not
very widely distributed but you should be able to get a copy from them if you
write to : DOE, PO Box 135, Bradford, West Yorkshire BD9 4HU, quoting ref 91
PLAN 0084. Read it and inwardly digest all the good advice and warnings about
the many and various things that can go wrong.
Once you’ve found a suitable
position consider the impact a dish will have on your property, and your
neighbours, assuming of course that you’re allowed to erect a dish in the first
place. Make quite sure you check with your local authority, housing association,
landlord or leaseholder before you begin.
Make one hundred per cent
sure that the chosen site can support the weight of a dish, check the brickwork
to make sure it is sound, any loose bricks or mortar will need to be repaired
before you mount the dish. Is the mounting point stable? Its no good bolting a
dish to wooden eaves or thin panelling, it will flex in high winds, and you’ll
loose the signal. Wood also rots, what would happen if the dish fell down? Don’t
forget the downlead that connects the dish to the set-top tuner, next to the
TV. If the cable run is longer than twenty or 30 metres, say, there could be a reduction
in picture quality
If you don’t like the look
of a conventional dish it may be worth considering some alternative designs,
though it has to said that solid metal parabolic dishes are the most efficient;
in poor signal areas many of the more exotic designs simply won’t work. Black
mesh dishes can be quite discreet, and flat-plate antennas can be tucked away
out of sight, beneath the eaves of a house. Transparent dishes or ‘clearials’
work for some people but one of the most successful dish disguises is a
colour-cordinated paint job or cover, which can be matched to its surroundings;
from a distance the dish can be almost invisible.
5. WATCHING THE INSTALLERS
Hopefully by now you’ve
decided to play safe and call in the experts, but should you just trust them to
get on with it? No chance! Even before you decide on a dish installation
company make sure they’re members of the Confederation of Aerial Industries or
CAI. This industry association sets out codes of practice, demands a minimum
level of competence and ensures that members have adequate insurance cover,
just in case something goes wrong.
The first thing the
installer will want to do is to carry out a site survey, be on hand to answer
any questions about your property and adjoining buildings. Before any holes are
drilled or cables laid, insist that they show you exactly where everything is
going to go. If you’ve got any problems with holes being drilled through walls
and window frames, now is the time to sort them out. If you’re having a dish
installed in the Autumn or winter pay special attention to the proximity of any
trees, you would be surprised how many STV installations develop mysterious
picture problems in the Spring...
By all means keep an eye on
the engineers when they’re at work, but keep out of their way, and don’t stand
under ladders, it can be especially unlucky when there’s someone above juggling
with a heavy dish or tools. It’s as well to clear a path to your living room,
and once they’ve shown you where the downlead will be emerging in the room,
make sure there’s no ornaments that will get knocked over by long drills or trailing
leads. Ask them to leave plenty of spare lead at the receiver end, you may not
always want to have your satellite receiver where it is now.
Check that the lead entry point
is adequately waterproofed, and there’s a drip-loop on the outside, to stop
rainwater running down the lead and into the hole. Finally make sure they clean
up the mess after they’ve finished, but a good installer will do that anyway.
---end---
y 1994 2309
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