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Itís 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 Earthís 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).



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 didnít reckon with the ingenuity (and avarice) of dish installation engineers. However, if there is a physical barrier between your home and the satellite thereís simply nothing you can do, apart from subscribe to a cable TV service, providing thereís 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 thatís to look at neighbouring properties, see if thereís any dishes and take note of which way theyíre 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 youíre 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. Youíre looking for a clear expanse of sky; donít despair if thereís something in the way, try it from an upstairs window, or up a ladder, you may get lucky. If you donít you can always call on the experts.



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 itís 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, itís 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 youíre 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 itís 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 Earthís atmosphere. Beyond the Shetlands itís probably best to find something else to do in the evenings...



DIY dish installation is possible but inadvisable for most people. The first problem is to find a suitable position for the dish. Itís 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 youíre comfortable working at heights itís worth bearing in mind that a satellite dish is a heavy and unwieldy lump of metal, theyíre 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 itís 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.  



Okay, so we havenít 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 ĎA Householderís Planning Guide for the Installation of Satellite Television Dishesí. Itís 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 youíve found a suitable position consider the impact a dish will have on your property, and your neighbours, assuming of course that youíre 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 youíll loose the signal. Wood also rots, what would happen if the dish fell down? Donít 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 donít 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 wonít 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 Ďclearialsí 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.



Hopefully by now youíve 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 theyíre 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 youíve got any problems with holes being drilled through walls and window frames, now is the time to sort them out. If youíre 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 theyíre at work, but keep out of their way, and donít stand under ladders, it can be especially unlucky when thereís someone above juggling with a heavy dish or tools. Itís as well to clear a path to your living room, and once theyíve shown you where the downlead will be emerging in the room, make sure thereís 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 thereís 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 theyíve finished, but a good installer will do that anyway.



y 1994 2309


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