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Using ordinary TV aerial cable for a satellite dish
The good news is that it works. The cable from a satellite dish, down the wall, into the house, into the set-top box, should be special low-loss satellite cable, but replaced with normal tv aerial cable, it will work and pictures can be received ok.
Now the BAD NEWS. Ordinary co-ax at satellite cable frequencies is electromagnetically incontinent, and will LEAK high frequency radio waves all over the place. This is antisocial and can cause severe mucking-up of your neighbours' television/radio reception. So, if you don't want to be accused of interfering with your neighbours, don't install ordinary co-ax telly cable on a satellite dish! Also, if your satellite installers are tacking a nice piece of new cable to the wall, it's worth giving it the once-over just to make sure it's real LOW-LOSS satellite cable and not normal telly co-ax.
WHY it makes a difference
Normal UHF television radio waves travel through the air quite smoothly and can be picked up on a television aerial which has elements that ring like a tuning fork at the right radio frequencies. At such frequencies (UHF), the signals are quite happy to travel along electrical wires, from the aerial to the television set.
Satellite television is different, and the frequencies involved are much higher. They are more like the kind of thing going on in a microwave oven and prefer to travel inside tubes rather than along copper wires. Typically a system like Sky TV uses frequencies around 11-12 gigahertz. That's too high to go down wires, so you have a thing at the focus of the satellite dish called an LNB (low noise block). This is a superheterodyne device which converts the signal down to about 1 GHz ready to put into the cable. But even at that frequency it's still too high to be going along normal co-ax. That's why LOW LOSS cable is used. This is much better at keeping the signal inside the cable. It's also slightly more expensive.
How to tell the difference between LOW LOSS satellite cable and basic television aerial coaxial cable
Low Loss co-ax cable usually has a label on the cable real saying "low loss cable" or some other technical specification such as "suitable for satellite installations". The cable sometimes, but not always, has words printed at intervals along its length saying it is genuine low-loss cable.
On inspection of a bare end of cable, low loss cable sometimes has a copper foil layer around it a bit like kitchen foil, and/or the insulating material inbetween the core and the sheath has gaps in, rather than being solid white soft plastic.
Just as surely as you shouldn't be offended when a supermarket cashier holds your banknote up to the light to make sure it's not a forgery, reputable satellite installers should not be offended if you are such a fusspot customer that you check the cable yourself and insist on looking at the cable reel, etc. In contrast, if you've got cowboy cable fitters in they'll either object to you checking or they'll claim that ordinary TV flex "will do". ... But you know better!
Other useful references: Satellite TV, Alternative Satellite TV, Sky TV, what to do about radio interference, misconceptions, radio and electronics
You may be interested to know that you can get some proper low-loss satellite TV cable from Wickes. They sell lots of hardware and stuff, but low loss satellite cable is available in 100 metre reels for less than £30 (2011 price).