Which cable to use for Sky - Freesat - Freeview?
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25 October 2008
Coaxial cable has a limited life outdoors because sunlight and microbes cause the outer plastic sheath to become slightly porous and moisture can then permeate through, resulting in corrosion of the metal shield. This causes the signal losses to increase until there's insufficient signal for your equipment. So, whatever cable you use, make sure it's located for easy replacement. A conduit trough which it can be pulled is preferable to embedding in concrete or plaster. Cable outdoors can be painted to protect it against weather. It should never be buried underground without the protection of a conduit made of Alkathene or similar.
The once-popular CT100 coaxial cable hasn't been manufactured since 2005 and is now difficult to obtain, so beware of anyone offering "CT100" as it's likely to be a cheaper equivalent which might not perform as well or be as reliable. Even if it's the real thing, it will be several years old and may not be as good if it has been stored outside or in a damp warehouse.
There are good equivalents but you'll generally get what you pay for. The price of copper has rocketed so "cheap" usually means "less copper" - which is not good because the signal loss will be higher.
The replacement for CT100 was initially H109F but this has been superseded by WC100. There are various **100 types and many are fine but make sure that they have a thick copper foil wrap with copper braid on top. Aluminium foil is "OK" for short distances but has higher losses than copper and doesn't last as long outdoors.
WC100 has an "air-spaced dielectric". This means that the internal insulator is made up of a number of plastic straws. If water gets into these, the capillary action can cause it to be sucked into your equipment in seconds. The much-recommended "drip-loop" will not prevent this, as its only purpose is to let water drip off the outside of the cable.
WF100 has a plastic "foam" dielectric. This does not carry water and is less easy to kink, so it's usually a better choice all round, but slightly more expensive.
Cable length is important
Even the best cable loses a lot of signal so arrange it so the cable run is as short as possible. Don't leave a coil behind the TV "just in case". Every additional metre will make your "rain margin" worse!
Don't use an amplifier
There are certain situations where a satellite TV LNB amplifier might be required. Usually it won't help. For terrestrial TV, a masthead amplifier is sometimes required if the cable run is long or if you want to split the signal to more than one room. (Note than an LNB signal can not be split. If you need more than one feed, install a quad-output or 8-output (Octo) LNB on your dish.
Use a larger dish
To combat loss of signal due to cable length, bad weather or trees, use a larger dish. A "zone 2 minidish" is a little wider than a standard minidish but has 50% greater area.
Use a better terrestrial aerial
In 85% of the UK, a log-periodic aerial is by far the best choice and the most likely to be successful. It is a true "wideband" aerial and, although its peak gain is lower than that of a "Yagi" type, the gain is almost constant across the UHF frequency band. It is also unobtrusive and has a lower wind resistance. In only 15% of cases will a high-gain Yagi do a better job!
Screening out interference
WC100 and WF100 are sometimes called "double-screened" cables because they have copper foil and copper braid. The shielding is much better than that of ordinary so-called "low loss TV cable" (which should never be used) so it is essential to use it where interference is highest (close to the TV set and other equipment). The "fly-leads" connecting the equipment together should be double-screened, as should the one connected to the wall socket (which itself should be the shielded type of wall plate).
Twin "shotgun" cable
Sky often uses CT63 or WF65 twin "shotgun" cable for Sky+ and SkyHD installations. This cable is thin and can be passed through the 10mm hole required for ordinary single cable. However, "shotgun" cable has high losses, which can result in signal problems. If you DIY it's best to avoid "shotgun" cable. You can use two runs of single WF100 or one run of "twin" WF100 instead.
Low Loss cable
CT125 cable (obsolete) is thicker than CT100 (obsolete) and is used where it's important to minimise signal losses as much as possible. It has been superseded by WF125, which requires a special connector. WF125 is stiff, heavy and expensive and should be used only where a larger dish is not an option.
Whichever cable you choose, be sure to buy matching 'F' plugs. There are tiny (often invisible) variations in size between them but size matters. Use of the wrong plug can cause an impedance mismatch or leave the plug loose. Either way, you might experience "no signal" problems on some channels.
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