A filter is used to prevent unwanted signals from reaching your equipment, whilst allowing the wanted ones to pass through unaffected.
Some filters may need to be installed before any amplification, while others should be installed directly before the receiving equipment.
A qualified installer should be able to suggest the best option for you.
Filters stop unwanted signals from radio amateurs and CB enthusiasts which can interfere with television and radio reception. Since many amateur transmissions are lower in frequency than television and FM signals, a high-pass filter can be fitted to the receiver to prevent the low frequency amateur signals from reaching it and causing problems. High-pass filters are a common component in what are known as ‘TVI' filters, sometimes called ‘TETRA' filters.
Band-pass filters allow only a range of required frequencies through, rejecting all others. Band-pass filters must be specified for the correct use. For example, using a television band-pass filter on an FM tuner will prevent reception of FM signals - and vice versa.
Braid-breakers work by preventing low frequency signals from reaching television or FM equipment down the outside of the aerial cable. If you have several devices connected to your equipment, you may need to fit filters to the inputs of all of them.
Sometimes strong, amateur signals can interfere with audio equipment as well as television or radio. This usually happens because the loudspeaker wires or mains cables act as ‘aerials' and conduct the signals inside the case. You can wind a short section of the cable in question around a ferrite ring using a number of turns, and to do so as near to the hi-fi /television/radio as possible.
The BBC cannot recommend individual Installers. The CAI (Confederation of Aerial Industries) is a recognised trade body which will be able to put you in touch with one of its members in your area.