An RF cable is a basic cable used primarily for carrying audio-visual signals. The name comes from an abbreviation of "radio frequencies." It is a type of coaxial cable, which involves a series of casings to protect the signal from interference.
The coaxial design used in an RF cable is designed to prevent potential interference. To counteract this, the coaxial cable uses four circular layers. From the inside to the outside they are: the wire carrying the signal; an insulating material which is usually solid plastic; a metal shield; and a plastic casing which protects the materials inside.
RF cables have several important drawbacks. It can only carry sound between two devices in mono rather than stereo. As well as being unable to produce a stereo signal, this also means it can't carry surround sound information broadcast in Dolby Pro Logic™. This means that if an RF cable is used, it is impossible to get true surround sound audio even when using a decoding receiver.
Another drawback is that while the design of the cable does block interference in theory, in practice this is often not achieved. Cables, particularly cheaply made ones, can be subject to interference from magnetic sources or power cables. This can lead to visible picture interference such as ghosting.
Most RF cables will simply slide into a socket and can be pulled out easily. Some versions involve tightening a cap, rather like a screw. These connections are more secure and less likely to work loose and lose picture quality, but are not as convenient as the standard RF connection.
While using an RF cable is usually the cheapest option, better quality cable choices are usually available at an affordable price. For this reason, the only real reason to use an RF cable is where no alternative is possible because the TV set or VCR does not have suitable inputs. It's important to note this guideline does not apply to the lead between a TV aerial, whether rooftop or indoor, and the TV equipment.
In this situation, an RF cable is still the standard option and will usually be hard-wired into the aerial. However, it is best to only use RF cable between the aerial and the first device it is connected to. For other connections, such as from a set-top box to a television, it is best to use better quality connections such as composite or component video.