RF cable is consist an inner conductor or several uninsulated conductors tightly twisted together, often surrounded by an insulating spacer, surrounded by an outer cylindrical conducting shield (sheath), and usually surrounded by a final insulating layer (jacket).

It is often used as a high-frequency transmission line to carry a high-frequency or broadband signal but may also be used for frequencies as low as audio frequency. The electromagnetic field carrying the signal exists (ideally) only in the space between the inner and outer conductors.

The shielding reduces interference from external electromagnetic fields, although coax cable does radiate energy, shielding does somewhat reduce the possibility of a transmitting device causing undesired interference through transmission line leakage.