A co-axial cable is a transmission line that consists of a solid or stranded ‘core’ conductor, surrounded by an insulator, surrounded by an outer woven-wire or foil ‘earth’ conductor - and then wrapped in a protective sleeve of a toughness depending on the use of the cable.
Co-ax cables are used for the transmission of Radio Frequency (RF) signals and although they will of course conduct electricity, are not a suitable medium for low-frequency AC or DC current.
The transmission of RF energy through the cable takes place between the core and the earthed conductors. Any RF energy hitting the cable externally from another source, will get to the earthed conductor and be shielded from the core i.e. any induced electro-magnetic energy is earthed through the outer conductor without getting to the inner conductor. That means an external source of RF cannot influence the signal that is being transmitted along the co-axial cable.
Co-ax cables are a robust transmission medium for RF energy, but should not be ‘kinked’ or bent through corners. As a transmission line, their dimensions give the cable an ‘impedance’ (e.g. 75 Ohms, or 50 Ohms), and a termination plug/socket must be chosen to match the impedance of the cable. In turn, the cable must be chosen to match the impedance of the equipment on each end e.g. a 50 Ohm antenna socket on a transmitter, must connect to a 50 Ohm antenna, using 50 Ohm co-axial cable. Mismatches (e.g. 50 to 75 to 50 Ohms) in the transmission connection will cause losses! Things may have changed now with crimping tools - but manually installing a plug on a co-ax cable was something that needed to be done with fairly precise measurements and a fair amount of skill.
