A coax cable consists of two conductors separated by a dielectric material. The center conductor carries the signal. The outer conductor acts as an electrical shield. The two conductors are insulated from each other by the dielectric. The dielectric can be solid or foam. On the outside layer, the cable is protected by a jacket.
The center conductor is either solid or stranded. Solid conductors are used in permanent, infrequently handled, or low flex applications; stranded conductors are used in flexible cable applications.
The outer conductor is typically made from a number of smaller aluminum or copper conductors combined together. These conductors are woven together to form a braid around the dielectric core. For higher frequency applications, a second braid or aluminum foil are added to improve attenuation and shield effectiveness.
The longer a cable, the more the signal is lost. The loss is called attenuation, which can be measured in dB per 100 ft. Part of the loss depends on the coax's shield and dielectric. The shield is the outer wire braid that surrounds the inside of the cable. A thick, tight braid will result in less loss. The dielectric (the plastic type material that separates the inside wire from the outside braid) also has an effect on cable loss. Foam dielectric has low loss, solid dielectric has relatively greater loss.
Impedance refers to the cable's opposition to current flow. Radio and wireless computer networking use 50 ohm cable. Video and broadcast applications use 75 ohm cable. RCA, BNC, and TV RF cables are 75 ohm.