Networking Guide : Physical Media - Coaxial Cable

coaxial cable

Picture: Coaxial cable (coax) structure

Coaxial cable contains a solid or stranded wire in the core that is insulated with a  dielectric layer, then protected with a solid or braided metallic shield, and covered with an outer insulator. Electromagnetic wave propagation in a coaxial cable is confined within the space between the core and the outer conductors. The structure of a coaxial cable makes it less susceptible to interference, noise, and crosstalk than the twisted pair cable.

Coaxial cable is often classified based on its characteristic impedance. Most coaxial cables have characteristic impedance of 50 or 75 Ohms. Coaxial cables in the market are usually named with RG prefix which may stand for Radio Grade. Each RG type is related with certain characteristic impedance and outer diameter. For example RG-6 which has impedance of 75 Ohms is used for connecting cable modem or TV to a CATV network. RG-58 (50 Ohms) is used in earlier Ethernet networks (10Base2). Coaxial cable is terminated with RF (BNC) connectors.

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