Coaxial cables were first used in cable television networks. It has better shielding than twisted pair, so it can transmit at a very high rate over a long distance. The pair of conductors used to transmit information are made according to a structure in which a cylindrical outer conductor is wrapped outside the inner conductor (thin core), and two conductors are separated from each other by insulating materials. The center of the outer conductor and the central axis of the core line are on the same axis, so it is called coaxial cable.
Coaxial cables also consist of a pair of conductors, such as twisted pairs, but they are paired in a “coaxial” manner. The innermost layer is the inner core, the outermost layer is the insulating layer and shielding layer, and the outermost layer is the protective plastic sheath. The core and the shielding layer form a pair of conductors. Coaxial cables are divided into baseband coaxial cables (500 impedance) and broadband coaxial cables (750 impedance). Baseband coaxial cable can be divided into thick cable and thin cable, which are used for direct transmission of digital signals; Broadband coaxial cable is used for frequency division multiplexing analog signal transmission, and can also be used without frequency division multiplexing. Multiplexing high-speed digital and analog signal transmission. CATV cable used in CCTV is broadband coaxial cable. Coaxial cable takes a single copper wire as the inner core, is wrapped with a layer of insulating material, is covered with dense network conductor, and the outermost layer is a layer of protective plastic. The metal shielding layer can reflect the magnetic field back to the central conductor, and also can protect the central conductor from external interference. Therefore, coaxial cables have higher bandwidth and better noise suppression characteristics than twisted pair cables.