同轴线（Coaxial line）.doc

同轴线（Coaxial line） Coaxial line structure The structure of the coaxial line is composed of a sheath, an outer conductor (Ping Biceng), an insulating medium and an inner conductor, wherein the outer part is composed of 4 parts. Now lets introduce each part separately. Sheath, that is, the outermost layer is an insulating layer, plays a protective role, outdoor cable should be used with good climate characteristics of black polyethylene, indoor users cable from the aesthetic considerations, should use light colored polyethylene. Outer conductor (Ping Biceng), the outer conductor of coaxial cable, has double function. It is not only used as a conductor of transmission circuit, but also transmits low level and shielding. External conductor usually has 3 structures. (1) metal tubular. The structure is made of copper or aluminum strip longitudinal welded or seamless copper tube extruded and drawn. The shielding performance of this structure is the best, but its softness is poor. It is often used in trunk cables. (2) aluminum plastic composite belt longitudinal cladding lap joint. The structure has better shielding effect and low manufacturing cost, but because the outer conductor is a round tube with longitudinal slits, the electromagnetic wave will leak out from the gap and should be used with caution. (3) woven net and aluminum plastic composite belt longitudinal package combination. This is from the development of network and the structure of a single braid, it has good flexibility, light weight and reliable joint characteristics. Experiments show that the composite structure is reasonable, and greatly improve the shielding performance, at present this kind of structure has been widely used. Coaxial line type According to the location of coaxial lines, they can be broadly divided into 3 types. 1, trunk cable: its outer diameter of insulation is generally more than 9mm thick cable, requiring small loss, soft requirements are not high. Shanghai satellite TV installation n