What is the structure of coaxial cable?

Coaxial cable consists of four parts: inner conductor, outer conductor, insulating medium and protective sheath. The task of the inner conductor is to transmit high-frequency currents. Due to the skin effect when high-frequency current flows in the conductor, that is, it only flows along the surface of the body, and there is no current inside the conductor. Therefore, the inner conductor can be made of a hollow metal tube or made of copper-clad aluminum and copper-clad steel materials. Generally, the inner conductor is made of solid copper wire.

  In addition to transmitting high-frequency current, the outer conductor also plays the role of shielding external electromagnetic interference and preventing the leakage of TV signals. In addition to the small resistance, the outer conductor should also have better sealing performance. The outer conductor can be made of densely braided copper mesh, or aluminum-plastic composite film and sparsely braided copper mesh. Thicker cables generally use seamless aluminum tubes or argon arc welded aluminum tubes as outer conductors.

  The function of the insulating medium is to prevent the leakage current along the radial direction, and also to support the inner and outer conductors, so that the entire cable forms a stable whole. The smaller the dielectric constant of the insulating medium, the smaller the attenuation and temperature coefficient of the cable (the percentage increase in the attenuation of the cable when the temperature increases rc). At present, the commonly used cables are coupled core cables and physical foam cables. Coaxial Cable has developed the fourth generation of physical foam cables.

  When the insulating layer is extruded during the production process, high-pressure nitrogen gas is passed through, and nitrogen, nucleating agent and polyethylene are fully mixed under suitable process conditions such as air pressure, temperature and rotation speed. When the insulating material leaves the extrusion die, the external pressure suddenly decreases, and the nitrogen gas expands rapidly, forming closed pores in the polyethylene. Even if this kind of cable enters the water, it only exists in a small local area and has no effect on the transmission of the signal. It is the cable commonly used in the cable TV network at present.