Talk about the working principle of coaxial cable

Coaxial cable can be used for the transmission of analog and digital signals, and is suitable for a variety of applications, important among which are television broadcasting, long-distance telephone transmission, short-distance connections between computer systems, and local area networks. It has developed rapidly as a means of spreading television signals to thousands of households, which is cable television. A cable TV system can load dozens or even hundreds of TV channels, and its transmission range can reach tens of kilometers. It has long been an important part of the long-distance telephone network. Today, it faces increasing competition from fiber optics, terrestrial microwaves and satellites.

  working principle:

The coaxial cable is divided into four layers from the inside to the outside: the central copper wire (single-strand solid wire or multi-stranded stranded wire), plastic insulator, mesh conductive layer and wire sheath. The central copper wire and the mesh-like conductive layer form a current loop. It is named because the central copper wire and the mesh conductive layer are in a coaxial relationship. It conducts alternating current rather than direct current, which means that the direction of the current is reversed several times per second.

If a normal wire is used to transmit high-frequency currents, the wire acts as an antenna that emits radio outward. This effect loses the power of the signal and reduces the strength of the received signal.

It is designed to solve this problem. The radio emitted by the center wire is isolated by the mesh conductive layer, which can control the emitted radio by grounding. It also has a problem that if a certain section of the cable is squeezed or twisted, the distance between the center wire and the mesh conductive layer is not consistent, which will cause the internal radio waves to be reflected back. source of the signal. This effect reduces the acceptable signal power. To overcome this problem, a plastic insulator is added between the center wire and the mesh conductive layer to ensure a consistent distance between them. This also causes the cable to be relatively stiff and not easy to bend.

In essence, the shielding material of coaxial cable is mainly to improve the outer conductor, from the initial tubular outer conductor to single-layer braid and double-layer metal. Although the tubular outer conductor has very good shielding performance, it is not easy to bend and is inconvenient to use. The shielding efficiency of single-layer braiding is poor, and the transfer impedance of double-layer braiding is 3 times lower than that of one-layer braiding. It can be seen that the shielding effect of double-layer braiding is greatly improved than that of single-layer braiding. The major coaxial cable manufacturers are constantly improving the outer conductor structure of the cable to maintain its performance.