Coaxial cable from the inside out is divided into four layers: the central copper (single strand of solid or stranded strand), plastic insulator, mesh conductive layer and wire sheath. The central copper wire and the mesh conductive layer form a current loop. Because the central copper wire and mesh conductive layer for the coaxial relationship named.
Coaxial cable conduction AC rather than direct current, that is, every second there will be several times the direction of the current reversal.
If a high-frequency current is transmitted using a general wire, the wire will correspond to an antenna that emits radio outwards, which forces the power of the signal so that the received signal strength decreases.
Coaxial cable design is to solve this problem. The radio from the center wire is isolated by the mesh-like conductive layer, and the mesh-like conductive layer can control the emitted radio by grounding.
Coaxial cable also has a problem, that is, if a cable over a large extrusion or twisting deformation, then the central wire and the network between the conductive layer is not always the same distance, which will cause the internal radio waves will be Reflected signal source. This effect reduces the available signal power. In order to overcome this problem, the center wire and mesh conductive layer is added between a layer of plastic insulators to ensure that the distance between them is always the same. This also causes the cable to be stiff and not easy to bend.
Coaxial cable can be divided into two basic types, baseband coaxial cable and wide
With coaxial cable. The current baseband is a commonly used cable, the shield line is made of copper mesh, the characteristic impedance of 50 (such as RG-8, RG-58, etc.); broadband coaxial cable commonly used cable shielding is usually aluminum Stamping, the characteristic impedance of 75 (such as RG-59, etc.).
Coaxial cable according to its diameter can be divided into: thick coaxial cable and thin coaxial cable. The coarse cable is suitable for the larger local network, its standard distance is long and the reliability is high. Since the cable is not needed to be cut at the time of installation, the computer can be adjusted flexibly according to the needs. However, the cable network must be installed with the cable Difficult, so the overall high cost. On the contrary, the cable installation is relatively simple, low cost, but because the installation process to cut off the cable, two must be fitted with the basic network connector (BNC), and then connected to the T-connector at both ends, so when the connector for a long time prone to bad Hidden danger, which is currently running Ethernet one of the most common failures.
Whether it is a thick cable or a thin cable are bus topology, that is, a cable on a number of machines, this topology for machine-intensive environment, but when a contact failure, the fault will affect the whole cable in series On all the machines. Fault diagnosis and repair are very troublesome, therefore, will be gradually replaced by unshielded twisted pair or cable.