Working principle of concentric cable:
The concentric cable is divided into four layers from the inside to the outside: the center copper wire (single-strand solid wire or multi-strand wire), plastic insulator, mesh conductive layer and wire sheath, and the center copper wire and mesh conductive layer form a current loop . It is named because the central copper wire and the mesh conductive layer are in a coaxial relationship.
Concentric cables conduct alternating current rather than direct current, which means the direction of the current reverses several times per second.
If you use ordinary wires to transmit high-frequency currents, this wire will act as an antenna that transmits radio to the outside. This effect consumes the power of the signal and reduces the strength of the received signal. Concentric cables are designed to solve this problem.
The radio emitted by the central wire is isolated by the mesh conductive layer, and the mesh conductive layer can control the emitted radio by grounding.
There is also a problem with concentric cables, that is, if a certain section of the cable undergoes relatively large extrusion or twisting deformation, the distance between the central wire and the mesh conductive layer will not be consistent, which will cause internal radio waves to be reflected back to the source of the signal. This effect reduces the received signal power.
To overcome this problem, a plastic insulator is inserted between the central wire and the mesh conductive layer to ensure a consistent distance between them. This also contributes to the relatively rigid nature of the cable and makes it less prone to bending.
Advantages and disadvantages of concentric cables:
The advantage of concentric cable is that it can support high-bandwidth communication on a relatively long line without repeaters, but its disadvantages are also obvious:
One is the large volume, the diameter of the thin cable is 3/8 inches thick, and it takes up a lot of space in the cable duct;
The second is that it cannot withstand tangles, pressure and severe bending, which will damage the cable structure and prevent the transmission of signals;
Finally, the cost is high, and all these shortcomings can be overcome by twisted pair, so in the current LAN environment, it has basically been replaced by the Ethernet physical layer specification based on twisted pair.
