Coaxial cable is a kind of wire and signal transmission line. It is generally made of four layers of materials: the innermost is a conductive copper wire, the outside of the wire is surrounded by a layer of plastic (for insulator, dielectric), and there is a thin layer on the outside of the insulator. Net-shaped conductor (usually copper or alloy), and then the outermost insulating material is used as the outer skin of the conductor.
Coaxial cables can be used for the transmission of analog signals and digital signals, and are suitable for a variety of applications, the most important of which are television broadcasting, long-distance telephone transmission, short-distance connections between computer systems, and local area networks. Coaxial cable has developed rapidly as a means of spreading TV signals to thousands of households. This is cable TV. A cable TV system can load dozens or even hundreds of TV channels, and its transmission range can reach tens of kilometers. Coaxial cable has long been an important part of long-distance telephone networks. Today, it faces increasing competition from fiber optics, terrestrial microwaves and satellites
Coaxial cables can be divided into two basic types, baseband coaxial cables and broadband coaxial cables.
Baseband coaxial cable
The shielding layer of the baseband coaxial cable is usually a mesh structure made of copper, and its characteristic impedance is 50Ω. This cable is used to transmit digital signals, and the commonly used models are generally RG-8 (thick cable) and RG-58 (thin cable). The most intuitive difference between a thick cable and a thin cable is the cable diameter. Thick cable is suitable for relatively large local networks. It has a long standard distance and high reliability. However, the thick cable network must be equipped with transceivers and transceiver cables, which is difficult to install, and therefore the overall cost is high. On the contrary, the thin cable is relatively simple and the cost is lower; but because the cable has to be cut during the installation process, it is easy to cause the hidden danger of poor contact when there are many connectors.
Whether it is a network connected by a thick cable or a thin cable, the point of failure often affects all machines on the entire cable, and it is troublesome to diagnose and repair the fault. Therefore, baseband coaxial cables have been gradually replaced by unshielded twisted pairs or optical cables.
Broadband coaxial cable
The shielding layer of broadband coaxial cable is usually stamped from aluminum, and its characteristic impedance is 75Ω. This kind of cable is usually used to transmit analog signals. The commonly used model is RG-59. It is a standard transmission cable used in cable television networks. It can transmit multiple channels of TV signals in one cable at the same time. Broadband coaxial cable can also be used as the transmission medium of some computer networks.