Coaxial cable

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 outer side of the wire is surrounded by a layer of plastic (for insulator, dielectric), and the outer side of the insulator has a thin layer. Net-shaped conductor (usually copper or alloy), and then the outermost insulating material is used as the outer skin of the conductor.

1. What is coaxial cable

Coaxial cable refers to a cable with two concentric conductors, and the conductor and the shielding layer share the same axis. The most common coaxial cable consists of a copper conductor isolated by an insulating material. Outside the inner insulating material is another layer of ring conductor and its insulator, and then the entire cable is covered by a polyvinyl chloride or Teflon material sheath. .

Coaxial cables can be divided into baseband coaxial cables and broadband coaxial cables (that is, network coaxial cables and video coaxial cables) in terms of usage. Coaxial cables are divided into 50Ω baseband cables and 75Ω broadband cables. Baseband cables are divided into thin coaxial cables and thick coaxial cables. The baseband cable is only used for digital transmission, and the data rate can reach 10Mbps.

2. Coaxial cable model specifications

Coaxial cables can be divided into two basic types according to their uses: baseband coaxial cables and broadband coaxial cables. At present, the commonly used cable for baseband, the shielding wire is made of copper mesh, and the characteristic impedance is 50 (such as RG-8, RG-58, etc.); the shielding layer of the commonly used broadband coaxial cable is usually stamped with aluminum The characteristic impedance is 75 (such as RG-59, etc.).

According to the diameter of the coaxial cable, it is divided into: thick coaxial cable and thin coaxial cable. Thick cables are suitable for relatively large local networks, with long standard distances and high reliability. For thick-cable networks, transceivers and transceiver cables must be installed, which is difficult to install, so the overall cost is high. On the contrary, the installation of thin cables is relatively simple and low in cost. However, because the cable must be cut during the installation process, the basic network connector (BNC) must be installed at both ends, and then connected to the two ends of the T-connector, so poor contact is likely to occur when there are too many connectors. This is one of the most common faults that occur in the current running Ethernet network.

Commonly used coaxial cable model specifications and main parameters:

3. The role of coaxial cable

Coaxial cable (Coaxial) is a composite composed of two conductors. The center wire of the coaxial cable is used to transmit signals, and the metal shielding net plays two roles: one is to provide current for the signal as a common ground wire for the signal The loop, the second is as a shielding net for the signal, to suppress the interference of electromagnetic noise on the signal. The center wire and the shielding net are between the semi-foamed polypropylene insulation layer. The insulation layer determines the transmission characteristics of the cable and effectively protects the wires in the middle.