Introduction to coaxial cable:
1. how it works
Coaxial cable is divided into four layers from the inside out: central copper wire (single solid or multiple stranded wire), plastic insulator, reticular conductive layer and wire sheath. A central copper wire and a network of conductive layers form a current loop. Because the central copper wire and the network of conductive layer for coaxial relationship, so called. Details: wang,
Coaxial cable conducts alternating current instead of direct current, which means the current reverses direction several times per second.
If a normal wire is used to transmit high-frequency current, it will act like an antenna that sends out a radio. this effect loses the power of the signal and makes the received signal less powerful.
Coaxial cable is designed to solve this problem. the radio from the center wire is isolated by a grid of conductive layers that control the radio by grounding it.
the problem with coaxial cable is that if a section of the cable is squeezed or distorted too much, the distance between the central wire and the network layer is not consistent, which causes the radio waves inside to be reflected back to the source of the signal. this effect reduces the power of the received signal. To overcome this problem, a layer of plastic insulation is added between the central wire and the reticulated conductive layer to ensure that the distance between them is consistent. this also results in the cable being stiffer and less prone to bending.
2. Basic information
Coaxial cable is one that has two concentric conductors and the conductor and shield share the same axis. Zui's common coaxial cable consists of a copper conductor isolated by an insulating material. On the outside of the insulating material is another ring conductor and insulator, and then the whole cable is covered by a sheath of PVC or teflon material.
at present, the commonly used coaxial cable has two kinds: 50 Ω and 75 Ω coaxial cable. 75 Ω coaxial cable used in CATV network, so called CATV cable, transmission bandwidth can reach 1 GHZ, current CATV cable transmission bandwidth of 750 MHZ. 50 Ω coaxial cable is mainly used for baseband signal transmission, the transmission bandwidth of 1 ~ 20 MHZ, main line is the use of Ethernet 50 Ω coaxial cable, in Ethernet, 50 Ω fine coaxial cable zui big transmission distance of 185 meters, thick coaxial cable up to 1000 meters.
3. Classification
Coaxial cable can be divided into two basic types, baseband coaxial cable and broadband coaxial cable. at present, baseband is a common cable, and its shielding wire is made of copper network, with a characteristic impedance of 50(such as rg-8, rg-58, etc.). the shielding layer of the commonly used broadband coaxial cable is usually made of aluminum and has a characteristic impedance of 75(e.g., rg-59, etc.).
Coaxial cable according to its diameter can be divided into: thick coaxial cable and thin coaxial cable.
Coaxial cable
Coaxial cable is suitable for large local network, its standard distance is long, high reliability, because the installation does not need to cut the cable, so can flexibly adjust the computer network access position according to the need, but the thick cable network must install transceiver cable, installation is difficult, so the overall cost is high. On the contrary, the installation of thin cable is relatively simple and low cost. however, since the installation process requires cutting the cable and installing the basic network connector (BNC) at both ends and connecting them to the t-connector, it is easy to generate the potential trouble when the connector is too long. this is one of the common faults of zui in the current running Ethernet.
both thick and thin cables are bus topologies, that is, multiple machines are connected to one cable. this topology is applicable to a machine-intensive environment, but when a failure occurs at one contact point, the failure will affect all the machines on the whole cable in series. Fault diagnosis and repair are very troublesome, therefore, will be gradually replaced by non-shielded twisted pair or cable.



Video signal transmission generally adopts direct modulation technology in the form of baseband frequency (about 8MHz bandwidth). the commonly used transmission medium of zui is coaxial cable. Coaxial cable is specially designed to transmit video signal, and its frequency loss, image distortion and image attenuation amplitude are relatively small, which can well complete the task of transmitting video signal. Video signal transmission line coaxial cable (unbalanced cable), balanced symmetric cable (cable), cable. Balanced symmetrical cable and optical cable are generally used for long-distance transmission. For hotels and other buildings, coaxial cable is generally used to transmit video baseband signals. Cable compensators should be considered when using 75-5 coaxial cable over a 300m transmission range. If 75-9 coaxial cable is used, no cable compensator is required for the distance between the camera and the monitor within 500m