Coaxial cable is composed of two concentric conductors, conductor and shielding layer. The most common coaxial cable is composed of copper wires isolated by insulating material. On the outside of the inner insulating material is another layer of ring conductor and insulator, and then the whole cable is wrapped in PVC or Teflon sheath. Coaxial cable is widely used in radio frequency or audio and video transmission. The transmission impedance is generally 75 Ω, which has become the standard impedance of video transmission. High quality standard coaxial cable is generally more expensive than twisted pair, because coaxial cable has reliable physical properties, which can provide good performance for audio and video. Frequency, resolution and effective transmission distance of cable have a significant impact on the performance of audio and video system.
Syv-50-2-1 solid polyethylene coaxial cable
From the use, coaxial cable is divided into: rg-58, thick cable rg-11 two kinds. And rarely used semi-rigid coaxial cable and feeder.
粗缆绳：粗缆绳(RG-11)直径1.27厘米， 传输距离可达500米。因为RG-11的直径相当粗，所以它的弹性也较差，也不适合在室内狭小的环境下架设，同时RG-11接头的制作方法也比较复杂，而且还不能直接与电脑连接，需要通过转接器转成AUI接头，然后再接到电脑上。因为粗绳具有更强的强度和 的传输距离，所以粗绳的主要作用就是充当网络 ，把许多细绳连接在一起，形成细绳。粗缆的阻抗为75Ω。
Thick cable: the diameter of the thick cable (rg-11) is 1.27cm, and the maximum transmission distance can reach 500m. Because the diameter of rg-11 is quite thick, its elasticity is also poor, and it is not suitable to be erected in the narrow indoor environment. At the same time, the manufacturing method of rg-11 connector is relatively complex, and it can not be directly connected with the computer, so it needs to be converted into AUI connector through the adapter, and then connected to the computer. Because the thick rope has stronger strength and the largest transmission distance, the main function of the thick rope is to act as the network center, connecting many ropes together to form a rope. The impedance of thick cable is 75 Ω
Thin cable: the diameter of the thin cable is 0.26cm, the maximum transmission distance is 185m, and it can be used with 50 meters ω The terminal resistance, T-type connector and BNC connector are connected to the network card, so the wire price and connector cost are low, and there is no need to buy the hub and other equipment, so the length of the cable line should not exceed 185m, otherwise the signal will be seriously attenuated. The impedance of the thin cable is 50 Ω.
Semi rigid coaxial cable: this kind of cable is rarely used, usually used in the modular connection inside the communication transmitter, because the transmission loss of this kind of cable is very small, but it also has some disadvantages, such as "hard and not easy to bend". In addition, the extremely high transmission frequency of this kind of cable can reach 30ghz. For example, the typical structure of cxj -- 505-3 cable is shown in the table below, the diameter of structural material (mm) is 1. The inner conductor is silver plated copper wire 0.932. The insulator is polytetrafluoroethylene (PTFE) 3.003. The outer conductor is copper wire 0.932.
① 3.58 tin (alloy) seamless copper pipe.
② Seamless annealed copper tube
③ Silver plated seamless copper tube
At present, the technology of coaxial cable is also gradually improving, and it is suggested that the traditional copper tube outer conductor should be used where the flexibility requirement is not high, so as to ensure its stability.
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