Coaxial cable It mainly refers to the cable with two concentric conductors, and the conductor and the shield share the same coaxial cable. The most common coaxial cable is composed of insulated copper wire conductors. On the outside of the inner insulation material is another layer of the ring conductor and its insulator. The entire cable is then sheathed with a PVC or Teflon sheath. . The following small series introduces coaxial cable standards and coaxial cable types for everyone.
Coaxial cable standard
Coaxial cable adopts GB/T14864-1993 national standards. The coaxial cable consists of two concentric, mutually insulated cylindrical metal conductors that form a basic unit (coaxial pair) and then a single or multiple coaxial pair of cables. The coaxial cable is divided into four layers from the inside to the outside: the center copper wire, the plastic insulator, the mesh conductive layer and the wire sheath. The center copper wire and the mesh conductive layer form a current loop. Because the center copper wire and mesh conductive layer is named after the coaxial relationship.
Coaxial cable type
1, thin cable
The thin cable has a diameter of 0.26 cm and a maximum transmission distance of 185 meters. When used, it is connected to a 50 Ω termination resistor, a T-connector, a BNC connector and a network card. The wire price and connector cost are relatively low, and no equipment such as a hub is required. It is suitable for setting up a small Ethernet network with concentrated terminal equipment. The total cable length should not exceed 185 meters, otherwise the signal will be severely attenuated. The impedance of the thin cable is 50Ω.
2, thick cable
The thick cable (RG-11) has a diameter of 1.27 cm and a maximum transmission distance of 500 meters. Due to its relatively large diameter, it is less flexible and is not suitable for installation in a narrow indoor environment. Moreover, the production method of RG-11 connector is relatively complicated and cannot be directly connected to a computer. It needs to be passed through a switch. Turn the device into an AUI connector and then connect it to your computer. Due to the strength of the thick cable, the maximum transmission distance is also longer than the thin cable, so the main purpose of the thick cable is to play the role of the backbone of the network to connect several networks formed by thin cables. The thick cable has an impedance of 75Ω.
Coaxial cable use taboo
1. Never use counterfeit coaxial cable, because counterfeit and shoddy products are often cut corners, rough production, poor product quality, technical performance is not guaranteed, such as internal and external conductors and insulating media use of poor quality materials, various parameters Inaccurate, resulting in too many characteristic impedance deviation, attenuation constant is too large, poor frequency characteristics, poor temperature characteristics, low shielding performance.
2. Do not use wrong characteristic impedance. The characteristic impedance is an important technical parameter of the coaxial cable, commonly used are several kinds such as 75Ω, 50Ω, etc. In the use, the impedance does not match the bad many, such as the signal to noise ratio of the transmitted signal decreases, the image produces ghost or coarse and sparse network pattern Interference, deteriorating the frequency characteristics of the system, resulting in increased data bit error rate in the data transmission system.
3, to prevent the connection between the inner and outer conductors. Coaxial cable is a special structure of transmission line, its internal and external conductors have a specific structural relationship and role, circuit connections also have their own specific connection, internal and external conductors can not be used interchangeably, otherwise it will affect the normal signal Transmission, unable to obtain satisfactory results.
4. Improve the installation quality of cable ends and cable connectors. When the end of a coaxial cable is connected to a terminal box, amplifier, etc., the connection quality of the outer conductor (mainly a braided net) cannot be ignored. If the connection is loosened or disconnected, the signal level will be greatly reduced in the cable television system. In the middle of the TV screen, there is often an obvious horizontal black belt, and there is a slow left-shift interference band in the vertical direction. The system is also vulnerable to nearby power frequency, radio frequency, etc. interference; when the outer conductor and the joint contact resistance is too large ( If the outer conductor connection is oxidized, there is rust on the joint, etc.), reverse attenuation will occur, and the attenuation in the low-frequency band will be even greater; if the coaxial cable at the joint and the connection point of the cable is not standardized, the connection may be caused. The characteristic impedance changes greatly, resulting in reflections and standing wave interference.
5. Prevent the coaxial cable and the power line from being interfered in parallel. Transmission lines, power transformers, electric motors, industrial electrical equipment, and various types of household appliances are all sources of electromagnetic pollution. Coaxial cables must not run parallel to the power lines and must not pass through the cables. It is best to keep away from electrical equipment. As well as its wiring, it can avoid such interference to a certain extent, and it can also be protected from damage caused by power line leakage, overheating and fire.
6. Strengthen moisture-proof and waterproof measures. In open-air and visible water areas, equipment such as amplifiers and branch distributors must be equipped with a waterproof box; the joints of the coaxial cable should be made with waterproof bends (curved downward curved paths) at the proximal end to prevent water droplets from flowing along the cable. In the joint and other circuits, the cable end (joint) should be waterproofed with sealant; the main way for moisture and water vapor to invade the cable is the cable head and sheath, so the inspection and maintenance of the sheath must not be ignored. If it is found that the sheath is damaged, it should be timely treated.
7, line reservation can not be too much. The attenuation of the signal in the cable increases with the length of the cable. Usually, the cable will be attenuated by 2dB per 10m cable. Therefore, it is hoped that the cable path will be as short as possible, and the cable cannot be reserved too much. Some people are neat and beautiful. , The cable that was left was rolled up into a small plate and then fastened with wires. As a result, the signal loss was increased, and the frequency characteristics of the system were changed, resulting in deterioration of the high frequency band performance of the signal.
8, the impact on high temperature can not be ignored. According to the temperature characteristics of the coaxial cable, the metal (inner and outer conductor) losses and dielectric loss of the cable will increase when the ambient temperature increases, and the attenuation of the coaxial cable will increase by approximately 0.2% for every 1°C increase in temperature. Therefore, try to keep the coaxial cable away from the high temperature heat source and high temperature environment when wiring. When the temperature rises excessively, it may reduce the signal quality and damage the stability of the system.
Editor's summary: About coaxial cable standards and coaxial cable types are introduced here, and I hope to be helpful to everyone. If you want to know more about yourself, you can follow the information on this site.
Coaxial cable coaxial cable standard
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