Concentric cable（Coaxial cable） is a type of telecommunications equipment that is widely used in wireless communication systems, data communication systems and multimedia communication systems. Coaxial cable mainly refers to a cable with two concentric conductors, and the conductor and shielding layer share the same axis. The most common coaxial cable consists of copper wire conductors isolated by insulating material. Outside the inner layer of insulation material is another layer of ring conductors and their insulators. The entire cable is then sheathed by a polyvinyl chloride or Teflon material. . Next, Zhengzhou Jinshui Cable Group will introduce coaxial cable standards and coaxial cable types.
Coaxial cable adopts GB/T14864-1993 national standard. A coaxial cable is first composed of two coaxial, mutually insulated cylindrical metal conductors to form a basic unit (coaxial pair), and then a cable composed of single or multiple coaxial pairs. Coaxial cable is divided into four layers from the inside to the outside: central copper wire, plastic insulator, mesh conductive layer and wire sheath. The central copper wire and mesh conductive layer form a current loop. It is named because the central copper wire and the mesh conductive layer are in a coaxial relationship.
Because counterfeit and shoddy products often cut corners and are shoddy during production, the product quality is poor and the technical performance is not guaranteed. For example, the materials used for the inner and outer conductors and insulating media are of poor quality, and various parameters are inaccurate, resulting in excessive deviations in characteristic impedance and attenuation. The constant is too large, the frequency characteristics are poor, the temperature characteristics are poor, the shielding performance is poor, etc.
Characteristic impedance is an important technical parameter of coaxial cables. Commonly used ones include 75Ω, 50Ω, etc. Impedance mismatch in use has many disadvantages, such as the signal-to-noise ratio of the transmitted signal is reduced, and the image produces ghosting or thick and sparse patterns. Interference, deteriorating the frequency characteristics of the system, causing an increase in the data bit error rate in the data transmission system, etc.
Concentric cable (Coaxial cable) is a transmission line with a special structure. Its inner and outer conductors each have specific structural relationships and functions, and circuit connections also have their own specific connection methods. The inner and outer conductors cannot be used interchangeably, otherwise the normal signal will be affected. transmission, unable to obtain satisfactory results.
When the end of the concentric cable is connected to the terminal box, amplifier and other components, the connection quality of the outer conductor (mainly the braided mesh) cannot be ignored. If the connection is loose or disconnected, the signal level will be greatly reduced. In the cable TV system , there is often an obvious horizontal black band in the middle of the TV screen, and an interference band that slowly moves to the left in the vertical direction. The system is also extremely susceptible to interference from nearby power frequency, radio frequency, etc.; when the contact resistance between the outer conductor and the connector is too large ( For example, when the outer conductor connection is oxidized, there is rust on the connector, etc.), reverse attenuation characteristics will appear, and the attenuation in the low frequency band will be greater; irregular coaxial cable assembly at the cable joints and connection points may cause the connection to The characteristic impedance changes greatly, resulting in reflection and standing wave interference.
Transmission lines, power transformers, motors, industrial electrical equipment, various household appliances, etc. are all strong sources of electromagnetic pollution. When wiring coaxial cables, they should neither run parallel to power lines nor pass through the same pipe. It is best to keep them away from electrical equipment. and its wiring, so that the above-mentioned interference can be avoided to a certain extent, and damage caused by leakage, overheating and fire of the power lines can be avoided.
In open air and places with visible water, amplifiers, branch distributors and other equipment must be installed with waterproof boxes; the joints of coaxial cables should have a waterproof bend (a downward curved path of an arc) at the proximal end to prevent water droplets from flowing along the cable. At the joints and other circuits, sealant should be applied to the end of the cable (joint) to make it waterproof; the main way for moisture and water vapor to invade the cable is through the head and sheath of the cable, so the inspection and maintenance of the sheath cannot be ignored. , if the sheath is found to be damaged, it should be bandaged in time.
The attenuation of the signal in the cable increases as the length of the cable increases. Usually, every 10m of cable will attenuate 2dB. Therefore, it is hoped that the cable path is as short as possible. When wiring, not too much should be reserved. Some people want neatness and beauty. , roll the remaining cable into a small disk and tie it firmly with wires. As a result, the attenuation of the signal is increased, the frequency characteristics of the system are changed, and the high-frequency band performance of the signal is degraded.
According to the temperature characteristics of coaxial cables, when the ambient temperature increases, the metal (inner and outer conductor) losses and dielectric losses of the cable will increase. For every 1°C increase in temperature, the attenuation of the coaxial cable will increase by approximately 0.2%. Therefore, when wiring, try to keep the coaxial cable away from high-temperature heat sources and high-temperature environments. When the temperature rises excessively, it may reduce the signal quality and destroy the stability of the system.
The above is an introduction to the precautions for the use of coaxial cable products. Zhengzhou Jinshui Wire And Cables Group tells everyone that you must have detailed knowledge of related cable products when using cables and selecting cables.