Weekend, the charge is charged! This article mainly introduces coaxial cable, twisted pair, and the use of fiber and their respective functions, as well as the distinction between them and other aspects of the knowledge points.
1, coaxial cable
Coaxial cable is a layer of insulated wire wrapped around the central copper conductor cable. It is characterized by good anti-interference ability, stable transmission data, the price is cheap, the same is widely used, such as closed-circuit television lines. Coaxial fine cable general market price of a few dollars a meter, not too expensive. Coaxial cable and BNC head used to connect the market to sell coaxial cable and BNC are generally connected with the finished product, we can directly use.
However, according to the analysis of the characteristics of the coaxial cable itself, when the signal is transmitted in the coaxial cable, the attenuation is related to the transmission distance and the frequency of the signal itself. In general, the higher the signal frequency, the greater the attenuation. The video signal has a large bandwidth of 6MHz, and the color part of the image is modulated at the high end of the frequency, so that when the video signal is transmitted in the coaxial cable, not only the overall amplitude of the signal is attenuated, but also the attenuation of each frequency component is very different , Especially the color part of the largest attenuation. Therefore, the coaxial cable is only suitable for close transmission of image signals, when the transmission distance of about 200 meters, the image quality will be significantly decreased, especially the color becomes dim, there is distortion.
In engineering practice, in order to extend the transmission distance, use coaxial amplifiers. The coaxial amplifier has a certain amplification of the video signal, and can also be adjusted by equalization of different frequency components were different size of the compensation, so that the output of the output video signal distortion as small as possible. However, the coaxial amplifier can not be unlimited cascade, generally in a point to point system coaxial amplifier can only cascade up to 2 to 3, or can not guarantee the quality of video transmission, and adjust it is also very difficult. Therefore, in the monitoring system using coaxial cable, in order to ensure a better image quality, the general transmission range is limited to four or five hundred meters.
In addition, the coaxial cable in the monitoring system to transmit image signals there are some shortcomings:
1) coaxial cable itself by the impact of climate change, the image quality is affected;
2) coaxial cable thicker, in the intensive monitoring applications wiring is not convenient;
3) coaxial cable can only pass video signals, if the system needs to transmit control data, audio and other signals, you need another wiring;
4) coaxial cable anti-interference ability is limited, can not be applied to strong interference environment;
5) coaxial amplifier also has the difficulty of adjusting the shortcomings.
2, twisted pair
Twisted pair common 3 lines, 5 lines and over 5 lines, 6 lines, and 7 lines. The former diameter is fine and the latter diameter is thick, the model is as follows:
1) A class of lines: mainly used for transmission of voice (a class of standards mainly used for the early eighties before the telephone cable), different from the data transmission.
2) Two lines: transmission frequency of 1MHZ, for voice transmission and the maximum transmission rate of 4Mbps data transmission, common in the use of 4MBPS specification token transfer protocol of the old token network.
3) Three types of cables: cables specified in the ANSI and EIA / TIA568 standards, the transmission frequency of the cable is 16MHz, and the data transmission for voice transmission and maximum transmission rate of 10Mbps is mainly used for 10BASE - T.
4) four lines: the type of cable transmission frequency of 20MHz, for voice transmission and the maximum transmission rate of 16Mbps data transmission is mainly used for token-based LAN and 10BASE-T / 100BASE-T.
5) Five lines: This type of cable increases the winding density, jacket A high quality insulation material, the transmission rate of 100MHz, for voice transmission and the maximum transmission rate of 100Mbps data transmission, mainly for 100BASE-T and 10BASE-T network. This is the most commonly used Ethernet cable.
6) Super five lines: Super 5 has low attenuation, less crosstalk, and has a higher attenuation and crosstalk ratio (ACR) and signal to noise ratio (Structural Return Loss), a smaller delay error, performance is very Greatly improved. Super 5 line of the maximum transfer rate of 250Mbps.
7) Six lines: This type of cable transmission frequency of 1MHz ~ 250MHz, six cabling system at 200MHz integrated attenuation crosstalk ratio (PS-ACR) should have a larger margin, it provides 2 times in the super five bandwidth. Six types of wiring transmission performance is much higher than the ultra-five standard, the most suitable for transmission rates higher than 1Gbps applications.