1. coaxial cable
coaxial cable for cctv mainly uses solid core polyethylene insulated 75Ω RF coaxial cable to transmit video signals, the selection of the main consideration of video signal attenuation and anti-interference problems. The length of the transmission distance of each type of wire is related to the front and back end equipment, site conditions and construction quality. The unflatness of the baseband signal frequency point of the color TV at 5.5MHz should not be greater than 3dB, otherwise a cable equalizer should be added.
In the actual project, due to the limitation of detection conditions, the acceptance is mostly subjectively assessed according to the image level 5 damage standard. When conditions are possible, the signal compensator can be added on the line to extend the transmission distance, but the series connection of compensators is generally not used.
2.Optical fiber cable
cat6a f utp cable is the best choice for long-distance transmission, and the signal transmission process is free from electromagnetic interference. For established living communities and other areas that are not easy to re-trench, optical fiber and power cable overhead transmission is the least engineering option, and sometimes the only option. When lightning protection is required, metal-free optical fibers should be used.
Generally, the backbone video signal has two transmission methods: uncompressed or compressed. The biggest advantage of the non-compression method is that the image quality is clear, which can achieve the broadcast effect, and the transmission has no delay. Compression transmission bandwidth is small, the system network is convenient, the control mode is simple, but the disadvantage is that the signal must be A/D conversion first, after digital compression coding to upload, this series of processes will produce hardware delay, multiple A/D, D/A conversion will also produce image quality decline.
3.100Ω digital communtication cable
The digital communication cable used in CCTV system should pay attention to two parameters: (1) Because the capacitor has high connectivity, so the capacitor is too large to inhibit the low-frequency signal is very strong, the cable distribution capacitance must be less than 60pF/m; ② The loop resistance of the twisted pair must be less than 18Ω/100m. These two parameters directly affect the transmission distance and distortion degree of the image.
Coaxial cable is thick, multi-point intensive monitoring wiring is not very convenient, while there are defects such as anti-interference ability in a strong interference environment and coaxial amplifier adjustment difficulties, digital communication cable system can be considered when more than 1 km distance transmission. A five-type twisted pair can better suppress common mode interference, and can also transmit video, audio, control and power signals at the same time, saving a lot of copper power cable for connection.
Post time: 2024-01-22 15:01:19