Today, we’ll introduce the coaxial cable to let you know more about the coaxial cable.
A coaxial cable (Coaxial Cable) refers to a cable with two concentric conductors, while the conductor and the shielding layer share the same axis. The most common coaxial cable consists of insulated copper conductor. Inside the insulating layer is another layer of ring conductor and its insulator. Then the whole cable is covered by PVC or Teflon sheath. It is characterized by its good anti-interference ability, stable transmission of data, and cheap prices, which are also widely used, such as closed-circuit television. The common market price of coaxial cable is a few yuan a meter, not too expensive. The coaxial cable is used to connect with the BNC head. The coaxial cable sold on the market is generally the finished product which has been connected with the BNC head, and we can choose the coaxial cable directly.
However, according to the analysis of the characteristics of the coaxial cable, 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 frequency of the signal, the greater the attenuation. Video signal bandwidth is large, up to 6MHz, and the color image part is modulated at high frequency, so that the video signal transmission in a coaxial cable not only signal amplitude of each frequency component is attenuated and the attenuation varies greatly, especially the color part of the maximum attenuation. Therefore, coaxial cable is only suitable for transmitting image signals at close distance. When the transmission distance reaches 200 meters, the image quality will decrease obviously, especially the color becomes dim and distorted.
In engineering practice, in order to extend the transmission distance, a coaxial amplifier is used. The coaxial amplifier amplifies the video signal, and it can compensate the different frequency components with different sizes through equalization adjustment, so that the video signal at the receiving end is distorted as little as possible. However, coaxial amplifiers can not be cascaded without constraints. Generally, a coaxial amplifier can only cascade 2 to 3 points in a point-to-point system, otherwise, the quality of video transmission can not be guaranteed, and the adjustment is also very difficult. Therefore, when using coaxial cable in the monitoring system, in order to ensure a good image quality, the transmission distance is generally limited to four or five hundred meters.
In addition, there are some shortcomings in the transmission of image signals in the monitoring system of the coaxial cable.
1) the coaxial cable itself is affected by the climate change, and the image quality is affected.
2) the coaxial cable is coarser, and the wiring is not very convenient in intensive monitoring and application.
3) the coaxial cable can only transmit video signal. If the system needs to transmit the control data, audio and other signals at the same time, it needs other wiring.
4) the coaxial cable has limited anti-interference ability and can not be applied to the strong interference environment.
5) the disadvantages of the coaxial amplifier are also difficult to adjust.