Coaxial Cable is a cable with two concentric conductors, and the conductor and shielding layer share the same axis. The most common coaxial cable consists of insulated copper conductors, another ring conductor and its insulator outside the inner insulating material,
and then the whole cable is enclosed by a sheath of polyvinyl chloride or Teflon material. It is characterized by good anti-jamming ability, stable data transmission and low price. It is also widely used, such as closed-circuit television lines. Coaxial thin cable generally sells for several yuan and one meter in the market, which is not too expensive. Coaxial cable is used to connect with BNC head. The coaxial cable sold in the market is generally the finished product which has been connected with BNC head. You can choose it directly.
However, according to the analysis of the characteristics of coaxial cable itself, the attenuation of signal when it is transmitted in coaxial cable is related to the transmission distance and the frequency of the signal itself. Generally speaking, the higher the signal frequency, the greater the attenuation. The bandwidth of video signal is very large, reaching 6MHz, and the color part of the image is modulated at the high end of the frequency. In this way, 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 has the greatest attenuation. Therefore, coaxial cable is only suitable for short-distance transmission of image signals. When the transmission distance reaches about 200 meters, the image quality will be significantly reduced, especially when the color becomes dim and distorted.
In engineering practice, coaxial amplifier is used to extend transmission distance. Coaxial amplifier enlarges the video signal to a certain extent, and can compensate different frequency components by equalization adjustment, so as to minimize the distortion of the video signal output by the receiver. However, coaxial amplifiers can not be cascaded indefinitely. Generally, in a point-to-point system, coaxial amplifiers can only be cascaded up to two or three, otherwise the quality of video transmission can not be guaranteed, and it is difficult to adjust. Therefore, when coaxial cable is used in monitoring system, in order to ensure better image quality, the transmission distance is generally limited to about four or five hundred meters.