75-3和75-5视频线参数（国外英文资料）.doc

75-3和75-5视频线参数（国外英文资料） 75-3 and 75-5 video line parameters Coaxial cable laid with cheaper price, the advantages of convenient (relative to the optical fiber), so, usually in a small range of monitoring system, due to the transmission distance is very near, directly using coaxial cable transmission monitoring image on image quality of damage is not big, can meet the practical requirements. However, according to the analysis of the characteristics of the coaxial cable itself when the signal in a coaxial cable transmission attenuation and transmission distance and the frequency of the signal itself. Generally speaking, the higher the signal frequency, the greater the attenuation. The bandwidth of the video signal is very large, 6 MHZ, and part of the color of the image is in high frequency modulation, in this way, the video signal transmission in the coaxial cable of the signal not only the overall amplitude attenuation, and each frequency component attenuation vary widely, especially the color part of the attenuation is the largest. So, coaxial cable is only suitable for close range image signal transmission, when the transmission distance of 200 meters, image quality will be significantly lower, especially the color is pale, have a sense of distortion. In the engineering practice, the coaxial amplifier is used to extend the transmission distance. Coaxial amplifier for video signal is amplified, and it also can be adjusted through equilibrium of different frequency components respectively for different sizes of compensation, in order to make the receiver output video signal distortion as far as possible. Coaxial amplifier, however, cannot unlimited cascade, generally in a point-to-point system coaxial amplifier cascade can be at most 2 to 3, otherwise unable to guarantee the quality of video transmission, and adjustment is also very difficult. Therefore, when using coaxial cable in the monitoring system, the range limit is limited to four or five hundred meters in or