The difference between coaxial cable and optical fiber

A. Coaxial cable

 Coaxial cable, is a cable line with a layer of insulated wire wrapped around a central copper conductor. It is characterized by good anti-interference ability, stable transmission data and cheap price, and is also widely used, such as closed-circuit television lines. Coaxial thin cable wire is generally sold in the market for a few dollars a meter, not too expensive. Coaxial cable is used to connect with BNC head, and the coaxial cable sold in the market is generally connected with BNC head, so you can choose it directly.

　　However, according to the analysis of the coaxial cable's own characteristics, when the signal is transmitted in the coaxial cable, the attenuation is related to the transmission distance and the frequency of the signal itself. Generally speaking, the higher the frequency of the signal, the greater the attenuation. The bandwidth of the video signal is very large, reaching 6MHz, and the color part of the image is modulated at the high end of the frequency, so that the video signal is not only attenuated by the overall amplitude of the signal when transmitted in the coaxial cable, but also the attenuation of each frequency component is very different, especially the color part of the attenuation is the largest. Therefore, the coaxial cable is only suitable for close transmission of image signals, and when the transmission distance reaches about 200 meters, the image quality will be significantly reduced, especially the color becomes dull and distorted.

　　In engineering practice, in order to extend the transmission distance, coaxial amplifiers are used. Coaxial amplifier has a certain amplification of video signal, and it can also compensate different size of different frequency components by equalization adjustment, so that the distortion of video signal output from the receiver is as small as possible. However, coaxial amplifiers cannot be cascaded without limitation. Generally, coaxial amplifiers can only be cascaded at most 2 or 3 in a point-to-point system, otherwise the video transmission quality cannot be guaranteed and it is difficult to adjust them. Therefore, when using coaxial cables in surveillance systems, the transmission distance is generally limited to about four or five hundred meters in order to ensure a good image quality.

　　In addition, the coaxial cable in the monitoring system to transmit the image signal there are some disadvantages.

　　1, the coaxial cable itself is affected by climate change, the image quality is affected to a certain extent;

　　2, coaxial cable is thicker, less convenient wiring in intensive monitoring applications;

　　3, coaxial cable can only transmit video signals, if the system needs to transmit control data, audio and other signals at the same time, it needs to be wired separately;

　　4、Coaxial cable has limited anti-interference ability and cannot be used in strong interference environment;

　　5、Coaxial amplifier also has the disadvantage of difficult adjustment.

B. Optical Fiber

    Optical fiber (Fiber Optic Cable) transmits signals in the form of light pulses, so the material is also mainly glass or plexiglass. It consists of a fiber core, cladding and protective cover.

 　The structure of fiber optic cable is similar to that of coaxial cable in that the center is an optical fiber made of glass or transparent plastic, surrounded by a protective material, and multiple fibers can be combined in a single fiber optic cable as needed. Depending on how the optical signal is generated, optical fibers can be divided into single-mode fibers and multimode fibers. 

(A "mode" is a beam of light that enters the fiber at an angle). Multimode fiber is generally used to connect networks in the same office building or in relatively close proximity to each other. Single-mode fiber, on the other hand, delivers higher quality data over longer distances and is often used to connect networks between office buildings or in more geographically dispersed areas. If you use fiber optic cable as a network transmission medium, you also need to add optical transceivers and other equipment, so the cost investment is greater, in general applications are less used.

　　The most important feature of optical fiber is that it conducts optical signals, so it is not subject to interference from external electromagnetic signals, and the signal attenuation rate is very slow, so the signal transmission distance is much farther than the above transmission of electrical signals of various network cables, and is especially suitable for places with harsh electromagnetic environment. Due to the optical reflection characteristics of optical fiber, an optical fiber can transmit multiple signals at the same time, so the transmission speed of optical fiber can be very high, the current 1Gbps 1000Mbps fiber optic network has become the mainstream high-speed network, theoretically the highest fiber optic network can reach 50000Gbps 50Tbps speed. However, the use of optical fiber as a network transmission medium requires a certain level of expertise and specialized equipment such as optical transceivers, so the cost investment is greater and less used in general applications.