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Prospect Analysis of Data Cable Replacing Security Video Surveillance Cable
Release time:
2018-06-21
A set of installation and debugging, the construction of a good video security system is used to produce or process high-quality video cameras, lenses, monitors, video recorders, but if there is no good transmission system, the final image on the monitor will not be satisfactory to achieve the ideal state of the device. According to the "barrel rule", the final image quality will depend on the worst part of the whole system; and the worst part is often the data transmission system. System designers and installers must choose the appropriate transmission mode, high-quality transmission cables and equipment according to actual needs, and install them according to professional standards in order to achieve the ideal transmission effect.
A set of installation and debugging, the construction of a good video security system is used to produce or process high-quality video cameras, lenses, monitors, video recorders, but if there is no good transmission system, the final image on the monitor will not be satisfactory to achieve the ideal state of the device. According to the "barrel rule", the final image quality will depend on the worst part of the whole system; and the worst part is often the data transmission system. System designers and installers must choose the appropriate transmission mode, high-quality transmission cables and equipment according to actual needs, and install them according to professional standards in order to achieve the ideal transmission effect.
1. Coaxial cable
Generally in a small range of monitoring system, due to the transmission distance is very close, the use of coaxial cable to directly transmit the monitoring image to the image quality damage is not big, can meet the actual requirements. However, according to the analysis of the characteristics of the coaxial cable itself, the attenuation of the signal when it is transmitted in the coaxial cable is related to the transmission distance and the frequency of the signal itself. In general, the higher the signal frequency, the greater the attenuation. The bandwidth of the video signal is very large, reaching 5.8MHz, 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 is the largest. Therefore, coaxial cable is only suitable for short-distance transmission of image signals, when the transmission distance of about 220 meters, the image quality will be significantly reduced, especially the color becomes dim, there is a sense of distortion.
In engineering practice, in order to extend the transmission distance, to use coaxial amplifier. The coaxial amplifier has a certain amplification of the video signal, and can also compensate for different frequency components by equalization adjustment, so that the distortion of the video signal output at the receiving end is as small as possible. However, coaxial amplifiers cannot be cascaded indefinitely. Generally, in a point-to-point system, coaxial amplifiers can only be cascaded by 2 to 3 at most, otherwise the video transmission quality cannot be guaranteed and it is difficult to adjust. Therefore, when using coaxial cable in the monitoring system, in order to ensure better image quality, the transmission distance is generally limited to about 500 meters.
In addition, coaxial cable in the monitoring system to transmit image signals there are still some shortcomings:
1) The coaxial cable itself is greatly affected by climate change, and the image quality is affected to a certain extent;
2) Coaxial cable is thicker, and wiring is not convenient in intensive monitoring applications;
3) Coaxial cable generally can only transmit video signals. If the system needs to transmit control data, audio and other signals at the same time, additional wiring is required;
4) Coaxial cable has limited anti-interference ability and cannot be applied to strong interference environment;
5) The coaxial amplifier also has the disadvantage of difficult adjustment.
2. Data cable
The use of data cables has a long history. Twisted pair is used in telephone transmission. Twisted pair is used in many industrial control systems and places with large interference and long-distance transmission. Twisted pair is also used in the local area network that we widely use today. The reason why twisted pair is so widely used is that it has many advantages, such as strong anti-interference ability, long transmission distance, easy wiring, low price and so on. Since the data line also has a large attenuation of the signal, the frequency of the signal cannot be too high when the transmission distance is far, and the high-speed signal such as Ethernet can only be limited to within 110m. For video signals, the bandwidth reaches 6MHz. If they are transmitted directly in the data line, they will also be attenuated greatly. Therefore, the video signal must be amplified and compensated for long-distance transmission on the twisted pair. This function is completed by the data line video transmission equipment. With a pair of twisted-pair video transceiver equipment, the image can be transmitted to 1 to 2km. Data line and data line video transmission equipment prices are very cheap, not only did not increase the cost of the system, but when the distance increases, its cost and coaxial cable decreased a lot.
Therefore, the use of data lines for transmission in the monitoring system has obvious advantages:
1) The transmission distance is long and the transmission quality is high. Due to the use of advanced processing technology in the twisted-pair transceiver, the attenuation of the amplitude of the twisted-pair video signal and the attenuation difference between different frequencies are well compensated, and the brightness, color and real-time of the original image are maintained. When the transmission distance reaches 1km or more, the image signal is basically undistorted. If the relay method is adopted, the transmission distance will be farther.
2) Convenient wiring and high cable utilization. A pair of ordinary telephone lines can be used to transmit video signals. In addition, any pair of the five types of unshielded twisted pairs widely laid in buildings can transmit video signals all the way without additional wiring. Even if rewiring, the five types of cables are easier than coaxial cables. In addition, there are 4 pairs of twisted pairs in a category 5 cable. If one pair of wires is used to transmit video signals, the other pairs of wires can also be used to transmit audio signals, control signals, power supply or other signals, thus improving the utilization rate of cables, avoiding the trouble caused by separate wiring of various signals and reducing the engineering cost.
3) Strong anti-interference ability. Twisted pair can effectively suppress common mode interference, even in strong interference environment, twisted pair can transmit excellent image signal. Moreover, several pairs of twisted pairs within a cable are used to transmit different signals without interfering with each other.
4) High reliability and easy to use. Using twisted pair to transmit video signals, a dedicated transmitter should be accessed at the front end and a dedicated receiver should be accessed at the control center. This twisted pair transmission equipment is cheap and simple to use. It does not require professional knowledge or much operation. It can be installed once and work stably for a long time.
5) cheap, easy to obtain. Due to the use of the current widely used ordinary category 5 unshielded cable or ordinary telephone line, easy to buy, and the price is also very cheap, to bring great convenience to engineering applications.
Therefore, the design and construction of the data cable in the security video to replace the security cable, no matter from the final use effect, or from the economic cost and human construction aspects, is an irreversible trend.
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