According to the "bucket rule", the final image quality will depend on the worst link in the whole system, which is often the transmission system.

The designers and installers of the system must choose the appropriate transmission mode, high-quality transmission cables and equipment according to the actual needs, and install them in accordance with professional standards, so as to achieve the desired transmission effect.

With the continuous development of digitization and networking, the advantages of data cable become prominent. According to statistics, the use of data cables has a long history, telephone transmission is the use of twisted-pair, in many industrial control systems and interference in large places and long-distance transmission have used twisted-pair, we are widely used today in the LAN is also the use of twisted-pair.

Twisted-pair cable is so widely used because it has many advantages such as strong anti-interference ability, long transmission distance, easy wiring and low price. Since the data line also attenuates the signal greatly, the frequency of the signal cannot be too high when the transmission distance is long, while the high-speed signal such as Ethernet can only be limited to within 110m.

For video signal, the bandwidth reaches 6MHz. If it is transmitted directly in the data line, it will also attenuate greatly. Therefore, amplification and compensation must be carried out to realize the long-distance transmission of video signal on twisted pair. Add a pair of twisted-pair video transceivers and the picture can be transmitted to 1 to 2km. Both the data line and the data line video transmission equipment are very cheap, not only does not increase the cost of the system, but when the distance increases, the cost is much lower than that of coaxial cable.

There are obvious advantages of data line transmission in monitoring system:

1. Long transmission distance and high transmission quality. Because advanced processing technology is adopted in the twisted-pair transceiver, the attenuation of video signal amplitude and the attenuation difference between different frequencies of twisted-pair cable are well compensated, and the brightness, color and real-time of the original image are maintained. When the transmission distance reaches 1km or further, the image signal is basically free from distortion. If relay is used, the transmission distance will be further.

2. Convenient wiring and high utilization rate of cables. A pair of regular telephone lines can be used to transmit video signals. In addition, any pair of the 5 types of unshielded twisted pair wires widely laid in buildings can transmit a video signal without additional wiring. Even if rewiring, the 5 types of cables are easier than coaxial cables.

In addition, there are 4 pairs of twisted-pair cables in one of the 5 types of cables. If a pair of cables is used to transmit video signal, other pairs of cables can also be used to transmit audio signal, control signal, power supply or other signals, which improves the utilization rate of cables and avoids the trouble caused by separate wiring of various signals and reduces the project cost.

3. Strong anti-interference ability. Twisted pair can effectively suppress common mode interference, even under strong interference environment, twisted pair can transmit excellent image signal. In addition, 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. Video signal is transmitted by twisted-pair cable. Special transmitter should be connected at the front end and special *** machine should be connected at the control center. This twisted pair transmission equipment is cheap, easy to use, no professional knowledge, nor too much operation, a installation, long-term stable work.

The price is cheap and the materials are convenient. Due to the use of common 5 types of non-shielded cable or common telephone line widely used at present, it is easy to purchase, and the price is very cheap, which brings great convenience to engineering applications.

Therefore, the design and construction of data cables to replace security cables in security video is an irreversible trend no matter from the perspective of the final use effect, economic cost and human construction.