Hello, welcome to Zhuhai Hanqin Cable Co.,Ltd. In this article, we will talk about the difference between coaxial cable and twist pair network cables.
First, COAXIAL CABLE:
Coaxial cable has the advantages of being cheaper and easier to lay
(Relative to optical fiber), so, generally in a small-scale monitoring system, by
Because the transmission distance is very short, the use of coaxial cables to directly transmit the monitoring image does not cause much damage to the image quality, which can meet the actual requirements.
However, according to the analysis of the characteristics of the coaxial cable itself, when the signal is transmitted in the coaxial cable, its attenuation is related to the transmission distance and the signal itself.
The frequency is related. Generally speaking, the higher the signal frequency, 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. In this way, when the video signal is transmitted in the coaxial cable, not only the overall signal amplitude is attenuated, but also the attenuation of each frequency component varies greatly, especially the color part attenuation is the largest. Therefore, coaxial cables are only suitable for short-distance transmission of image signals. When the transmission distance reaches about 200 m, the image quality will be significantly reduced, especially the color becomes dim and there is a sense of distortion.
In engineering practice, in order to extend the transmission distance, a coaxial amplifier is used. The coaxial amplifier can amplify the video signal to a certain extent, and also
Different frequency components can be compensated in different sizes through equalization adjustment, so that the distortion of the video signal output by the receiving end is as small as possible. But
Yes, coaxial amplifiers cannot be cascaded indefinitely. Generally, coaxial amplifiers can only be cascaded up to 2 to 3 in a point-to-point system.
Otherwise, the video transmission quality cannot be guaranteed, and it is difficult to adjust. Therefore, when using a coaxial cable in a monitoring system, in order to ensure a better
Generally, the transmission distance is limited to about four or five hundred meters.
In addition, coaxial cables still have some shortcomings in the transmission of image signals in the monitoring system:
1) The coaxial cable itself is greatly affected by climate change, and the image quality is affected to a certain extent;
2) The coaxial cable is relatively thick, which is not convenient for wiring in intensive monitoring applications;
3) Generally, coaxial cables 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.
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4) Coaxial cable has limited anti-interference ability and cannot be used in strong interference environment;
5) The coaxial amplifier also has the disadvantage of difficulty in adjustment.
Second, Twisted pair
Twisted pair has been used for a long time. Telephone transmission uses twisted pair, which is used in many industrial control systems and places with greater interference and long distances.
Twisted-pair cables are used in remote transmission, and the local area network that we widely use today also uses twisted-pair cables. The reason why twisted pair is so widely used,
It is because it has many advantages such as strong anti-interference ability, long transmission distance, easy wiring, and low price. Since the twisted pair signal also exists
Larger attenuation, so when the transmission distance is long, the frequency of the signal cannot be too high, while high-speed signals such as Ethernet can only be restricted to
Within 100m. For video signals, the bandwidth reaches 6MHz. If it is directly transmitted in a twisted pair cable, it will also attenuate greatly. Therefore, the video signal is
To achieve long-distance transmission on a twisted wire, amplification and compensation must be carried out. The twisted pair video transmission equipment is to complete this function. Plus a pair of twisted pairs
After the line video transceiver equipment, the image can be transmitted from 1 to 2km. Twisted-pair and twisted-pair video transmission equipment are very cheap, not only without
Increasing the cost of the system, on the contrary, when the distance increases, its cost is much lower than that of the coaxial cable. Therefore, in the monitoring system, the twisted pair is used for transmission.
Transmission has obvious advantages: 1) Long transmission distance and high transmission quality. Due to the advanced processing technology used in the twisted pair transceiver, it perfectly compensates for the attenuation of the twisted pair to the video signal amplitude and the attenuation difference between different frequencies, and maintains the brightness and color of the original image and the real-time performance. When the transmission distance reaches 1km or more, the image signal is basically without distortion. If the relay mode is adopted, the transmission distance will be longer.
2) Convenient wiring and high cable utilization. A pair of ordinary telephone lines can be used to transmit video signals. In addition, the extensively paved buildings in the building
Any pair of unshielded twisted pair cables of category 5 can transmit one video signal without additional wiring. Even if it is re-wiring, category 5 cables are better than the same
Shaft cable is easy. In addition, a category 5 cable has 4 pairs of twisted-pair wires. If a pair of wires is used to transmit the video signal, the other pairs of wires can also be used.
To transmit audio signals, control signals, power supply or other signals, improve cable utilization, and avoid separate wiring of various signals
The trouble here has reduced the project cost.
3) Strong anti-interference ability. Twisted-pair cable can effectively suppress common mode interference. Even in a strong interference environment, twisted-pair cable can transmit excellent image signals.
Number. Moreover, the use of several pairs of twisted pairs in a cable to transmit different signals respectively without interference with each other.
4) High reliability and easy to use. Use twisted pair cables to transmit video signals, and a dedicated transmitter must be connected at the front end, and a dedicated transmitter must be connected at the control center.
Receiver. This kind of twisted pair transmission equipment is cheap and easy to use. It does not require professional knowledge and does not require much operation.
Installation, long-term stable work.
5) The price is cheap and it is convenient to obtain materials. Because it uses the general 5 unshielded cable or general telephone line that is widely used at present, it is easy to purchase.
And the price is also very cheap, which brings great convenience to engineering applications.