Twisted pair has been used for a long time. The telephone transmission uses twisted pair. Twisted pair is used in many industrial control systems, places with large interference, and long-distance transmission. The LAN we use today is also used. Twisted pair.
The reason why twisted pair is so widely used is because it has many advantages such as strong anti-interference ability, long transmission distance, easy wiring, and low price. Due to the large attenuation of the signal of the twisted pair, the frequency of the signal cannot be too high when the transmission distance is long, and high-speed signals such as Ethernet can only be limited to 100m.
For the video signal, the bandwidth reaches 6MHz, and if it is directly transmitted in the twisted pair, it will also be greatly attenuated. Therefore, to achieve long-distance transmission of the video signal on the twisted pair, it must be amplified and compensated. Twisted pair video transmission The device performs this function. With the addition of a pair of twisted pair video transmission equipment, the image can be transmitted to 1 to 2km. Twisted pair and twisted pair video transmission equipment are very cheap, not only did not increase the cost of the system, but when the distance increases, its cost has dropped a lot compared with the coaxial cable. Therefore, the use of twisted pair transmission in the monitoring system has obvious advantages:
1. Long transmission distance and high transmission quality. Due to the use of advanced processing technology in the twisted pair transceiver, it perfectly compensates the attenuation of the video signal amplitude of the twisted pair and the attenuation difference between different frequencies, maintaining the brightness and color of the original image and real-time, When the transmission distance reaches 1km or more, the image signal is basically free of distortion. 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 one of the 5 types of unshielded twisted pair widely laid in the building can transmit one video signal without additional wiring. Even if it is re-wired, 5 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 cables is used to transmit video signals, the other pairs can also be used to transmit audio signals, control signals, power supply or other signals, which improves the cable. The utilization rate, while avoiding the trouble caused by the separate wiring of various signals, reduces the cost of the project.
3. Strong anti-interference ability. Twisted pair can effectively suppress common mode interference, even in a strong interference environment, the twisted pair can also transmit excellent image signals. Moreover, several pairs of twisted pairs in a cable are used to transmit different signals without interference.
4. High reliability and easy to use. To use twisted pair to transmit video signals, a dedicated transmitter should be connected at the front end and a dedicated receiver should be connected at the control center. This kind of twisted pair transmission equipment is cheap and easy to use. It does not require professional knowledge and too much operation. It can be installed once and work stably for a long time.
5. The price is cheap and the material is convenient. Because it is a common type 5 unshielded cable or common 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.