Comparison between Coaxial Transmission and transmission

What is the length of Coaxial Transmission compared with that of twisted pair wires?

1. Coaxial Transmission Line is a high-quality broadband shielded Transmission Line

[Excellent]: low transmission attenuation.

[Broadband]: the current product level in China has already reached 0 ~ 20Gz; twisted pair transmission bandwidth is about 1/10 of the same axis;

[Shielding]: It limits all electromagnetic fields of transmitted signals to the inside of the shielding layer and does not radiate outward. According to the reversible principle of sending and receiving, external electromagnetic fields cannot pass through the shielding layer to enter the interior.

The Generation Principle of coaxial interference is another matter. Because of the difference in twisted pair wires, the signal transmission electromagnetic field is theoretically distributed in an infinite space. Based on the reversible principle of sending and receiving, the external space electromagnetic field can also directly enter the twisted pair. Twisted Pair wires cannot prevent external electromagnetic fields from entering. However, they use a spiral twist method to make the signals received by the two wires "try to be exactly the same" and adopt balanced differential signal processing technology, suppress this completely identical "common mode signal. The key here is the "balance" feature of twisted pair wires. Once there is a difference in "balance", interference will be passed in, and external objects will also affect the balance. In engineering, the "balance" is relative, not absolute. The "common mode rejection" performance of the circuit has a fixed range. These two problems determine the anti-interference capability of twisted pair wires. They are limited. In the case of strong interference specified in the integrated network wiring rules, the shielded twisted pair wires must be used.

2. The transmission characteristics of coaxial and twisted pair wires are stipulated by the national standard and cannot be changed. For example, the video signal above the frequency is 6 M, for the transmission distance of 2000 M, the SYWV-75-5 cable attenuation is 40db, that is, the voltage attenuation is 100 times, 1 vp-p 6 M video signal attenuation to 10mv, or 80 dB micro-volts, video restoration at this level can ensure high signal-to-noise ratio. Engineers with experience in cable TV system design are very clear about this. For unshielded twisted pair wires, the 6M attenuation of 2km is 92db, and the attenuation is nearly 40 thousand times, 400 dB (nearly times) larger than-5 coaxial cable );

3. twisted Pair Wires transmit 2 km, 1 vp-p signal attenuation to 25 micro-volts, that is, the level is 28db micro-volts, can be close to the circuit noise level, only use the end compensation, the signal-to-noise ratio will seriously deteriorate, the way out can only be to increase the front-end level. This is the "Push-forward and pull-back" technical solution that must be used for twisted pair wire transmission. It is required that the total capacity of the front and back equipment must be greater than 92db, and the actual capacity should be 100db. Currently, I only see data from a manufacturer that provides 60 dB improvement capabilities. I still don't know the data at that frequency. Note that the inherent noise produced by the front-end large signal amplification and lifting circuit itself is much greater than the inherent noise produced by the small signal circuit at the end, and the signal-to-noise ratio of the system is faster, some people have suggested that the relay series of twisted pair transmission equipment can be done much more than that of Coaxial Transmission Equipment. This is simply an ignorant imagination and cannot be explained theoretically or practically;

4. Conclusion: when comparing coaxial and twisted pair wire transmission systems, there are two key points that must be grasped: one is to compare the differences between the two transmission characteristics, and the other is to look at the level and performance of transmission equipment;