In our daily life, we are exposed to a variety of wires, such as video transmission lines, audio transmission lines, network lines and power transmission lines. If we do not look at the connectors, ordinary people can hardly distinguish them. The most intuitive difference is that some are thick, some are thin, some are hard, and some are soft. It is easy to understand the difference between thick and thin. For example, if high-power power transmission is required, the wire will be much thicker, and more groups of data need to be transmitted, such as USB2.0 and USB3.0. The number of data lines will be more, and the wire material will be thicker. Why are some wires of the same thickness very hard, while others are relatively soft? This has a lot to do with the internal structure of the wire rod.
The signal lines on the market can be divided into coaxial lines and twisted pairs. As the name implies, the coaxial line is composed of layers of insulating layers wrapped around the central copper conductor, and metal mesh layers wrapped around the outside of the insulating layer. Since the outer metal mesh and the central axis are on the same axis, it is called the coaxial line. The metal mesh can shield the electromagnetic interference of the outer layer, as shown in the figure below.
As can be seen from the anatomical structure of the coaxial line, from inside to outside, they are: central conductor, insulation layer, outer conductive layer (metal mesh), and wire sheath.
Multiple groups of coaxial lines and independent power transmission lines form a lightning line.
The opposite to the coaxial line is twisted pair, which is a twisted pair of two conductors with insulation protection layer, twisted together according to a certain degree of helicity.
The above figure shows the signal line composed of six twisted pairs.
What is the difference between these two lines?
Part of the interference of the data line comes from the external magnetic field, and the other part comes from the magnetic field generated by itself when transmitting the changing signal.
Due to the existence of metal shielding mesh, the external magnetic field of coaxial cable cannot pass through the shielding layer, and the internal magnetic field cannot pass through the shielding layer. When the signal is transmitted in the coaxial cable, its attenuation is related to the transmission distance and the frequency of the signal itself. For high-frequency signals, the longer the transmission distance, the greater the signal attenuation. In order to achieve the purpose of long-distance transmission of high-frequency signals, coaxial amplifiers are usually used to amplify and compensate the signals.
Intel's Thunderbolt 3 data cable uses the coaxial line. Due to the high-frequency attenuation of the coaxial line Lightning 3-wire , only the passive chip is needed, and when it exceeds 0.5m, the active chip is needed to amplify the signal. The price of the active chip and the passive chip is several times different, so Lightning 3-wire Generally not more than 0.5m. Of course, Apple has made a 0.8m Thunderbolt 3 data line using passive chips, which is the limit.
CHOETECH's 2m Thunderbolt 3 data line uses active chips, which sell for 500 or 600 yuan.
The twisted pair is lack of metal shielding layer, and the interference signals generated by internal and external electromagnetism will cancel out part of each other by intertwining, so it has the advantage of strong anti-interference ability. If strong interference resistance is required, shielded twisted pair must be used. Our common CAT 6 network cable is unshielded twisted pair, and CAT 7 network cable is shielded twisted pair. In addition, twisted pair has many advantages, such as long transmission distance, easy wiring and low price. Of course, the feel is not as good as coaxial line.
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