In daily life, we will be exposed to a variety of wire, such as video transmission line, audio transmission line, network cable, power transmission line, if you do not look at the connector, ordinary people are difficult to distinguish. The most intuitive difference is that some are thick, some are thin, some are hard and some are soft. Thick and thin are easy to understand. 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 will be thicker. Why is it that some of the same thickness are hard and some are soft? This has a lot to do with the internal structure of the wire.
The signal line on the market can be divided into coaxial line and twisted pair. As the name implies, the coaxial line is composed of layers of insulating layer wrapping the central copper conductor, and the metal mesh layer wrapping outside the insulating layer. Since the outer metal mesh and the central axis are on the same axis, it is called coaxial line. The metal mesh can shield the electromagnetic interference from the outer layer, as shown in the figure below.
From the anatomical structure of the coaxial line, we can see that from the inside to the outside, they are: central wire, insulation layer, outer conductive layer (metal mesh), wire sheath.
Multiple groups of coaxial lines and independent power transmission lines constitute the lightning line.
Opposite to the coaxial line is the twisted pair. Twisted pair is to wrap two wires with insulation protection layer together according to a certain helicity.
The figure above shows the signal line composed of 6 groups of twisted pair.
What is the difference between the 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 network, the external magnetic field 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, the attenuation is related to the transmission distance and the frequency of the signal itself. For high frequency signals, the further the transmission distance, the greater the signal attenuation. In order to achieve the purpose of long-distance transmission of high-frequency signal, the coaxial amplifier is usually used to amplify and compensate the signal.
Intel's lightning 3 data line uses the coaxial line. Due to the high frequency attenuation of the coaxial line, for the length of 0.5m Lightning line 3 Only a passive chip is needed, and when it is more than 0.5m, the active chip is required to amplify the signal. The price difference between the active chip and the passive chip is several times Lightning line 3 Generally less than 0.5m. Of course, Apple's use of passive chips to make a 0.8m lightning 3 data line is already the limit.
Choetech's 2m lightning 3 data line is an active type chip, which is sold for RMB 5600.
The twisted pair is short of metal shielding layer, and the interference signals generated by the internal and external electromagnetic fields will cancel out part of each other by means of mutual winding, so it has the advantages of strong anti-interference ability. If it is required to have strong anti-interference ability, it is necessary to use shielded twisted pair. Our common category 6 network cable is unshielded twisted pair, and category 7 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 handle of twisted pair is not as good as that of coaxial line.
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