Why does Lightning 3 data line generally not exceed 0.5 meters?

Signal lines on the market can be divided into coaxial lines and twisted pairs.

As the name implies, a coaxial line is composed of a layer of insulating layer wrapped with a central copper conductor, and a metal mesh layer wrapped outside the insulating layer. Because the outer metal network and the central axis are on the same axis, it is called a coaxial line.

The metal mesh can shield the electromagnetic interference from the outer layer, as shown in the following figure:

From the anatomical structure of the coaxial line, it can be seen that from the inside to the outside are: central conductor, insulating layer, outer conductive layer (metal mesh), wire outer skin.

Lightning data line is composed of several groups of coaxial lines plus independent power transmission lines.

The opposite of the coaxial line is the twisted pair, that is, two conductors with insulating protective layer are intertwined with each other according to a certain helicity.

Signal line composed of six pairs of twisted pairs

What's the difference between the two lines?

The interference of the data line comes partly from the external magnetic field, and partly from the magnetic field generated by itself when transmitting the changed signal.

Because of the existence of metal shielding network, the external magnetic field of coaxial cable can not pass through the shielding layer, and the internal magnetic field can not pass through the shielding layer. When the signal is transmitted in coaxial cable, the attenuation is related to the transmission distance and the frequency of the signal itself.

For high frequency signals, the farther the transmission distance is, the greater the signal attenuation is. In order to achieve long-distance transmission of high-frequency signals, coaxial amplifiers are usually used to amplify and compensate the signals.

Intel Lightning 3 Data Line uses coaxial line. Because of high frequency attenuation of coaxial line, only passive chip is needed for Lightning 3 Line with length of 0.5m. When it exceeds 0.5m, active chip is needed to amplify the signal. The price difference between active chip and passive chip is several times, so Lightning 3 Line generally does not exceed 0.5m. .5m.

Of course, Apple has made a 0.8m Lightning 3 data line using passive chips, which is already very limited.

CHOETECH's 2m Lightning 3 data line uses active chips, which sell for 5600 yuan.

Twisted pair cable lacks metal shield layer, so it has the advantage of strong anti-jamming ability because of the way of winding each other, and the interference signals generated by internal and external electromagnetic will cancel out part of each other.

If strong interference resistance is required, shielded twisted pairs must be used. Our common super six types of wire are unshielded twisted pair, while the seventh type is shielded twisted pair.

In addition, twisted pair has many advantages, such as long transmission distance, easy wiring, low price and so on. Of course, the feel is different from the axis.