Difference between coaxial cable and twisted pair cable

In daily life, we will be exposed to a variety of wires, such as video transmission lines, audio transmission lines, network cables, power transmission lines, if you do not see the connector, it is difficult to distinguish. The most intuitive difference is that there are some thick, some thin, some hard, some soft. For example, if high-power power transmission is required, the wires will be much thicker. If you need to transfer more data, such as USB2.0 and USB3.0 data cable, the number of data cables will be more and the wire will be thicker. Why are the same thick lines, some are very hard, and some are softer? This is related to the internal structure of the wire.

Signal lines can be divided into coaxial lines and twisted pairs. The coaxial cable is composed of an insulating layer wrapped with a copper conductor, and a metal mesh layer is wrapped around the insulating layer, as shown in the following figure.

It can be seen from the anatomical structure of the coaxial cable that from the inside to the outside are: the center wire, the insulating layer, the outer conductive layer (metal mesh), and the wire sheath.

Multiple sets of coaxial cables plus separate power transmission lines constitute lightning cable.

The opposite of the coaxial cable is the twisted pair cable. The twisted pair is a wire with two insulating layers wound together at a certain degree of helix.

What is the difference between these two cables?

Part of the interference from the data cable comes from the external magnetic field, and the other part comes from the magnetic field generated by itself when transmitting the changing signal.

Coaxial cable due to the presence of a metal shield, the external magnetic field cannot pass through the shield and the internal magnetic field cannot pass through the shield. The attenuation experienced by a signal as it travels within a coaxial cable 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.

Intel’s lightning 3 data cable uses a coaxial line. Because of the high frequency attenuation of the coaxial cable, only a passive chip is required for a lightning 3 cable with a length of 0.5 m. When it exceeds 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, so the lightning 3 cable generally does not exceed 0.5m. Of course, Apple used a passive chip to make a 0.8m lightning 3 data cable.