What is the difference between unshielded twisted pair and shielded twisted pair?

Twisted pair (TP) is the most commonly used transmission medium in integrated wiring engineering. It consists of two copper wires with an insulating protective layer. The two insulated copper wires are twisted together at a certain density, and the electric wave radiated by each wire in the transmission is cancelled by the electric wave emitted from the other wire, thereby effectively reducing the degree of signal interference. The twisted pair is usually made up of two insulated copper wires of 22 to 26, and the name of the "twisted pair" is also derived from this. In actual use, the twisted pair is enclosed by a pair of twisted pairs in an insulated cable sleeve. If one or more pairs of twisted pairs are placed in an insulating sleeve, they become twisted pair cables, but in daily life, "twisted pair cables" are generally referred to as "twisted pair".

According to the presence or absence of the shielding layer, the twisted pair is divided into an Unshielded Twisted Pair (UTP) and a shielded twisted pair. So what is the difference between unshielded twisted pair and shielded twisted pair?

Unshielded Twisted Pair (UTP) is a data transmission line consisting of four pairs of transmission lines of different colors, widely used in Ethernet and telephone lines.

Of the four pairs of UTP cables, two are used as data communication lines, and the other two are used as voice communication lines. Therefore, in the integrated wiring of the telephone and the computer network, one UTP cable can simultaneously provide one computer network line and two telephone communication lines.

The disadvantage of unshielded twisted-pair cable is that it uses simple twisting of electromagnetic radiation and cancels each other. Therefore, in terms of resistance to electromagnetic radiation, UTP cables are at a disadvantage against coaxial cables (television cables and early 50 ohm network cables).

Unshielded twisted pair cables have the following advantages:

1. Unshielded jacket with small diameter, saving space occupied and low cost;

2, light weight, easy to bend, easy to install;

3. Minimize crosstalk or eliminate it;

4, with flame retardancy;

5, with independence and flexibility, suitable for structured integrated wiring.

Therefore, unshielded twisted pair is widely used in integrated wiring systems.

The shielded twisted pair has a metal shield between the twisted pair and the outer insulating envelope. Shielded twisted pair is divided into STP (Shielded Twisted Pair) and FTP (Foil Twisted-Pair). STP means that each line has its own shielding layer, and FTP only has shielding device for the entire cable, and both ends are properly grounded. It only works. Therefore, the entire system is required to be a shielding device, including cables, information points, crystal heads and patch panels, and the building needs to have a good grounding system. Generally speaking, the shielded twisted pair is usually STP. The shielding layer can reduce radiation, prevent information from being eavesdropped, and prevent external electromagnetic interference from entering, so that the shielded twisted pair has a higher transmission rate than the similar unshielded twisted pair.

In Ethernet, STP can completely eliminate electromagnetic crosstalk between pairs. The outermost shield shields electromagnetic EMI interference and radio RFI interference from outside the cable.

There are two main disadvantages of STP cable, one is expensive, and the other is complicated installation. Installation is complicated because of the shielding grounding of the STP cable. Both the shield and the outer shield of the cable pair are reliably connected to the shielded metal casing of the connector at the connector. Switching equipment and patch panels also need to be well grounded. Therefore, the STP cable is not only costly but also the cost of installation.

The shielded twisted pair is highly resistant to electromagnetic radiation and is suitable for deployment in industrial environments and other situations where there is severe electromagnetic radiation interference or radio radiation interference. In addition, the outer shield of the shielded twisted pair effectively shields the cable itself from radiation from the outside. In military, intelligence, embassy, ​​and government departments such as the National Audit Office and the Ministry of Finance, shielded twisted pair cables can be used to effectively prevent external electromagnetic interference from line data. For sensitive instruments around the line, shielded twisted pairs can avoid interference with them.

However, the termination of the shielded twisted pair requires reliable grounding. Otherwise, it will introduce more serious noise. This is because the shield of the shielded twisted pair now senses all surrounding electromagnetic signals like an antenna.

1. The outer layer of the shielded twisted pair cable is wrapped by aluminum pouch to reduce radiation. The radiation protection is better than the unshielded twisted pair cable, but the radiation cannot be completely eliminated.

2, similar to coaxial cable, shielded twisted pair must be equipped with a special connector to support the shielding function and the corresponding installation technology, not shielded twisted pair is not required.

3. Compared with unshielded twisted pair cable, shielded twisted pair cable has a higher transmission rate and can reach 155 Mbps within 100 meters.

3. Shielded twisted pair is often used for high-efficiency information transmission. It has higher transmission performance than unshielded twisted pair, and is often used for sections with large interference.

In summary, we can see that the main difference between unshielded twisted pair and shielded twisted pair is the presence or absence of a metal shield. In practical applications, unshielded twisted pair cables are more widely used, and shielded twisted pair cables are used only in a few areas where there is a strict requirement for radiation interference, such as industrial shielded wiring systems, transmission bandwidths greater than 500 MHz, and confidential information. Transmission, environmental interference sources are complicated.