Choice: six categories of blocking OR one-to-one blocking

The purpose of twisted pair wire shielding is to cut off the path of Space electromagnetic radiation to the core line of the twisted pair wire, or to reduce the intensity of Space electromagnetic radiation.

The traditional shielded twisted pair wires (such as F/UTP and SF/UTP) are used to add multiple shielding layers (such as aluminum foil shielding layer and copper mesh braided shielding layer) to the outer layer of the four core wires ), if one layer is not enough, add another layer.

They are used to suppress electromagnetic interference and radiation leaks between the external space and the twisted pair, rather than the electromagnetic interference between the line and the line. This method is very effective in three types of twisted pair wires and five types of twisted pair wires. However, when the above shielding method is still used in six types of shielded twisted pair wires, you need to add a cross skeleton between the line pairs (a single field is not yet added) to resist the electromagnetic interference between the line pairs. In this way, the outer diameter of the shielded twisted pair is significantly increased (the thickness of the Screen Layer + space of the Cross skeleton ).

 

Wire shielding twisted pair wires (U/FTP) are coated with a layer of aluminum foil on each wire, but the total shielding layer is not set for the four wires, which play three roles at the same time.

First, the electromagnetic radiation between the external space and twisted pair wires is blocked to prevent radiation leaks. Because each wire has a shielding layer, the external anti-electromagnetic interference capability is significantly stronger than the aluminum foil with the same thickness to shield twisted pair wires (qualitative description: When the electromagnetic interference comes from one direction, the two lines facing it have only one layer of shield protection, and the effect is the same as that of the total shield. The last two lines have at least two layers of shield protection, and the effect is higher than the total shield. The four pairs of twisted wires are always twisted. Therefore, the average result is that the electromagnetic radiation of each wire pair is smaller than that of the aluminum foil of the same thickness );

The second is to resist the electromagnetic radiation interference between various pairs in the same twisted pair, and no cross skeleton is required. At the same time, the same line can transmit four confidential phone signals to the shielded twisted pair; there will be no electromagnetic interference (ANEXT) between the two adjacent twisted pair with the same color line ).

Third, in terms of near-end crosstalk, quantitative analysis can be carried out through the test of the dedicated cable tester, according to the data shown in the inspection data of the Data Product Quality Testing Center of the Ministry of Information Industry. Different cat6 products produced by the same manufacturer (cat6 unshielded twisted pair wires without cross skeleton, cat6 unshielded twisted pair wires with cross skeleton, and cat6 unshielded twisted pair wires with shielded cables) have obvious differences:

Cat6 unshielded twisted pair wires with a cross skeleton provide an average of 4 ~ 5 dB of wealth;

The NEXT value of cat6 wires for shielded twisted pair wires is about 3.5dB higher than that of cat6 unshielded twisted pair wires with cross skeleton cables, which is significantly better than that of unshielded twisted pair wires;

There are two aluminum foil cables between the wire pairs that shield twisted pair wires. The inhibition capacity of a single aluminum foil is about 17 ~ 20 dB. This is basically the same as the saying "FTP is an order of magnitude higher than UTP's anti-interference capability" described in the Beijing Architectural Design Institute's study to Europe in the 1990s S.

It should be noted that the shielded twisted pair will introduce "secondary radiation", that is, the voltage induced on the shield layer will re-launch the radiation. Because of this, the shielding layer needs to be grounded to convert the induction voltage into current emissions to the earth. At this time, because the residual induction voltage on the shielding layer is very low, the interference of secondary radiation becomes very small. Secondary radiation will not cause damage to twisted pair wires.

In the Integrated Wiring shielding system, selecting appropriate shielding products based on your own needs and the surrounding environment is a prerequisite for ensuring information security.