Hello, everyone!
Today, I will continue to explain UTP testing. In the previous article, I explained tests: wiremap and length. Now, in this last article about UTP cables, I will explain another testing.
Attenuation and crosstalk testing are in the range of operating frequency.
Attenuation
Measuring attenuation is very important. During propagation, the signal intensity decreases. A sufficient signal level should be provided at the reception. Attenuation depends on both the operating frequency range and external factors such as temperature. At high temperatures, the attenuation of UTP cable is increasing.
The test of attenuation consists of a tester at both ends of the UTP cable. One tester sends a signal, the other tester receives and calculates the attenuation. There is a pass/fail depending on the category of UTP cable at max frequencies. This test is specified in the 568 standards.
Crosstalk
Crosstalk is one of the most important problems with twisted pairs. This problem is one of the main limitations of high data rates. With UTP cables, in order to reduce crosstalk, in addition to the fact that the pairs are twisted, great care must be taken to ensure that the termination is very good - to eliminate very little jacket with wires.
The most important crosstalk are NEXT (Near End Cross Talk) and FEXT (Far End Cross Talk). These problems are shown in the images below.
Figure 1. NEXT and FEXT
There are special testers that can measure crosstalk and give a pass/fail result. Some of these instruments can calculate the ACR (Attenuation/Crosstalk Ratio). This relationship should give as much value as possible.
Other testing
UTP cables for Gigabit Ethernet and 10 Gigabit Ethernet require additional tests. These tests refer to the simultaneous testing of all four pairs in both directions. Tests can be delay skew, return loss, “alien” crosstalk, powesum crosstalk, etc.
Delay Skew is a test that measures the transfer rate on all four pairs. Propagation delay is measured by testers, these situations we can see in the next figure.
Figure 2. Delay skew
The return loss is due to a change in the impedance of the UTP cable. These reflections can cause signal degradation.
Figure 3. Return loss
"Alien" crosstalk measurements depend a lot on the physical location of the cables.
Thank you!
