Hello, everyone!
Today, I will start to explain UTP testing. Testing UTP cables include three basic tests: wiremap, length and high speed performance. These tests are part of the EIA/TIA-568 specs for all UTP cables.
Wiremap
Most UTP cable testers test the wiremap. This is a simple test that checks the continuity and termination of pins. Problems, which we can find, are reversed wired in a pair, crossed pairs, opens or shorts.
The problem with crossed pairs is caused by incorrect terminations at the ends of the UTP cable. On one side of the UTP cable is T568A, and on the other side is T568B.
Figure 1. Transposed or crossed pair
If one wire of each pair is incorrectly connected it leads to a problem called split pair. This is one of the very complicated problems. We can see this problem in the pictures below.
Figure 2. Split pair
Reversed pair is a situation when the wires of the same pair are connected to the wrong connector pins. We can see this problem in the next figure.
Figure 3. Reversed pair
Short or open is a very common problem with UT cables. In the next figure, we can see this problem. One wire from the first pair is not connected to pin 1 (OPEN). Wires from the second pair are connected to the same pin 6 (SHORT).
Figure 4. Short or open
Length
The maximum length UTP cable in the channel is 100 m. With the exception of patch cords, the maximum for UTP cables in the permanent link is 90 m. Some categories have a much shorter range, for example, Cat 8. Because of that, measuring the length of UTP cables is very important. For this measuring, there is TDR (Time Domain Reflectometer). TDR is like OTDR. It is a radar for UTP cables. Instrument knows speed for propagation of the puls. TDR emits a pulse and waits for reflection and measures the time. After that, it can calculate the length.
Figure 5. Length of UTP cable
Based on the polarity of the reflected signal, the TDR can find out if the problem is shorts or opens. As we can see in the figure above. If the polarity of the signal is the same as that sent by the instrument, then the problem is - OPEN. If the polarities of the sent and reflected signal are different, then the problem is - SHORT. If there is no reflected signal, UTP cable is well terminated.
I will continue the theme about testing on the next article >> UTP cables (6): UTP testing.
Thank you!
