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Case Study 2 - NEXT Fails on DTX CableAnalyzer due to cable

You can also click here to see a video of Adrian Young from our Technical Assistance Center walking you through these steps. 

In this case study, the installer was failing NEXT when certifying a number of category 6 permanent links. With the DTX CableAnalyzer, it is possible to discover why these links were failing. 

After the AUTOTEST, the installer was presented with the following DTX CableAnalyzer test result.

Your DTX CableAnalyzer can help you diagnose the NEXT failure. Let's review the process. Do not skip Step 1 please.

Step 1
Find out which pair combination of NEXT is causing the marginal pass. 

  • Highlight NEXT.
  • Press the ENTER key.
  • Press the F3 to display the worst pair.

Here we see that Pair 1,2-4,5 is the cause of the NEXT failing. Make a note of this failing pair.

Step 2
Look at the HDTDX Analyzer trace for this marginal pair.

  • Press the EXIT key twice to return to the main screen.
  • Highlight HDTDX Analyzer.
  • Press the ENTER key.
  • Press the F3 until you get to the marginal pair, in this case: Pair 1,2-4,5.

Step 3
Analyze the trace. What you are seeing is where the crosstalk is happening in the link. The cursor automatically goes to the largest source of crosstalk. In this case, ignore that. The two red lines represent the ends of the test leads of the DTX CableAnalyzer. So you can assume the red lines are the location of your first and last connection. You can zoom in on this event to get a better picture:

  • Press the F2 key.
  • Press the up cursor key until you see 8X in the upper right of the screen.

As a rule of thumb (not in the standards), you should not expect any events exceeding 5% or -5% in the cable. If you see more than 4 or 5 events in the cable exceeding 5% or -5%, then it suggests a cable issue. In this example, we have multiple events exceeding the 5% and -5% so we know we have a cable issue.

If you have "Store Plot Data" enabled in your DTX CableAnalyzer, these graphs will be available to analyze in LinkWare PC Software.

Conclusion:

The cable is the principle cause of the NEXT failure. Re-terminating the connectors is not going to improve the result. This cable needs to be replaced.

Tip:

For every batch of cable you receive, put a side at least 50 m (164 ft) of cable. If there becomes an issue with the cable and a dispute over whether it was damaged during the installation or manufactured incorrectly, you can take the cable you set aside and test it. You would pull it from the reel/box and lay it flat on the ground. Terminate it and test it. If the HDTDX trace looks the same as your installation, time to call the cable vendor. To help, you will have a "virgin" piece of cable to be shipped back to the cabling vendor's lab for verification.