Diagnosing failing patch cords - DSP Patch Cord Adapter

This paper will enable you to diagnose patch cords that fail NEXT when using the DSP-PCI-6S Patch Cord Adapters. This is possible by using the HDTDX feature built into the DSP-4000 Series Cable Analyzers. But first........
 
Myth
Terminating an RJ45 plug on a category 6 cable just as you do with a category 5e cable will produce a category 6 patch cord. FALSE.
 
Reality
Some 80% of the so called category 6 compliant cords on the market today fail to meet the specific requirements of ANSI/TIA-568-C.2 and ISO/IEC 11801:2002. If in doubt, ask the vendors are these cords component compliant. The truth is that the termination of the RJ45 plug is so critical, specific RJ45 plugs have been developed by manufacturers to ensure the termination meets the above standards. It is all in the alignment of the individual pairs entering the RJ 45 plug (see below). Up until now, there has been no commercially viable way to test the patch cords. The introduction of the DSP-PCI-6S enables testing of manufactured cords for the first time. 

Example (Information Only)
 
Many quality manufacturers have already revisited their termination techniques and choice of components. These include companies such as Panduit, SYSTIMAX, Ortronics, Krone and many more. 
    
What is HDTDX?
High Definition Time Domain Crosstalk (HDTDX) is used to troubleshoot links that fail Near-End-Crosstalk (NEXT). Measurements for certification are made in the frequency domain (MHz). However, for diagnostic purposes, this is of little use. We need to be able to see where the crosstalk is happening, so the failing link can be fixed / replaced. This is where time domain data comes into play. Time Domain Reflectometry is the analysis of a conductor (wire, cable, or fiber optic) by sending a pulsed signal into the conductor, and then examining the reflection of that pulse. Hence, frequency domain is in Hz, time domain is in meters (ft). Using a time domain measurement will allow us to see the sources of crosstalk and troubleshoot the links. HDTDX is a very good example of a time domain measurement.
 
Diagnostic guidelines
The HDTDX time domain plot needs to be obtained along with the NEXT frequency plot. In cases of dispute, it is better to download the result(s) to a PC. For the DSP-4100 and DSP-4300 CableAnalyzers, the HDTDX plot data is stored automatically for links that fail the Autotest. However, with the DSP-4000, you can get the graphical information of the last link measurement only. To do this, make your measurement using the DSP-4000. Connect the DSP-4000 to a PC with LinkWare running.
 
In LinkWare, click on Utilities > DSP-4x00/LT CableAnalyzer > Detailed Test Data

                                                                    Figure 1. Accessing Detailed Test Data from a DSP-4000





Once you have saved the CSV file, you can open it by clicking on File │ Open and change the file type to CSV. CSV is an acronym for comma-separated value; it is a common format used by computers since the early 1980s.
 
How can I view the HDTDX plot?
In LinkWare, open the file that contains the failure(s). An example is shown below. If you do not have LinkWare, you can download it free of charge from http://www.flukenetworks.com/lwsoftware. By clicking on the column header Headroom, LinkWare will put the worst result at the top and the best result at the bottom of the summary screen. 

                                                                                 Figure 2. LinkWare summary screen 
 
Now that you have your file open, click once on one of the test results you wish to analyze, the double click on NEXT in the summary window.
A new window will pop up. Click on the NEXT tab as shown below to see which pair has the worst margin in dB. Note this pair, in this case 36-45.

                                                                              Figure 3. Viewing NEXT results in LinkWare 
 

Now click on the Pair Data tab. Then click on HDTDX Analyzer Plot to view the HDTDX graph.

                                                                             Figure 4. Viewing HDTDX plots in LinkWare
 
 

                                                                     Figure 5. Viewing the HDTDX plot in LinkWare
 
 
In this example, we see a peak of 50% at 1.1 meter. In this example, our patch cord is 1.1 meters, so we know this peak represents the RJ45 Plug / Jack interaction at the remote end of the patch cord. Using the tables below, we can see that, 50% represents 46.4 dB @ 100 MHz, thats 8 dB worse than the Category 6 connecting hardware standard (54 dB). The near-end connection at 39 % is better although does no meet the desired 35-36%. Values highlighted in yellow represent the standard requirement. Solution for this example: re-terminate the patch panel. 
  


 
For Category 5e patch cords, a different table is used. The mated connection requirement is 43 dB @ 100 MHz. 


If we have the plot data, we know the lookup table then it is possible to create a utility in Excel that converts this for you automatically.
 
 
Requirements
You will need Microsoft Excel 2000/2002 to run this utility.
Click here to download the utility. (1.0 MB)
 
You will also need to ensure that the Numeric Format in LinkWare is set to 00.0 and not 00,0. 


 
To save the plot data, click on File > Save As


 
Now that you have saved the HDTDX Plot Data, you can open the HDTDX Conversion Utility. Click here to download it.
When you open it, you will be prompted with the following warning 

In order for the conversion to work, you need to click on Enable Macros. If you are unsure about doing this, please contact your IT Manager.
 
You will be prompted to open the HDTDX CSV File you just saved, do that now. 


Below is an example conversion.

How do I read this?
You will note that the connecting hardware limit for Category 6 is 54 dB @ 100 MHz. The first spike represents the mated connection in the DSP-4000 Main Unit Adapter. The second spike represents the mated connection in the remote adapter. On this occasion, the news is not so good. Both spikes are below the minimum 54 dB requirement for Category 6 connecting hardware and hence the worst case margin for this pair was a failing -3.4 dB.
What happens if it falls below 54 dB? This 54 dB is not easy to achieve.
 
Here are some guidelines: 

  • Patch Cords less than 3.5 meters (11 ft) MUST have connecting hardware spikes better than 54 dB in order to achieve a PASS for the Autotest .
  • Links greater than 3.5 meters (11 ft) can have connecting hardware spikes as low as 52 dB; so long as there is no activity in the cable.

Any crosstalk in the cable will require the mated connection at each end to be better than the guidelines in 1) and 2) it is normal to see little or no crosstalk appear in the cable 
  
Additional Information
You cannot use standard RJ45 plugs to make Category 6 Patch Cords. Vendors have had to develop new styles of RJ45 plugs to meet the specific requirements of ANSI/TIA-568-C.2 Category 6 and ISO/IEC11801:2002.



Learn About:
- Troubleshooting LANs
- Fiber Testing

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Author:A.Young
Creation Date:6/24/2003
Last Modified:12/16/2009