DTX2CU exercises

Introduction

The best way to learn to is do.

These test results are real results taken from the field.

• Open the file Exercises01to16LinkWare.flw in LinkWare
• Double click one of the result records; another windows will open with detailed test data
• Select Pair Data near the top and HDTDR or HDTDX Analyzer near the bottom of the window

 

Solution

Exercise 01 - cable too long

Notice that the length has exceeded 90m but not failed.

Accept? No.

Why? Insertion Loss failed. Even when the length limit can be exceeded by 10%, cables lengthes exceeding the design length are likely to fail the insertion loss test.

HDTDR/HDTDX: you could look at HDTDR to make sure there is nothing unusual.

Corrective Action: try and remove some slack from the cable run. 

 

Exercise 02 - cable too long

With ISO/IEC11801, length is not a required field test parameter.

Notice that Length is marked with an "i".

Accept? No.

Why? Insertion Loss failed. Even when there is no field test limit for length like in ISO/IEC11801, cables lengthes exceeding the design length are likely to fail the insertion loss test.

HDTDR/HDTDX: you could look at HDTDR to make sure there is nothing unusual.

Corrective Action: try and remove some slack from the cable run. 

 

Exercise 03 - damaged cable

The result for Return Loss (RL) in marginal. Cabling standards deem a marginal PASS* as a PASS. However, the customer or the cabling vendor offering the warranty may not.

Accept? Depends on the contract.

Why? RL is marginal

HDTDR/HDTDX: with HDTDR, in almost all cases, you need to zoom in on the vertical axis so that in the right corner of the screen you see 1X  32X. HDTDR shows the cable to be bad in the last part of the link; consistent with a cable handling issue.

Corrective action: this cable will have to be replaced.

 

Exercise 04 -  bad connector

The result for Near End Crosstalk (NEXT) in marginal. Cabling standards deem a marginal PASS* as a PASS. However, the customer or the cabling vendor offering the warranty may not.

Accept? Depends on the contract.

Why? NEXT is marginal.

HDTDR/HDTDX: HDTDX shows the connection at the near end to be bad with a value of 44.5. The value for a compliant connector should be less than 17.5.  Notice that the far end termination is not great either.

Corrective Action: assuming the connector is compliant, re-terminate the connector at the near end and run the AUTOTEST again.  If NEXT still doesn't PASS, re-terminate the connector at the far end as well.

 

Exercise 05 - bad cable

Return Loss fails. The frequency/RL graph fails at a the low frequency. If Return Loss fails at the lower frequency, it is most likely a cable issue.

Accept? No.

Why? RL failed.

HDTDR/HDTDX: use HDTDX to confirm the hypothesis that this is a cable problem. The HDTDR show the cable to be bad down the entire length of the cable. Whilst HDTDR can only tell  if the cable is bad or not, it can suggest that the installer damaged it or whether it left the factory that way. If the cable run has been visually inspected and there is no obvious signs of damage, it would suggest bad cable. Testing at regular intervals during an installation is clearly a good idea to catch manufacturing issues.

Corrective action: this cable will have to be replaced.

 

Exercise 06 - bad connector

NEXT is marginal. Cabling standards deem a marginal PASS* as a PASS. However, the customer or the cabling vendor offering the warranty may not. NEXT fails at low and high frequency; no cable/connector suggestions this time. Notice that this is a really short Cat 6A link, so "it must be marginal". This statement is not entirely incorrect: some cabling vendors do have a minimum distance for Category 6A. However, vendors have improved the Cat 6A connectors and the minimum length requirement has come down to 5m  or less. You will need to ask the vendor what their requirements are.

Accept? Depends on the contract.

Why? NEXT is marginal.

HDTDR/HDTDX: HDTDX shows 66.6 at the remote connector when it should be less than 17.5; it is obvious that the remote connection is bad and needs fixing.

Corrective Action: re-terminate the connector at the remote.

 

Exercise 07 - bad connector

NEXT is marginal. Cabling standards deem a marginal PASS* as a PASS. However, the customer or the cabling vendor offering the warranty may not. Notice that NEXT fails at medium frequency; no cable/connector suggestions this time.

Accept? Depends on the contract.

Why? NEXT is marginal.

HDTDR/HDTDX: HDTDX shows 32.7 at the remote connector when it should be less than 17.5.

Corrective Action: re-terminate the connector at the near end.

 

Exercise 08 - AC wire map

Notice that Resistance is missing from the menu. The technician has enabled AC Wire Map and hence Resistance as well as Shield Integrity can no longer be measured and is missing from the menu. ?

Accept? You would have to check with the vendor offering the cabling warranty. If this was a shielded cabling system, then the answer would be a definite NO.

Why? AC Wire Map enabled

HDTDR/HDTDX: Not applicable.

Corrective Action: Verify if AC Wire Map was activated for a valid reason. If not, deactivate and rerun AUTOTEST.

 

Exercise 09 - bad connector

NEXT fails at low and high frequency so no cable/connector suggestions.

Accept? No.

Why? NEXT failed.

HDTDR/HDTDX: HDTDX shows 76.7 at the main connector end when it should be less than 17.5.  The remote end shows a less than impressive 33.9.

Corrective Action: re-terminate the connector at the near end and rerun  AUTOTEST.  If NEXT still doesn't pass, re-terminate the connector at the far end as well.

 

Exercise 10 - bad termination

The Return Loss graph shows the marginal result to be at the lower frequencies suggesting a cable issue. Remember that is likely - but not alays  the case and needs confirmation. 

Accept? Depends on the contract.

Why? RL is marginal.

HDTDR/HDTDX: when we look at the HDTDR for Pair 1,2 we see a value of 8.1 at the remote connector. We’re looking for nothing greater than 3 at the connector (guidance value only). There seems to be a contradiction: the frequency plot is suggesting cable and the HDTDR says connector. Whenever HDTDR suggests connector issue, you should check Resistance. Go and look at Resistance and you will see a higher Resistance reading on Pair 1,2 compared to the other pairs. This suggests a contact issue between the test lead and the installed connector. It could be that Pair 1,2 was not punched down correctly or there was dirt on the contacts.

Corrective Action: re-terminate the connector at the far end, retest.

 

 

Exercise 11 - bad cable

Notice the narrow frequency band at which Return Loss is failing. This suggests a cable issue, even more than a failure at low frequency. We still need HDTDR to verify this. 

Accept? NO.

Why? Return FAILs badly.

HDTDR/HDTDX: HDTDR shows close events greater than 0.8 down the entire length of the cable. Because only one pair shows issues and it is pretty much all the way down the cable, it suggests a manufacturing problem with the cable. There should be other links in the installation showing the same HDTDR plot assuming there are other cables that came from the same batch. When the Return Loss fails this badly, it will impact Insertion Loss. Have a look at the Insertion Loss trace. The two spikes on the Insertion Loss trace are at the same frequency as those found on the Return Loss trace.

Corrective Action: replace cable.

 

Exercise 12 -