All test data above significance condition - DTX Alien Crosstalk
Where's the data?
This is caused by the significance condition, defined in the cabling standards as:
The significance condition equals the average frequency response expressed in dB between 100 MHz and 250 MHz. If the average measured ANEXT loss or AFEXT loss between 100 MHz and 250 MHz exceeds the significance condition, then the entire ANEXT loss or AFEXT loss response is excluded (discarded) in the power sum computation. If the average measured ANEXT loss or AFEXT loss between 100 MHz and 250 MHz does not exceed the significance condition, then the entire ANEXT loss or AFEXT loss response is included in the power sum computation. The value of the significance condition is 90 dB.
You can verify this by clicking on Significance Detail:
In the above example, I have taken the alien near end crosstalk (ANEXT) measurement from Pair 12 - 12 and displayed it below:
As you can see, there is very little alien crosstalk going on here. It has met the significance condition of 90 dB. The majority of this trace is random noise from external noise sources, the noise floor and residual NEXT of the the test instrument with its adapters. You've heard of people talking about the importance of noise floors. This is the reason why. If the field tester had a poor random noise floor, your alien crosstalk measurements would include the random noise floor of the field tester - potentially resulting in false failures.
If we disabled the significance condition check in our result above, we would see: (customers are not able to do this of course)
Retenez ceci : This is all taken care of for you in the software.