There are three principle causes of failures/marginal passes on short Class EA Permanent Links:
- Not using the DTX-PLA002 Permanent Link Adapter
Almost all connecting hardware vendors have tuned their jacks to the Test Plug definition found in IEC 60512-27-100. The tip on the end of the DTX-PLA002 meets the requirements for the IEC Test Plug for NEXT, FEXT and Return Loss. So much so, most vendors use the tip from the DTX-PLA002 in their laboratories for testing jacks. Therefore, the best result will always be achieved using the DTX-PLA002, not the DSP-PM06.
- Your connector choice
Check with your vendor on their minimum length requirements. It will vary from vendor to vendor. Try getting your technicians to terminate some short links to verify the expected performance. Minimally compliant components will be an issue.
- Your termination technique
The quality of the termination will be critical. It will have to be perfect in order to avoid a fail or marginal passing result - assuming you have verified 2) above. Expect to see the occasional marginal pass on these short links due to variations in terminations and jacks. Marginal passes are considered a pass unless the contract specifies otherwise. If the contract does not permit marginal passes, you can expect to have to re-terminate some of the jacks in the installation due to variation in terminations, and less likely, replace some of the jacks. The very reason why you test 100% of the links.
Let's look at passing example result from a 5,1 m (17 ft) Class EA Permanent Link:
Notice how the limit line seems to have two colors, red and black. That's the 3 dB rule in action, where we ignore the result if the Insertion Loss is less than 3 dB.
Notice how the entire limit line is black and not red. That's the 4 dB rule in action, where we ignore the result if the Insertion Loss is less than 4 dB. In this example, the link is so short the Insertion Loss never reached 4 dB. That is why you see "i" next to the result in the summary screen above.
When you look at the NEXT plots above, you will observe that the NEXT traces follow the limit line - they are parallel to each other. Now take a moment to look at the NEXT plot below from a different link:
You will observe that the NEXT trace "drops off" around 290 MHz. This is an indication that the connector is not component compliant to ISO/IEC 11801. Re-terminating this jack is unlikely to yield a different result. Component choice is critical.