Cat5E Return Loss

[randall5]

We are installing a Cat 5E cabling system. A large portion of the cables are installed in PVC consuit under the slab floor to recessed floor boxes. Upon testing, many of the cables failed the test on return loss. When viewing the test data, it appears to spike at about 5 feet from the tester at the WAO end. What causes Return Loss failure and how do you correct it?

Randy

 

[daronwilson]

Return Loss is the power of the reflected signal, which is derived from the Reflection Coefficient of the circuit. In short, the better the impedance matching, the lower the reflected energy and the higher the return loss. In this measurement, higher is better.

Generally any impedance mismatch in the circuit will result in signal reflections. Unless the cable was physically damaged on installation, the impedance mismatch is more likely in the termination hardware. If your tester is saying about 5' from the test unit, and you are using a patch cable from the test unit to the wall outlet, then I would certainly look at the plug/jack combination of the wall outlet as the most likely problem.

I would first inspect the modular jack, and probably reterminate or replace it, then test again. Perhaps pick one bad circuit and carefully replace components/terminations one at a time, then test again until you locate whatever it is that seems to be causing you the problem.

Good Luck!
It is only my opinion, based on my experience and education...I am always willing to learn, educate me!
Daron J. Wilson, RCDD
daron.wilson@lhmorris.com

 

[Bobg1]

What Daron said.
Plus make sure the patch cable you are using with your tester is good quality cat5e also. If not you will not get accurate results.

 

[randall5]

Guys, thanks for the responses. We did try using different components and switching the tester. Also, we are using the patchcords built into the tester. (Permanent Link Adapter) We also terminated the cable onto jacks from a different manufacturer and got the same result. Is this most likely a cable problem as opposed to a hardware issue. I have read some tech papers on the subject and it seems that there is no clear indication of how to isolate the problem, so I was hoping for someone who has encountered this and what they did to fix it.

Randy

 

[daronwilson]

Well you are on the right track, next I'd pull the cable out and replace it. Very rarely do we find damaged cable in conduit pulls, unless it was really abused during installation.

Were it me, because I like to know, I would carefully repull the cable and examine the old cable, probably even reterminate and test it out on the floor if I didn't see anything obvious. But..a good kink in the cable can certainly upset the impedance enough to do this, perhaps you will locate something physical and easy to spot like that.

Good Luck, let us know what you find, I'm curious as well.

It is only my opinion, based on my experience and education...I am always willing to learn, educate me!
Daron J. Wilson, RCDD
daron.wilson@lhmorris.com

 

[cxrs01]

Look at this URL

http://www.cabletesting.com/NR/rdonlyres/etjhnen4foxrvt6u53v

5ip42gffrohvs5fdwa66mcgexdovlo2lanwwjrmogwrq2mlabmt6idbrn7mw
rjrctalarkfb/Field+_Test_Copper_+Cabling_WP_150dpi.pdf.

It gives a lot of good info on testing cablws. Maybe it will be some help. Pay close attention to your termination.

 

[62838]

randall5 before you pull the cable out please check you tester by connecting the tester Patch cord to the injector and test it, if it connected in to the tester and injector use a dual femal to connect both patch cords of thr tester and injector and then tes, it seems that your problm is with the tester, there is a way ofre;lacing the tester cable by openning the end, mustly the cable is connected by screws.