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Cat5e Return Loss Pair 7,8

Cat5e Return Loss Pair 7,8

(OP)
thread575-506253: Cat5E Return Loss

We purchased some new cat5e cable and the first time using it, the cable failed on return loss only on pair 7,8 with margin -1.8dB at 29.1MHz on two separate lines. Of course I was thinking it was the cable and that it was poor quality. However, we used a third cable along with those; this failed also. I re-terminated the ends, on both sides to no avail (same outcome). The failure seems to be around 30mhz on all wires but ONLY on pair 7,8.  

Cable footage: 67ft.

Since all other pairs passed, I am going to leave it since 7,8 is not used. The only thing I can think of is that maybe the cables are kinked something in the middle or they are running near something that is causing interference. But I would imagine is that was the case that the other pairs would have the same issues.

Anyone have any thoughts?

 

RE: Cat5e Return Loss Pair 7,8

If you are installing this cable for your own use, then I wouldn't sweat it.  However, if you're installing for a paying customer, the installation really should meet whatever minimum specs you've agreed as the standard.  True that 7 & 8 may not be used today.  But what happens next year when they are used?
Mike

RE: Cat5e Return Loss Pair 7,8

Did the test equipment you were using pass calibration using whatever patch cords/connectors you did the readings with? Seems strange that both passed with the same issue, unless you reused the same connectors ......

RE: Cat5e Return Loss Pair 7,8

(OP)
mforrence:  I agree with you..

trvlr1:  I am using a Fluke DSP-4000 and it has been calibrated from Fluke...

I am thinking it is something within the ceiling... Maybe the wires are kinked or possibly they are next to some high voltage... I will have to look at where one of the "new" guys ran the wires..

 

RE: Cat5e Return Loss Pair 7,8

Most of the RL problems I've seen involved connectors or terminations.

RE: Cat5e Return Loss Pair 7,8

I would be tempted to redo the connections with the pairs swapped around so one set that passed as 1,2 or 4,5 became 7,8 to see what difference a pair with a different twist rate had on the test.

I think it unlikely that you'll find any kinks that would cause this without causing another pair to fail and with cable from the second manufacturer indicating the same it pretty well rules out bad cable.

All my stuff is 10/100 so this is speculation on my part.

Ed Fair
Give the wrong symptoms, get the wrong solutions.

RE: Cat5e Return Loss Pair 7,8

What brand was the cable?

RE: Cat5e Return Loss Pair 7,8

Some folks i have seen have been terminating solid cable with stranded connectors. This could cause serious problems when testing. Also causes long term connectivity issues.

Also, running across lighting ballast can cause issues as well.

I agree though, most return loss problems are faulty connectors.

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