A $100 Cat5 tester?

January 4, 2007 12:44 PM

Please recommend a cat5/RJ45/network cable tester to troubleshoot existing wiring.

I have three jacks (out of 25) that aren't working right; I don't know if they have ever worked right. I'd like to know whether the cable between the switch and the wall plate is broken, whether it is simply miswired, or whether I am missing something else.

I can't get inside the plates at the switch without moving heaven and Earth, there's not enough slack in the wire at the walljack end for me to visually inspect whether the wires appear correct (visually), and trying a crossover cable at one end (the obvious first guess) provides no relief.

Also, if I can get a good tester (within my budget) that will tell me whether the wiring can handle gigabit, that's a bonus.

Budget is about $100.

posted by Kwantsar to computers & internet (9 comments total)

Used Tektronix TDRs can sometimes be found for $300 or so and will verify / localize problems on concealed cabling. eBay territory.

Here's a non-Tek TDR that is about to close. I am unfamiliar with it, but TDR is the way to go:


http://cgi.ebay.com/TDR-Cable-fault-identifier_W0QQitemZ170065322290QQihZ007QQcategoryZ97139QQrdZ1QQcmdZViewItem


Good luck
posted by FauxScot at 1:19 PM on January 4, 2007

Be aware that a TDR (Time Domain Reflectometer - one of my favorite names ever) will be much more accurate than a standard cable tester, as it sends waves down the wire, and listens for reflections to tell you the distance to the fault, what the fault most likely is, etc.

Fluke makes awesome stuff, but it will probably be expensive.

A non-TDR cable tester will require you to have something plugged on both sides, and will likely only tell you pass or fail , and not where the issue resides.
posted by stovenator at 1:30 PM on January 4, 2007

I dunno.. TDR seems like overkill when you can get this for $10. Hard to tell from the picture that the tester does RJ45, rather than just BNC, but they seem very emphatic in all the text. I've dealt with that company before, and they are reliable, I might still ask to make sure though..
posted by Chuckles at 1:39 PM on January 4, 2007

Chuckles.... 10 bux gets you continuity, only. Useful, but not if you have a problem in a wall.

TDR tells you how far away the problem is. Lovely little tools. One of my favorites, too.
posted by FauxScot at 1:48 PM on January 4, 2007

Ya.. There was this story that used to be told about A prof. of mine. Apparently he was part of the Polish resistance during WWII, and one common task was cutting Nazi telegraph lines. After the lines were cut, they would be bombarding the location within a couple of minutes, and he couldn't understand how they were able to pinpoint the spot so quickly. It was said that trying to solve the puzzle inspired him to study electromagnetism.

I should also add, "Biot-Savart is not a law! It is a formula" and "This is not a Roman orgy."
posted by Chuckles at 2:25 PM on January 4, 2007

Wouldn't a cable tester with a tone generator work for this?

like this
posted by crypticgeek at 2:32 PM on January 4, 2007

I think you want something like this LAN tester.

The price is a little higher than you wanted, but not by much. The unit can tell you about "shorts, opens, miswires, reversals and split pairs".

I have one and it's great. FWIW, most of the time I don't care where the wire is bad. I care to know IF it's bad, because if so, I need to replace it (or abandon it for oh, wireless or something) anyway.
posted by disclaimer at 5:12 PM on January 4, 2007

disclaimer did an exceptional job of reading my mind. Everyone else, thank you very much. I have much to learn about Time Domain Reflectometry.
posted by Kwantsar at 7:42 PM on January 4, 2007

call the people who manage the wall-to-switch and further along connection and tell them to "fix it!". :) the very easiest way to test is to use a 'known good machine' with a 'known good PC-to-wall' cable and test. upload some stuff, download some stuff, does it work as well as the 'good' connection? if not, call in the problem and tell them that you've tested with a known good machine with a known good drop and make *them* fix the problem. if it works as expected, then it's either the particular machine or the drop cable. if they come and test from the wall to the switch and everything is good, then it's the switchport, make them move your connection to a different switchport.

the $$ cable testers are for the sub-contractors who are installing the cable who don't have access to the error counters on the switch/computer side. if your connection works at all, then the error counters on either end of the link will be more than enough to determine whether the link is good or not. unless the wall-to-switch wiring is your concern, don't worry about testing equipment, you don't need it.

(zengargoyle is network administrator for 70,000+ users at a large U.S. university. in general, testing from wall to switch is *not* something that enduser should be worried about.) on the other hand, if wiring is your thing, move a known good computer/drop combination to the wall-jack in question, test looking for errors, if errors, swap with a known-good port on the switch, if still errors, it's the wiring, if no errors, it's the switch port. buying some expensive test equipment is overkill for someone who isn't responsible for the wiring.
posted by zengargoyle at 11:27 PM on January 4, 2007