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Can You Build a Fiber Test Kit On a Budget?

Posted by timothy on from the un-un-explained-acronyms dept.

An anonymous reader writes "Have any Slashdot readers hacked together cheap test kits for fiber optic cable? More and more IT infrastructure is using multimode and single mode fiber optic cabling. Commercial test equipment is extremely expensive, running the gamut from a few hundred dollars for a basic light source, to tens of thousands for an OTDR. What equipment do you consider essential to your fiber kit? Is there a way to save costs when it comes to fiber test equipment? It is worth it to do so?"

7 of 53 comments (clear)

  1. Just get.... by b96miata · · Score: 3, Informative

    Two Media converters. If you can run ethernet over it, it's good.

    1. Re:Just get.... by juiceboxfan · · Score: 5, Informative

      Two Media converters. If you can run ethernet over it, it's good.

      That's true but only to a certain extent.
      It is possible that 1Gig ethernet will work fine on a cable that will not work or has a high error rate at 10Gig.

      You also will not be able to determine if a long run of single mode fiber has a multi mode patch in the middle of it (OTDR is the only thing that might give you that info).
      An Optical Power Meter is your best investment. That along with a good cleaning kit will give you the best results. A lot of "bad" fibers can be traced back to dirty connectors. _Always_ clean the fiber before plugging it into an interface - it is much easier to clean the fiber than it is to clean interface optics that have been contaminated by a dirty connector end.

      Beyond that if this is for in-house work just plan on using your fastest interface as a tester during downtime - setup the interface to expect loopback and put a short loopback patch at the far end. Run data through the cable and check for errors.

      Or as the parent said get a couple of cheap O/E converters for field work - not as good as a fast interface but better than a power meter alone.

    2. Re:Just get.... by mbeckman · · Score: 3, Informative

      Two Media converters. If you can run ethernet over it, it's good.

      Alas, this can give you very misleading results. Ethernet is such an error-tolerant protocol that you can "run it" over even a very poor fiber link. You'll get rotten performance, but most people won't notice right away, and won't know how to isolate the problem to the fiber link even if they do notice.

      One particularly insidious performance degradation occurs when only one fiber in a send-receive pair has high power loss: random spanning-tree packet storms that can take down an entire network. Even pros have trouble curing this kind of systemic problem.

      If you verify the optical integrity of your fiber network, then you'll be able to troubleshoot other components -- such as transceivers and pach cables -- much more easily (since these parts can be readily swapped out to check for failures). By far the single most common cause of campus LAN problems I see as a network engineer are defective but working fiber links.

      Sometimes it's just dirty connectors (cleaning fiber cables consistently every time you manipulate them is the best defense against this), but often it's poor installation quality, remedied by re-terminating high-loss connectors.

  2. Heh by Xtense · · Score: 2, Informative

    Try a flashlight!

    --
    "We are the music makers, and we are the dreamers of dreams [...]."
    1. Re:Heh by phreakngeek · · Score: 3, Informative

      Bad moderator! No cookie! The parent is NOT offtopic. A flashlight works for a basic transmission test. I was a fiber optic technician in a former life and after terminating the ends with connectors we would shine a maglite on one end and turn out the lights on the other and if we saw the "light at the end of the tunnel" we'd call it good. If you want to get fancy you're going to need an optical time domain reflectometer. Probably not the cheapest thing.

  3. You use this word, 'gambit...' by Khakionion · · Score: 4, Informative

    "running the gambit" I don't think it means what you think it means.

    --
    OMG! Wau!
  4. cheap "laser" detector... by ak_hepcat · · Score: 3, Informative

    There's a really cheap "laser" detector that nearly every tech carries, although you may have forgotten it.

    It's that camera on your cell-phone.

    Yup, in a pinch, you'll see a nice little purple dot appear on your screen if you've got IR coming down the fiber. Works well enough to identify active cables.

    You can also pick up a mag-lite->fiber adapter that'll shine visible down the line fairly cheap.

    --
    Support FSF: Stop thinking with your wallet, and think with your imagination. (cc/non-commercial)