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vswr?

3 posts by 3 authors in: Forums > CWNA - Enterprise Wi-Fi Admin
Last Post: May 5:
  • When reading chapter 4, I came across the section on vswr. Most of it made sense, however ... How can you tell the vswr of cable when its cat 5/6? I haven't been able to find where there is a listing for the ohm rating of standard cable.

  • By Howard - edited: May 13

    I can't believe I missed this question so many years ago.

    The best way to test signal quality on an Ethernet cable is to use a dedicated cable tester.   Many cable parameters are tested including resistance and for NEXT (Near End Cross Talk).   These testers are expensive and can cost thousands of dollars.   Usually any certified installer would carry this gear to any installation site.   Simple automated continuity testers, often available for less than $20, are not adequate. 

    Due to the difficulties of making certifiable connections, I no longer attach my own connectors for gigabit cables.  I buy preasembled ones of the correct length.  IMHO it's worth the extra cost. 

    Normally, an Ethernet cable would not be used for transmitting a signal meant to be (directly) radiated.  However, just like any decent cable, it does have an impedance specification.    Both category Five-E and Six have a nominal impedance of 100 ohms, but the "slop" in the specification is much looser than a  communications grade, coaxial cable, would have.   The range for Cat-6 is plus or minus 10 %, which equates to 90 to 110 ohms.   That is still much better than CAT-5 impedance limits, which is 30 %, which would mean from 70 to 130 Ohms,

    Follow this link for further information:

    http://www.engineeringradio.us/blog/2010/09/category-5e-cable-in-aesebu-applications/

  • Not much to say other than what Howard already mentioned. If you do want to learn more about SWR and RF in general (which will help with wifi understanding), I would look at amateur radio material. There is some really good info there that can help with the RF theory understanding if you are having difficulty. That is something most people, in my experience, will not suggest and think about. Just a friendly piece of advice that could be helpful.

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