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VSWR

5 posts by 3 authors in: Forums > CWNA - Enterprise Wi-Fi Admin
Last Post: May 29, 2014:
  • I just hit a section covering VSWR and it explains it well but failed to describe how to detect/test for VSWR. How can I test for VSWR and get readings? Is there a piece of hardware that can help with this?

    Just curious. Thanks in advance,

    Charlie

  • By Howard - edited: May 27, 2014

    For Ham radio bands there are numerous VSWR meters.   The same thing can be done with an RF Power Meter, a 4 port directional coupler, and two 50 Ohm terminators.

    I just finished some experiments with some Wi-Fi gear and a power meter.   Unfortunately the radio put out such a small power level to begin with that by the time the Reflected signal came back to the meter, it was too far low for the meter to measure accurately.

    Very telling and informative tests can be performed against antennas using a (RF) Network Analyzer.    These can display Return Loss graphs and Smith Charts as well.   All very interesting and good for comparing one antenna to another.

  • As Howard mentioned, it is easy to test in the ham bands. It is also much more necessary to test considering us ham operators like to make our own antennas.

    Not to mention, if we have a high swr and push 50 watts through it, it can back up in the transmitter and fry the finals in the radio, not good and costly. That reminds me, I lent me VHF swr meter out and need to get it back hehe.

    As for wifi, most of the equipment we use is already set and should be properly set with a good vswr.

  • I have seen a few Wi-Fi radios burn up because they didn't have their antennas connected.    You wouldn't necessarily expect that with their low power, relative to Ham radios, but it can happen just as it can with bigger radios.

    The biggest issues that I have seen involve nonsense band and gain  claims by antenna manufacturers.   Also frequency (sensitivity) shifts greater than 100 MHz due to the dielectrics (plastics) adjacent to an antenna.   A network analyzer works well in this case.

    This does not mean that you should remove the plastics around your antennas.   Properly designed antennas account for this in their design and removing the plastic will only de-tune the antenna.

  • Thanks guys for your input. Just something that sparked my curiosity. Btw, any of you fellows got some good CWNA notes/memorable mentions? 

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