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10486Re: [loopantennas] Measuring very small AC resistances

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  • Richard (Rick) Karlquist
    Feb 12, 2014
      On 2/12/2014 7:34 PM, John Maxwell wrote:

      > And it occurred to me: I have no idea how to measure _any_ AC
      > resistance (as distinct from impedance), let alone the sub-ohm values
      > he's talking about in that context.
      >
      > A few minutes work with Google turned up this:
      >
      > http://www.tnlc.ncsu.edu/files/testing/manuals/ImpedanceMeasurementHandbookRev3.pdf
      >
      > which looks to be a decent introduction to the subject; I'm digesting
      > it now, but I thought I'd ask if anyone has any advice/pointers/lore on
      > the subject.

      Forget about this handbook. What you want to do to
      measure a low impedance is to use a TWO port network
      analyzer (not a one port NA or an impedance analyzer)
      and connect the ports to an SMA tee. Connect your DUT
      at the third port of the SMA tee. By measuring S21,
      it is possible to work backwards and calculate the
      impedance on the 3rd port. This technique works
      down to extremely low impedances. In some cases,
      you may want to replace the SMA tee with a more
      precision fixture that puts the DUT in shunt with
      a through line.

      Full disclosure: I work for Agilent doing advanced network
      analyzer R&D...

      until March 14, when I will be retiring.

      Rick Karlquist N6RK
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