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Measuring IMD of a balanced loop amplifier

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  • John McKee
    Has anyone measured IMD of a balanced loop amplifier? The main thing I m trying to figure out is how to couple the test signals into the balanced amplifier
    Message 1 of 3 , Mar 8, 2011
      Has anyone measured IMD of a balanced loop amplifier? The main thing I'm trying to figure out is how to couple the test signals into the balanced amplifier input from a 50 Ohm unbalanced source.
      Thanks - John WB4OFT


      [Non-text portions of this message have been removed]
    • Jack Smith
      I use a North Hills balun for measurements of balanced amplifiers, but a home brew balun should work as well. Of course, it should be checked to verify the
      Message 2 of 3 , Mar 8, 2011
        I use a North Hills balun for measurements of balanced amplifiers, but a
        home brew balun should work as well.

        Of course, it should be checked to verify the balun does not contribute
        to the IMD test floor. This can be a problem when the amplifier has an
        OIP2 > +100 dBm and OIP3 > +50 dBm.

        Jack K8ZOA
        www.cliftonlaboratories.com


        On 3/8/2011 3:42 PM, John McKee wrote:
        >
        >
        > Has anyone measured IMD of a balanced loop amplifier? The main thing
        > I'm trying to figure out is how to couple the test signals into the
        > balanced amplifier input from a 50 Ohm unbalanced source.
        > Thanks - John WB4OFT
        >
        > [Non-text portions of this message have been removed]
        >
        >


        [Non-text portions of this message have been removed]
      • Chris Trask
        ... For a loop amplifier having a very low input impedance and a balanced input, I have a 4:1 BalBal transformer with a balanced L-pad that is tailored to the
        Message 3 of 3 , Mar 8, 2011
          >
          > Has anyone measured IMD of a balanced loop amplifier? The main thing I'm
          > trying to figure out is how to couple the test signals into the balanced
          > amplifier input from a 50 Ohm unbalanced source.
          >

          For a loop amplifier having a very low input impedance and a balanced
          input, I have a 4:1 BalBal transformer with a balanced L-pad that is
          tailored to the amplifier input impedance. I use a similar arrangement for
          making noise figure measurements, except that the transformer is a 4:1 UnBal
          and I carefully determine the power loss so as to correct the NF
          measurement.


          Chris Trask
          N7ZWY / WDX3HLB
          Senior Member IEEE
          http://www.home.earthlink.net/~christrask/
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