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Re: [loopantennas] Re: Trask Active antenna design #2 tested (addendum)

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  • Steve Ratzlaff
    Just for completeness, I should mention that I use 3 and 4 MHz tones for all my IMD testing, and for these circuits, set for -10 dBm each tone at the output,
    Message 1 of 1 , Jun 10, 2007
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      Just for completeness, I should mention that I use 3 and 4 MHz tones for all
      my IMD testing, and for these circuits, set for -10 dBm each tone at the
      output, as seen on the spectrum analyzer.
      Steve
      ----- Original Message -----
      From: "Chris Trask" <christrask@...>
      To: <loopantennas@yahoogroups.com>
      Sent: Sunday, June 10, 2007 3:14 PM
      Subject: Re: [loopantennas] Re: Trask Active antenna design #2 tested


      > Prior to breadboarding this, I went back and forth with the PSpice
      > models to determine where the discrepancies. I went so far as to remove
      > the
      > 2N2907 emitter bypass capacitor, but that resulted in a loss of -6dB. So,
      > I
      > rearranged the input to place the 50-ohm termination ahead of the blocking
      > capacitor, changed the blocking capacitor to 10pF, then added a 100K
      > resistor from the JFET gate to ground, and then I saw the -3dB of midband
      > loss.
      >
      > So now I see why my model gain and your measured gain are so far apart
      > this last time around. I was measuring the gain grom the JFET gate to the
      > output, and you're measuring it from the 50-ohm load AHEAD of the 10pF
      > capacitor to the output.
      >
      > That being the case, I now have to wonder what effect this 10pF
      > coupling
      > capacitor has on the IMD performance. So, could you take both of these
      > circuits, replace the 10pF capacitor with 0.1uF, and then measure again?
      > My
      > suspicion here is that the JFET drain voltage in my circuit is feeding
      > back
      > to the gate and combined with your 10pF coupling capacitor is causing the
      > IMD performance to degrade.
      >
      >
      > Chris
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