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4410Re: [linrad] Fwd: [softrock40] Ver 7 28Mhz preamp? Yes

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  • Giancarlo
    May 6, 2006
      --- In softrock40@yahoogroups.com, KD5NWA <KD5NWA@...> wrote:
      >
      > I notice that the amplifier has a attenuation pad on it's output,
      > rendering the impedance problem to be moot.
      >
      > I have some MMIC's that I'm planning to experiment with for the
      upper
      > bands and use a SoftRock, since their gain is a little excessive I
      > was planning on using a 3dB to 6dB pad, which will help setting
      the
      > impedance of the filter at a more stable value
      >

      Hi Cecil,

      Regarding the W7AAZ Post-Mixer amplifier in the CDG2000 has a 50 ohm
      output for the very simple reason to permit a testing point. The
      4xJ310 output is 200 ohm. This would make an easier matching to the
      post amplifier xtal filter Zin = 500 ohm. The amplifier has around
      14dB gain and very low noise. The output IP3 is lower than expected,
      measured at +27dBm. Probably this is due to the changing input Z of
      following xtal filter. Adding an attenuator will reduce this effect
      and increase the OIP3 before the filter.
      I am sure that in the SoftRock an OIP3 of +27dBm of a preamplifier
      will be more than necessary.

      73

      Gian
      I7SWX
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