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4874Re: [perseus_SDR] Re: Amazing Preamp

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  • Roelof Bakker
    Apr 1, 2009
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      Hello Alberto,

      Thank you for the tuneable pre-amp information.
      I have been using similar amplifiers for years and they work very well
      indeed.
      There are some finer points to consider.

      At full gain the bandwidth can be very small, especially at LF.
      So small that it will effect the readability of a broadcast AM signal.
      At 400 kHz it is easy to peak the signal at either sideband of a NDB with
      1020 Hz modulation.
      This problem can be solved by placing a 1 to 5 K RF-gain potentiometer at
      the input.
      Reducing the gain to 20 dB, the bandwidth is large enough for all
      practical purposes.

      I have build one covering the 100 kHz to 1600 kHz range in four 1:2 bands,
      with a gain variation of smaller than +/- 2 dB. This was not a trivial
      task. See the attachment.

      The amplifier is just a buffer and the (noiseless?) gain results from the
      impedance transformation from low to high. Before PERSEUS, I used it to
      prevent overload in my SPM-30 selective level meter.
      With the excellent strong signal handling properties of PERSEUS, I do not
      longer use it.
      It has been used here also as a narrow band amplifier for an EWE antenna.

      Is it possible to use SPICE for noise figure simulation of this amplifier?

      Best regards,

      Roelof Bakker, pa0rdt
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