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17218missing 70 dB

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  • xeloradio
    Jan 1, 2008
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      I have a question about what is displayed as dBm in Winrad,
      SpectrumLab, etc. Using a Softrock lite at 10.7 MHz, If I put in a
      calibrated signal of -40 dBm, the peak is shown at -70 dBm. I would
      expect to see both the -40dBm I put in, and a gain in power of 40 dB
      from the op-am voltage gain of 100 in the Softrock,,ie 0dBm total.

      details: the soundcard is a delta44, noise level displayed is around
      -125 dBm with no input. The overall system, preamp, mixer, softrock,
      works well for real signals. The calibrated signal is from an AN9951
      DDS with programmable power output from I0CG. A calculation of
      received signal strength from TV stations gives roughly the same 70 dB
      issue.

      Dave
      K0IMH
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