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6335Re: Big signal at 0 Hz even with SR40 is off

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  • n3hkn
    Oct 1, 2006
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      I switched off the spread pectrum BIOS option in my "home made" PC
      and the width of the noise spike is now vey narrow. Looks like almost
      a single frequency carrier.

      Dick N3HKN

      --- In softrock40@yahoogroups.com, Marco IK1ODO <ik1odo@...> wrote:
      > At 21.19 30/09/2006, you wrote:
      > >This is an artifact from the sound card which was not intended to
      > >digitize below 10~20 Hz. It's a kind of "noise" from the ADC
      > >to digital converter).
      > >
      > >It is not 60 Hz line hum, which can be easily seen on zoomed
      > >spectrograph display at 60, 120 , 180 Hz and also at negative
      > >frequencies. Rather, the SDR software treats as single signal, you
      > >can hear it as a carrier as you tune across it.
      > >
      > >73,
      > >
      > >João De Marco, PY2WM
      > Also, soundcards have significant noise at low
      > frequencies. It's called 1/f noise since it increases decreasing
      the frequency.
      > To give a figure, the Audiophile 192 has a 30dB
      > noise increment going down from 1000Hz to 20Hz.
      > This is intrinsic, and independent from PC noise
      > and hum (that are present too in a typical setup, of course).
      > There would be also a peak at 0Hz due to DC
      > imbalance of the ADC inputs, but the ADCs used in
      > 24bit souncards have an internal high pass filter
      > cutting under 1 or 2Hz, suppressing that.
      > 73 - Marco IK1ODO
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