6335Re: Big signal at 0 Hz even with SR40 is off
- Oct 1, 2006I 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.
--- In firstname.lastname@example.org, 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.
> >João De Marco, PY2WM
> Also, soundcards have significant noise at low
> frequencies. It's called 1/f noise since it increases decreasing
> 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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