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Re: [softrock40] Re: Big signal at 0 Hz even with SR40 is off

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  • Marco IK1ODO
    ... 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
    Message 1 of 21 , Oct 1, 2006
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      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 (analog
      >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
    • n3hkn
      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
      Message 2 of 21 , 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
        (analog
        > >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
        >
      • Sam Morgan
        ... just curious, how new is your motherboard? I guess if u told me what cpu it s running that might also help. I m thinking everything I have it to old, I
        Message 3 of 21 , Oct 1, 2006
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          n3hkn wrote:
          > 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.
          >
          just curious, how new is your motherboard? I guess if u told me what cpu it's
          running that might also help. I'm thinking everything I have it to old, I don't
          remember seeing anything like that in the settings on any of them.

          --
          GB & 73's
          KA5OAI
          Sam Morgan
        • Alberto I2PHD
          Marco IK1ODO wrote: 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
          Message 4 of 21 , Oct 1, 2006
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            Marco IK1ODO wrote:
            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.
              
            Marco is quite right, as demonstrated by these two screen captures. The first is the digitizing process carried on by Adobe Audition, using the onboard AC'97 chipset, with the card input left open. As you can easily see, there is a substantial DC offset produced by the ADC.



            The same chipset produced this strong zero frequency peak, entirely caused by the DC offset :


            73  Alberto  I2PHD

          • John
            I am playing with mine also. Maybe those of us with Cheap sound cards fine this, I do. Two things: If just a single frec it is most likely the math finding a
            Message 5 of 21 , Oct 1, 2006
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              I am playing with mine also.

              Maybe those of us with “Cheap” sound cards fine this, I do.

               

              Two things:

                If just a single frec it is most likely the math finding a 0 hrz tone.

                If two peaks close together it may be 60 hz pickup in the audio cord.&nbs

              (Message over 64 KB, truncated)

            • Cecil Bayona
              ... The picture of the single stand alone spike is what one of PC s has, the other four have the typical spike with noise going out quite a ways slowly and
              Message 6 of 21 , Oct 1, 2006
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                Alberto I2PHD wrote:
                > Marco IK1ODO wrote:
                >> 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.
                >>
                > Marco is quite right, as demonstrated by these two screen captures. The
                > first is the digitizing process carried on by Adobe Audition, using the
                > onboard AC'97 chipset, with the card input left open. As you can easily
                > see, there is a substantial DC offset produced by the ADC.
                >
                >
                >
                > The same chipset produced this strong zero frequency peak, entirely
                > caused by the DC offset :
                >
                >
                > 73 Alberto I2PHD
                >
                >
                The picture of the single stand alone spike is what one of PC's has, the
                other four have the typical spike with noise going out quite a ways
                slowly and meeting the noise floor about 2-3 KHz away.

                On most PC's that is a rare item most people don't have that kind of
                response.

                --

                Cecil
                KD5NWA
                www.qrpradio.com www.hpsdr.com

                "Sacred Cows make the best Hamburger!" Don Seglio Batuna
              • n3hkn
                Spread Spectrum... CPU=AMD 2600 ECS is motherboadr mfg. KT-600 Dick N3HKN It is about 2 years old--- In softrock40@yahoogroups.com, Sam Morgan ... PC ...
                Message 7 of 21 , Oct 2, 2006
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                  Spread Spectrum...

                  CPU=AMD 2600
                  ECS is motherboadr mfg. KT-600

                  Dick N3HKN


                  It is about 2 years old--- In softrock40@yahoogroups.com, Sam Morgan
                  <ka5oai@...> wrote:
                  >
                  > n3hkn wrote:
                  > > 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.
                  > >
                  > just curious, how new is your motherboard? I guess if u told me
                  what cpu it's
                  > running that might also help. I'm thinking everything I have it to
                  old, I don't
                  > remember seeing anything like that in the settings on any of them.
                  >
                  > --
                  > GB & 73's
                  > KA5OAI
                  > Sam Morgan
                  >
                • Sparkes, John
                  Yep, same here. Big peak at 0 with no inputs to D44. Totally goes away when 9V battery powered SR40V6 on-line. John JX________________________________From:
                  Message 8 of 21 , Oct 2, 2006
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                    Yep, same here. Big peak at 0 with no inputs to D44. Totally goes away when 9V battery powered SR40V6 on-line.
                     
                    John JX


                    From: softrock40@yahoogroups.com [mailto:softrock40@yahoogroups.com] On Behalf Of Mike
                    Sent: Sunday, 1 October 2006 00:41
                    To: softrock40@yahoogroups.com
                    Subject: [softrock40] Re: Big signal at 0 Hz even with SR40 is off

                    The big signal is 60 Hz pickup. The solution is isolation transformer
                    (s), in the audio lines and/or at the antenna connection. Running on
                    battery can help to, or a non-grounded power cube. These will help to
                    reduce the mountain at the center but may not eliminate it entirely.

                    73 - Mike WA8BXN

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