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Re: [softrock40] 30.5KHz Harmonics on all bands, SoftRock Ensemble II

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  • Randall family
    Does the frequency move about a bit with time or are the harmonics always on the same frequency? Switching power supply noise moves around a bit with
    Message 1 of 6 , Sep 9, 2013
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      Does the frequency move about a bit with time or are the harmonics always on the same frequency?  Switching power supply noise moves around a bit with temperature changes etc because of the RC oscillator setting the frequency are not real stable.  Computer monitor noise is frequency stable because the horizontal update rate comes from a quartz crystal.  I seem to remember 30.5KHz being used in some computer displays.  Switching supplies usually run above 50KHz
       
      If your monitor is powered separate from the computer, try turning off the monitor while listening to a harmonic.  If noise goes away you know the source.
       
      Put a small 1 turn loop, about 5 cm diameter, at the end of a 3 meter piece of coax.  The other end of the coax goes into the softrock receiver.  "sniff" everything electronic in the area with the loop & see if something is radiating EMI.  Small loops like this have proved useful in my job for finding WHY my new creation is failing EMI testing.
       
      Also note that devices that create EMI below the legal level can interfere with sensitive amateur receivers. 
       
      Bruce Randall  NT4RT
       
      ----- Original Message -----
      From: Alan
      Sent: Monday, September 09, 2013 2:44 AM
      Subject: Re: [softrock40] 30.5KHz Harmonics on all bands, SoftRock Ensemble II

       


      ----- Original Message -----
      Subject: [softrock40] 30.5KHz Harmonics on all bands, SoftRock Ensemble II

      > Hello! Just got my softrock working with SDR# and a long wire at 24'.
      >
      > I have a problem that I would welcome thoughts on. Across all bands, I'm seeing harmonics, spaced evenly every 30.5KHz. Every
      > second harmonic (call them the even ones) is about 2x as strong as its neighbors (the odd ones). Any idea what the source of
      > this noise might be?
      >
      > I've tried shielding the softrock from the PC, but to no effect. If I disconnect my antenna, the level of the harmonics drops
      > about 30db, but you can still see them in the spectrum display.
      >

      Curt,

      These sort of signals may come from almost any electric device. PSU?
      It really is a matter of elimination, switching things off. If its in the room a really short wire may show it strongly.
      Sometimes a portable radio will show bad sources.
      A short wire like you describe is not the best, coax to a remote antenna is better.

      73 Alan G4ZFQ

    • carpentercurt45
      Bruce and Alan: Thanks for the replies. With your help, I ve found the problem (my harmonics are coming from another computer that s located not far from my
      Message 2 of 6 , Sep 9, 2013
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        Bruce and Alan:

        Thanks for the replies. With your help, I've found the problem (my harmonics are coming from another computer that's located not far from my softrock setup). The on/off process of elimination got me in the ball park, and the 5cm sniffer approach confirmed the source.

        With the problem diagnosed, I can move on now to seeing if I can cure it.

        Thanks to you both again for the help.

        Curt Carpenter

        --- In softrock40@yahoogroups.com, "Randall family" <brandall@...> wrote:
        >
        > Does the frequency move about a bit with time or are the harmonics always on the same frequency? Switching power supply noise moves around a bit with temperature changes etc because of the RC oscillator setting the frequency are not real stable. Computer monitor noise is frequency stable because the horizontal update rate comes from a quartz crystal. I seem to remember 30.5KHz being used in some computer displays. Switching supplies usually run above 50KHz
        >
        > If your monitor is powered separate from the computer, try turning off the monitor while listening to a harmonic. If noise goes away you know the source.
        >
        > Put a small 1 turn loop, about 5 cm diameter, at the end of a 3 meter piece of coax. The other end of the coax goes into the softrock receiver. "sniff" everything electronic in the area with the loop & see if something is radiating EMI. Small loops like this have proved useful in my job for finding WHY my new creation is failing EMI testing.
        >
        > Also note that devices that create EMI below the legal level can interfere with sensitive amateur receivers.
        >
        > Bruce Randall NT4RT
        >
        > ----- Original Message -----
        > From: Alan
        > To: softrock40@yahoogroups.com
        > Sent: Monday, September 09, 2013 2:44 AM
        > Subject: Re: [softrock40] 30.5KHz Harmonics on all bands, SoftRock Ensemble II

        > These sort of signals may come from almost any electric device. PSU?
        > It really is a matter of elimination, switching things off. If its in the room a really short wire may show it strongly.
        > Sometimes a portable radio will show bad sources.
        > A short wire like you describe is not the best, coax to a remote antenna is better.
        >
        > 73 Alan G4ZFQ
        >
      • Bill Cromwell
        ... Hi Curt, I had a nasty pc power supply problem here. Some of them do not have the power line filter parts installed to save a few pennies. If you remove
        Message 3 of 6 , Sep 9, 2013
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          On 09/09/2013 10:17 AM, carpentercurt45 wrote:
          >
          > Bruce and Alan:
          >
          > Thanks for the replies. With your help, I've found the problem (my
          > harmonics are coming from another computer that's located not far from
          > my softrock setup). The on/off process of elimination got me in the
          > ball park, and the 5cm sniffer approach confirmed the source.
          >
          > With the problem diagnosed, I can move on now to seeing if I can cure it.
          >
          > Thanks to you both again for the help.
          >
          > Curt Carpenter
          >
          Hi Curt,

          I had a nasty pc power supply problem here. Some of them do not have the
          power line filter parts installed to save a few pennies. If you remove
          the power supply and look inside at the board near the power connector
          you may see an empty area where some inductors and capacitors should be.
          In mine there were two wire jumpers and no filter parts! I installed the
          parts and that power supply got civilized right away.

          Another option is to buy a connector with the filter built in and
          replace the one that is in your power supply with new one. Those are
          available in numerous places like Mouser and Digikey for not very much
          money. Sometimes you can find those connectors in thge junk boxes at
          hamfests. I bought two of them for fifty cents each at one hamfest!

          Good luck taming your power supply.

          73,

          Bill KU8H
        • carpentercurt45
          Bill: Thanks -- I ll keep that in mind. I have a few snap-on filters in my junk somewhere, and I ll give those a try. Right now, I m just enjoying not having
          Message 4 of 6 , Sep 9, 2013
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            Bill:

            Thanks -- I'll keep that in mind. I have a few snap-on filters in my junk somewhere, and I'll give those a try. Right now, I'm just enjoying not having those huge spikes all over the spectrum (and knowing that the problem isn't some botch in my Softrock construction...) :-)

            The computer that's the source is an old one, and I can live without it being up for a while!

            Regards,
            Curt

            > Hi Curt,
            >
            > I had a nasty pc power supply problem here. Some of them do not have the
            > power line filter parts installed to save a few pennies. If you remove
            > the power supply and look inside at the board near the power connector
            > you may see an empty area where some inductors and capacitors should be.
            > In mine there were two wire jumpers and no filter parts! I installed the
            > parts and that power supply got civilized right away.
            >
            > Another option is to buy a connector with the filter built in and
            > replace the one that is in your power supply with new one. Those are
            > available in numerous places like Mouser and Digikey for not very much
            > money. Sometimes you can find those connectors in thge junk boxes at
            > hamfests. I bought two of them for fifty cents each at one hamfest!
            >
            > Good luck taming your power supply.
            >
            > 73,
            >
            > Bill KU8H
            >
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