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RE: [softrock40] DDS spurs, was Got my 5.0....Now what do I need?

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  • S. Cash Olsen
    Bill and group, A fellow named Brian Davis has put together a very interesting document on spur pile-up in the DDS. If your interested in some of the dirty
    Message 1 of 27 , Jan 1, 2006
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      Bill and group,

      A fellow named Brian Davis has put together a very interesting document
      on spur pile-up in the DDS. If your interested in some of the dirty
      details of the DDS you might be interested in the following reference:

      http://members.aol.com/fpgastuff/dds_oddities.pdf


      Cash Olsen, KD5SSJ

      Kits to build Scotty's Spectrum Analyzer http://www.zianet.com/erg
      Scotty's Spectrum Analyzer website http://users4.ev1.net/%7Ewsprowls/
      Yahoo Builders Group http://groups.yahoo.com/group/spectrumanalyzer/

      -----Original Message-----
      From: softrock40@yahoogroups.com [mailto:softrock40@yahoogroups.com] On
      Behalf Of Bill Tracey
      Sent: Friday, December 30, 2005 10:14 PM
      To: softrock40@yahoogroups.com
      Subject: [softrock40] DDS spurs, was Got my 5.0....Now what do I need?


      I think what you are seeing is normal and is a fact of life with DDS's
      --
      they will generate spurs, and they will be dependent on the frequency
      the
      DDS is set to. I don't claim to understand all the details of the
      mathematics behind it, but I believe the root cause of the spurs are
      essentially round off errors in the DAC in the DDS generating the sin
      wave. As the DDS produces the sin wave it only has so many bits (10? in

      the case of a 9851) to represent the current value of the sin wav. The
      round off error on these bits is the root cause of the spurs. There are

      frequencies you can tune the DDS to where the round off error is less
      than
      others, and you will get fewer spurs.

      This is not fatal for an SDR - we've got 30-40 khz of DDS tuning
      flexibility with an SDR, one just needs to find a spot where the DDS
      spurs
      are minimal and then tune appropriately in software. The current SDR
      1000
      code has a spur reduction tuning algorithm that tunes to a minimal spur
      DDS
      point within about +/- 3khz of the desired DDS frequency and then varies

      the software tuning to compensate. This is based on some work Bob
      McGweir
      (N4HY) did to figure out where the minimal spur points for the SDR
      1000's
      DDS are (a 9854 I believe). More aggressive spur dodging is possible
      by
      mapping out where the spurs actually are and use that data to pick DDS
      frequencies.

      Cheers,

      Bill (kd5tfd)

      At 10:42 PM 12/30/2005, qrper723 wrote:

      >But I don't understand that the spurious occures or not as I change the

      >frequency of DDS. The spurious should occur constantly?
      >
      >73...hidehiko ja9mat






      Yahoo! Groups Links
    • qrper723
      Cash, Thanks for your info. I find that the DDS is not clean. I will study more in this new year holidays. I wish to express my gratitude for introducing
      Message 2 of 27 , Jan 1, 2006
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        Cash,

        Thanks for your info.
        I find that the DDS is not clean.
        I will study more in this new year holidays.

        I wish to express my gratitude for introducing literary treasures.

        hidehiko ja9mat

        > Bill and group,
        >
        > A fellow named Brian Davis has put together a very interesting
        document
        > on spur pile-up in the DDS. If your interested in some of the dirty
        > details of the DDS you might be interested in the following reference:
        >
        > http://members.aol.com/fpgastuff/dds_oddities.pdf
        >
        >
        > Cash Olsen, KD5SSJ
      • Bill Dumke
        Thanks, Cash, for the link. That looks so bad, I feel like going back to a Tuned Radio Frequency receiver. Bill WB5TCO
        Message 3 of 27 , Jan 1, 2006
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          Thanks, Cash, for the link.

          That looks so bad, I feel like going back to a Tuned Radio Frequency
          receiver.

          Bill WB5TCO

          S. Cash Olsen wrote:

          > Bill and group,
          >
          > A fellow named Brian Davis has put together a very interesting document
          > on spur pile-up in the DDS. If your interested in some of the dirty
          > details of the DDS you might be interested in the following reference:
          >
          > http://members.aol.com/fpgastuff/dds_oddities.pdf
          >
          >
          > Cash Olsen, KD5SSJ
          >
          > Kits to build Scotty's Spectrum Analyzer http://www.zianet.com/erg
          > Scotty's Spectrum Analyzer website http://users4.ev1.net/%7Ewsprowls/
          > Yahoo Builders Group http://groups.yahoo.com/group/spectrumanalyzer/
          >
          > -----Original Message-----
          > From: softrock40@yahoogroups.com [mailto:softrock40@yahoogroups.com] On
          > Behalf Of Bill Tracey
          > Sent: Friday, December 30, 2005 10:14 PM
          > To: softrock40@yahoogroups.com
          > Subject: [softrock40] DDS spurs, was Got my 5.0....Now what do I need?
          >
          >
          > I think what you are seeing is normal and is a fact of life with DDS's
          > --
          > they will generate spurs, and they will be dependent on the frequency
          > the
          > DDS is set to. I don't claim to understand all the details of the
          > mathematics behind it, but I believe the root cause of the spurs are
          > essentially round off errors in the DAC in the DDS generating the sin
          > wave. As the DDS produces the sin wave it only has so many bits (10? in
          >
          > the case of a 9851) to represent the current value of the sin wav. The
          > round off error on these bits is the root cause of the spurs. There are
          >
          > frequencies you can tune the DDS to where the round off error is less
          > than
          > others, and you will get fewer spurs.
          >
          > This is not fatal for an SDR - we've got 30-40 khz of DDS tuning
          > flexibility with an SDR, one just needs to find a spot where the DDS
          > spurs
          > are minimal and then tune appropriately in software. The current SDR
          > 1000
          > code has a spur reduction tuning algorithm that tunes to a minimal spur
          > DDS
          > point within about +/- 3khz of the desired DDS frequency and then varies
          >
          > the software tuning to compensate. This is based on some work Bob
          > McGweir
          > (N4HY) did to figure out where the minimal spur points for the SDR
          > 1000's
          > DDS are (a 9854 I believe). More aggressive spur dodging is possible
          > by
          > mapping out where the spurs actually are and use that data to pick DDS
          > frequencies.
          >
          > Cheers,
          >
          > Bill (kd5tfd)
          >
          > At 10:42 PM 12/30/2005, qrper723 wrote:
          >
          > >But I don't understand that the spurious occures or not as I change the
          >
          > >frequency of DDS. The spurious should occur constantly?
          > >
          > >73...hidehiko ja9mat
          >
          >
          >
          >
          >
          >
          > Yahoo! Groups Links
          >
          >
          >
          >
          >
          >
          >
          >
          >
          >
          >
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        • Bill Dumke
          Alberto, Where did you buy the AD9951 board? Bill WB5TCO
          Message 4 of 27 , Jan 1, 2006
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            Alberto,

            Where did you buy the AD9951 board?

            Bill WB5TCO

            Alberto I2PHD wrote:

            > An interesting comparison between the spurs produced by DDSs of the
            > 98xx family
            > against those of the 99xx family can be found here :
            > http://www.radioamatore.it/i0cg/add9951.html
            >
            > I have bought that DDS board and plan to use it in the future for my SDR.
            > It even has a function that optionally displays a frequency value one
            > fourth
            > of what actually is generated, to take into account a possible use of
            > a Johnson counter for I/Q generation.
            >
            > 73 Alberto I2PHD
            > -------------------------------------
            >
            > dmcmicro wrote:
            > > There is an interesting post in the Spectrum Analyizer group regarding
            > > DDS spurs.
            > > [snip]
            >
            >
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          • Alberto I2PHD
            ... Bill, if you go to the page I referred to in my message, that is: http://www.radioamatore.it/i0cg/add9951.html at the end of the page you will find this
            Message 5 of 27 , Jan 2, 2006
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              Bill Dumke wrote:
              > Alberto,
              >
              > Where did you buy the AD9951 board?
              >
              > Bill WB5TCO

              Bill, if you go to the page I referred to in my message, that is:
              http://www.radioamatore.it/i0cg/add9951.html

              at the end of the page you will find this sentence:

              If intersted to this project please write to giulianori@...

              Just do that. Ask for the PDF with the price list. You can buy the kit
              in various forms, PCB only, mechanical or optical encoder, cased or not
              cased, etc. etc.
              I bought it assembled, cased and tested, and received it in a couple of
              weeks. Now I have to find a way to discipline its clock with a GPS...

              73 Alberto I2PHD
            • Bill Dumke
              Alberto, I already did that, but haven t heard a response back. I will be patient. Bill WB5TCO
              Message 6 of 27 , Jan 2, 2006
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                Alberto,

                I already did that, but haven't heard a response back. I will be patient.

                Bill WB5TCO

                Alberto I2PHD wrote:

                >Bill Dumke wrote:
                >
                >
                >>Alberto,
                >>
                >>Where did you buy the AD9951 board?
                >>
                >>Bill WB5TCO
                >>
                >>
                >
                > Bill, if you go to the page I referred to in my message, that is:
                >http://www.radioamatore.it/i0cg/add9951.html
                >
                >at the end of the page you will find this sentence:
                >
                > If intersted to this project please write to giulianori@...
                >
                >Just do that. Ask for the PDF with the price list. You can buy the kit
                >in various forms, PCB only, mechanical or optical encoder, cased or not
                >cased, etc. etc.
                >I bought it assembled, cased and tested, and received it in a couple of
                >weeks. Now I have to find a way to discipline its clock with a GPS...
                >
                >73 Alberto I2PHD
                >
                >
                >
                >
                >Yahoo! Groups Links
                >
                >
                >
                >
                >
                >
                >
                >
                >
                >
                >
              • Alberto I2PHD
                ... Maybe he hasn t received your email. Try again. In the meantime I will send you in a private message the price list PDF that I received when buying the
                Message 7 of 27 , Jan 2, 2006
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                  Bill Dumke wrote:
                  > Alberto,
                  >
                  > I already did that, but haven't heard a response back. I will be patient.
                  >
                  > Bill WB5TCO
                  >

                  Maybe he hasn't received your email. Try again. In the meantime I will send you
                  in a private message the price list PDF that I received when buying the kit.

                  73 Alberto I2PHD
                • Duncan Munro
                  ... Alberto, I also sent a request for prices - would you be good enough to mail me too? -- Duncan Munro http://www.m0kgk.co.uk/
                  Message 8 of 27 , Jan 2, 2006
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                    Alberto I2PHD wrote:
                    > Bill Dumke wrote:
                    >
                    >>Alberto,
                    >>
                    >>I already did that, but haven't heard a response back. I will be patient.
                    >>
                    >>Bill WB5TCO
                    >>
                    >
                    >
                    > Maybe he hasn't received your email. Try again. In the meantime I will send you
                    > in a private message the price list PDF that I received when buying the kit.

                    Alberto, I also sent a request for prices - would you be good enough to
                    mail me too?

                    --
                    Duncan Munro
                    http://www.m0kgk.co.uk/
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