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Re: DDS-60 kit problems

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  • n3hkn
    I had a somewhat similar problem but with a PIC-El driving the DDS- 60. Upon start-up a bogus frequency function word seemed to be generated at times and I had
    Message 1 of 3 , Aug 1, 2006
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      I had a somewhat similar problem but with a PIC-El driving the DDS-
      60. Upon start-up a bogus frequency function word seemed to be
      generated at times and I had to reset the PIC software. Maybe you are
      giving the DDS a function word that it cannot act upon.

      Dick N3HKN

      PS: I found that spurious "stuff" made the DDS-60 unusable with my V6
      and V5. It works but signals in the 2 to 7 db above noise range
      competed with the spurs.


      --- In softrock40@yahoogroups.com, John Parkins <john@...> wrote:
      >
      > Hello All,
      >
      > I've just built a DDS-60 kit with the idea of linking with my v6
      board
      > but I'm having a few problems with it.
      >
      > The builders notes say there should be 5v p-p at the output of U4,
      > well I only have just under 1v p-p. Is this enough to drive the
      > AD5851? It wouldn't seem so as I have no output from the chip.
      >
      > It also only draws 50mA most of the time with none of the chips
      > getting hot, I know they do run hot. Every now and then though it
      will
      > suddenly draw about 150mA and the chips do get hot but I still don't
      > have an output.
      >
      > Unless the oscillator module is bad I can't see a problem with that,
      > after all it's just one chip and a cap, the supply voltage is
      correct.
      >
      > I've checked all the solder joints under a microscope and looked for
      > bridges but I can't find anything wrong. Is it just a bad oscillator
      > module giving low output?
      >
      >
      >
      > --
      > Best regards,
      > John mailto:kvp@...
      >
    • zs6buj
      Hi John The AD9851 remains cold if it does not get the 30 MHz reference oscillator signal, and also if the control word is invalid. When it is running
      Message 2 of 3 , Aug 1, 2006
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        Hi John

        The AD9851 remains cold if it does not get the 30 MHz reference
        oscillator signal, and also if the control word is invalid. When it
        is running properly, it dissipates more than 500 mW and gets quite
        hot.

        So I would check to see if you have the reference signal, and make
        sure the code word is good. Then check to see if you have rf out of
        pin 21. Finally, check to see if the AD8008 is amplifying the output
        signal. I'm only getting about 2.5 v p-p out, but it's easily enough
        to drive SRv6.

        My DDS-60 produces a resonably clean signal, but does have one or two
        small spurs. Neverthless, it's quite usable, and you can always shift
        frequency slightly. It is important to ensure the output looks into a
        resistive 50 ohm load, otherwise the signal quality is compromised.

        Good luck
        73
        Eric
        ZS6BUJ


        --- In softrock40@yahoogroups.com, "n3hkn" <n3hkn@...> wrote:
        >
        > I had a somewhat similar problem but with a PIC-El driving the DDS-
        > 60. Upon start-up a bogus frequency function word seemed to be
        > generated at times and I had to reset the PIC software. Maybe you
        are
        > giving the DDS a function word that it cannot act upon.
        >
        > Dick N3HKN
        >
        > PS: I found that spurious "stuff" made the DDS-60 unusable with my
        V6
        > and V5. It works but signals in the 2 to 7 db above noise range
        > competed with the spurs.
        >
        >
        > --- In softrock40@yahoogroups.com, John Parkins <john@> wrote:
        > >
        > > Hello All,
        > >
        > > I've just built a DDS-60 kit with the idea of linking with my v6
        > board
        > > but I'm having a few problems with it.
        > >
        > > The builders notes say there should be 5v p-p at the output of U4,
        > > well I only have just under 1v p-p. Is this enough to drive the
        > > AD5851? It wouldn't seem so as I have no output from the chip.
        > >
        > > It also only draws 50mA most of the time with none of the chips
        > > getting hot, I know they do run hot. Every now and then though it
        > will
        > > suddenly draw about 150mA and the chips do get hot but I still
        don't
        > > have an output.
        > >
        > > Unless the oscillator module is bad I can't see a problem with
        that,
        > > after all it's just one chip and a cap, the supply voltage is
        > correct.
        > >
        > > I've checked all the solder joints under a microscope and looked
        for
        > > bridges but I can't find anything wrong. Is it just a bad
        oscillator
        > > module giving low output?
        > >
        > >
        > >
        > > --
        > > Best regards,
        > > John mailto:kvp@
        > >
        >
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