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Re: DDS-60 kit problems

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  • 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 1 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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