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30673Re: [softrock40] DDS-34 / Re: Kits and a Website

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  • Stelian Valceanu
    Feb 2, 2009
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      Thanks for your response, sounds really professional advice.
      it means that I still can use it, and as I see and you mention it, pretty much, the DDS has the spur far from the center freq. as all DDS's
      But I am curios about this new freq. generator with Si570 and I will do some research on it.
      AE6OR

      --- On Mon, 2/2/09, Mark J. Dulcey <mark@...> wrote:
      From: Mark J. Dulcey <mark@...>
      Subject: Re: [softrock40] DDS-34 / Re: Kits and a Website
      To: softrock40@yahoogroups.com
      Date: Monday, February 2, 2009, 3:33 AM

      ad9850 wrote:
      >
      > please avoid using this DDS34 for a RXTX. Have a look at the output
      > spectrum of this oscillator:
      >
      > http://softrock. raisdorf. org/images/ 80mx4.jpg
      > <http://softrock. raisdorf. org/images/ 80mx4.jpg>
      >
      > This an example for a center frequeny of 14.600 MHz to operate on 80m
      > around 3.650 MHz. In case of the receiver the various spurious signals
      > are just your personal problem. But in case of transmitting you will
      > be outside of the regulations regarding suprious signals and you will
      > surely disturb other services and hams.

      It might be possible to use that DDS with careful selection of output
      frequencies (DDS spurs are highly dependent on that, and some choices
      are MUCH worse than others), but that would require the use of a
      spectrum analyzer to study its output. Output filtering would also help,
      as the really bad spurs in the example are well away from the center
      frequency. That said, it would be a lot easier to use an Si570-based
      frequency source instead.

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