Clean DDS as a LO replacement?

Discussion in 'Homebrew and Kit Projects' started by N8YX, Apr 8, 2019.

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  1. N8YX

    N8YX Ham Member QRZ Page

    Who's investigated using a DDS as a heterodyne/local oscillator signal source, replacing its crystal oscillator counterpart?

    I'm looking at an upper range of 45MHz. The AD9851 will generate a signal at that frequency but it begins to develop spurs above 20MHz.

    Is there a counterpart DDS which will develop a clean signal at 45MHz? Or another uncomplicated approach, such as running a lower-frequency DDS into a doubler then using a band pass filter on its output?
  2. KL7AJ

    KL7AJ Ham Member QRZ Page

    I've built numerous direct conversion receivers using the DDS as the local oscillator.
  3. AD5GH

    AD5GH XML Subscriber QRZ Page

  4. AJ4SN

    AJ4SN Ham Member QRZ Page

    I have used both DDS and the Si570. The Si570 was much quieter in my homebrew receiver.

  5. KX4OM

    KX4OM Ham Member QRZ Page

    The Si5351A is popular. Some have used it as a very inexpensive "drop-in" replacement for the AD9850/51 devices where the LO is a separate board. It works up to 200 MHz, and it has 3 programmable outputs. Lots of microcontroller code and libraries online for it. It does not have the spurs that the AD98xx devices have, but the tradeoff is phase noise. The Si5351A can generate LO and HFO (or USB and LSB BFO) signals, if desired from the same device. See for info.

    Ted, KX4OM

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