Before I forget, I would NOT use a schmitt trigger gate to do the
comparison function. The hysteresis in the gate will cause an output
which does not have a 50% duty cycle. You should use a good, fast
comparator like the LT1016, LM319, LM360, or LMV7219. You may still
want to add a little bit of hysteresis, but not as much as the gate
would have.

You probably could do an active filter at these frequencies, but it
would require using RF op-amps or other not-so-trivial amplifier
circuits. So, I would, as you say, use a multi-stage "ladder" type LC
filter.

Here is a great page which has a calculator for LC ladder filter values:

http://www-users.cs.york.ac.uk/~fisher/lcfilter/

I put in some sample values and I am sending you a private email with
the PDF file output from this web page.

Sean


On Wed, Aug 19, 2009 at 1:41 PM, Harold
Hallikainen<harold@hallikainen.org> wrote:
>
> Thanks! I'm using the AD9833 eval board. I'm guessing a multi-stage LC LPF
> would be best here instead of doing something active, right?
>
> Harold
>
>
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