Thank you for the EXCELLENT response! From a brief reading of the
resources you posted plus a few more I found at Analog Devices, it appears
the spurious output is at the master clock frequency plus and minus the
final output frequency. If the final output frequency is considerably
below the master clock, it seems that it should be fairly easy to filter
it out. I'm using an AD eval board with a 25MHz master clock and output
frequencies of 3.45MHz and below. I'll go ahead and add an LPF to the sine
wave output, then run it in to a comparator. Maybe I can just use a
Schmitt trigger (like 74HC14) instead of a comparator to make it easier.
This is a local oscillator for an FM receiver that receives 2.3MHz and
2.8MHz. The IF is 650kHz. I decided to use a DDS instead of a PLL
synthesizer (such as the programmable crystal oscillator modules) thinking
that the PLLs are using RC oscillators which have a fair amount of FM
noise.

Again, THANKS for the response!

Harold



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