Hi The “sure fire” way to reduce the spurs is to go to a divisor that “fits” in to the DAC bit width. If you have a 12 bit dac, those points happen at Fclock / 2^12. For Time Nut sort of stuff that’s pretty coarse tuning.
Bob > On Nov 13, 2016, at 11:03 AM, Tim Shoppa <tsho...@gmail.com> wrote: > > Some AD DDS app notes give examples of spurs and choosing nearby (but not > exactly on freq) numbers that are much less bad for spurs - or at least > that move the spurs outside the cleanup filters/loops. I don't know of a > general example or even code that does this in a general way. > > One paper I like on the subject is this: > http://ttcla.org/vsreinhardt/DDS%20spur%20reduction%20techniques.pdf > > P.S. I just like saying "Wheatley Jitter Injector". Not for those who are > embarrassed easily... Almost as good as "Wankel Rotary Engine". > > One of > > On Sat, Nov 12, 2016 at 8:13 PM, Hal Murray <hmur...@megapathdsl.net> wrote: > >> >> kb...@n1k.org said: >>> Yes, the FE-405 uses a DDS and a cleanup. Inside the cleanup loop the DDS >>> spurs come straight through. Since the FE-405 compensates for all sorts >> of >>> things, the DDS moves around a lot. Even a one bit change on a DDS will >> move >>> spurs around. With an ever changing DDS, you have an ever changing >> forest >>> of “stuff” on the output. >> >> Is there a web page or such telling me where the spurs will be on a DDS >> for a >> particular constant? >> >> >> -- >> These are my opinions. I hate spam. >> >> >> >> >> _______________________________________________ >> time-nuts mailing list -- time-nuts@febo.com >> To unsubscribe, go to https://www.febo.com/cgi-bin/ >> mailman/listinfo/time-nuts >> and follow the instructions there. >> > _______________________________________________ > time-nuts mailing list -- time-nuts@febo.com > To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > and follow the instructions there. _______________________________________________ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.