[EMAIL PROTECTED] wrote on 06/04/2008 08:05:16 PM: > WB6BNQ wrote: > > Ulrich, > > > > One of things I noticed when playing with that DDS design > tool is you can achieve > > the same output frequency using a different clock frequency, > thus removing the > > spurs. THe trick is to look at clock frequencies that you > can lock to your house > > reference for stability. Also, it might be possible to use > cascading DDS chips, > > one providing the clock for the other. > > > > What are the thoughts on such an approach ? > > > > Bill....WB6BNQ > > > > > > Ulrich Bangert wrote: > > > > > Cascaded DDS systems together with PLLs have been widely investigated: > See US patents: 4965533, 5028887, 5146186, 5216389, 5467294, 5517156, > 5598440. 7143125 > > > It's much better to use a DDS that employs noise shaping techniques to > shift the spur energy to higher offset frequencies that are easily > cleaned up by a PLL.
A question occurs to me. Perhaps we can turn this upsidedown. While the DDS won't necessarily generate the frequency we want without spurs, can't we set the DDS to generate a nearby frequency that is free or sufficiently free of nearby spurs? We may not be able to get nice power-of-ten phase amplification ratios, but we will know the ratios we do get quite precisely. Joe Gwinn > For the particular case of an offset generator for a dual mixer system > it is much easier to use the JPL generation technique using cascaded LSB > and USB mixers even though 4 mixers are required, generating the in > phase and quadrature signals to drive each mixer pair is easily done by > the associated digital frequency divider. > > Bruce > > _______________________________________________ > time-nuts mailing list -- [email protected] > To unsubscribe, go to https://www.febo.com/cgi- > bin/mailman/listinfo/time-nuts > and follow the instructions there. _______________________________________________ time-nuts mailing list -- [email protected] To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
