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
Its 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. 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.
