Joseph M Gwinn wrote: > [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 > > Joe
Thats essentially what JPL do with their latest DMTD system which uses a commercial synthesizer as an offset generator. They use a 100MHz mixer input frequency and use a 123 Hz beat frequency. Bruce 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.
