> > The newer DDSes have lower power, faster clocks, lower > spurs, more bits in the DAC, etc. Although, I'm not sure how > important all these things would be in this application. > > > > There are also some very low phase noise, low jitter XO > available that > > can drive these things (not temperature compensated, > though, so as the > > XO temp changes, so does the frequency) > > > > > > Using a low phase noise XO with a suitable frequency would > probably be preferable as there would be fewer potential > problems with spurs. > With appropriate algorithms the drift in beat frequency with > temperature shouldn't be too much of a problem. >
There's low phase noise oscillators intended for the SONET market from Valpey Fisher, etc. that have fairly good performance. A VF161 is a <$50 sort of part and is speced at 1ps jitter (1 sigma, fj>1kHz). VF has "jitter attenuators" too, which are a low jitter pll with <0.18ps jitter (RMS 12kHz-20MHz).. Pick a XO at 200-300 MHz or so (whatever frequency is readily available), then set your DDS for a "spur free" frequency (where it divides nicely into the SIN table size) (on the AD9584 running at 200MHz which has a 48 bit phase accumulator, 17 bit phase table, and a 12 bit DAC, these are about every 3 kHz or so) _______________________________________________ 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.
