AD replied to my message on the AD forums: (upon inspection they will revise the datasheet to say the resolution is 47 bits now... ha!) https://ez.analog.com/dds/f/q-a/107510/ad9912-ftw-lsb-always-zero the datasheet has a copyright "2007-2010" so maybe the chip has been out for 11-12 years already (?) but nobody bothered to measure the frequency resolution!?
We might give the visual oscilloscope-method a go also at some point - just for kicks. For example one could set the DDS frequency so that there's a "beat" of 3600 seconds (1 h) - i.e. the 10MHz reference and the DDS output drift one period (100ns) during an hour. If I calculated correctly when the frequency is changed by one LSB that 3600s beat should change by around +/-45 seconds. If the change is 2LSB the beat-period changes by around 90seconds. To see the 'coincidence', maybe we need to collect traces from the oscilloscope at 5s or 10s intervals, and do cross-correlation... Anders On Wed, Feb 20, 2019 at 2:00 AM John Miles <[email protected]> wrote: > > A friend of mine has a x96 multiplier from 108 MHz to 10 GHz but we don't > > have access to any counters capable if measuring the difference. > > For sanity-checking an extremely small frequency discrepancy, perhaps you > could set up the DDS to output a signal very close to a plesiochronous > reference of some kind. E.g., a binary fraction of its own clock frequency > plus or minus 1 LSB. Then trigger a scope from the DDS output while > watching the clock slide past it on the other channel. > > This turns the question into one that can be answered definitively with a > stopwatch, rather than ambiguously with a counter. :) > > -- john, KE5FX > Miles Design LLC > > > > _______________________________________________ > time-nuts mailing list -- [email protected] > To unsubscribe, go to > http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com > and follow the instructions there. > _______________________________________________ time-nuts mailing list -- [email protected] To unsubscribe, go to http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com and follow the instructions there.
