Surely all that's required is a simplistic worst case analysis. Just assume that the value of Tau is always the worst possible so the full effect of the modulation is always seen.
If the worst case phase modulation is say phi then the worst case ADEV (Tau) will be proportional to phi*T/Tau where T is the nominal signal period. i.e. ADEV(Tau) < constant*phi*T/Tau Bruce > On 07 August 2018 at 10:37 "Richard (Rick) Karlquist" <[email protected]> > wrote: > > > The discussion has gotten off track. > I probably didn't make myself clear. > > When I talked about cleaning up the signal, I meant > exactly that, cleaning up the signal using a filter. > As opposed to cleaning up the measurement after the > fact. I just need to know how well I need to filter > the signal to meet a certain ADEV measurement level. > > The FM I have is not "slow". The rate > is in the MHz range. Can Stable 32 simulate that? > > Again, this is analogous to the 5071A having 1 MHz > spurs of about -90 dBc, yet the ADEV is not much > different than an open loop 10811. How high would > the 1 MHz spurs have to be to affect ADEV? > > Thanks. > > Rick > > On 8/6/2018 1:56 PM, Tom Van Baak wrote: > >> If you know the *source* of the bias you're trying to remove (i.e. you > >> know it's a sinusoidal frequency modulation), I don't know that it's any > >> different than removing long term drift. > > > > The TimeLab 'n' command (apply notch filter to phase records) is > > specifically for this purpose. JohnM added it when he ran into an H-maser > > which suffered from some sort of consistent periodic modulation. It spoiled > > the ADEV plots, but it did so in a deterministic manner. In a case like > > this you either debug the root cause of the h/w problem and make the > > repair, or just "repair it" in s/w. Like you say, it's the same concept > > (and danger) as removing linear drift or other deterministic / model-able > > effects. > > > > To explore this for yourself, you can use Stable32 to generate synthetic > > phase/frequency data with your choice of noise and modulation. Then use > > TimeLab to view the raw data and to apply the notch filter. > > > > I've written up some quick examples here: www.leapsecond.com/pages/adev-fm/ > > > > The plots dramatically show what effect slow FM can have on an ADEV plot. > > It also shows how well the TimeLab notch filter works. If you don't have > > time to look at that page, I've attached one plot to whet your appetite. > > > > /tvb > > > > > > > > _______________________________________________ > > 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. _______________________________________________ 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.
