Thanks guys, Like usual more complicated than I thought. I was hoping that this would cancel any stability issues common to both the reference and the signal thus giving me best case ability. I seem to be getting numbers too good to be true so there must be a hitch. I get an ADEV 5x10-13 at 1 s mostly linear to 7x10-16 at 10,000 s with a small hump at 20s-80s. Figured there was some kind of gotcha.
Doc On Mon, Nov 5, 2012 at 2:26 AM, Magnus Danielson <[email protected] > wrote: > On 11/05/2012 06:30 AM, Tom Van Baak wrote: > >> Ah, I see what you mean now. Yes, that setup can give you a rough >> estimate of the counter's noise floor. >> >> I can't give you specific numbers but one danger with this sort of test >> is that the input and the timebase are artificially locked together (i.e. >> fixed phase relationship) through the common reference. Your measurements >> may thus show artificially less noise than a real-life case of independent >> input(s) and reference. >> >> This can happen if your sub-ns counter is based on interpolators. Because >> the input and the timebase are locked in phase, the counter lands near the >> same point of the interpolator scale on every single measurement, rather >> than experiencing the noise (and non-linearity) of the entire scale. >> > > It's a little more complex than interpolator non-linearities alone. You > also need to include cross-talk between the signals. This cross-talk is > usually higher between A and B inputs than from reference, but never the > less. > > You would need to sweep the trigger input delays to illustrate these > non-linearities. From a single measurement you can get both a better or > worse number compared to the average which is what you would expect to see > for free-running signals. > > So, you can get a rough idea about the baseline, but it is not a > sufficient method. > > See the SR620 manual for a plot of non-linearities. > > Cheers, > Magnus > > > ______________________________**_________________ > time-nuts mailing list -- [email protected] > To unsubscribe, go to https://www.febo.com/cgi-bin/** > mailman/listinfo/time-nuts<https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts> > and follow the instructions there. > -- Doc Bill Dailey KXØO _______________________________________________ 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.
