John,
In the past I've allowed TimeLab to pick the sampling interval (usually
.07s for the 5370B) but when I use Acquire, Sampling Interval and set
that to 1 sec I get very different results. Apparently the result is
not the same as Edit, Trace, Sample Interval. All of the foregoing in
TI mode.
BTW, thanks for the program.
Bob Darby
On 7/7/2013 8:57 PM, John Miles wrote:
-----Original Message-----
From: [email protected] [mailto:[email protected]] On
Behalf Of Robert Darby
Sent: Sunday, July 07, 2013 3:33 PM
To: [email protected]
Subject: Re: [time-nuts] Question about effect of sample interval on ADEV
Thanks to all who responded. I didn't phrase my question very well I'm
afraid. The periodic noise/beat note issue is what lead me to try a
different sample interval. Previously I had always let TimeLab set the
sample interval (about .07s for the5370B).
I was surprised by the difference in the adev traces when I varied the
sample interval from .07s to .25s to .5s to 1.0s and that is what I
hoped someone could explain.
When I edit a trace and change the sample interval there is not a
substantial change to the Tau / Sigma (Tau) values yet when I actually
run at the different sample intervals I get minimum values for each run
of 400s 5.60e-13, 600s 1.70e-13, 1000s 9.55e-14, 3000s 4.15e-14. The
traces are totally different; same oscillators and counter, just
different sample intervals. That's what I hoping one of you could
explain.
So the only difference between the test setups is the setting of the Display
Rate control on the 5370, correct? You're allowing TimeLab to estimate the
sample rate automatically, and giving it enough time to converge on a stable
reading before hitting 'Start Measurement'?
You're correct in that changing the real-world sample rate should yield
results that are identical (or at least very similar) to resampling the
phase data after the fact. In frequency mode, dead time between readings
would make that an iffy proposition, but for data taken in TI mode the
outcomes should be close.
-- john, KE5FX
Miles Design LLC
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