[time-nuts] 53230A TIC and TimeLab
Ole Petter Ronningen
opronningen at gmail.com
Thu Oct 4 02:56:16 EDT 2018
Somewhat longer answer; I assume you have set up a frequency measurement
(as opposed to time interval)
1. Timelab uses SCPI-command "READ" to fetch readings from the 53230a (and
most other counters *). The 53230a does not return gap free frequency
measurements in this case. There will be deadtime which will be ignored, as
you say, but the measurements will also be biased. In addition, the
CONTinous gap free mode is broken when it comes to ADEV, as has been
documented elsewhere. From my experience, using the 53230a in a time
interval measurement takes care of these issues, at the expense of a
slighly more cumbersome setup.
2. You may know this, but from your text it could be a misunderstanding:
timelab does not configure the instrument; whichever sample interval you
select in timelab should match the sample interval you have set up the
53230a to use.
3. Regarding the ADEV number discrepancy; are the measurements made *at the
same time*? For "long enough"? (The numbers jump all over the place before
they settle down, thats normal from my experience.)
Of course, theres the question of what reference you are measuring against.
* at least this was the case the last time I checked, but I have not
looked at the source for 1.31 to verify.
On Thu, Oct 4, 2018 at 7:42 AM AC0XU (Jim) <James.Schatzman at ac0xu.com>
> I have recently acquited a 53230A counter and have tried to measure ADEV
> of a GPSDO with it. I am suspicious of the ADEV numbers reported by TimeLab
> V1.31 because
> 1) Timelab disagrees significantly with the ADEV numbers reported by the
> 53230A itself. In this case, with 1 sec sample intervals, the 53230A
> reports an ADEV of about 370 micro Hz (or 3.7e-11). Time lab reports
> 1.5e-11 @0.01 sec sample period, 2e-11 @0.1 sec sample period, 6e-11 @1sec
> sample period - all at tau=1sec.
> 2) When I use TimeLab to select different sample intervals, the whole ADEV
> curve shifts left (with smaller sample intervals) or right (with larger
> sample intervals).
> Its as if TimeLab does not correctly account for the sample interval, but
> am I just not using the Timelab/counter setup correctly?
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