[time-nuts] question Alan deviation measured with Timelab and counters
john at miles.io
Sun Jan 18 21:23:45 EST 2015
> One way to get around problems with things like GPSDO’s is to have multiple
> standards and use them for different ranges of Tau. OCXO’s have good ADEV
> close in. Picking up a few and comparing them is pretty cheap. Rb’s have better
> ADEV at longer tau (> 300 sec). Comparing three or four is not as cheap as with
> OCXO’s but it’s not totally crazy. Running several GPSDO’s long enough to
> settle to their longest time constant is another way to go.
On that subject, I should probably mention that the current TimeLab beta (at http://www.miles.io/timelab/beta.htm ) has a realtime N-cornered hat display. I needed that feature to measure a bunch of OCXOs against a pair of Corby's trick 5065As, so I finally bit the bullet and added it. It is very cool, subject to the (many!) caveats with separated-variance measurements in general.
This feature should work with measurements taken by counters as well, but I haven't tested that yet. Even worse, I won't have time in the immediate future to document it very extensively. Short version: measure three devices against each other, and then use the 'e'dit dialog to assign Source A and Source B labels to each of the resulting three plots. Go to the ADEV or other xDEV measurement view and hit ctrl-h to toggle the N-cornered hat display mode. The program will use your assigned source labels to separate the individual source variances.
It won't work if you don't spell the source names consistently between each pair of measurements; if any of the measurements have different t0 intervals, bin counts, or trace history settings; if you don't read the mouseover help text for the Source A/B fields in the trace properties dialog; or if you don't read everything Bill Riley has written about 3-corner hat measurements.
TimePod users can assign the source labels at acquisition time, via the new fields in the Advanced tab. Read the new mouseover text for the Stability and Ch0/Ch1/Ch2 fields _carefully_. Users of counters, or those who want to render existing files in 3-cornered hat mode, will need to add source labels in the 'e'dit dialog.
Symmetricom/Microsemi 3120A users should email me offline if interested. I don't have a beta for the 3120A app yet, but it will be there eventually...
-- john, KE5FX
Miles Design LLC
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