[time-nuts] question Alan deviation measured with Timelab and counters

Magnus Danielson magnus at rubidium.dyndns.org
Sun Jan 18 22:16:11 EST 2015


Your new three-corner hat feature is really cool. Already tried it, even 
if I did not spend quality time on setting source labels correctly.

Whenever I have a setup capable of running it, I will test-spin it again.

I suspect that when you make separate measurements, the noise of the 
individual sources does not match up perfectly which may reduce quality, 
especially systematics like hum.


On 01/19/2015 03:23 AM, John Miles wrote:
>> 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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