[time-nuts] More Allan deviation data

[Dr Bruce Griffiths]

Didier Juges wrote:
> Ulrich Bangert wrote:
>   
>> Hi Didier,
>>
>> you may use the DRIFT section of the graphic editor of PLOTTER to remove
>> a phase drift due to a constant frequency offset as seen in this data,
>> with the result that you get more "visual resolution" out of it, as in
>> the attached PDF.
>>
>> 73 de Ulrich, DF6JB
>>
>>   
>>     
> Ulrich,
>
> I ran the OCXO with the new antenna location overnight, except that the 
> laptop went to sleep some time in the night, so I have lost several 
> hours of data, which may explain the sudden slope change in the plot 
> below (I need to save timestamps I guess). However, the remaining data 
> is good I think. There was no sudden noise, and about 5 phase jumps due 
> to the OCXO drifting during the observation period.
>
> I downloaded the latest version of Plotter (10-27) and it's all there. I 
> was able to quickly remove the phase jumps when the OCXO drifted past 
> the divided down period, and then remove the remaining slow drift.
>
> What a nice piece of software!
> (even the menu now has a *normal* File->Open :-)
>
> The latest plots are at the usual place:
> http://www.ko4bb.com/Test_Equipment/HP10811-GPS_10-29-2.png
> http://www.ko4bb.com/Test_Equipment/HP10811-GPS_10-29-2_Allan.png
>
> Now that the data collection method seems to be getting close, I wonder 
> how I should use the data, and what it means.
>
> The Allan deviation seems to taper around e-10 at 1000 seconds, then it 
> looks like it wants to keep getting lower.
>
> As a reminder, this is the HP10811 against the GPS receiver. I am not 
> sure what I should expect?
>
> Didier
>
> PS: I am still planning to measure ambient temperature at the same time 
> as I collect TI, via the GPIB, using a HP 3478A voltmeter and a 
> thermistor. This way, I should be able to correlate frequency changes 
> and temperature changes. I assume I can tell Plotter to ignore the 
> temperature field or display it with its own scaling. Should I use a 
> specific character as field delimiter? (such as a comma, or just spaces?)
>
> (In the short term, temperature data will be thermistor values, until I 
> write the code to convert in degrees. )
>
> Also, if I use time stamps, should I use field delimiter between the 
> time stamp and the data?
>
> What is the time stamps are discontinuous (as if the laptop falls asleep 
> again), will that mess up Plotter?
>
>
>
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>   
Didier

Unless you have a particularly poor 10811 it is likely that the measured 
Allan deviation is limited by your the instability of your GPS receiver 
PPS output.
With a good GPS timing receiver setup you should expect an Allan 
variance perhaps 5x lower than this as illustrated in Ulrich's article 
for the AMSAT journal.

Bruce