[time-nuts] Setting loop TC using thunderbolt internal data.

Bruce Griffiths bruce.griffiths at xtra.co.nz
Mon Jan 26 15:36:43 EST 2009


Bruce

What was the record length?

TOTDEV and TOTHadamard should give more reliable estimates over a
greater tau range.

Bias corrected Theo_1 and the Hadamard equivalent should be even better
at longer tau.

Bruce

Bruce Walker wrote:
> Thanks for the suggestion.  Here is a composite plot with Allan and Hadamard
> deviations for my tbolt run last night with disciplining disabled.  I think
> I computed Hadamard correctly.
>
> OADEV (blue) has a minimum of 9.6e-12 around tau=790
> OHDEV (red) has a minimum of 4.9e-12 around tau=1660
>
> --bruce W1BW
>
>
> On Mon, Jan 26, 2009 at 2:05 PM, Bruce Griffiths <bruce.griffiths at xtra.co.nz
>   
>> wrote:
>>     
>
>   
>> Some idea of the shift in the minimum can be gleaned by plotting the
>> Hadamard deviation vs tau.
>>
>> Bruce Walker wrote:
>>     
>>> I ran the same test as Bruce Griffiths on my tbolt; that is, I turned off
>>> osc disciplining altogether and created an OADEV plot from the internal
>>> phase measurements taken from its GPS solution.  The plot is attached.
>>>       
>>  It
>>     
>>> has a minimum of about 1e-11 at tau=800, and it has the sane general
>>>       
>> shape
>>     
>>> as Griffiths'.
>>>
>>> The next experiment I plan to do is to repeat the same thing using manual
>>> holdover mode rather than "Disable disciplining".  That should continue
>>>       
>> to
>>     
>>> try to compensate for temperature and long-term drift (just not steered
>>>       
>> by
>>     
>>> GPS), whereas the data taken last night use a fixed DAC.
>>>
>>> --bruce W1BW
>>>
>>>
>>>       





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