[time-nuts] GPSDO time constant

[Magnus Danielson]

Hej Bruce,

>>> The good news is that if you, the time-nut, have the gear and
>>> the time to measure the stability of the OCXO in your GPSDO,
>>> and know your environment well, then you can probably safely
>>> lengthen the TC and achieve much better mid-term stability out
>>> of your GPSDO as shown in the plot above.
>>>     
>> Agreed. But also recall that long-term effects like frequency drift is 
>> pretty easy to measure with a GPS. It would not take too much research 
>> to figure out some suitable drift-TC relationship such that you could 
>> either just look the charts to find a good match or even apply them in 
>> real time steering.
>>
>> For ThunderBolt owners it is pretty straightforward to adjust the TC and 
>> damping, which is very nice. Use this oppertunity!
> 
> How exactly can one measure the resultant performance or even select the
> optimum time constant and damping factor if one doesn't have a quieter
> reference?
> Can one really resort to some sort of N cornered hat?

If time constants is allowed to be limited by frequency drift 
(regardless of its source) then you can use a long term drift estimate 
to control the time constant of the control loop. Essentially being an 
adaptive filter.

It is still a gross oversimplification, but may still be a handy one.

Cheers,
Magnus