[time-nuts] My GPSDO project: OCXO Thermal Oscillation?

[Volker Esper]

Hi Bob,

treat your GPSDO like a closed loop control system. If  you could 
optimize the process itself, e.g. make it's behaviour linear or 
eliminate environmental inluences, you should. Then you have to know the 
characteristics of your process (the transfer coefficients of the 
controlled system). You can test it with a "test pulse" (e.g. put a 
voltage jump at the process input (EFC) and observe the process output 
(frequency)). You then can calculate the controller parameters and wich 
type of controller you want to use (P, PID,...). In the case of a 
precision system you shouldn't handle it straight intuitivly, rather use 
a little bit of control theory.

Volker




Am 16.08.2013 17:09, schrieb Bob Stewart:
> I'm converting the code for the VE2ZAZ FLL to a PLL.  I'm seeing the phase correction change the EFC up and down about .02V to .03V over a period of 5 minutes or so (it varies).  The full range on the OCXO is about +/- 4Hz varied by 0 to +6V, so at least this is a tiny value.  I feel pretty confident with my code at this point.  I'm using a Trimble 34310-T OCXO for which I've been able to find almost no information.  Could this oscillating phase correction be some sort of thermal oscillation?  I've tried two separate 34310s and both act more or less the same.  My GPS device is normally a UT+, but I just now swapped in an "Adafruit Ultimate GPS Breakout" to the same effect.  Is this good, bad, or indifferent for a GPSDO?  I started this project not knowing what to expect, and I still don't.  Experienced help, speculation, or even just kind words at this point would be appreciated!  =)  I don't have a known good/stable reference to compare this
>   to.
>
> Bob - AE6RV
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