[time-nuts] Is your Thunderbolt holdover filter trained?

Mark Sims holrum at hotmail.com
Fri Mar 13 21:08:27 UTC 2009

While playing with putting the Thunderbolt in holdover mode,  I noticed that the unit either displays "OCXO Comp" or "Undisciplined" as the unit's status when you enter holdover mode.  I believe that this is how you can tell if your unit's holdover filter algorithm is sufficiently trained to do meaningful holdover compensation.

If the unit says Undisciplined,  you will see a constant DAC voltage.  I suspect that this is becuase the holdover filter does not know enough to be able to meaningfully compensate the oscillator.  If the unit says "OCXO Comp" the DAC voltage will be varying with temperature and the unit is attempting to adjust the oscillator control voltage for temperature changes.

I also think that the unit will not switch between Undisciplined and OCXO Comp modes while in holdover mode.  It seems to check the filter state only when holdover mode is entered.


Windows Live™ Groups: Create an online spot for your favorite groups to meet.

More information about the time-nuts mailing list