[time-nuts] Weird GPSDO behavior - update

Tim Shoppa tshoppa at gmail.com
Wed Oct 4 06:45:46 EDT 2017


Is there a way you can force your currently disciplined oscillator to
free-run, and log the phase difference between oscillator and GPS over a
couple of days?

Tim N3QE

On Tue, Oct 3, 2017 at 2:15 PM, Skip Withrow <skip.withrow at gmail.com> wrote:

> Hello Time-Nuts,
>
> Well, I think I know a little more about my GPSDO problem, but
> probably have more questions now than before.  Thanks for all the
> replies to the first post with thoughts and suggestions.
>
> I first tried restarting Lady Heather and doing a cold boot on the
> NTGS50AA (then entering the same disciplining values). Same behavior.
>
> I let it run over the weekend and the same behavior happened on
> Saturday and Sunday morning.
>
> So, yesterday (Monday morning) I changed the gain to the gain of the
> oscillator (.0072Hz/V), damping to 1.2, and time constant to 900s.  On
> the attached PRS10-2 plot you can see that it quickly settled.  This
> morning, it looks like all is well from the plot (about an hour before
> the furnace kicks in at the right of the plot).  HOWEVER, when the
> plot is expanded there is still funny business going on with the DAC
> control voltage at the same time of day.  I just think the changed
> parameters limit the disturbance.  The expanded plot is the attached
> PRS10-1.
>
> At this point I'm beginning to think that the NTGS50AA is the issue,
> but there are lots of questions left.
>
> 1. There are various version of the NTBW50AA/NTGS50AA GPS/operating
> firmware.  Mine is 10.3 and I notice that it has the LH 'ro'
> designation (as does the 10.4 version).  The 10.5 version does not
> give the LH ro notice.  Maybe it behaves better with the disciplining?
>  I will have to give a 10.5 a try.
>
> 2. Why does the glitch occur at 8am in the morning?  Will have to try
> powering the NTGS50AA up at different times and see it the glitch
> moves around.
>
> 3. Which disciplining parameters are affected by this glitch and which are
> not?
>
> 4. Have other people seen this same behavior?  Does it happen on
> Thunderbolts too?
>
> I'll update again when I have more data.
>
> Regards,
> Skip Withrow
>
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