[time-nuts] Looking for info/help on TruePosition GPSDO behavior

[Skip Withrow]

Hello Time-Nuts,
I'm looking for a GPSDO for a project and have found some interesting
behavior in the TruePosition GPSDO.

My requirements for the GPSDO are to be relatively small and that Lady
Heather knows about the unit.  I have several of the TruePosition
GPSDOs around, so started playing.  I first had to update my LH from
ver. 5 to ver. 6, but that was pretty easy.  After firing up the
TruePosition and doing a survey I noticed that the EFC decides to
take a 4mV jump every now and then and quickly settles back to where
it was (looks like time constant is 60-100s or so).  I have tried 3 or
4 units so far and they all do the same thing.

Some of my questions are:
Have other people seen this behavior?
LH displays an oscillator gain and the number seems to be there from
the beginning. Is this jump something that either the TruePosition or
LH uses to get that gain number?
Could this behavior be caused by something LH is doing to the unit?

I have also noticed that there is a very regular pattern to the number
of satellites.  This is due to PRN138 (a WAAS bird) going in and out
(about a once per 2 min. period).  I would have to think that this is
a function of the FURUNO GT-8031 GPS receiver.

I suppose my next step is to look at the 10MHz output and see if the
jumps are there (I would bet they are).  Then seeing if they go away
when LH is shut down.

I have included a LH screen shot to show these behaviors.

Regards,
Skip Withrow
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