[time-nuts] Newbie question about thunderbolts

Paul Berger phb.hfx at gmail.com
Wed Feb 27 15:08:07 EST 2013


Hello all:

I am an electronic technician with 30+ years experience fixing
computers.   In my spare time I like to play with old computers and
electronics.  Recently I got bit by the precision timing bug, partially
after running across the wonderful leapsecond.com site, which lead me
here.   First I got  a FE-5680A, then after reading some of the archives
here I bought a Nortel / Trimble 45000   GPSDO and still later a used
Thunderbolt-E.

My main interest in these devices at this time is for a accurate bench
top frequency source, however I do have a 59309A running off of each of
the GPSDOs.  I am wondering if they will drift apart, but I suspect I
will need to wait a long time to see evidence of that. I set them
simultaneously by setting them both to the same GPIB address and
connecting them to the same bus on my HP-86B, this works well for
setting them but I have to remember to disconnect one or change the
address on one before I try to read them.

MY question concerns the thunderbolt-E, I have been using LH to monitor
both of the GPSDOs and was quite surprised to see that the Nortel 45000
seems to perform much better than the thunderbolt-E, I thought that the
E being a newer device it would perform better.  I will admit that I
have a much less than ideal antenna setup however the antenna location
is the same for both devices, they are  only a couple feet apart.  The
antenna's are a Trimble magnet mount antenna and a the dome antenna that
came with the thunderbolt-E kit. Initially I had the magnet mount
attached to the Nortel and the dome antenna attached to the E, but I
have now swapped antennas but it has not made any difference , and I am
beginning to wonder if my E is in fact defective.  I have been in
contact with one other person who has an E and his experiences have been
similar to mine, even though he has a much better antenna setup, so I
would like to ask if there is anyone else out there with an E, and ask
the group for comments on what I am seeing.

My observations have been that the 10MHz is not very stable, on LH I
will see relatively large spikes  in the DAC voltage that of course
impacts the 10MHZ, I had it connected to my 5316A counter that was
running with the FE-5680A as a timebase, with a 10 second gate time and
logging counts with my 86B and I was seeing excursions og over 100Hz
which I guess percentage wise is not huge but I do not see anything like
that on the Nortel.  Now some of these excursions do occur when there
are satellite switches, and if they all occurred coincident to satellite
switches I would mark it up to my crummy antenna arrangement, but they
don't they occur even when the satellite tracking is stable and often
come in groups of several transition first positive followed by an equal
transition in the negative direction.     There is also a constant
chatter of about 100uV on the DAC line as reported by LH which also
translates to noise on the OSC and PPS lines, my technician sense thinks
that looks like power supply noise, but I have not looked under the hood
yet.   One really annoying thing I have noticed is the E reports having
saved my location, however it apparently has not so every time it resets
for whatever reason it goes into a self survey, which because of my less
than ideal antenna setup usually takes some time to complete, even a
warm reset resulted in it losing it location and entering self survey.





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