[time-nuts] Expected 10 MHz offset from a GPSDO?

Tim Lister listertim at gmail.com
Fri Aug 19 14:20:40 EDT 2016

Hi all, I am starting to dip my toes into time-nuttery after being
interested in precise time/position for quite a while (I'm an
astronomer IRL). I have acquired a used OCXO and LPRO-101 rubidium,
along with a HP5334B (with Option 10) and a HP5370B from ebay and
almost done assembling a TADD-2 kit from TAPR.

I recently acquired one of the re-packaged Trimble UCCM GPSDO's (it
doesn't seem to be one of the bg7tbl ones) from ebay and have it setup
with the supplied puck antenna outside (it's not in a great location
(close to the house) but I have set the elevation mask to 20 degrees
in the GPSDO) and it's been running for 2 days. The results of the
SYST:STAT? command indicate it is in position hold and tracking 3-4+
satellites.  Connecting the 10 MHz output to the Channel A input (on
the 5334B) or the frequency input (on the 5370B) and setting 50 Ohm
termination and AC signals but without any other input or external
reference results in a frequency that is off by about 0.1-0.2 Hz. Is
this amount of offset expected or a sign something is not right with
the GPSDO?


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