Hi!
I have been using USRP N200 with GPSDO for several years. I have more
than ten sets of N200 with GPSDO purchased more than two years ago and
they have been working very well.
However, I recently purchased three new sets of N200 (with LFRX) and
GPSDO and found that all of them have serious PPS drifting problem which
I have rarely seen with the old sets.
Because the accurate timing is essential for our application, with every
set of N200 and GPSDO, I always do a simple test. I record the PPS
signal from the GPSDO using the LFRX board with a sampling rate of 10M.
With the old N200s and GPSDOs, I can confirm that samples between two
PPSs are always exactly 10M. However, with the three new sets, I found
that once every several minutes, the samples between two PPSs are not
exactly 10M, typically several points fewer or more than 10M. I also
tried to record PPS signals from two GPSDOs with the two channels of the
same LFRX board. With the old sets, two PPS signals usually agree
exactly with each other, at most having one point difference. However,
with the new sets, two PPS signals sometimes have several points
difference, and occasionally more than ten points difference.
I also tried to install the new GPSDO on the old N200 with old LFRX and
it also had the problem, so I can confirm the problem is due to the new
GPSDO.
I am now having both old and new sets placed at the same location, with
GPS antennas also at the same location. They are using the same
programs, PCs with the same specs. The old one seems to have perfect
timing while the new one seems to have serious PPS drifting problem.
Does anyone have any idea what is the possible reason for this problem
and how can I solve it? We were planning to purchase more sets of USRPs,
but with such problem it will be very difficult to use USRP for our
application.
Thanks in advance!
Ting Wu
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