On 06/06/2020 08:54 AM, Sidd Subramanyam wrote:
Thank you for this clarification regarding the 10 MHz drift and the 1
PPS pulse. When you mention that the 10 MHz outputs will not precisely
track each other in the short run but better in the long run, could
you provide an estimate for the duration at which the behavior will
track better? My previous email had stated how in a 1 second interval
I was experiencing around a ~300 nanosecond drift. However, in other
samples I had taken spanning upto 30 seconds, this drift seemed to
worsen upto ~15-17 microseconds. From your email regarding how much
the 10 MHz deviates during the short run as well as its long term
behavior I’m very sure I must be doing something wrong in my code setup.
I have provided some code sections of how I am attempting to
synchronize the time. I start this script at roughly the same time
(within about a couple of seconds) on both USRPs, and they begin to
initialize settings such as bandwidth and center frequency. I then
have them wait to start collection at the nearest rounded up 10 second
time multiple of GPS time in seconds, since the initialization can
take varying time for both USRPs to initialize. I also attached the
full code to this email.
**
I don't immediately see anything wrong with your code, but of course,
this code is just recording samples, which you are presumably
cross-correlating in an "offline" manner post-facto?
Something you might try is to use integer-N tuning, which may result in
a more mutually-coherent LO setting across your two
synthesizers:
tune_req.args = uhd::device_addr_t
<https://files.ettus.com/manual/classuhd_1_1device__addr__t.html>("mode_n=integer");
Also, you log the time when the recording is expected to take place--are
these values actually the same in the two instances?
What sample rate are you using? How much data are you recording?
Is this code ever triggered?
if (time_tmp > 0.000001)
{
std::cout << boost::format("XX %d Get Time of USRP %f\n") %
f % num_dropped_samps;
}
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