[Discuss-gnuradio] Delay of synchronization with PPS and UHD on USRP2

Hi,

These days I am trying to synchronize two USRP2 with PPS signal  and UHD. The two USRP2 is connect with same reference clock and PPS signal. I use function "set_time_next_pps(uhd::time_spec_t(0))" to set time to be zero, and make two USRP2 start sampling after 3 seconds. The result shows that there is still phase difference, which means a delay( about 30ns) between USRP2s.

I used 10MHz reference clock as input and set DDC frequence to 10MHz. Then I get two complex DC signal. The phase difference is about 0.3*2pi.   It seems that the PPS impedence difference between USRP2s is the reason of delay. Any clues or solution???




By the way, the stream mode " STREAM_MODE_NUM_SAMPS_AND_DONE" does not work with "set_time_next_pps" function. It works with "set_time_now". But stream mode " STREAM_MODE_START_CONTINUOUS " works well with  "set_time_next_pps" function.


Thank you!

Liang

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