[USRP-users] GPSDO Time Synchronization

Scott Johnston scott.johnston at ll.mit.edu
Tue Feb 19 14:17:48 EST 2013


Hello,

I am having trouble with GPSDO Time Synchronization across multiple 
USRPs that are connected to separate computers and each one has its own 
GPSDO.

I am observing that about half the time, two or more USRPs will disagree 
about what time it is. I'm testing this by transmitting from one USRP 
and receiving that signal split into two USRPs. I then compare the 
difference in time in the stream tags of the two receiving USRPs to the 
difference in time when they start receiving the common transmitted signal.

Sometimes its the same and sometimes it is exactly 1 second off.

The GRC file I used on the receive side is attached. The transmit side 
is irrelevant, as long as the signal is split into receivers.

I have ensured that the GPSDO units are locked to GPS.

Can someone please explain how to fix this 1 second ambiguity?

Thanks

Scott Johnston

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