USRP timing offset

Hi everyone!

I’m new to Gnuradio e USRP. I use a USRP N210 with WBX daughterboards
loop back cable to connect TX e RX. I have tested USRP with a simple
flowgraph (sine , usrp_sink , usrp_source) and I have observed that the
output signal from usrp_source block is time shifted. I mean, the
output signal starts after 0.0105 seconds. How can avoid this? I have
to use “issued_stream_cmd”, setting time_spec=0.0105 s but nothing has

I want to use this USRP in a more complex project and I need to remove
initial time-shift.

I attach a plot of input and output signal and my flowgraph.

Thanks in advance for help,


Hi Leonard,

you should try to use set_start_time(time_spec_t(x)) on both the USRP
sink and source, but only after setting a device time using
set_time_now() before, that should be sufficiently (>0.1s) earlier than
x, before you start the flow graph.

Best regards,

Thank you Marcus for help!

Now I’ m using Usrp with SCFDMA chain. I set_time_now and start_time_now

uhd_usrp_source.set_time_now (uhd.time_spec_t(time.time()))

and I haven’t time shift.

But I see a lot of “L” (late packet) printed and some “U” (underflow).
can solve the problem? I have tried to use low sample rate but after few
seconds L and U appear.



2015-09-02 16:41 GMT+02:00 Leonard F. [email protected]:

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