Re: [Discuss-gnuradio] USRP2 and external clock (from GPS receiver)

[Eric Blossom]

On Wed, Feb 18, 2009 at 02:20:38AM +0100, Changkyu Seol wrote:
> Hi!
> 
> I am planning to implement multiple synchronized transmitters using
> USRP2 and GPS receiver. Before that I checked whether the USRP2 is
> locked to external clock through following experiment.
> 
> 1) Connect the 10MHz and 1PPS from GPS receiver (EP1S, Spectracom) to
> USRP2's REF and PPS in port, respectively. (I definitely checked the
> electrical specifications...)
> 
> 2) Generate 10MHz tone from the USRP2 using usrp2_siggen.py. I have
> included following lines in python code.
> 
> self._u.config_mimo((0x0001 | 0)) <--- I added this method in usrp2.i,
> etc...
> self._u.sync_to_pps()
> 
> 3) Compare the 10MHz tones coming from GPS and the USRP2 through
> oscilloscope (triggered to 10MHz sine wave from GPS).
> 
> I expect that timing drift of the 10 MHz sine wave from USRP2 will be
> nearly 0 or at least very slow, but it is still very fast. It seems that
> including "self._u.config_mimo((0x0001 | 0))" doesn't change anything.
> (I did update the fpga programming file and the firmware in SDcard.)
> Am I missing something? Any comments will be appreciated.
> 
> Changkyu Seol

That should be sufficient.  Are you sure that the config_mimo command
is getting sent?  It's easy to check using wireshark.

Eric