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

From: Changkyu Seol
Subject: [Discuss-gnuradio] USRP2 and external clock (from GPS receiver)
Date: Wed, 18 Feb 2009 02:20:38 +0100


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,

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
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