Hi all
I am trying to create a simple direction finding device using the Ettus
USRP1 and 2 DBSRX receivers. However I am finding a large amount of phase
noise between the two receivers. Even across a 128 sample collection I
find over 60 degrees of phase change. Because the two receivers are driven
from the same 64M clock I had hoped and read that they would be coherent
over the short term. Is there something special I need to program to get
the receivers more in sync?
I have read many of the comments about phase noise on the boards and while
there are reports I did not get the feel that the values were so high. I
have found that using an FFT and calculating the phase at the peak provides
processing improvements, however there is still a 2 - 6 degree standard
deviation in the phase. This calculated phase was for 200 FFTs of 128
points.
I am using the gnuradio-3.2 software to control the usrp and simply
collecting raw I& Q data to a file. I have a signal generator outputting a
tone signal at 1.88 GHz, -50dBM. The signal goes in to a splitter and then
directly into the receivers. I modified the software to be able to set the
frequency& gain of both receivers. The data is then written to a file and
I process the data using Matlab. I am using the std_2rxhb_2tx_dig.rbf
firmware file but have also used the std_2rxhb_2tx.rbf firmware and
collected complex data with the same results.