On 11/12/2010 08:32 AM, tom_wgs wrote:
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.
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What phase noise improvements are seen in the new DBSRX2 daughter boards?
The DBSRX2 has much better close in phase noise, so it will improve on this. However, I think what you are seeing with the original DBSRX should look better than that. Can you do an FFT of each input signal and send a link to them? I think you might see a lot more noise on one than the other, indicating a problem with one board.
Matt _______________________________________________ Discuss-gnuradio mailing list [email protected] http://lists.gnu.org/mailman/listinfo/discuss-gnuradio
