osmocom-sdr December 2014

osmocom-sdr@lists.osmocom.org

2 participants
2 discussions

How to cross-correlate two I/Q streams of same radio-station?
by Andreas Hornig 25 Dec '14

25 Dec '14

Hi everyone and merry Christmas! :) I want to find the same snippet of I/Q data of a radio station in another I/Q recording of the same station but recorded with another dongle. Of course both with rtl-sdr dongles. I did this here http://filebin.net/8nevid3yk3 and played around with a python script and numpy math-lib to find this "needle" in the "haystack" and the timeshift. But it didn't work. That's why I am here to ask you how to do that. First of all, I would like to ask you if you could somehow check if both streams are actually containing the "same" I/Q data. Perhaps you can do that with one other software if you can find it. What I did was to use the numpy correlate function and added there some lines to have it normalized to have the results between -1 and 1 as explained here http://en.wikipedia.org/wiki/Cross-correlation#Normalized_cross-correlation But it couldn't find a needle sequence of 1000 samples that could be refound in the haystack (about 2000000 samples) when the starting of the needle samples were shifted a bit with some new 1000 samples. I guess that the analogue radio channel on this carrier and thus the I/Q doesn't form the I/Q enough to use each sample on that 2MHz sample rate, but much less in the KHz range. But I am not fully sure if this is true. This is why I am also here to ask about the influences on a cross correlation and how to set it up. So, any answer is very welcome. I hope it will work out in the end :). Best regards, Andreas

1 0

rtl_sdr for Yocto?
by Petter Gustad 18 Dec '14

18 Dec '14

Is there a meta layer or other method to include rtl_sdr in Yocto? Thanks! //Petter

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osmocom-sdr December 2014