I dont know if this helps. I once ran spectrum_sense.py and also got peak spur at the first several fft points. I think it might relate to the hardware communication between PC and USRP at the initial stage.
-- Yang Sent with Sparrow On 2011年5月26日星期四 at 下午4:14, Lebowski80 wrote: > > Thank you for answering but I cannot understand what you mean with "The USRP > is not a measurement receiver". If USRP was not a measurement receiver, > which is its utility? Moreover, if it is not a measurement receiver what is > the result memorized in m.data that is the output of usrp_spectrum_sense.py? > When I use a WiFi antenna I can receive (and measure) the energy of WiFi > channels. The problem arises without antenna becasue USRP measures a signal > that cannot exist! Furthermore, such a signal is always at the beginning of > the sensed bandwidth, so this has not any sense! > > Any idea about that? Thank you! > > > Nick Foster-4 wrote: > > > > On Wed, 2011-05-25 at 08:51 -0700, Lebowski80 wrote: > > > Hello everyone > > > > > > I’m using an USRP with a XCVR2450 daughter board working at 2.4 - 2.5 > > > GHz. I > > > want to find a threshold between thermal noise and signals energy using > > > the > > > script usrp_spectrum_sense.py and sensing from 2.400 GHz to 2.500 GHz. To > > > do > > > that, I replaced the WiFi antenna with a resistor of 50 Ω to measure the > > > noise. I obtained a very strange peak at the beginning of the bandwidth > > > (around 2.405 GHz) and this result was totally unexpected because I > > > supposed > > > to sense only thermal noise without any particular peak. So, I repeated > > > the > > > experiment from 2.420 GHz to 2.500 GHz and I achieved the same peak > > > always > > > at the beginning of the bandwidth (in this case around 2.425 GHz). > > > Therefore, I'm quite sure this is a problem linked to USRP or to the > > > script > > > usrp_spectrum_sense.py, isn’t it? Can someone give me a hint about that > > > please? > > > > The USRP is not a measurement receiver, and some small spurs are to be > > expected. You can plan for this, or work around it by changing the LO > > offset at a given center frequency using the advanced tuning parameters: > > http://www.ettus.com/uhd_docs/doxygen/html/structuhd_1_1tune__request__t.html > > > > --n > > > > > > > > Regards > > > > > > > > _______________________________________________ > > Discuss-gnuradio mailing list > > Discuss-gnuradio@gnu.org > > https://lists.gnu.org/mailman/listinfo/discuss-gnuradio > > -- > View this message in context: > http://old.nabble.com/Unexpected-energy-peak-sensing-thermal-noise-and-using-usrp_spectrum_sense.py-tp31700266p31705762.html > Sent from the GnuRadio mailing list archive at Nabble.com. > > > _______________________________________________ > Discuss-gnuradio mailing list > Discuss-gnuradio@gnu.org > https://lists.gnu.org/mailman/listinfo/discuss-gnuradio >
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