Hi Soumaya, while tuning, there will simply be transients, mostly of oscillator energy leaking into the receiver. You cannot use the data that you get while tuning.
You might want to define "strange power values"; 2.4 GHz is an ISM band, so a lot of traffic is to be expected there, and that traffic is also probably very bursty, so that your observed values might temporarily vary a lot, since your observation time is much longer than the bursts in e.g. WiFi, your observed power is basically the product of number of burst, burst energy of the individual transmitter, and path loss between your receiver and the transmitter. Still, why are you using such small sampling rates as 8 MS/s? With a good USB3 controller and a reasonably fast computer, you should easily be able to do 40 MS/s with the usrp_spectrum_sense program. In fact, on my throttled thinkpad X240, I'm currently doing ./usrp_spectrum_sense.py -s 40e6 -g 76 -F $((2**16)) 2.4e9 2.5e9 and it works just fine. Best regards, Marcus On 01/16/2017 10:32 AM, Soumaya el barrak wrote: > > Hi Marcus, > > > Thank you so much for your reply, I followed your recommendations, I > used a sample-rate of 8MS/s and FFT-size 1024 and I kept the > tune-delay and dwell-delay at 0.25 s. But I still receive some strange > power values while scanning the 2.4 GHz band. > > > I also obtained high power picks while tuning from one center > frequency to another. Could you please explain for me where I am > mistaken? And what is the explanation of those power picks? > > > Best.. > > Soumaya > > > 2017-01-13 14:46 GMT+01:00 Marcus Müller <marcus.muel...@ettus.com > <mailto:marcus.muel...@ettus.com>>: > > Hi Soumaya, > > the B200 tunes slower and might need up to half a second when > tuning further. > > You should hence minimize the amount of tuning, and instead of > 4MS/s use a higher rate, a larger FFT size, and tune less often. > > The power normalization is truly, 100%, arbitrary. Since these dB > are all "relative to digital 1", they only have linear relation > with real-world powers. > > > Best regards, > > Marcus > > > On 01/13/2017 11:40 AM, Soumaya el barrak wrote: >> Dear all, >> >> I am working with USRP B200 for spectrum sensing, I want to scan >> the band from 2.4 to 2.5 Ghz, I use fft size 256, and sample_rate >> 4M, and tune _delay 0,001s. I am not sure if the parameters are >> correctely chosen because when I try to scan another band without >> wireless activities, I still receive hight power levels. Can >> anyone has any idea about where I am mistaken ? >> >> Also, in the formula used to calculate the PSD : >> >> Power_dB = 10*math.log10(m.data[i_bin]/tb.usrp_rate); >> >> Normally it is the magnitude squared averaged , I want to know >> why it is averaged by the usrp_rate ? >> >> >> Thank you in advance ! >> >> Soumaya >> >> -- >> >> *EL BARRAK Soumaya* >> >> *Telecommunication & Networking Engineer / Phd Student* >> >> *Innovative Technologies Laboratory* >> >> *National School of Applied Sciences of Tangier - (ENSA Tanger)* >> >> *Abdelmalek Essaâdi University - Morocco* >> >> *Tel : (+212) 6 65 9 625 40/ (+ 39) 327 198 5064 >> <tel:+39%20327%20198%205064>* >> >> >> >> _______________________________________________ >> Discuss-gnuradio mailing list >> Discuss-gnuradio@gnu.org <mailto:Discuss-gnuradio@gnu.org> >> https://lists.gnu.org/mailman/listinfo/discuss-gnuradio >> <https://lists.gnu.org/mailman/listinfo/discuss-gnuradio> > _______________________________________________ Discuss-gnuradio > mailing list Discuss-gnuradio@gnu.org > <mailto:Discuss-gnuradio@gnu.org> > https://lists.gnu.org/mailman/listinfo/discuss-gnuradio > <https://lists.gnu.org/mailman/listinfo/discuss-gnuradio> > > -- > > *EL BARRAK Soumaya* > > *Telecommunication & Networking Engineer / Phd Student* > > *Innovative Technologies Laboratory* > > *National School of Applied Sciences of Tangier - (ENSA Tanger)* > > *Abdelmalek Essaâdi University - Morocco* > > *Tel : (+212) 6 65 9 625 40/ (+ 39) 327 198 5064* >
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