Hi Mike, Thank you for your reply.
So what if I want to sense with the sensing threshold set by the FCC for white spaces at -114 dBm or -107 dBm. How does the value of "power_db" relates to the value I should compare against given the FCC thresholds ? Kind regards, Ahmed Saeed. On Sat, Jul 27, 2013 at 1:35 PM, Mike Jameson <m...@scanoo.com> wrote: > Hi Ahmed, > > Dividing the bin power by the sample rate in the calculation for > noise_floor_db and power_db (lines 286 and 287 of > https://github.com/gnuradio/gnuradio/commit/cc12277f64207ff79a40094268c843e6b3e2d2d3#L0R286) > was done so that the power level stays constant if the sample rate is > increased. This is required because the bin statistics function sums > together more samples if the usrp_rate is increased and therefore increases > the bin value result. > > The noise_floor_db value is subtracted from the power_db value to give a > relative signal strength above the noise floor to make it easier to set the > squelch and catch signals: > > noise_floor_db = 10*math.log10(min(m.data)/tb.usrp_rate) > power_db = 10*math.log10(m.data[i_bin]/tb.usrp_rate) - noise_floor_db > > Regards, > > Mike > > -- > Mike Jameson M0MIK BSc MIET > Email: m...@scanoo.com > Web: http://scanoo.com > > > On Thu, Jul 25, 2013 at 10:11 PM, Ahmed Saeed <ah...@gmx.us> wrote: > >> Dear all, >> >> I checked your latest submission of "usrp_spectrum_sense.py" and I don't >> understand why there is a division of the value of each bin by the sampling >> rate. Also I don't understand why there is a subtraction of the noise >> floor from the power db value to calculate an actual db value. >> >> Kindly explain those modifications. >> >> I am working with a USRP N210 and when I run uhd_fft to display an analog >> TV channel I get values around -60's db for the central frequencies of both >> the audio and video signals. When I used the latest version of >> "usrp_spectrum_sense.py", I got positive values for power_db and when I >> removed the deduction of the noise floor, I got readings almost near the >> noise floor for all bins (including the ones at the central frequency of >> the audio and video signals). I hope you can point me to the right >> direction and correct my misunderstanding of the code. >> >> Thank you for your time. >> >> Kind regards, >> Ahmed Saeed. >> -- >> Ahmed Saeed >> Research Assistant >> Department of Computer Science and Engineering >> Egypt-Japan University of Science and Technology (E-JUST) >> >> email: ahmed.sa...@ejust.edu.eg >> mobile: +201112389430 >> web: http://wrc.ejust.edu.eg/people/saeed >> >> _______________________________________________ >> Discuss-gnuradio mailing list >> Discuss-gnuradio@gnu.org >> https://lists.gnu.org/mailman/listinfo/discuss-gnuradio >> >> > -- Ahmed Saeed Research Assistant Department of Computer Science and Engineering Egypt-Japan University of Science and Technology (E-JUST) email: ahmed.sa...@ejust.edu.eg mobile: +201112389430 web: http://wrc.ejust.edu.eg/people/saeed
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