Hi Ahmed, You will need to use a calibrated rf source to compare your USRP N210 SDR receiver against and adjust the power_db result (without subtracting the noise floor result from it) to match. I assume it will be a simple case of adding or subtracting 'X' db's to the power_db result for each calibration power level tested against. Unfortunately I haven't any calibrated rf signal sources to hand so am unable to confirm how easy it will be to calibrate.
Regards, Mike -- Mike Jameson M0MIK BSc MIET Email: m...@scanoo.com Web: http://scanoo.com On Sat, Jul 27, 2013 at 1:07 PM, Ahmed Saeed <ah...@gmx.us> wrote: > 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 >
_______________________________________________ Discuss-gnuradio mailing list Discuss-gnuradio@gnu.org https://lists.gnu.org/mailman/listinfo/discuss-gnuradio
