Re: [Discuss-gnuradio] About the latest submission of usrp_spectrum_sense.py

[Mike Jameson]

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: address@hidden
Web: http://scanoo.com

On Thu, Jul 25, 2013 at 10:11 PM, Ahmed Saeed <address@hidden> 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: address@hidden

mobile: +201112389430

web: http://wrc.ejust.edu.eg/people/saeed

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