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From: | Ahmed Saeed |
Subject: | Re: [Discuss-gnuradio] About the latest submission of usrp_spectrum_sense.py |
Date: | Sat, 27 Jul 2013 14:07:50 +0200 |
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
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 SaeedResearch AssistantDepartment of Computer Science and EngineeringEgypt-Japan University of Science and Technology (E-JUST)email: address@hiddenmobile: +201112389430
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