I'm having trouble trying to implement an energy detector in GNU Radio. I want to find empty channels that have a signal power less than or equal to the FCC's -114 dBm detection threshold. I've been modifying the usrp_spectrum_sense.py code that came with GNU Radio, and it's been a headache trying to convert the magnitude squared values from the FFT block to proper dBm values. I am using the USRP N200 along with the WBX daughterboard.
I am simply trying to get the averaged values to match up with the values in uhd_fft, but they seem to be off. I've got tune delay and dwell delay both set to 0.05 seconds, and changing these options along with the sampling rate and FFT size seem to give drastically different results. How is uhd_fft able to get the dBm values that it uses? Right now I take the 10 * log10(bin[i]) - 20 * log10(fft_size) - 10 * log10(tb.power / fft_size) for each sample, but they don't seem to match up. Should I even bother using usrp_spectrum_sense? Using bin statistics is for looking at really wide ranges of spectrum that are outside the range of maximum bandwidth the USRP can look at, but here I only want to look at 6MHz TV channels consecutively. Here is the code I am working on: http://uploaded.to/file/0gqabz13
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