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N210 + SBX High peaks at center frequency.

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N210 + SBX High peaks at center frequency.

maiconkist
Hi list,

I'm using a N210 + SBX daughterboard (vert 2450 antenna). Currently I'm using the "uhd_fft" to check the spectrum at all wifi channels. Strange is that a peak with almost 0dB appears in every frequency I try.

Also, I changed the code from usrp_spectrum_sensing to output the sum of the mag_square of the FFT and the output is always like:


###
freq = 2900000000.000000, energy = 16689.216661
freq = 2900000000.000000, energy = 12815.735905
freq = 2900000000.000000, energy = 1570.022886
freq = 2900000000.000000, energy = 192.350267
freq = 2900000000.000000, energy = 23.569094
freq = 2900000000.000000, energy = 2.889016
freq = 2900000000.000000, energy = 0.354752
freq = 2900000000.000000, energy = 0.043869
freq = 2900000000.000000, energy = 0.005605
freq = 2900000000.000000, energy = 0.000880
freq = 2900000000.000000, energy = 0.000269
freq = 2900000000.000000, energy = 0.000216
freq = 2900000000.000000, energy = 16675.043848
freq = 2900000000.000000, energy = 16666.115685
freq = 2900000000.000000, energy = 2280.756275
freq = 2900000000.000000, energy = 279.419596
freq = 2900000000.000000, energy = 34.236761
freq = 2900000000.000000, energy = 4.196034
freq = 2900000000.000000, energy = 0.514922
freq = 2900000000.000000, energy = 0.063638
freq = 2900000000.000000, energy = 0.008021
freq = 2900000000.000000, energy = 0.001167
freq = 2900000000.000000, energy = 0.000309
freq = 2900000000.000000, energy = 0.000235
freq = 2900000000.000000, energy = 20142.803262
freq = 2900000000.000000, energy = 16666.054669
freq = 2900000000.000000, energy = 3313.974010
freq = 2900000000.000000, energy = 406.000443
freq = 2900000000.000000, energy = 49.743476
freq = 2900000000.000000, energy = 6.096459
freq = 2900000000.000000, energy = 0.747946
freq = 2900000000.000000, energy = 0.092179
freq = 2900000000.000000, energy = 0.011596
freq = 2900000000.000000, energy = 0.001642
freq = 2900000000.000000, energy = 0.000362
freq = 2900000000.000000, energy = 0.000226
####

A high value decreses until near zero and then a high value appears again.

Any suggestion of what I'm doing wrong ?
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Re: N210 + SBX High peaks at center frequency.

maiconkist
One more thing: the FFT in the "uhd_fft" is mirrored around the central frequency.
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Re: N210 + SBX High peaks at center frequency.

maiconkist
I attached an image of the output of the uhd_fft program. Any frequency that I try give the same output.

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