# N210 + SBX High peaks at center frequency

**URL:** <https://www.ruby-forum.com/t/n210-sbx-high-peaks-at-center-frequency/229824>\
**Category:** GNU Radio\
**Created:** [February 8, 2013, 2:37pm UTC](https://www.ruby-forum.com/t/n210-sbx-high-peaks-at-center-frequency/229824 "2013-02-08T14:37:10Z")\
**Posts on this page:** 3\
**Page:** 1

<div class="post-metadata">

**Author:** ![maiconkist](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/m/7bcc69/32.png) [@maiconkist](https://www.ruby-forum.com/u/maiconkist)\
**Post date:** [February 8, 2013, 2:37pm UTC](https://www.ruby-forum.com/t/n210-sbx-high-peaks-at-center-frequency/229824/1 "2013-02-08T14:37:10Z")

</div>

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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---

<div class="post-metadata">

**Author:** ![maiconkist](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/m/7bcc69/32.png) [@maiconkist](https://www.ruby-forum.com/u/maiconkist)\
**Post date:** [February 8, 2013, 4:48pm UTC](https://www.ruby-forum.com/t/n210-sbx-high-peaks-at-center-frequency/229824/2 "2013-02-08T16:48:02Z")

</div>

One more thing: the FFT in the “uhd\_fft” is mirrored around the central  
frequency.

–  
View this message in context:  
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Sent from the GnuRadio mailing list archive at [Nabble.com](http://Nabble.com).

---

<div class="post-metadata">

**Author:** ![maiconkist](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/m/7bcc69/32.png) [@maiconkist](https://www.ruby-forum.com/u/maiconkist)\
**Post date:** [February 13, 2013, 6:51pm UTC](https://www.ruby-forum.com/t/n210-sbx-high-peaks-at-center-frequency/229824/3 "2013-02-13T18:51:49Z")

</div>

I attached an image of the output of the uhd\_fft program. Any frequency  
that  
I try give the same output.

[http://gnuradio.4.n7.nabble.com/file/n39601/uhd\_fft.jpg](http://gnuradio.4.n7.nabble.com/file/n39601/uhd_fft.jpg)

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View this message in context:  
[http://gnuradio.4.n7.nabble.com/N210-SBX-High-peaks-at-center-frequency-tp39489p39601.html](http://gnuradio.4.n7.nabble.com/N210-SBX-High-peaks-at-center-frequency-tp39489p39601.html)  
Sent from the GnuRadio mailing list archive at [Nabble.com](http://Nabble.com).