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Re: [Discuss-gnuradio] What's the meaning of the m.data in usrp_spectrum
Re: [Discuss-gnuradio] What's the meaning of the m.data in usrp_spectrum_sense.py?
Tue, 23 Dec 2008 17:01:45 -0800 (PST)
Thanks！Now I get it.
Eric Blossom wrote:
> On Tue, Dec 23, 2008 at 05:52:03AM -0800, Ling Huang wrote:
>> I've change the usrp_spectrum_sense.py to print out the m.data. And I got
>> the numbers like 9376200 2976546 34170452.... But I just don't understand
>> what these numbers stand for . Are they stand for the power or the
>> And what's these numbers' dimension?
>> Sorry for my bad English.
> They are the single precision floating point magnitude squared of the
> FFT output. That is, for each FFT bin[i], mag_squared[i] = re[i]*re[i] +
> If you want power, take the square root. We don't do it by default
> since most users are going to be computing a log somewhere downstream,
> and the square root can be trivially folded into that calculation.
> To see what the FFT bins contain, see the FFTW documentation (fftw.org).
> The actual mapping from the levels at the daughterboard antenna port
> to sample values depends on a lot of factors including any
> daughterboard gain and decimation specific gain in the digital down
> converter. You'll need to calibrate the system if you need something
> that maps to dBm.
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