Re: [Discuss-gnuradio] sensed spectrum in dB???

[Brian Padalino]

On Mon, Sep 22, 2008 at 9:19 AM, kaleem ahmad <address@hidden> wrote:
>
> Hi All,
>
> I am using USRP+RFX2400+SUSI 10.3.
>
> Many people have already discussed "usrp_spectrum_sense.py" and I read all
> those threads but unfortunately it didnt solve my problem and didnt help me
> to understand the file completely, I have two questions in this file and
> will be thankful if some one can help me.
>
> First, what is in m.data???
>
> First, what the following piece of code is doing??? Is it converting m.data
> to power in dB?? If not please help me to find how this code can be changed
> so that I get power dB at any given center frequency.
> ///////////////////////////////////////////////////////////////////////////////////////////////////////////////////
> power = 0
>        for tap in mywindow:
>            power += tap*tap
>
>        c2mag = gr.complex_to_mag_squared(self.fft_size)
>
>        # FIXME the log10 primitive is dog slow
>        log = gr.nlog10_ff(10, self.fft_size,
>
> -20*math.log10(self.fft_size)-10*math.log10(power/self.fft_size))
> ////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////

It sure looks like it's calculating power in dB with all those
log10's.  A quick Googling led me here for a discussion on FIR filters
and normalization:

    http://www.hydrogenaudio.org/forums/index.php?showtopic=43195

Good luck!

Brian