Re: [Discuss-gnuradio] usrp_spectrum_sense.py FFT bin values are all zero.

[Jincheng Zhang]

Thanks Mike. I'm a little confused. The parameters are listed as follows:

sample-rate: 

channel-bandwidth:

freq_step:

fft_size:

You mean that I should set sample-rate be 25e6, channel-bandwidth be 8e6, freq_step be 8e6 and fft_size be 25?

If we set the fft-size be 25, then which 8 bins I should select to calculate the power? By the way, since the magnitude of FFT bin is decimal, maybe I should change the magnitude of FFT bin values to mw and add the 8 bins, and then transfer to decimal again? Since we cannot straightly add the FFT bin values in decimal. 

By the way, how about the "self.connect", should I add the log parameter to it? 

Thanks. Hope for your reply.

On Mon, Apr 8, 2013 at 12:11 AM, Mike Jameson <address@hidden> wrote:

Hi Jincheng,

Try setting the UHD sample rate to 25e6 and the number of fft bins to 25 which will give you 1e6 Hz per bin.  Adding up the magnitude of 8 bins (1MHz * 8 = 8MHz) will therefore give you the wanted channel power in decimal format (magnitude).

In case you are confused, I recently updated usrp_spectrum_sense.py to include a --channel-bandwidth setting which rounds up the frequency displayed to the nearest frequency.  I'm working on making it cleaner by adjusting the fft size to match the wanted channel.  In the meantime, set '--channel-bandwidth=8e6' to make the frequency round to the nearest 8MHz frequency.

Hope that helps,

Mike

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Mike Jameson M0MIK BSc
Email: address@hidden
Web: http://scanoo.com

On 7 April 2013 16:23, Jincheng Zhang <address@hidden> wrote:

I want to use usrp_spectrum_sense.py to sweep the Hong Kong TV band which ranges from 470MHz to 806MHz and get every channel's power in dB. Each channel's frequency band is 8MHz. 

Now I'm using USRP2 with TVRX2 daughter board. I have installed the latest gnuraio and uhd. But when I use the usrp_spectrum_sense.py to get the power of each channel, some FFT bin values are extremely big. In particular, I'm not sure abou the self.connect(self.u, s2v, fft, c2mag, stats). It doesn't take "log" as the parameter, 

FFT size is 2048, sample-rate is 12.5MHz(to let the decimation be 8M), freq_step is 8MHz. Anyone has any ideas about how to use usrp_spectrum_sense.py to calculate each channel's power?

On Sun, Apr 7, 2013 at 8:24 PM, Jincheng Zhang <address@hidden> wrote:

Hi, all,

   I use the usrp_spectrum_sense.py to sweep the TV band from 470MHz to 806MHz. But when I use self.connect(self.u, s2v, fft, c2mag, log, stats), the FFT bin values I got are all zero. 

  Also, what's the magnitude of FFT bin value? Thanks. 

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Best regards,

Jincheng Zhang

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Best regards,

Jincheng Zhang
Department of Information Engineering

The Chinese University of Hong Kong

http://personal.ie.cuhk.edu.hk/~zj012/

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Best regards,

Jincheng Zhang
Department of Information Engineering

The Chinese University of Hong Kong

http://personal.ie.cuhk.edu.hk/~zj012/