Re: [Discuss-gnuradio] working with WFM sample data

[mleech]

It's very likely that your on-disk sample format isn't what you've declared to Gnu Radio, and it's seeing some garbage numbers.

Is it possible that it's stored as 16-bit I 16-bit Q in the file?   If so, you'll need to convert it before any of your complex-float blocks do anything with it.

 

On Tue, 14 Feb 2012 12:02:34 -0800, emilio gonzalez wrote:

> hello!
>
> i'm a new user embarking on some exploration to evaluate GNUradio and 
> the USRP platform for some multichannel radio monitoring.  i am starting 
> with sample file processing before buying any hardware, as CPU usage is 
> my chief concern.
>
> my problem is with using a large sample file captured from the FM 
> broadcast-band:  i can't get it to work with the simplest of graphs in 
> GRC.  i was able to use Sharlene Katz's handy GRC tutorials to get her 
> AM sample file running through an FFT scope and demodulated to audio, so 
> i know my GNUradio install is working.  however, running my WFM sample 
> file results in no activity on the FFT scope, and i get errors when 
> mousing over the FFT window.
>
> the sample file was described to me as 32-bit complex IQ baseband, 
> 98.0MHz center, 25Msps, gain 30 from an N200r4 + WBX.  to try a very 
> simple graph, i loaded it in to the GRC like this:
> [ File Source (complex) ]
>    -> [ Throttle (complex, 25M) ]
>      -> [ FFT Sink (complex, 25M rate, baseband 98M) ]
>
> running this graph results in an FFT scope with no activity; cutting 
> the sample rates to 250k has no effect.  if i mouse over the FFT window 
> i get this error:
> ****
> Traceback (most recent call last):
>    File 
> "/opt/local/lib/python2.6/site-packages/gnuradio/wxgui/plotter/plotter_base.py", 
> line 187, in _on_paint
>      for fcn in self._draw_fcns: fcn[1]()
>    File 
> "/opt/local/lib/python2.6/site-packages/gnuradio/wxgui/plotter/plotter_base.py", 
> line 59, in draw
>      self._draw()
>    File 
> "/opt/local/lib/python2.6/site-packages/gnuradio/wxgui/plotter/grid_plotter_base.py", 
> line 395, in _draw_point_label
>      label_str = self._populate_point_label(x_val, y_val)
>    File 
> "/opt/local/lib/python2.6/site-packages/gnuradio/wxgui/plotter/channel_plotter.py", 
> line 150, in _populate_point_label
>      label_str += '\n%s: %s'%(channel, common.eng_format(y_value, 
> self.y_units))
>    File 
> "/opt/local/lib/python2.6/site-packages/gnuradio/wxgui/plotter/common.py", 
> line 82, in eng_format
>      coeff, exp, prefix = get_si_components(num)
>    File 
> "/opt/local/lib/python2.6/site-packages/gnuradio/wxgui/plotter/common.py", 
> line 48, in get_si_components
>      exp = get_exp(num)
>    File 
> "/opt/local/lib/python2.6/site-packages/gnuradio/wxgui/plotter/common.py", 
> line 37, in get_exp
>      return int(math.floor(math.log10(abs(num))))
> ValueError: cannot convert float NaN to integer
> ****
>
> relevant info:  GNUradio 3.3.0, Python 2.6, Mac OS 10.7.3, MacPorts 
> install.  sample data is stored on an internal hard drive.
>
> this seems like a pretty simple task, so there's either something 
> simple i'm missing or there's a bug or misconfiguration in my install.  
> any help would be appreciated - i've got a lot to figure out with this 
> file, but i can't seem to get past this step.
>
> thank you,
> - emilio gonzalez
>    KI6NVO
>
>
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