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

From: mleech
Subject: Re: [Discuss-gnuradio] working with WFM sample data
Date: Tue, 14 Feb 2012 15:18:47 -0500
User-agent: Roundcube Webmail/0.5.1

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:


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):
line 187, in _on_paint
     for fcn in self._draw_fcns: fcn[1]()
line 59, in draw
line 395, in _draw_point_label
     label_str = self._populate_point_label(x_val, y_val)
line 150, in _populate_point_label
     label_str += '\n%s: %s'%(channel, common.eng_format(y_value, 
line 82, in eng_format
     coeff, exp, prefix = get_si_components(num)
line 48, in get_si_components
     exp = get_exp(num)
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

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