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[Discuss-gnuradio] working with WFM sample data

From: emilio gonzalez
Subject: [Discuss-gnuradio] working with WFM sample data
Date: Tue, 14 Feb 2012 12:02:34 -0800
User-agent: RoundCube Webmail/0.5.2


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
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

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