Working with WFM sample data

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: fcn1
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

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: fcn1
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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