Hi-
I have a python app which seems to corrupt points when I use it to
demodulate a data stream stored in a file and write the de-modulated
result back to a file. I've attached the python code, and an image of
the problem can be seen at
www.nd.edu/~ematlis/z.gnuradio/waveform.jpg
The modulated waveform is shown in the top plot and the demodulated output
in the bottom plot.
The signal was acquired with a Lecroy digital oscilloscope; it's a 100 kHz
sine AM modulated at 10 kHz.
As you can see from the image, while the original modulated data shows no
corruption in 10002 points, the demodulated data has the first 875-900
points incorrectly set to close to zero. This is repeatable.
Could it have anything to do with the fact that I'm generating a gui?
Could the time it takes to generate the gui window interfere with the
operation of the demodulation? If I were to make this just a script, ie
with no scope or fft sink, and no gui box, would it affect things? (And
p.s., how would I do that?)
thanks,
eric
************************************
Eric H. Matlis, Ph.D.
Aerospace & Mechanical Engineering Dept.
120 Hessert Center for Aerospace Research
University of Notre Dame
Notre Dame, IN 46556-5684
Phone: (574) 631-6054
Fax: (574) 631-8355
#!/usr/bin/env python
from gnuradio import gr, gru
from gnuradio.wxgui import stdgui, fftsink, scopesink, form, slider
from gnuradio.eng_option import eng_option
from optparse import OptionParser
import sys
import os
import wx
import scopesink_mod as scopesink
plot1 = 0
plot2 = 0
plot3 = 0
record = 1
class app_flow_graph (stdgui.gui_flow_graph):
def __init__(self, frame, panel, vbox, argv):
stdgui.gui_flow_graph.__init__ (self, frame, panel, vbox, argv)
usage = "usage: %prog filename \n Demodulates AM from filename "
parser = OptionParser (option_class=eng_option, usage=usage)
parser.add_option("-N", "--nsamples", type="eng_float", default=2000,
help="number of samples to collect [default=+inf]")
(options, args) = parser.parse_args ()
if len (args) != 1:
parser.print_help ()
sys.exit (1)
FILENAME = args[0]
SHOW = True
sampling_freq = 5e6
filename = argv[1]
lpf_coeffs = gr.firdes.low_pass (1, # gain
sampling_freq, # sampling rate
150e3, # passband cutoff
10e3, # width of transition
band
gr.firdes.WIN_HANN)
self.lpf = gr.fir_filter_fff (1,lpf_coeffs)
# file is our source.
self.src = gr.file_source (gr.sizeof_float, filename, 1)
self.throttle = gr.throttle(gr.sizeof_float,sampling_freq)
self.head = gr.head(gr.sizeof_float, int(options.nsamples))
self.recording = gr.file_sink(gr.sizeof_float, "test.bin")
if plot1:
self.pre_demod = fftsink.fft_sink_f (self, panel, title="Source
Spectrum", fft_size=8192, sample_rate=sampling_freq, size=(50,100))
self.connect (self.src, self.pre_demod)
vbox.Add (self.pre_demod.win, 1, wx.EXPAND)
# demodulate AM
self.hilb_filt = gr.firdes_hilbert (201, gr.firdes.WIN_BLACKMAN)
self.hilb_delay = gr.filter_delay_fc (self.hilb_filt)
self.mag = gr.complex_to_mag ()
self.connect (self.src, (self.hilb_delay,0))
self.connect ((self.hilb_delay,0),self.mag)
self.connect (self.mag, self.lpf)
if record:
self.connect (self.lpf,self.head,self.recording)
#self.connect (self.lpf,self.recording)
#self.connect (self.mag,self.head,self.recording)
if plot2:
self.src_fft = fftsink.fft_sink_f (self, panel, title="FFT",
fft_size=4096,sample_rate=sampling_freq, size=(50,100))
self.connect (self.lpf, self.src_fft)
vbox.Add (self.src_fft.win, 1, wx.EXPAND)
if plot3:
self.scope = scopesink.scope_sink_f(self, panel, title="Time
Series", sample_rate=sampling_freq,
size=(50,100), t_scale=1.0e-3, v_scale=None)
self.connect(self.lpf, self.scope)
vbox.Add (self.scope.win, 1, wx.EXPAND)
def main ():
app = stdgui.stdapp(app_flow_graph, "Plasma Probe Spectrum", nstatus=1)
app.MainLoop()
if __name__ == '__main__':
main ()
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