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#!/usr/bin/env python
from gnuradio import gr, eng_notation
from gnuradio import audio
# from gnuradio import usrp
from gnuradio.eng_option import eng_option
from optparse import OptionParser
import sys
import math
#
# return a gr.flow_graph
#
def build_graph (input_filename, repeat):
adc_rate = 64e6 # USRP A/D sampling rate
decim = 250 # FPGA decimated by this amount
quad_rate = adc_rate / decim # 256 kHz (the sample rate of the file)
audio_decimation = 8
audio_rate = quad_rate / audio_decimation # 32 kHz
fg = gr.flow_graph ()
# usrp is data source
# src = usrp.source_c (0, decim)
# src.set_rx_freq (0, -IF_freq)
src = gr.file_source (gr.sizeof_gr_complex, input_filename, repeat)
(head, tail) = build_pipeline (fg, quad_rate, audio_decimation)
# sound card as final sink
audio_sink = audio.sink (int (audio_rate))
# now wire it all together
fg.connect (src, head)
fg.connect (tail, (audio_sink, 0))
return fg
def build_pipeline (fg, quad_rate, audio_decimation):
'''Given a flow_graph, fg, construct a pipeline
for demodulating a broadcast FM signal. The
input is the downconverteed complex baseband
signal. The output is the demodulated audio.
build_pipeline returns a two element tuple
containing the input and output endpoints.
'''
fm_demod_gain = 2200.0/32768.0
audio_rate = quad_rate / audio_decimation
volume = 1.0
# input: complex; output: float
fm_demod = gr.quadrature_demod_cf (volume*fm_demod_gain)
# compute FIR filter taps for audio filter
width_of_transition_band = audio_rate / 32
audio_coeffs = gr.firdes.low_pass (1.0, # gain
quad_rate, # sampling rate
audio_rate/2 - width_of_transition_band,
width_of_transition_band,
gr.firdes.WIN_HAMMING)
TAU = 75e-6 # 75us in US, 50us in EUR
fftaps = [ 1 - math.exp(-1/TAU/quad_rate), 0]
fbtaps= [ 0 , math.exp(-1/TAU/quad_rate) ]
deemph = gr.iir_filter_ffd(fftaps,fbtaps)
# input: float; output: float
audio_filter = gr.fir_filter_fff (audio_decimation, audio_coeffs)
fg.connect (fm_demod, deemph)
fg.connect (deemph, audio_filter)
return ((fm_demod, 0), (audio_filter, 0))
def main ():
usage = "usage: %prog [options] filename"
parser = OptionParser (option_class=eng_option, usage=usage)
parser.add_option ("-r", "--repeat", action="store_true", default=False)
# parser.add_option (... your stuff here...)
(options, args) = parser.parse_args ()
if len (args) != 1:
parser.print_help ()
sys.exit (1)
fg = build_graph (args[0], options.repeat)
fg.start () # fork thread(s) and return
raw_input ('Press Enter to quit: ')
fg.stop ()
if __name__ == '__main__':
main ()
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