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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
from gnuradio.wxgui import stdgui, fftsink
import wx
class am_rx_graph (stdgui.gui_flow_graph):
def __init__(self,frame,panel,vbox,argv):
stdgui.gui_flow_graph.__init__ (self,frame,panel,vbox,argv)
station = parseargs(argv[1:])
offset_freq = 30e3
IF_freq = offset_freq - station
adc_rate = 64e6
usrp_decim = 250
if_rate = adc_rate / usrp_decim # 256 kHz
if_decim = 4
demod_rate = if_rate / if_decim # 64 kHz
audio_decimation = 2
audio_rate = demod_rate / audio_decimation # 16 kHz
# usrp is data source
src = usrp.source_c (0, usrp_decim)
src.set_rx_freq (0, IF_freq)
actual_IF_freq =src.rx_freq(0)
actual_offset = actual_IF_freq + station
#print actual_IF_freq
#print actual_offset
src.set_pga(0,20)
# sound card as final sink
audio_sink = audio.sink (int (audio_rate))
channel_coeffs = \
gr.firdes.low_pass (1.0, # gain
if_rate, # sampling rate
9e3, # low pass cutoff freq
10e3, # width of trans. band
gr.firdes.WIN_HANN)
ddc = gr.freq_xlating_fir_filter_ccf (if_decim,channel_coeffs,-actual_offset,if_rate)
magblock = gr.complex_to_mag()
volumecontrol = gr.multiply_const_ff(.003)
# Deemphasis. Is this necessary on AM?
TAU = 75e-6 # 75us in US, 50us in EUR
fftaps = [ 1 - math.exp(-1/TAU/if_rate), 0]
fbtaps= [ 0 , math.exp(-1/TAU/if_rate) ]
deemph = gr.iir_filter_ffd(fftaps,fbtaps)
# compute FIR filter taps for audio filter
width_of_transition_band = audio_rate / 8
audio_coeffs = gr.firdes.low_pass (1.0, # gain
if_rate, # sampling rate
9e3, #audio_rate/2 - width_of_transition_band,
4e3, # width_of_transition_band,
gr.firdes.WIN_HANN)
# input: float; output: float
audio_filter = gr.fir_filter_fff (audio_decimation, audio_coeffs)
print len(channel_coeffs)
print len(audio_coeffs)
# now wire it all together
self.connect (src, ddc)
self.connect (ddc, magblock)
self.connect (magblock, volumecontrol)
self.connect (volumecontrol,deemph)
self.connect (deemph,audio_filter)
self.connect (audio_filter, (audio_sink, 0))
if 1:
pre_demod = fftsink.fft_sink_c (self, panel, title="Pre-Demodulation", fft_size=128, sample_rate=if_rate)
self.connect (src, pre_demod)
vbox.Add (pre_demod.win, 1, wx.EXPAND)
if 0:
post_demod = fftsink.fft_sink_c (self, panel, title="Post Demodulation", fft_size=256, sample_rate=demod_rate)
self.connect (ddc, post_demod)
vbox.Add (post_demod.win, 1, wx.EXPAND)
if 0:
post_filt = fftsink.fft_sink_f (self, panel, title="Post Filter", fft_size=512, sample_rate=audio_rate)
self.connect (magblock,post_filt)
vbox.Add (post_filt.win, 1, wx.EXPAND)
def parseargs (args):
nargs = len (args)
if nargs == 1:
freq1 = float (args[0]) * 1e3
else:
sys.stderr.write ('usage: am_rcv freq1\n')
sys.exit (1)
return freq1
if __name__ == '__main__':
app = stdgui.stdapp (am_rx_graph, "AM RX")
app.MainLoop ()
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