3 from gnuradio import gr, eng_notation
4 from gnuradio import audio
5 from gnuradio import usrp
6 from gnuradio.eng_option import eng_option
7 from optparse import OptionParser
11 from gnuradio.wxgui import stdgui, fftsink
14 class am_rx_graph (stdgui.gui_flow_graph):
15 def __init__(self,frame,panel,vbox,argv):
16 stdgui.gui_flow_graph.__init__ (self,frame,panel,vbox,argv)
18 station = parseargs(argv[1:])
20 IF_freq = offset_freq - station
24 if_rate = adc_rate / usrp_decim # 256 kHz
26 demod_rate = if_rate / if_decim # 64 kHz
28 audio_rate = demod_rate / audio_decimation # 16 kHz
31 src = usrp.source_c (0, usrp_decim)
32 src.set_rx_freq (0, IF_freq)
33 actual_IF_freq =src.rx_freq(0)
34 actual_offset = actual_IF_freq + station
40 # sound card as final sink
41 audio_sink = audio.sink (int (audio_rate))
44 gr.firdes.low_pass (1.0, # gain
45 if_rate, # sampling rate
46 9e3, # low pass cutoff freq
47 10e3, # width of trans. band
50 ddc = gr.freq_xlating_fir_filter_ccf (if_decim,channel_coeffs,-actual_offset,if_rate)
52 magblock = gr.complex_to_mag()
53 volumecontrol = gr.multiply_const_ff(.003)
55 # Deemphasis. Is this necessary on AM?
56 TAU = 75e-6 # 75us in US, 50us in EUR
57 fftaps = [ 1 - math.exp(-1/TAU/if_rate), 0]
58 fbtaps= [ 0 , math.exp(-1/TAU/if_rate) ]
60 deemph = gr.iir_filter_ffd(fftaps,fbtaps)
62 # compute FIR filter taps for audio filter
63 width_of_transition_band = audio_rate / 8
64 audio_coeffs = gr.firdes.low_pass (1.0, # gain
65 if_rate, # sampling rate
66 9e3, #audio_rate/2 - width_of_transition_band,
67 4e3, # width_of_transition_band,
70 # input: float; output: float
71 audio_filter = gr.fir_filter_fff (audio_decimation, audio_coeffs)
76 print len(channel_coeffs)
77 print len(audio_coeffs)
79 # now wire it all together
80 self.connect (src, ddc)
81 self.connect (ddc, magblock)
82 self.connect (magblock, volumecontrol)
83 self.connect (volumecontrol,deemph)
84 self.connect (deemph,audio_filter)
85 self.connect (audio_filter, (audio_sink, 0))
88 pre_demod = fftsink.fft_sink_c (self, panel, title="Pre-Demodulation", fft_size=128, sample_rate=if_rate)
89 self.connect (src, pre_demod)
90 vbox.Add (pre_demod.win, 1, wx.EXPAND)
93 post_demod = fftsink.fft_sink_c (self, panel, title="Post Demodulation", fft_size=256, sample_rate=demod_rate)
94 self.connect (ddc, post_demod)
95 vbox.Add (post_demod.win, 1, wx.EXPAND)
98 post_filt = fftsink.fft_sink_f (self, panel, title="Post Filter", fft_size=512, sample_rate=audio_rate)
99 self.connect (magblock,post_filt)
100 vbox.Add (post_filt.win, 1, wx.EXPAND)
102 def parseargs (args):
105 freq1 = float (args[0]) * 1e3
107 sys.stderr.write ('usage: am_rcv freq1\n')
112 if __name__ == '__main__':
113 app = stdgui.stdapp (am_rx_graph, "AM RX")