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   1 #
   2 # Copyright 2005,2006 Free Software Foundation, Inc.
   3 #
   4 # This file is part of GNU Radio
   5 #
   6 # GNU Radio is free software; you can redistribute it and/or modify
   7 # it under the terms of the GNU General Public License as published by
   8 # the Free Software Foundation; either version 3, or (at your option)
   9 # any later version.
  10 #
  11 # GNU Radio is distributed in the hope that it will be useful,
  12 # but WITHOUT ANY WARRANTY; without even the implied warranty of
  13 # MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  14 # GNU General Public License for more details.
  15 #
  16 # You should have received a copy of the GNU General Public License
  17 # along with GNU Radio; see the file COPYING.  If not, write to
  18 # the Free Software Foundation, Inc., 51 Franklin Street,
  19 # Boston, MA 02110-1301, USA.
  20 #
  21
  22 from gnuradio import gr
  23 from gnuradio.blks2impl.fm_emph import fm_deemph
  24 import math
  25
  26 class wfm_rcv_fmdet(gr.hier_block2):
  27     def __init__ (self, demod_rate, audio_decimation):
  28         """
  29         Hierarchical block for demodulating a broadcast FM signal.
  30
  31         The input is the downconverted complex baseband signal (gr_complex).
  32         The output is two streams of the demodulated audio (float) 0=Left, 1=Right.
  33
  34         @param demod_rate: input sample rate of complex baseband input.
  35         @type demod_rate: float
  36         @param audio_decimation: how much to decimate demod_rate to get to audio.
  37         @type audio_decimation: integer
  38         """
  39         gr.hier_block2.__init__(self, "wfm_rcv_fmdet",
  40                                 gr.io_signature(1, 1, gr.sizeof_gr_complex), # Input signature
  41                                 gr.io_signature(2, 2, gr.sizeof_float))      # Output signature
  42         lowfreq = -125e3
  43         highfreq = 125e3
  44         audio_rate = demod_rate / audio_decimation
  45
  46
  47         # We assign to self so that outsiders can grab the demodulator
  48         # if they need to.  E.g., to plot its output.
  49         #
  50         # input: complex; output: float
  51
  52         self.fm_demod = gr.fmdet_cf (demod_rate, lowfreq, highfreq, 0.05)
  53
  54         # input: float; output: float
  55         self.deemph_Left  = fm_deemph (audio_rate)
  56         self.deemph_Right = fm_deemph (audio_rate)
  57
  58         # compute FIR filter taps for audio filter
  59         width_of_transition_band = audio_rate / 32
  60         audio_coeffs = gr.firdes.low_pass (1.0 ,         # gain
  61                                            demod_rate,      # sampling rate
  62                                            15000 ,
  63                                            width_of_transition_band,
  64                                            gr.firdes.WIN_HAMMING)
  65         # input: float; output: float
  66         self.audio_filter = gr.fir_filter_fff (audio_decimation, audio_coeffs)
  67         if 1:
  68             # Pick off the stereo carrier/2 with this filter. It attenuated 10 dB so apply 10 dB gain
  69             # We pick off the negative frequency half because we want to base band by it!
  70             ##  NOTE  THIS WAS HACKED TO OFFSET INSERTION LOSS DUE TO DEEMPHASIS
  71
  72             stereo_carrier_filter_coeffs = gr.firdes.complex_band_pass(10.0,
  73                                                                    demod_rate,
  74                                                                    -19020,
  75                                                                    -18980,
  76                                                                    width_of_transition_band,
  77                                                                    gr.firdes.WIN_HAMMING)
  78
  79             #print "len stereo carrier filter = ",len(stereo_carrier_filter_coeffs)
  80             #print "stereo carrier filter ", stereo_carrier_filter_coeffs
  81             #print "width of transition band = ",width_of_transition_band, " audio rate = ", audio_rate
  82
  83             # Pick off the double side band suppressed carrier Left-Right audio. It is attenuated 10 dB so apply 10 dB gain
  84
  85             stereo_dsbsc_filter_coeffs = gr.firdes.complex_band_pass(20.0,
  86                                                                      demod_rate,
  87                                                                      38000-15000/2,
  88                                                                      38000+15000/2,
  89                                                                      width_of_transition_band,
  90                                                                      gr.firdes.WIN_HAMMING)
  91             #print "len stereo dsbsc filter = ",len(stereo_dsbsc_filter_coeffs)
  92             #print "stereo dsbsc filter ", stereo_dsbsc_filter_coeffs
  93             # construct overlap add filter system from coefficients for stereo carrier
  94
  95             self.stereo_carrier_filter = gr.fir_filter_fcc(audio_decimation, stereo_carrier_filter_coeffs)
  96
  97             # carrier is twice the picked off carrier so arrange to do a commplex multiply
  98
  99             self.stereo_carrier_generator = gr.multiply_cc();
 100
 101             # Pick off the rds signal
 102
 103             stereo_rds_filter_coeffs = gr.firdes.complex_band_pass(30.0,
 104                                                                      demod_rate,
 105                                                                      57000 - 1500,
 106                                                                      57000 + 1500,
 107                                                                      width_of_transition_band,
 108                                                                      gr.firdes.WIN_HAMMING)
 109             #print "len stereo dsbsc filter = ",len(stereo_dsbsc_filter_coeffs)
 110             #print "stereo dsbsc filter ", stereo_dsbsc_filter_coeffs
 111             # construct overlap add filter system from coefficients for stereo carrier
 112
 113             self.rds_signal_filter = gr.fir_filter_fcc(audio_decimation, stereo_rds_filter_coeffs)
 114
 115
 116
 117
 118
 119
 120             self.rds_carrier_generator = gr.multiply_cc();
 121             self.rds_signal_generator = gr.multiply_cc();
 122             self_rds_signal_processor = gr.null_sink(gr.sizeof_gr_complex);
 123
 124
 125
 126             alpha = 5 * 0.25 * math.pi / (audio_rate)
 127             beta = alpha * alpha / 4.0
 128             max_freq = -2.0*math.pi*18990/audio_rate;
 129             min_freq = -2.0*math.pi*19010/audio_rate;
 130
 131             self.stereo_carrier_pll_recovery = gr.pll_refout_cc(alpha,beta,max_freq,min_freq);
 132             #self.stereo_carrier_pll_recovery.squelch_enable(False) #pll_refout does not have squelch yet, so disabled for now
 133
 134
 135             # set up mixer (multiplier) to get the L-R signal at baseband
 136
 137             self.stereo_basebander = gr.multiply_cc();
 138
 139             # pick off the real component of the basebanded L-R signal.  The imaginary SHOULD be zero
 140
 141             self.LmR_real = gr.complex_to_real();
 142             self.Make_Left = gr.add_ff();
 143             self.Make_Right = gr.sub_ff();
 144
 145             self.stereo_dsbsc_filter = gr.fir_filter_fcc(audio_decimation, stereo_dsbsc_filter_coeffs)
 146
 147
 148         if 1:
 149
 150             # send the real signal to complex filter to pick off the carrier and then to one side of a multiplier
 151             self.connect (self, self.fm_demod,self.stereo_carrier_filter,self.stereo_carrier_pll_recovery, (self.stereo_carrier_generator,0))
 152             # send the already filtered carrier to the otherside of the carrier
 153             self.connect (self.stereo_carrier_pll_recovery, (self.stereo_carrier_generator,1))
 154             # the resulting signal from this multiplier is the carrier with correct phase but at -38000 Hz.
 155
 156             # send the new carrier to one side of the mixer (multiplier)
 157             self.connect (self.stereo_carrier_generator, (self.stereo_basebander,0))
 158             # send the demphasized audio to the DSBSC pick off filter,  the complex
 159             # DSBSC signal at +38000 Hz is sent to the other side of the mixer/multiplier
 160             self.connect (self.fm_demod,self.stereo_dsbsc_filter, (self.stereo_basebander,1))
 161             # the result is BASEBANDED DSBSC with phase zero!
 162
 163             # Pick off the real part since the imaginary is theoretically zero and then to one side of a summer
 164             self.connect (self.stereo_basebander, self.LmR_real, (self.Make_Left,0))
 165             #take the same real part of the DSBSC baseband signal and send it to negative side of a subtracter
 166             self.connect (self.LmR_real,(self.Make_Right,1))
 167
 168             # Make rds carrier by taking the squared pilot tone and multiplying by pilot tone
 169             self.connect (self.stereo_basebander,(self.rds_carrier_generator,0))
 170             self.connect (self.stereo_carrier_pll_recovery,(self.rds_carrier_generator,1))
 171             # take signal, filter off rds,  send into mixer 0 channel
 172             self.connect (self.fm_demod,self.rds_signal_filter,(self.rds_signal_generator,0))
 173             # take rds_carrier_generator output and send into mixer 1 channel
 174             self.connect (self.rds_carrier_generator,(self.rds_signal_generator,1))
 175             # send basebanded rds signal and send into "processor" which for now is a null sink
 176             self.connect (self.rds_signal_generator,self_rds_signal_processor)
 177
 178
 179         if 1:
 180             # pick off the audio, L+R that is what we used to have and send it to the summer
 181             self.connect(self.fm_demod, self.audio_filter, (self.Make_Left, 1))
 182             # take the picked off L+R audio and send it to the PLUS side of the subtractor
 183             self.connect(self.audio_filter,(self.Make_Right, 0))
 184             # The result of  Make_Left  gets    (L+R) +  (L-R) and results in 2*L
 185             # The result of Make_Right gets  (L+R) - (L-R) and results in 2*R
 186             self.connect(self.Make_Left , self.deemph_Left, (self, 0))
 187             self.connect(self.Make_Right, self.deemph_Right, (self, 1))
 188         # NOTE: mono support will require variable number of outputs in hier_block2s
 189         # See ticket:174 in Trac database
 190         #else:
 191         #    self.connect (self.fm_demod, self.audio_filter, self)