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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_pll(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_pll",
  40                                 gr.io_signature(1, 1, gr.sizeof_gr_complex), # Input signature
  41                                 gr.io_signature(2, 2, gr.sizeof_float))      # Output signature
  42         bandwidth = 250e3
  43         audio_rate = demod_rate / audio_decimation
  44
  45
  46         # We assign to self so that outsiders can grab the demodulator
  47         # if they need to.  E.g., to plot its output.
  48         #
  49         # input: complex; output: float
  50         alpha = 0.25*bandwidth * math.pi / demod_rate
  51         beta = alpha * alpha / 4.0
  52         max_freq = 2.0*math.pi*90e3/demod_rate
  53
  54         self.fm_demod = gr.pll_freqdet_cf (alpha,beta,max_freq,-max_freq)
  55
  56         # input: float; output: float
  57         self.deemph_Left  = fm_deemph (audio_rate)
  58         self.deemph_Right = fm_deemph (audio_rate)
  59
  60         # compute FIR filter taps for audio filter
  61         width_of_transition_band = audio_rate / 32
  62         audio_coeffs = gr.firdes.low_pass (1.0 ,         # gain
  63                                            demod_rate,      # sampling rate
  64                                            15000 ,
  65                                            width_of_transition_band,
  66                                            gr.firdes.WIN_HAMMING)
  67         # input: float; output: float
  68         self.audio_filter = gr.fir_filter_fff (audio_decimation, audio_coeffs)
  69         if 1:
  70             # Pick off the stereo carrier/2 with this filter. It attenuated 10 dB so apply 10 dB gain
  71             # We pick off the negative frequency half because we want to base band by it!
  72             ##  NOTE  THIS WAS HACKED TO OFFSET INSERTION LOSS DUE TO DEEMPHASIS
  73
  74             stereo_carrier_filter_coeffs = gr.firdes.complex_band_pass(10.0,
  75                                                                    demod_rate,
  76                                                                    -19020,
  77                                                                    -18980,
  78                                                                    width_of_transition_band,
  79                                                                    gr.firdes.WIN_HAMMING)
  80
  81             #print "len stereo carrier filter = ",len(stereo_carrier_filter_coeffs)
  82             #print "stereo carrier filter ", stereo_carrier_filter_coeffs
  83             #print "width of transition band = ",width_of_transition_band, " audio rate = ", audio_rate
  84
  85             # Pick off the double side band suppressed carrier Left-Right audio. It is attenuated 10 dB so apply 10 dB gain
  86
  87             stereo_dsbsc_filter_coeffs = gr.firdes.complex_band_pass(20.0,
  88                                                                      demod_rate,
  89                                                                      38000-15000/2,
  90                                                                      38000+15000/2,
  91                                                                      width_of_transition_band,
  92                                                                      gr.firdes.WIN_HAMMING)
  93             #print "len stereo dsbsc filter = ",len(stereo_dsbsc_filter_coeffs)
  94             #print "stereo dsbsc filter ", stereo_dsbsc_filter_coeffs
  95             # construct overlap add filter system from coefficients for stereo carrier
  96
  97             self.stereo_carrier_filter = gr.fir_filter_fcc(audio_decimation, stereo_carrier_filter_coeffs)
  98
  99             # carrier is twice the picked off carrier so arrange to do a commplex multiply
 100
 101             self.stereo_carrier_generator = gr.multiply_cc();
 102
 103             # Pick off the rds signal
 104
 105             stereo_rds_filter_coeffs = gr.firdes.complex_band_pass(30.0,
 106                                                                      demod_rate,
 107                                                                      57000 - 1500,
 108                                                                      57000 + 1500,
 109                                                                      width_of_transition_band,
 110                                                                      gr.firdes.WIN_HAMMING)
 111             #print "len stereo dsbsc filter = ",len(stereo_dsbsc_filter_coeffs)
 112             #print "stereo dsbsc filter ", stereo_dsbsc_filter_coeffs
 113             # construct overlap add filter system from coefficients for stereo carrier
 114
 115             self.rds_signal_filter = gr.fir_filter_fcc(audio_decimation, stereo_rds_filter_coeffs)
 116
 117
 118
 119
 120
 121
 122             self.rds_carrier_generator = gr.multiply_cc();
 123             self.rds_signal_generator = gr.multiply_cc();
 124             self_rds_signal_processor = gr.null_sink(gr.sizeof_gr_complex);
 125
 126
 127
 128             alpha = 5 * 0.25 * math.pi / (audio_rate)
 129             beta = alpha * alpha / 4.0
 130             max_freq = -2.0*math.pi*18990/audio_rate;
 131             min_freq = -2.0*math.pi*19010/audio_rate;
 132
 133             self.stereo_carrier_pll_recovery = gr.pll_refout_cc(alpha,beta,max_freq,min_freq);
 134             #self.stereo_carrier_pll_recovery.squelch_enable(False) #pll_refout does not have squelch yet, so disabled for now
 135
 136
 137             # set up mixer (multiplier) to get the L-R signal at baseband
 138
 139             self.stereo_basebander = gr.multiply_cc();
 140
 141             # pick off the real component of the basebanded L-R signal.  The imaginary SHOULD be zero
 142
 143             self.LmR_real = gr.complex_to_real();
 144             self.Make_Left = gr.add_ff();
 145             self.Make_Right = gr.sub_ff();
 146
 147             self.stereo_dsbsc_filter = gr.fir_filter_fcc(audio_decimation, stereo_dsbsc_filter_coeffs)
 148
 149
 150         if 1:
 151
 152             # send the real signal to complex filter to pick off the carrier and then to one side of a multiplier
 153             self.connect (self, self.fm_demod,self.stereo_carrier_filter,self.stereo_carrier_pll_recovery, (self.stereo_carrier_generator,0))
 154             # send the already filtered carrier to the otherside of the carrier
 155             self.connect (self.stereo_carrier_pll_recovery, (self.stereo_carrier_generator,1))
 156             # the resulting signal from this multiplier is the carrier with correct phase but at -38000 Hz.
 157
 158             # send the new carrier to one side of the mixer (multiplier)
 159             self.connect (self.stereo_carrier_generator, (self.stereo_basebander,0))
 160             # send the demphasized audio to the DSBSC pick off filter,  the complex
 161             # DSBSC signal at +38000 Hz is sent to the other side of the mixer/multiplier
 162             self.connect (self.fm_demod,self.stereo_dsbsc_filter, (self.stereo_basebander,1))
 163             # the result is BASEBANDED DSBSC with phase zero!
 164
 165             # Pick off the real part since the imaginary is theoretically zero and then to one side of a summer
 166             self.connect (self.stereo_basebander, self.LmR_real, (self.Make_Left,0))
 167             #take the same real part of the DSBSC baseband signal and send it to negative side of a subtracter
 168             self.connect (self.LmR_real,(self.Make_Right,1))
 169
 170             # Make rds carrier by taking the squared pilot tone and multiplying by pilot tone
 171             self.connect (self.stereo_basebander,(self.rds_carrier_generator,0))
 172             self.connect (self.stereo_carrier_pll_recovery,(self.rds_carrier_generator,1))
 173             # take signal, filter off rds,  send into mixer 0 channel
 174             self.connect (self.fm_demod,self.rds_signal_filter,(self.rds_signal_generator,0))
 175             # take rds_carrier_generator output and send into mixer 1 channel
 176             self.connect (self.rds_carrier_generator,(self.rds_signal_generator,1))
 177             # send basebanded rds signal and send into "processor" which for now is a null sink
 178             self.connect (self.rds_signal_generator,self_rds_signal_processor)
 179
 180
 181         if 1:
 182             # pick off the audio, L+R that is what we used to have and send it to the summer
 183             self.connect(self.fm_demod, self.audio_filter, (self.Make_Left, 1))
 184             # take the picked off L+R audio and send it to the PLUS side of the subtractor
 185             self.connect(self.audio_filter,(self.Make_Right, 0))
 186             # The result of  Make_Left  gets    (L+R) +  (L-R) and results in 2*L
 187             # The result of Make_Right gets  (L+R) - (L-R) and results in 2*R
 188             self.connect(self.Make_Left , self.deemph_Left, (self, 0))
 189             self.connect(self.Make_Right, self.deemph_Right, (self, 1))
 190         # NOTE: mono support will require variable number of outputs in hier_block2s
 191         # See ticket:174 in Trac database
 192         #else:
 193         #    self.connect (self.fm_demod, self.audio_filter, self)