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   1 # This tries to push the hilbert transform for ssb demod back into the
   2 # freq. xlating filter.
   3 #
   4 # The usual gnuradio copyright notice is hereby included by reference.
   5 #
   6 # The starting point for this was weaver_isb_am1_usrp3.py.
   7 #
   8 # The tap coefficients for freq_xlating_fir_filter_ccf were generated
   9 # externally and are read from a file because I didn't want to learn how
  10 # to make fir filters with arbitrary phase response using python numeric
  11 # facilities.
  12 #
  13 # They were generated using Scilab which I am already familiar with.
  14 # M. Revnell Jan 06
  15
  16 from gnuradio import gr, gru
  17 from gnuradio import audio
  18 from gnuradio import usrp
  19
  20 class ssb_demod( gr.hier_block ):
  21     def __init__( self, fg, if_rate, af_rate ):
  22
  23         self.if_rate  = if_rate
  24         self.af_rate  = af_rate
  25         self.if_decim = if_rate / af_rate
  26         self.sideband = 1
  27
  28         self.xlate_taps = ([complex(v) for v in file('ssb_taps').readlines()])
  29
  30         self.audio_taps = gr.firdes.low_pass(
  31             1.0,
  32             self.af_rate,
  33             3e3,
  34             600,
  35             gr.firdes.WIN_HAMMING )
  36
  37         self.xlate = gr.freq_xlating_fir_filter_ccc(
  38             self.if_decim,
  39             self.xlate_taps,
  40             0,
  41             self.if_rate )
  42
  43         self.split = gr.complex_to_float()
  44
  45         self.lpf = gr.fir_filter_fff(
  46             1, self.audio_taps )
  47
  48         self.sum   = gr.add_ff( )
  49         self.am_sel = gr.multiply_const_ff( 0 )
  50         self.sb_sel = gr.multiply_const_ff( 1 )
  51         self.mixer  = gr.add_ff()
  52         self.am_det = gr.complex_to_mag()
  53
  54         fg.connect(   self.xlate,       self.split      )
  55         fg.connect( ( self.split,0 ), ( self.sum,0    ) )
  56         fg.connect( ( self.split,1 ), ( self.sum,1    ) )
  57         fg.connect(    self.sum,        self.sb_sel     )
  58         fg.connect(    self.xlate,      self.am_det     )
  59         fg.connect(    self.sb_sel,   ( self.mixer, 0 ) )
  60         fg.connect(    self.am_det,     self.am_sel     )
  61         fg.connect(    self.am_sel,   ( self.mixer, 1 ) )
  62         fg.connect(    self.mixer,      self.lpf        )
  63
  64         gr.hier_block.__init__( self, fg, self.xlate, self.lpf )
  65
  66     def upper_sb( self ):
  67         self.xlate.set_taps([v.conjugate() for v in self.xlate_taps])
  68         self.sb_sel.set_k( 1.0 )
  69         self.am_sel.set_k( 0.0 )
  70
  71     def lower_sb( self ):
  72         self.xlate.set_taps(self.xlate_taps)
  73         self.sb_sel.set_k( 1.0 )
  74         self.am_sel.set_k( 0.0 )
  75
  76     def set_am( self ):
  77         taps = gr.firdes.low_pass( 1.0,
  78                                    self.if_rate,
  79                                    5e3,
  80                                    2e3,
  81                                    gr.firdes.WIN_HAMMING )
  82         self.xlate.set_taps( taps )
  83         self.sb_sel.set_k( 0.0 )
  84         self.am_sel.set_k( 1.0 )
  85
  86     def set_bw( self, bw ):
  87         self.audio_taps = gr.firdes.low_pass(
  88             1.0,
  89             self.af_rate,
  90             bw,
  91             600,
  92             gr.firdes.WIN_HAMMING )
  93         self.lpf.set_taps( self.audio_taps )
  94
  95     def tune( self, freq ):
  96         self.xlate.set_center_freq( freq )
  97