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   1 #
   2 # Copyright 2005 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 2, 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, gru
  23
  24 _plot = None
  25
  26 def design_filter(interpolation, decimation, fractional_bw):
  27     """
  28     Given the interpolation rate, decimation rate and a fractional bandwidth,
  29     design a set of taps.
  30
  31     @param interpolation: interpolation factor
  32     @type  interpolation: integer > 0
  33     @param decimation: decimation factor
  34     @type  decimation: integer > 0
  35     @param fractional_bw: fractional bandwidth in (0, 0.5)  0.4 works well.
  36     @type  fractional_bw: float
  37     @returns: sequence of numbers
  38     """
  39
  40     global _plot
  41
  42     if fractional_bw >= 0.5 or fractional_bw <= 0:
  43         raise ValueError, "Invalid fractional_bandwidth, must be in (0, 0.5)"
  44
  45     beta = 5.0
  46     trans_width = 0.5 - fractional_bw
  47     mid_transition_band = 0.5 - trans_width/2
  48
  49     taps = gr.firdes.low_pass(interpolation,                     # gain
  50                               1,                                 # Fs
  51                               mid_transition_band/interpolation, # trans mid point
  52                               trans_width/interpolation,         # transition width
  53                               gr.firdes.WIN_KAISER,
  54                               beta                               # beta
  55                               )
  56     # print "len(resampler_taps) =", len(taps)
  57     # _plot = gru.gnuplot_freqz(gru.freqz(taps, 1), 1)
  58
  59     return taps
  60
  61
  62
  63 class _rational_resampler_base(gr.hier_block):
  64     """
  65     base class for all rational resampler variants.
  66     """
  67     def __init__(self, resampler_base, fg,
  68                  interpolation, decimation, taps=None, fractional_bw=None):
  69         """
  70         Rational resampling polyphase FIR filter.
  71
  72         Either taps or fractional_bw may be specified, but not both.
  73         If neither is specified, a reasonable default, 0.4, is used as
  74         the fractional_bw.
  75
  76         @param fg: flow graph
  77         @param interpolation: interpolation factor
  78         @type  interpolation: integer > 0
  79         @param decimation: decimation factor
  80         @type  decimation: integer > 0
  81         @param taps: optional filter coefficients
  82         @type  taps: sequence
  83         @param fractional_bw: fractional bandwidth in (0, 0.5), measured at final freq (use 0.4)
  84         @type  fractional_bw: float
  85         """
  86
  87         if not isinstance(interpolation, int) or interpolation < 1:
  88             raise ValueError, "interpolation must be an integer >= 1"
  89
  90         if not isinstance(decimation, int) or decimation < 1:
  91             raise ValueError, "decimation must be an integer >= 1"
  92
  93         if taps is None and fractional_bw is None:
  94             fractional_bw = 0.4
  95
  96         d = gru.gcd(interpolation, decimation)
  97         interpolation = interpolation // d
  98         decimation = decimation // d
  99
 100         if taps is None:
 101             taps = design_filter(interpolation, decimation, fractional_bw)
 102
 103         resampler = resampler_base(interpolation, decimation, taps)
 104         gr.hier_block.__init__(self, fg, resampler, resampler)
 105
 106
 107
 108 class rational_resampler_fff(_rational_resampler_base):
 109     def __init__(self, fg, interpolation, decimation, taps=None, fractional_bw=None):
 110         """
 111         Rational resampling polyphase FIR filter with
 112         float input, float output and float taps.
 113         """
 114         _rational_resampler_base.__init__(self, gr.rational_resampler_base_fff, fg,
 115                                           interpolation, decimation,
 116                                           taps, fractional_bw)
 117
 118 class rational_resampler_ccf(_rational_resampler_base):
 119     def __init__(self, fg, interpolation, decimation, taps=None, fractional_bw=None):
 120         """
 121         Rational resampling polyphase FIR filter with
 122         complex input, complex output and float taps.
 123         """
 124         _rational_resampler_base.__init__(self, gr.rational_resampler_base_ccf, fg,
 125                                           interpolation, decimation,
 126                                           taps, fractional_bw)
 127
 128 class rational_resampler_ccc(_rational_resampler_base):
 129     def __init__(self, fg, interpolation, decimation, taps=None, fractional_bw=None):
 130         """
 131         Rational resampling polyphase FIR filter with
 132         complex input, complex output and complex taps.
 133         """
 134         _rational_resampler_base.__init__(self, gr.rational_resampler_base_ccc, fg,
 135                                           interpolation, decimation,
 136                                           taps, fractional_bw)
 137