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Diffstat (limited to 'gr-analog/python/analog/fm_demod.py')
| -rw-r--r-- | gr-analog/python/analog/fm_demod.py | 108 |
1 files changed, 108 insertions, 0 deletions
diff --git a/gr-analog/python/analog/fm_demod.py b/gr-analog/python/analog/fm_demod.py new file mode 100644 index 0000000000..1976a076ca --- /dev/null +++ b/gr-analog/python/analog/fm_demod.py @@ -0,0 +1,108 @@ +# +# Copyright 2006,2007,2012 Free Software Foundation, Inc. +# +# This file is part of GNU Radio +# +# GNU Radio is free software; you can redistribute it and/or modify +# it under the terms of the GNU General Public License as published by +# the Free Software Foundation; either version 3, or (at your option) +# any later version. +# +# GNU Radio is distributed in the hope that it will be useful, +# but WITHOUT ANY WARRANTY; without even the implied warranty of +# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the +# GNU General Public License for more details. +# +# You should have received a copy of the GNU General Public License +# along with GNU Radio; see the file COPYING. If not, write to +# the Free Software Foundation, Inc., 51 Franklin Street, +# Boston, MA 02110-1301, USA. +# + +from gnuradio import gr, filter +from fm_emph import fm_deemph +from math import pi + +try: + from gnuradio import analog +except ImportError: + import analog_swig as analog + +class fm_demod_cf(gr.hier_block2): + """ + Generalized FM demodulation block with deemphasis and audio + filtering. + + This block demodulates a band-limited, complex down-converted FM + channel into the the original baseband signal, optionally applying + deemphasis. Low pass filtering is done on the resultant signal. It + produces an output float strem in the range of [-1.0, +1.0]. + + Args: + channel_rate: incoming sample rate of the FM baseband (integer) + deviation: maximum FM deviation (default = 5000) (float) + audio_decim: input to output decimation rate (integer) + audio_pass: audio low pass filter passband frequency (float) + audio_stop: audio low pass filter stop frequency (float) + gain: gain applied to audio output (default = 1.0) (float) + tau: deemphasis time constant (default = 75e-6), specify 'None' to prevent deemphasis + """ + def __init__(self, channel_rate, audio_decim, deviation, + audio_pass, audio_stop, gain=1.0, tau=75e-6): + gr.hier_block2.__init__(self, "fm_demod_cf", + gr.io_signature(1, 1, gr.sizeof_gr_complex), # Input signature + gr.io_signature(1, 1, gr.sizeof_float)) # Output signature + + k = channel_rate/(2*pi*deviation) + QUAD = analog.quadrature_demod_cf(k) + + audio_taps = filter.optfir.low_pass(gain, # Filter gain + channel_rate, # Sample rate + audio_pass, # Audio passband + audio_stop, # Audio stopband + 0.1, # Passband ripple + 60) # Stopband attenuation + LPF = filter.fir_filter_fff(audio_decim, audio_taps) + + if tau is not None: + DEEMPH = fm_deemph(channel_rate, tau) + self.connect(self, QUAD, DEEMPH, LPF, self) + else: + self.connect(self, QUAD, LPF, self) + +class demod_20k0f3e_cf(fm_demod_cf): + """ + NBFM demodulation block, 20 KHz channels + + This block demodulates a complex, downconverted, narrowband FM + channel conforming to 20K0F3E emission standards, outputting + floats in the range [-1.0, +1.0]. + + Args: + sample_rate: incoming sample rate of the FM baseband (integer) + audio_decim: input to output decimation rate (integer) + """ + def __init__(self, channel_rate, audio_decim): + fm_demod_cf.__init__(self, channel_rate, audio_decim, + 5000, # Deviation + 3000, # Audio passband frequency + 4500) # Audio stopband frequency + +class demod_200kf3e_cf(fm_demod_cf): + """ + WFM demodulation block, mono. + + This block demodulates a complex, downconverted, wideband FM + channel conforming to 200KF3E emission standards, outputting + floats in the range [-1.0, +1.0]. + + Args: + sample_rate: incoming sample rate of the FM baseband (integer) + audio_decim: input to output decimation rate (integer) + """ + def __init__(self, channel_rate, audio_decim): + fm_demod_cf.__init__(self, channel_rate, audio_decim, + 75000, # Deviation + 15000, # Audio passband + 16000, # Audio stopband + 20.0) # Audio gain |