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#
# Copyright 2005,2007,2012 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
import math
try:
from gnuradio import analog
except ImportError:
import analog_swig as analog
class wfm_rcv(gr.hier_block2):
def __init__ (self, quad_rate, audio_decimation):
"""
Hierarchical block for demodulating a broadcast FM signal.
The input is the downconverted complex baseband signal (gr_complex).
The output is the demodulated audio (float).
Args:
quad_rate: input sample rate of complex baseband input. (float)
audio_decimation: how much to decimate quad_rate to get to audio. (integer)
"""
gr.hier_block2.__init__(self, "wfm_rcv",
gr.io_signature(1, 1, gr.sizeof_gr_complex), # Input signature
gr.io_signature(1, 1, gr.sizeof_float)) # Output signature
volume = 20.
max_dev = 75e3
fm_demod_gain = quad_rate/(2*math.pi*max_dev)
audio_rate = quad_rate / audio_decimation
# We assign to self so that outsiders can grab the demodulator
# if they need to. E.g., to plot its output.
#
# input: complex; output: float
self.fm_demod = analog.quadrature_demod_cf(fm_demod_gain)
# input: float; output: float
self.deemph = fm_deemph(audio_rate)
# compute FIR filter taps for audio filter
width_of_transition_band = audio_rate / 32
audio_coeffs = filter.firdes.low_pass(1.0, # gain
quad_rate, # sampling rate
audio_rate/2 - width_of_transition_band,
width_of_transition_band,
filter.firdes.WIN_HAMMING)
# input: float; output: float
self.audio_filter = filter.fir_filter_fff(audio_decimation, audio_coeffs)
self.connect (self, self.fm_demod, self.audio_filter, self.deemph, self)
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