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#
# Copyright 2005,2012 Free Software Foundation, Inc.
#
# This file is part of GNU Radio
#
# SPDX-License-Identifier: GPL-3.0-or-later
#
#
import math
from gnuradio import gr
from gnuradio import filter
from . import analog_python as analog
from .fm_emph import fm_deemph
class nbfm_rx(gr.hier_block2):
"""
Narrow Band FM Receiver.
Takes a single complex baseband input stream and produces a single
float output stream of audio sample in the range [-1, +1].
Args:
audio_rate: sample rate of audio stream, >= 16k (integer)
quad_rate: sample rate of output stream (integer)
tau: preemphasis time constant (default 75e-6) (float)
max_dev: maximum deviation in Hz (default 5e3) (float)
quad_rate must be an integer multiple of audio_rate.
Exported sub-blocks (attributes):
squelch
quad_demod
deemph
audio_filter
"""
def __init__(self, audio_rate, quad_rate, tau=75e-6, max_dev=5e3):
gr.hier_block2.__init__(self, "nbfm_rx",
gr.io_signature(1, 1, gr.sizeof_gr_complex), # Input signature
gr.io_signature(1, 1, gr.sizeof_float)) # Output signature
# FIXME audio_rate and quad_rate ought to be exact rationals
self._audio_rate = audio_rate = int(audio_rate)
self._quad_rate = quad_rate = int(quad_rate)
if quad_rate % audio_rate != 0:
raise ValueError("quad_rate is not an integer multiple of audio_rate")
squelch_threshold = 20 # dB
#self.squelch = analog.simple_squelch_cc(squelch_threshold, 0.001)
# FM Demodulator input: complex; output: float
k = quad_rate / (2*math.pi*max_dev)
self.quad_demod = analog.quadrature_demod_cf(k)
# FM Deemphasis IIR filter
self.deemph = fm_deemph(quad_rate, tau=tau)
# compute FIR taps for audio filter
audio_decim = quad_rate // audio_rate
audio_taps = filter.firdes.low_pass(1.0, # gain
quad_rate, # sampling rate
2.7e3, # Audio LPF cutoff
0.5e3, # Transition band
fft.window.WIN_HAMMING) # filter type
print("len(audio_taps) =", len(audio_taps))
# Decimating audio filter
# input: float; output: float; taps: float
self.audio_filter = filter.fir_filter_fff(audio_decim, audio_taps)
self.connect(self, self.quad_demod, self.deemph, self.audio_filter, self)
def set_max_deviation(self, max_dev):
k = self._quad_rate / (2*math.pi*max_dev)
self.quad_demod.set_gain(k)
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