1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
|
#
# Copyright 2005,2012 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.
#
import math
from gnuradio import gr
from gnuradio import filter
from fm_emph import fm_deemph
try:
from gnuradio import analog
except ImportError:
import analog_swig as analog
class nbfm_rx(gr.hier_block2):
def __init__(self, audio_rate, quad_rate, tau=75e-6, max_dev=5e3):
"""
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
"""
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
audio_rate = int(audio_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
filter.firdes.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)
|
