This file is indexed.

/usr/bin/uhd_rx_nogui is in gnuradio 3.7.9.1-2ubuntu1.

This file is owned by root:root, with mode 0o755.

The actual contents of the file can be viewed below.

  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
 91
 92
 93
 94
 95
 96
 97
 98
 99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
#!/usr/bin/python
#
# Copyright 2006,2007,2011,2012 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, gru, uhd, audio
from gnuradio import filter
from gnuradio import analog
from gnuradio import eng_notation
from gnuradio.eng_option import eng_option
from optparse import OptionParser
import sys

"""
This example application demonstrates receiving and demodulating
different types of signals using the USRP.

A receive chain is built up of the following signal processing
blocks:

USRP  - Daughter board source generating complex baseband signal.
CHAN  - Low pass filter to select channel bandwidth
RFSQL - RF squelch zeroing output when input power below threshold
AGC   - Automatic gain control leveling signal at [-1.0, +1.0]
DEMOD - Demodulation block appropriate to selected signal type.
        This converts the complex baseband to real audio frequencies,
	and applies an appropriate low pass decimating filter.
CTCSS - Optional tone squelch zeroing output when tone is not present.
RSAMP - Resampler block to convert audio sample rate to user specified
        sound card output rate.
AUDIO - Audio sink for playing final output to speakers.

The following are required command line parameters:

-f FREQ		USRP receive frequency
-m MOD		Modulation type, select from AM, FM, or WFM

The following are optional command line parameters:

-R SUBDEV       Daughter board specification, defaults to first found
-c FREQ         Calibration offset.  Gets added to receive frequency.
                Defaults to 0.0 Hz.
-g GAIN         Daughterboard gain setting. Defaults to mid-range.
-o RATE         Sound card output rate. Defaults to 32000. Useful if
                your sound card only accepts particular sample rates.
-r RFSQL	RF squelch in db. Defaults to -50.0.
-p FREQ		CTCSS frequency.  Opens squelch when tone is present.

Once the program is running, ctrl-break (Ctrl-C) stops operation.

Please see fm_demod.py and am_demod.py for details of the demodulation
blocks.
"""

# (device_rate, channel_rate, audio_rate, channel_pass, channel_stop, demod)
demod_params = {
		'AM'  : (256e3,  16e3, 16e3,  5000,   8000, analog.demod_10k0a3e_cf),
		'FM'  : (256e3,  32e3,  8e3,  8000,   9000, analog.demod_20k0f3e_cf),
		'WFM' : (320e3, 320e3, 32e3, 80000, 115000, analog.demod_200kf3e_cf)
	       }

class uhd_src(gr.hier_block2):
    """
    Create a UHD source object supplying complex floats.

    Selects user supplied subdevice or chooses first available one.

    Calibration value is the offset from the tuned frequency to
    the actual frequency.
    """
    def __init__(self, args, spec, antenna, samp_rate, gain=None, calibration=0.0):
	gr.hier_block2.__init__(self, "uhd_src",
				gr.io_signature(0, 0, 0),                    # Input signature
				gr.io_signature(1, 1, gr.sizeof_gr_complex)) # Output signature

        self._src = uhd.usrp_source(device_addr=args, stream_args=uhd.stream_args('fc32'))

        # Set the subdevice spec
        if(spec):
            self._src.set_subdev_spec(spec, 0)

        # Set the antenna
        if(antenna):
            self._src.set_antenna(antenna, 0)

        self._src.set_samp_rate(samp_rate)
	dev_rate = self._src.get_samp_rate()
        self._samp_rate = samp_rate

        # Resampler to get to exactly samp_rate no matter what dev_rate is
        self._rrate = samp_rate / dev_rate
        self._resamp = filter.pfb.arb_resampler_ccf(self._rrate)

	# If no gain specified, set to midrange
        gain_range = self._src.get_gain_range()
	if gain is None:
	    gain = (gain_range.start()+gain_range.stop())/2.0
            print "Using gain: ", gain
        self._src.set_gain(gain)

        self._cal = calibration
	self.connect(self._src, self._resamp, self)

    def tune(self, freq):
        r = self._src.set_center_freq(freq+self._cal, 0)

    def rate(self):
        return self._samp_rate

class app_top_block(gr.top_block):
    def __init__(self, options):
	gr.top_block.__init__(self)
	self.options = options

	(dev_rate, channel_rate, audio_rate,
	 channel_pass, channel_stop, demod) = demod_params[options.modulation]

        DEV = uhd_src(options.args,             # UHD device address
                      options.spec,             # device subdev spec
                      options.antenna,          # device antenna
                      dev_rate,         	# device sample rate
                      options.gain, 	    	# Receiver gain
                      options.calibration)      # Frequency offset
	DEV.tune(options.frequency)

	if_rate = DEV.rate()
        channel_decim = int(if_rate // channel_rate)
	audio_decim = int(channel_rate // audio_rate)

	CHAN_taps = filter.optfir.low_pass(1.0,          # Filter gain
                                           if_rate, 	 # Sample rate
                                           channel_pass, # One sided modulation bandwidth
                                           channel_stop, # One sided channel bandwidth
                                           0.1, 	 # Passband ripple
                                           60) 	         # Stopband attenuation

	CHAN = filter.freq_xlating_fir_filter_ccf(channel_decim, # Decimation rate
                                                  CHAN_taps,     # Filter taps
                                                  0.0, 	         # Offset frequency
                                                  if_rate)       # Sample rate

	RFSQL = analog.pwr_squelch_cc(options.rf_squelch,    # Power threshold
                                      125.0/channel_rate,    # Time constant
                                      int(channel_rate/20),  # 50ms rise/fall
                                      False)		     # Zero, not gate output

	AGC = analog.agc_cc(1.0/channel_rate,  # Time constant
                            1.0,     	       # Reference power
                            1.0)	       # Gain

	DEMOD = demod(channel_rate, audio_decim)

	# From RF to audio
        #self.connect(DEV, CHAN, RFSQL, AGC, DEMOD)
        self.connect(DEV, CHAN, DEMOD)

	# Optionally add CTCSS and RSAMP if needed
	tail = DEMOD
	if options.ctcss != None and options.ctcss > 60.0:
	    CTCSS = analog.ctcss_squelch_ff(audio_rate,    # Sample rate
                                            options.ctcss) # Squelch tone
	    self.connect(DEMOD, CTCSS)
	    tail = CTCSS

	if options.output_rate != audio_rate:
	    out_lcm = gru.lcm(audio_rate, options.output_rate)
	    out_interp = int(out_lcm // audio_rate)
	    out_decim = int(out_lcm // options.output_rate)
	    RSAMP = filter.rational_resampler_fff(out_interp, out_decim)
	    self.connect(tail, RSAMP)
	    tail = RSAMP

	# Send to audio output device
        AUDIO = audio.sink(int(options.output_rate),
                           options.audio_output)
	self.connect(tail, AUDIO)

        # Direct asynchronous notifications to callback function
        if self.options.show_async_msg:
            self.async_msgq = gr.msg_queue(0)
            self.async_src = uhd.amsg_source("", self.async_msgq)
            self.async_rcv = gru.msgq_runner(self.async_msgq, self.async_callback)

    def async_callback(self, msg):
        md = self.async_src.msg_to_async_metadata_t(msg)
        print "Channel: %i Time: %f Event: %i" % (md.channel, md.time_spec.get_real_secs(), md.event_code)


def main():
    parser = OptionParser(option_class=eng_option)
    parser.add_option("-a", "--args", type="string", default="",
                      help="UHD device address args , [default=%default]")
    parser.add_option("", "--spec", type="string", default=None,
                      help="Subdevice of UHD device where appropriate")
    parser.add_option("-A", "--antenna", type="string", default=None,
                      help="select Rx Antenna where appropriate [default=%default]")
    parser.add_option("-f", "--frequency", type="eng_float",
                      default=None, metavar="Hz",
                      help="set receive frequency to Hz [default=%default]")
    parser.add_option("-c",   "--calibration", type="eng_float",
                      default=0.0, metavar="Hz",
                      help="set frequency offset to Hz [default=%default]")
    parser.add_option("-g", "--gain", type="eng_float",
                      metavar="dB", default=None,
                      help="set RF gain [default is midpoint]")
    parser.add_option("-m", "--modulation", type="choice", choices=('AM','FM','WFM'),
                      metavar="TYPE", default=None,
                      help="set modulation type (AM,FM,WFM) [default=%default]")
    parser.add_option("-o", "--output-rate", type="eng_float",
                      default=32000, metavar="RATE",
                      help="set audio output rate to RATE [default=%default]")
    parser.add_option("-r", "--rf-squelch", type="eng_float",
                      default=-50.0, metavar="dB",
                      help="set RF squelch to dB [default=%default]")
    parser.add_option("-p", "--ctcss", type="float",
                      default=None, metavar="FREQ",
		      help="set CTCSS squelch to FREQ [default=%default]")
    parser.add_option("-O", "--audio-output", type="string", default="default",
                      help="pcm device name.  E.g., hw:0,0 or surround51 or /dev/dsp")
    parser.add_option("", "--show-async-msg", action="store_true", default=False,
                      help="Show asynchronous message notifications from UHD [default=%default]")
    (options, args) = parser.parse_args()

    if options.frequency is None:
	sys.stderr.write("Must supply receive frequency with -f.\n")
	sys.exit(1)

    if options.modulation is None:
        sys.stderr.write("Must supply a modulation type (AM, FM, WFM).\n")
        sys.exit(1)

    tb = app_top_block(options)
    try:
        tb.run()
    except KeyboardInterrupt:
        pass

if __name__ == "__main__":
    main()