3 # Copyright 2006,2007 Free Software Foundation, Inc.
5 # This file is part of GNU Radio
7 # GNU Radio is free software; you can redistribute it and/or modify
8 # it under the terms of the GNU General Public License as published by
9 # the Free Software Foundation; either version 3, or (at your option)
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13 # but WITHOUT ANY WARRANTY; without even the implied warranty of
14 # MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
15 # GNU General Public License for more details.
17 # You should have received a copy of the GNU General Public License along
18 # with this program; if not, write to the Free Software Foundation, Inc.,
19 # 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
23 Here is a bit of code that will receive SCA analog subcarriers of FM
24 Broadcast Stations using the USRP. It is a modified version of
27 Common SCA frequencies are 67 kHz and 92 kHz. SCA is used for Reading
28 Services for the Blind, Background Music, Foreign Language Services, and
29 other services. Remember you may hear static when tuned to a FM station
30 because this code only outputs SCA audio.
32 The USRP gain is critical for good decoding. Adjust for minimum noise.
33 I use the Post FM Demod FFT to check for SCA subcarriers and to adjust
34 the USRP gain for the lowest noise floor. The stereo pilot at 19 KHz,
35 the stereo difference signal around 38 KHz, and RDS at 57 KHz are also
36 displayed on the Post FM Demod FFT if present.
38 The range below 67 kHz is used for SCA only when Stereo is not used.
40 The SCA recieve range is not as far as the main FM carrier receive range
41 so tune in strong local stations first.
43 I tried to comment the code with the various parameters. There seems to
44 be several choices for a couple of them. I coded the common ones I see
47 In the local area there are a couple of stations using digital SCA.
48 These look similar to narrow DRM signals and I wonder if they are using
53 from gnuradio import gr, gru, eng_notation, optfir
54 from gnuradio import audio
55 from gnuradio import usrp
56 from gnuradio.blks2impl.fm_emph import fm_deemph
57 from gnuradio.eng_option import eng_option
58 from gnuradio.wxgui import slider, powermate
59 from gnuradio.wxgui import stdgui2, fftsink2, form
60 from optparse import OptionParser
61 from usrpm import usrp_dbid
66 def pick_subdevice(u):
68 The user didn't specify a subdevice on the command line.
69 Try for one of these, in order: TV_RX, BASIC_RX, whatever is on side A.
73 return usrp.pick_subdev(u, (usrp_dbid.TV_RX,
74 usrp_dbid.TV_RX_REV_2,
75 usrp_dbid.TV_RX_REV_3,
77 usrp_dbid.TV_RX_REV_2_MIMO,
78 usrp_dbid.TV_RX_REV_3_MIMO,
82 class wfm_rx_sca_block (stdgui2.std_top_block):
83 def __init__(self,frame,panel,vbox,argv):
84 stdgui2.std_top_block.__init__ (self,frame,panel,vbox,argv)
86 parser=OptionParser(option_class=eng_option)
87 parser.add_option("-R", "--rx-subdev-spec", type="subdev", default=None,
88 help="select USRP Rx side A or B (default=A)")
89 parser.add_option("-f", "--freq", type="eng_float", default=100.1e6,
90 help="set frequency to FREQ", metavar="FREQ")
91 parser.add_option("-g", "--gain", type="eng_float", default=40,
92 help="set gain in dB (default is midpoint)")
93 parser.add_option("-V", "--volume", type="eng_float", default=None,
94 help="set volume (default is midpoint)")
95 parser.add_option("-O", "--audio-output", type="string", default="",
96 help="pcm device name. E.g., hw:0,0 or surround51 or /dev/dsp")
98 (options, args) = parser.parse_args()
112 self.u = usrp.source_c() # usrp is data source
114 adc_rate = self.u.adc_rate() # 64 MS/s
116 self.u.set_decim_rate(usrp_decim)
117 usrp_rate = adc_rate / usrp_decim # 320 kS/s
119 demod_rate = usrp_rate / chanfilt_decim
120 sca_chanfilt_decim = 5
121 sca_demod_rate = demod_rate / sca_chanfilt_decim #64 kHz
123 audio_rate = sca_demod_rate / audio_decimation # 32 kHz
125 if options.rx_subdev_spec is None:
126 options.rx_subdev_spec = pick_subdevice(self.u)
128 self.u.set_mux(usrp.determine_rx_mux_value(self.u, options.rx_subdev_spec))
129 self.subdev = usrp.selected_subdev(self.u, options.rx_subdev_spec)
130 print "Using RX d'board %s" % (self.subdev.side_and_name(),)
132 #Create filter to get main FM Channel we want
133 chan_filt_coeffs = optfir.low_pass (1, # gain
134 usrp_rate, # sampling rate
135 100e3, # passband cutoff
136 140e3, # stopband cutoff
137 0.1, # passband ripple
138 60) # stopband attenuation
139 #print len(chan_filt_coeffs)
140 chan_filt = gr.fir_filter_ccf (chanfilt_decim, chan_filt_coeffs)
142 #Create demodulator block for Main FM Channel
144 fm_demod_gain = demod_rate/(2*math.pi*max_dev)
145 self.fm_demod = gr.quadrature_demod_cf (fm_demod_gain)
147 # Note - deemphasis is not applied to the Main FM Channel as main audio is not decoded
149 # SCA Devation is 10% of carrier but some references say 20% if mono with one SCA (6 KHz seems typical)
152 # Create filter to get SCA channel we want
153 sca_chan_coeffs = gr.firdes.low_pass (1.0, # gain
154 demod_rate, # sampling rate
155 max_sca_dev, # low pass cutoff freq
156 max_sca_dev/3, # width of trans. band
157 gr.firdes.WIN_HANN) # filter type
159 self.ddc = gr.freq_xlating_fir_filter_fcf(sca_chanfilt_decim, # decimation rate
160 sca_chan_coeffs, # taps
161 0, # frequency translation amount (Gets set by the UI)
162 demod_rate) # input sample rate
164 #Create demodulator block for SCA Channel
165 sca_demod_gain = sca_demod_rate/(2*math.pi*max_sca_dev)
166 self.fm_demod_sca = gr.quadrature_demod_cf (sca_demod_gain)
169 # SCA analog audio is bandwidth limited to 5 KHz
170 max_sca_audio_freq = 5.0e3
171 # SCA analog deephasis is 150 uS (75 uS may be used)
174 # compute FIR filter taps for SCA audio filter
175 audio_coeffs = gr.firdes.low_pass (1.0, # gain
176 sca_demod_rate, # sampling rate
177 max_sca_audio_freq, # low pass cutoff freq
178 max_sca_audio_freq/2.5, # width of trans. band
179 gr.firdes.WIN_HAMMING)
181 # input: float; output: float
182 self.audio_filter = gr.fir_filter_fff (audio_decimation, audio_coeffs)
184 # Create deemphasis block that is applied after SCA demodulation
185 self.deemph = fm_deemph (audio_rate, sca_tau)
187 self.volume_control = gr.multiply_const_ff(self.vol)
189 # sound card as final sink
190 audio_sink = audio.sink (int (audio_rate),
191 options.audio_output,
194 # now wire it all together
195 self.connect (self.u, chan_filt, self.fm_demod, self.ddc, self.fm_demod_sca)
196 self.connect (self.fm_demod_sca, self.audio_filter, self.deemph, self.volume_control, audio_sink)
198 self._build_gui(vbox, usrp_rate, demod_rate, sca_demod_rate, audio_rate)
200 if options.gain is None:
201 # if no gain was specified, use the mid-point in dB
202 g = self.subdev.gain_range()
203 options.gain = float(g[0]+g[1])/2
205 if options.volume is None:
206 g = self.volume_range()
207 options.volume = float(g[0]+g[1])/2
209 if abs(options.freq) < 1e6:
214 self.set_gain(options.gain)
215 self.set_vol(options.volume)
216 if not(self.set_freq(options.freq)):
217 self._set_status_msg("Failed to set initial frequency")
218 self.set_sca_freq(67000) # A common SCA Frequency
221 def _set_status_msg(self, msg, which=0):
222 self.frame.GetStatusBar().SetStatusText(msg, which)
225 def _build_gui(self, vbox, usrp_rate, demod_rate, sca_demod_rate, audio_rate):
227 def _form_set_freq(kv):
228 return self.set_freq(kv['freq'])
230 def _form_set_sca_freq(kv):
231 return self.set_sca_freq(kv['sca_freq'])
234 self.src_fft = fftsink2.fft_sink_c(self.panel, title="Data from USRP",
235 fft_size=512, sample_rate=usrp_rate,
236 ref_scale=32768.0, ref_level=0, y_divs=12)
237 self.connect (self.u, self.src_fft)
238 vbox.Add (self.src_fft.win, 4, wx.EXPAND)
241 post_demod_fft = fftsink2.fft_sink_f(self.panel, title="Post FM Demod",
242 fft_size=2048, sample_rate=demod_rate,
243 y_per_div=10, ref_level=0)
244 self.connect (self.fm_demod, post_demod_fft)
245 vbox.Add (post_demod_fft.win, 4, wx.EXPAND)
248 post_demod_sca_fft = fftsink2.fft_sink_f(self.panel, title="Post SCA Demod",
249 fft_size=1024, sample_rate=sca_demod_rate,
250 y_per_div=10, ref_level=0)
251 self.connect (self.fm_demod_sca, post_demod_sca_fft)
252 vbox.Add (post_demod_sca_fft.win, 4, wx.EXPAND)
255 post_deemph_fft = fftsink2.fft_sink_f (self.panel, title="Post SCA Deemph",
256 fft_size=512, sample_rate=audio_rate,
257 y_per_div=10, ref_level=-20)
258 self.connect (self.deemph, post_deemph_fft)
259 vbox.Add (post_deemph_fft.win, 4, wx.EXPAND)
262 # control area form at bottom
263 self.myform = myform = form.form()
265 hbox = wx.BoxSizer(wx.HORIZONTAL)
267 myform['freq'] = form.float_field(
268 parent=self.panel, sizer=hbox, label="Freq", weight=1,
269 callback=myform.check_input_and_call(_form_set_freq, self._set_status_msg))
272 myform['freq_slider'] = \
273 form.quantized_slider_field(parent=self.panel, sizer=hbox, weight=3,
274 range=(87.9e6, 108.1e6, 0.1e6),
275 callback=self.set_freq)
277 vbox.Add(hbox, 0, wx.EXPAND)
279 hbox = wx.BoxSizer(wx.HORIZONTAL)
281 myform['sca_freq'] = form.float_field(
282 parent=self.panel, sizer=hbox, label="SCA", weight=1,
283 callback=myform.check_input_and_call(_form_set_sca_freq, self._set_status_msg))
286 myform['sca_freq_slider'] = \
287 form.quantized_slider_field(parent=self.panel, sizer=hbox, weight=3,
288 range=(38e3, 100e3, 1.0e3),
289 callback=self.set_sca_freq)
291 vbox.Add(hbox, 0, wx.EXPAND)
293 hbox = wx.BoxSizer(wx.HORIZONTAL)
297 form.quantized_slider_field(parent=self.panel, sizer=hbox, label="Volume",
298 weight=3, range=self.volume_range(),
299 callback=self.set_vol)
303 form.quantized_slider_field(parent=self.panel, sizer=hbox, label="Gain",
304 weight=3, range=self.subdev.gain_range(),
305 callback=self.set_gain)
307 vbox.Add(hbox, 0, wx.EXPAND)
310 self.knob = powermate.powermate(self.frame)
312 powermate.EVT_POWERMATE_ROTATE (self.frame, self.on_rotate)
313 powermate.EVT_POWERMATE_BUTTON (self.frame, self.on_button)
315 print "FYI: No Powermate or Contour Knob found"
318 def on_rotate (self, event):
319 self.rot += event.delta
320 if (self.state == "FREQ"):
322 self.set_freq(self.freq + .1e6)
325 self.set_freq(self.freq - .1e6)
328 step = self.volume_range()[2]
330 self.set_vol(self.vol + step)
333 self.set_vol(self.vol - step)
336 def on_button (self, event):
337 if event.value == 0: # button up
340 if self.state == "FREQ":
344 self.update_status_bar ()
347 def set_vol (self, vol):
348 g = self.volume_range()
349 self.vol = max(g[0], min(g[1], vol))
350 self.volume_control.set_k(10**(self.vol/10))
351 self.myform['volume'].set_value(self.vol)
352 self.update_status_bar ()
354 def set_freq(self, target_freq):
356 Set the center frequency we're interested in.
358 @param target_freq: frequency in Hz
361 Tuning is a two step process. First we ask the front-end to
362 tune as close to the desired frequency as it can. Then we use
363 the result of that operation and our target_frequency to
364 determine the value for the digital down converter.
366 r = usrp.tune(self.u, 0, self.subdev, target_freq)
369 self.freq = target_freq
370 self.myform['freq'].set_value(target_freq) # update displayed value
371 self.myform['freq_slider'].set_value(target_freq) # update displayed value
372 self.update_status_bar()
373 self._set_status_msg("OK", 0)
376 self._set_status_msg("Failed", 0)
379 def set_sca_freq(self, target_sca_freq):
381 self.ddc.set_center_freq(-target_sca_freq)
382 self.myform['sca_freq'].set_value(target_sca_freq) # update displayed value
383 self.myform['sca_freq_slider'].set_value(target_sca_freq) # update displayed value
384 self.update_status_bar()
385 self._set_status_msg("OK", 0)
388 def set_gain(self, gain):
389 self.myform['gain'].set_value(gain) # update displayed value
390 self.subdev.set_gain(gain)
392 def update_status_bar (self):
393 msg = "Volume:%r Setting:%s" % (self.vol, self.state)
394 self._set_status_msg(msg, 1)
395 self.src_fft.set_baseband_freq(self.freq)
397 def volume_range(self):
398 return (-20.0, 0.0, 0.5)
401 if __name__ == '__main__':
402 app = stdgui2.stdapp (wfm_rx_sca_block, "USRP WFM SCA RX")