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 import blks
57 from gnuradio.blksimpl.fm_emph import fm_deemph
58 from gnuradio.eng_option import eng_option
59 from gnuradio.wxgui import slider, powermate
60 from gnuradio.wxgui import stdgui, fftsink, form
61 from optparse import OptionParser
62 from usrpm import usrp_dbid
67 def pick_subdevice(u):
69 The user didn't specify a subdevice on the command line.
70 Try for one of these, in order: TV_RX, BASIC_RX, whatever is on side A.
74 return usrp.pick_subdev(u, (usrp_dbid.TV_RX,
75 usrp_dbid.TV_RX_REV_2,
79 class wfm_rx_sca_graph (stdgui.gui_flow_graph):
80 def __init__(self,frame,panel,vbox,argv):
81 stdgui.gui_flow_graph.__init__ (self,frame,panel,vbox,argv)
83 parser=OptionParser(option_class=eng_option)
84 parser.add_option("-R", "--rx-subdev-spec", type="subdev", default=None,
85 help="select USRP Rx side A or B (default=A)")
86 parser.add_option("-f", "--freq", type="eng_float", default=100.1e6,
87 help="set frequency to FREQ", metavar="FREQ")
88 parser.add_option("-g", "--gain", type="eng_float", default=40,
89 help="set gain in dB (default is midpoint)")
90 parser.add_option("-V", "--volume", type="eng_float", default=None,
91 help="set volume (default is midpoint)")
92 parser.add_option("-O", "--audio-output", type="string", default="",
93 help="pcm device name. E.g., hw:0,0 or surround51 or /dev/dsp")
95 (options, args) = parser.parse_args()
109 self.u = usrp.source_c() # usrp is data source
111 adc_rate = self.u.adc_rate() # 64 MS/s
113 self.u.set_decim_rate(usrp_decim)
114 usrp_rate = adc_rate / usrp_decim # 320 kS/s
116 demod_rate = usrp_rate / chanfilt_decim
117 sca_chanfilt_decim = 5
118 sca_demod_rate = demod_rate / sca_chanfilt_decim #64 kHz
120 audio_rate = sca_demod_rate / audio_decimation # 32 kHz
122 if options.rx_subdev_spec is None:
123 options.rx_subdev_spec = pick_subdevice(self.u)
125 self.u.set_mux(usrp.determine_rx_mux_value(self.u, options.rx_subdev_spec))
126 self.subdev = usrp.selected_subdev(self.u, options.rx_subdev_spec)
127 print "Using RX d'board %s" % (self.subdev.side_and_name(),)
129 #Create filter to get main FM Channel we want
130 chan_filt_coeffs = optfir.low_pass (1, # gain
131 usrp_rate, # sampling rate
132 100e3, # passband cutoff
133 140e3, # stopband cutoff
134 0.1, # passband ripple
135 60) # stopband attenuation
136 #print len(chan_filt_coeffs)
137 chan_filt = gr.fir_filter_ccf (chanfilt_decim, chan_filt_coeffs)
139 #Create demodulator block for Main FM Channel
141 fm_demod_gain = demod_rate/(2*math.pi*max_dev)
142 self.fm_demod = gr.quadrature_demod_cf (fm_demod_gain)
144 # Note - deemphasis is not applied to the Main FM Channel as main audio is not decoded
146 # SCA Devation is 10% of carrier but some references say 20% if mono with one SCA (6 KHz seems typical)
149 # Create filter to get SCA channel we want
150 sca_chan_coeffs = gr.firdes.low_pass (1.0, # gain
151 demod_rate, # sampling rate
152 max_sca_dev, # low pass cutoff freq
153 max_sca_dev/3, # width of trans. band
154 gr.firdes.WIN_HANN) # filter type
156 self.ddc = gr.freq_xlating_fir_filter_fcf(sca_chanfilt_decim, # decimation rate
157 sca_chan_coeffs, # taps
158 0, # frequency translation amount (Gets set by the UI)
159 demod_rate) # input sample rate
161 #Create demodulator block for SCA Channel
162 sca_demod_gain = sca_demod_rate/(2*math.pi*max_sca_dev)
163 self.fm_demod_sca = gr.quadrature_demod_cf (sca_demod_gain)
166 # SCA analog audio is bandwidth limited to 5 KHz
167 max_sca_audio_freq = 5.0e3
168 # SCA analog deephasis is 150 uS (75 uS may be used)
171 # compute FIR filter taps for SCA audio filter
172 audio_coeffs = gr.firdes.low_pass (1.0, # gain
173 sca_demod_rate, # sampling rate
174 max_sca_audio_freq, # low pass cutoff freq
175 max_sca_audio_freq/2.5, # width of trans. band
176 gr.firdes.WIN_HAMMING)
178 # input: float; output: float
179 self.audio_filter = gr.fir_filter_fff (audio_decimation, audio_coeffs)
181 # Create deemphasis block that is applied after SCA demodulation
182 self.deemph = fm_deemph (self, audio_rate, sca_tau)
184 self.volume_control = gr.multiply_const_ff(self.vol)
186 # sound card as final sink
187 audio_sink = audio.sink (int (audio_rate),
188 options.audio_output,
191 # now wire it all together
192 self.connect (self.u, chan_filt, self.fm_demod, self.ddc, self.fm_demod_sca)
193 self.connect (self.fm_demod_sca, self.audio_filter, self.deemph, self.volume_control, audio_sink)
195 self._build_gui(vbox, usrp_rate, demod_rate, sca_demod_rate, audio_rate)
197 if options.gain is None:
198 # if no gain was specified, use the mid-point in dB
199 g = self.subdev.gain_range()
200 options.gain = float(g[0]+g[1])/2
202 if options.volume is None:
203 g = self.volume_range()
204 options.volume = float(g[0]+g[1])/2
206 if abs(options.freq) < 1e6:
211 self.set_gain(options.gain)
212 self.set_vol(options.volume)
213 if not(self.set_freq(options.freq)):
214 self._set_status_msg("Failed to set initial frequency")
215 self.set_sca_freq(67000) # A common SCA Frequency
218 def _set_status_msg(self, msg, which=0):
219 self.frame.GetStatusBar().SetStatusText(msg, which)
222 def _build_gui(self, vbox, usrp_rate, demod_rate, sca_demod_rate, audio_rate):
224 def _form_set_freq(kv):
225 return self.set_freq(kv['freq'])
227 def _form_set_sca_freq(kv):
228 return self.set_sca_freq(kv['sca_freq'])
231 self.src_fft = fftsink.fft_sink_c (self, self.panel, title="Data from USRP",
232 fft_size=512, sample_rate=usrp_rate)
233 self.connect (self.u, self.src_fft)
234 vbox.Add (self.src_fft.win, 4, wx.EXPAND)
237 post_demod_fft = fftsink.fft_sink_f (self, self.panel, title="Post FM Demod",
238 fft_size=2048, sample_rate=demod_rate,
239 y_per_div=10, ref_level=0)
240 self.connect (self.fm_demod, post_demod_fft)
241 vbox.Add (post_demod_fft.win, 4, wx.EXPAND)
244 post_demod_sca_fft = fftsink.fft_sink_f (self, self.panel, title="Post SCA Demod",
245 fft_size=1024, sample_rate=sca_demod_rate,
246 y_per_div=10, ref_level=0)
247 self.connect (self.fm_demod_sca, post_demod_sca_fft)
248 vbox.Add (post_demod_sca_fft.win, 4, wx.EXPAND)
251 post_deemph_fft = fftsink.fft_sink_f (self, self.panel, title="Post SCA Deemph",
252 fft_size=512, sample_rate=audio_rate,
253 y_per_div=10, ref_level=-20)
254 self.connect (self.deemph, post_deemph_fft)
255 vbox.Add (post_deemph_fft.win, 4, wx.EXPAND)
258 # control area form at bottom
259 self.myform = myform = form.form()
261 hbox = wx.BoxSizer(wx.HORIZONTAL)
263 myform['freq'] = form.float_field(
264 parent=self.panel, sizer=hbox, label="Freq", weight=1,
265 callback=myform.check_input_and_call(_form_set_freq, self._set_status_msg))
268 myform['freq_slider'] = \
269 form.quantized_slider_field(parent=self.panel, sizer=hbox, weight=3,
270 range=(87.9e6, 108.1e6, 0.1e6),
271 callback=self.set_freq)
273 vbox.Add(hbox, 0, wx.EXPAND)
275 hbox = wx.BoxSizer(wx.HORIZONTAL)
277 myform['sca_freq'] = form.float_field(
278 parent=self.panel, sizer=hbox, label="SCA", weight=1,
279 callback=myform.check_input_and_call(_form_set_sca_freq, self._set_status_msg))
282 myform['sca_freq_slider'] = \
283 form.quantized_slider_field(parent=self.panel, sizer=hbox, weight=3,
284 range=(38e3, 100e3, 1.0e3),
285 callback=self.set_sca_freq)
287 vbox.Add(hbox, 0, wx.EXPAND)
289 hbox = wx.BoxSizer(wx.HORIZONTAL)
293 form.quantized_slider_field(parent=self.panel, sizer=hbox, label="Volume",
294 weight=3, range=self.volume_range(),
295 callback=self.set_vol)
299 form.quantized_slider_field(parent=self.panel, sizer=hbox, label="Gain",
300 weight=3, range=self.subdev.gain_range(),
301 callback=self.set_gain)
303 vbox.Add(hbox, 0, wx.EXPAND)
306 self.knob = powermate.powermate(self.frame)
308 powermate.EVT_POWERMATE_ROTATE (self.frame, self.on_rotate)
309 powermate.EVT_POWERMATE_BUTTON (self.frame, self.on_button)
311 print "FYI: No Powermate or Contour Knob found"
314 def on_rotate (self, event):
315 self.rot += event.delta
316 if (self.state == "FREQ"):
318 self.set_freq(self.freq + .1e6)
321 self.set_freq(self.freq - .1e6)
324 step = self.volume_range()[2]
326 self.set_vol(self.vol + step)
329 self.set_vol(self.vol - step)
332 def on_button (self, event):
333 if event.value == 0: # button up
336 if self.state == "FREQ":
340 self.update_status_bar ()
343 def set_vol (self, vol):
344 g = self.volume_range()
345 self.vol = max(g[0], min(g[1], vol))
346 self.volume_control.set_k(10**(self.vol/10))
347 self.myform['volume'].set_value(self.vol)
348 self.update_status_bar ()
350 def set_freq(self, target_freq):
352 Set the center frequency we're interested in.
354 @param target_freq: frequency in Hz
357 Tuning is a two step process. First we ask the front-end to
358 tune as close to the desired frequency as it can. Then we use
359 the result of that operation and our target_frequency to
360 determine the value for the digital down converter.
362 r = usrp.tune(self.u, 0, self.subdev, target_freq)
365 self.freq = target_freq
366 self.myform['freq'].set_value(target_freq) # update displayed value
367 self.myform['freq_slider'].set_value(target_freq) # update displayed value
368 self.update_status_bar()
369 self._set_status_msg("OK", 0)
372 self._set_status_msg("Failed", 0)
375 def set_sca_freq(self, target_sca_freq):
377 self.ddc.set_center_freq(-target_sca_freq)
378 self.myform['sca_freq'].set_value(target_sca_freq) # update displayed value
379 self.myform['sca_freq_slider'].set_value(target_sca_freq) # update displayed value
380 self.update_status_bar()
381 self._set_status_msg("OK", 0)
384 def set_gain(self, gain):
385 self.myform['gain'].set_value(gain) # update displayed value
386 self.subdev.set_gain(gain)
388 def update_status_bar (self):
389 msg = "Volume:%r Setting:%s" % (self.vol, self.state)
390 self._set_status_msg(msg, 1)
391 self.src_fft.set_baseband_freq(self.freq)
393 def volume_range(self):
394 return (-20.0, 0.0, 0.5)
397 if __name__ == '__main__':
398 app = stdgui.stdapp (wfm_rx_sca_graph, "USRP WFM SCA RX")