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,
78 class wfm_rx_sca_block (stdgui2.std_top_block):
79 def __init__(self,frame,panel,vbox,argv):
80 stdgui2.std_top_block.__init__ (self,frame,panel,vbox,argv)
82 parser=OptionParser(option_class=eng_option)
83 parser.add_option("-R", "--rx-subdev-spec", type="subdev", default=None,
84 help="select USRP Rx side A or B (default=A)")
85 parser.add_option("-f", "--freq", type="eng_float", default=100.1e6,
86 help="set frequency to FREQ", metavar="FREQ")
87 parser.add_option("-g", "--gain", type="eng_float", default=40,
88 help="set gain in dB (default is midpoint)")
89 parser.add_option("-V", "--volume", type="eng_float", default=None,
90 help="set volume (default is midpoint)")
91 parser.add_option("-O", "--audio-output", type="string", default="",
92 help="pcm device name. E.g., hw:0,0 or surround51 or /dev/dsp")
94 (options, args) = parser.parse_args()
108 self.u = usrp.source_c() # usrp is data source
110 adc_rate = self.u.adc_rate() # 64 MS/s
112 self.u.set_decim_rate(usrp_decim)
113 usrp_rate = adc_rate / usrp_decim # 320 kS/s
115 demod_rate = usrp_rate / chanfilt_decim
116 sca_chanfilt_decim = 5
117 sca_demod_rate = demod_rate / sca_chanfilt_decim #64 kHz
119 audio_rate = sca_demod_rate / audio_decimation # 32 kHz
121 if options.rx_subdev_spec is None:
122 options.rx_subdev_spec = pick_subdevice(self.u)
124 self.u.set_mux(usrp.determine_rx_mux_value(self.u, options.rx_subdev_spec))
125 self.subdev = usrp.selected_subdev(self.u, options.rx_subdev_spec)
126 print "Using RX d'board %s" % (self.subdev.side_and_name(),)
128 #Create filter to get main FM Channel we want
129 chan_filt_coeffs = optfir.low_pass (1, # gain
130 usrp_rate, # sampling rate
131 100e3, # passband cutoff
132 140e3, # stopband cutoff
133 0.1, # passband ripple
134 60) # stopband attenuation
135 #print len(chan_filt_coeffs)
136 chan_filt = gr.fir_filter_ccf (chanfilt_decim, chan_filt_coeffs)
138 #Create demodulator block for Main FM Channel
140 fm_demod_gain = demod_rate/(2*math.pi*max_dev)
141 self.fm_demod = gr.quadrature_demod_cf (fm_demod_gain)
143 # Note - deemphasis is not applied to the Main FM Channel as main audio is not decoded
145 # SCA Devation is 10% of carrier but some references say 20% if mono with one SCA (6 KHz seems typical)
148 # Create filter to get SCA channel we want
149 sca_chan_coeffs = gr.firdes.low_pass (1.0, # gain
150 demod_rate, # sampling rate
151 max_sca_dev, # low pass cutoff freq
152 max_sca_dev/3, # width of trans. band
153 gr.firdes.WIN_HANN) # filter type
155 self.ddc = gr.freq_xlating_fir_filter_fcf(sca_chanfilt_decim, # decimation rate
156 sca_chan_coeffs, # taps
157 0, # frequency translation amount (Gets set by the UI)
158 demod_rate) # input sample rate
160 #Create demodulator block for SCA Channel
161 sca_demod_gain = sca_demod_rate/(2*math.pi*max_sca_dev)
162 self.fm_demod_sca = gr.quadrature_demod_cf (sca_demod_gain)
165 # SCA analog audio is bandwidth limited to 5 KHz
166 max_sca_audio_freq = 5.0e3
167 # SCA analog deephasis is 150 uS (75 uS may be used)
170 # compute FIR filter taps for SCA audio filter
171 audio_coeffs = gr.firdes.low_pass (1.0, # gain
172 sca_demod_rate, # sampling rate
173 max_sca_audio_freq, # low pass cutoff freq
174 max_sca_audio_freq/2.5, # width of trans. band
175 gr.firdes.WIN_HAMMING)
177 # input: float; output: float
178 self.audio_filter = gr.fir_filter_fff (audio_decimation, audio_coeffs)
180 # Create deemphasis block that is applied after SCA demodulation
181 self.deemph = fm_deemph (audio_rate, sca_tau)
183 self.volume_control = gr.multiply_const_ff(self.vol)
185 # sound card as final sink
186 audio_sink = audio.sink (int (audio_rate),
187 options.audio_output,
190 # now wire it all together
191 self.connect (self.u, chan_filt, self.fm_demod, self.ddc, self.fm_demod_sca)
192 self.connect (self.fm_demod_sca, self.audio_filter, self.deemph, self.volume_control, audio_sink)
194 self._build_gui(vbox, usrp_rate, demod_rate, sca_demod_rate, audio_rate)
196 if options.gain is None:
197 # if no gain was specified, use the mid-point in dB
198 g = self.subdev.gain_range()
199 options.gain = float(g[0]+g[1])/2
201 if options.volume is None:
202 g = self.volume_range()
203 options.volume = float(g[0]+g[1])/2
205 if abs(options.freq) < 1e6:
210 self.set_gain(options.gain)
211 self.set_vol(options.volume)
212 if not(self.set_freq(options.freq)):
213 self._set_status_msg("Failed to set initial frequency")
214 self.set_sca_freq(67000) # A common SCA Frequency
217 def _set_status_msg(self, msg, which=0):
218 self.frame.GetStatusBar().SetStatusText(msg, which)
221 def _build_gui(self, vbox, usrp_rate, demod_rate, sca_demod_rate, audio_rate):
223 def _form_set_freq(kv):
224 return self.set_freq(kv['freq'])
226 def _form_set_sca_freq(kv):
227 return self.set_sca_freq(kv['sca_freq'])
230 self.src_fft = fftsink2.fft_sink_c(self.panel, title="Data from USRP",
231 fft_size=512, sample_rate=usrp_rate)
232 self.connect (self.u, self.src_fft)
233 vbox.Add (self.src_fft.win, 4, wx.EXPAND)
236 post_demod_fft = fftsink2.fft_sink_f(self.panel, title="Post FM Demod",
237 fft_size=2048, sample_rate=demod_rate,
238 y_per_div=10, ref_level=0)
239 self.connect (self.fm_demod, post_demod_fft)
240 vbox.Add (post_demod_fft.win, 4, wx.EXPAND)
243 post_demod_sca_fft = fftsink2.fft_sink_f(self.panel, title="Post SCA Demod",
244 fft_size=1024, sample_rate=sca_demod_rate,
245 y_per_div=10, ref_level=0)
246 self.connect (self.fm_demod_sca, post_demod_sca_fft)
247 vbox.Add (post_demod_sca_fft.win, 4, wx.EXPAND)
250 post_deemph_fft = fftsink2.fft_sink_f (self.panel, title="Post SCA Deemph",
251 fft_size=512, sample_rate=audio_rate,
252 y_per_div=10, ref_level=-20)
253 self.connect (self.deemph, post_deemph_fft)
254 vbox.Add (post_deemph_fft.win, 4, wx.EXPAND)
257 # control area form at bottom
258 self.myform = myform = form.form()
260 hbox = wx.BoxSizer(wx.HORIZONTAL)
262 myform['freq'] = form.float_field(
263 parent=self.panel, sizer=hbox, label="Freq", weight=1,
264 callback=myform.check_input_and_call(_form_set_freq, self._set_status_msg))
267 myform['freq_slider'] = \
268 form.quantized_slider_field(parent=self.panel, sizer=hbox, weight=3,
269 range=(87.9e6, 108.1e6, 0.1e6),
270 callback=self.set_freq)
272 vbox.Add(hbox, 0, wx.EXPAND)
274 hbox = wx.BoxSizer(wx.HORIZONTAL)
276 myform['sca_freq'] = form.float_field(
277 parent=self.panel, sizer=hbox, label="SCA", weight=1,
278 callback=myform.check_input_and_call(_form_set_sca_freq, self._set_status_msg))
281 myform['sca_freq_slider'] = \
282 form.quantized_slider_field(parent=self.panel, sizer=hbox, weight=3,
283 range=(38e3, 100e3, 1.0e3),
284 callback=self.set_sca_freq)
286 vbox.Add(hbox, 0, wx.EXPAND)
288 hbox = wx.BoxSizer(wx.HORIZONTAL)
292 form.quantized_slider_field(parent=self.panel, sizer=hbox, label="Volume",
293 weight=3, range=self.volume_range(),
294 callback=self.set_vol)
298 form.quantized_slider_field(parent=self.panel, sizer=hbox, label="Gain",
299 weight=3, range=self.subdev.gain_range(),
300 callback=self.set_gain)
302 vbox.Add(hbox, 0, wx.EXPAND)
305 self.knob = powermate.powermate(self.frame)
307 powermate.EVT_POWERMATE_ROTATE (self.frame, self.on_rotate)
308 powermate.EVT_POWERMATE_BUTTON (self.frame, self.on_button)
310 print "FYI: No Powermate or Contour Knob found"
313 def on_rotate (self, event):
314 self.rot += event.delta
315 if (self.state == "FREQ"):
317 self.set_freq(self.freq + .1e6)
320 self.set_freq(self.freq - .1e6)
323 step = self.volume_range()[2]
325 self.set_vol(self.vol + step)
328 self.set_vol(self.vol - step)
331 def on_button (self, event):
332 if event.value == 0: # button up
335 if self.state == "FREQ":
339 self.update_status_bar ()
342 def set_vol (self, vol):
343 g = self.volume_range()
344 self.vol = max(g[0], min(g[1], vol))
345 self.volume_control.set_k(10**(self.vol/10))
346 self.myform['volume'].set_value(self.vol)
347 self.update_status_bar ()
349 def set_freq(self, target_freq):
351 Set the center frequency we're interested in.
353 @param target_freq: frequency in Hz
356 Tuning is a two step process. First we ask the front-end to
357 tune as close to the desired frequency as it can. Then we use
358 the result of that operation and our target_frequency to
359 determine the value for the digital down converter.
361 r = usrp.tune(self.u, 0, self.subdev, target_freq)
364 self.freq = target_freq
365 self.myform['freq'].set_value(target_freq) # update displayed value
366 self.myform['freq_slider'].set_value(target_freq) # update displayed value
367 self.update_status_bar()
368 self._set_status_msg("OK", 0)
371 self._set_status_msg("Failed", 0)
374 def set_sca_freq(self, target_sca_freq):
376 self.ddc.set_center_freq(-target_sca_freq)
377 self.myform['sca_freq'].set_value(target_sca_freq) # update displayed value
378 self.myform['sca_freq_slider'].set_value(target_sca_freq) # update displayed value
379 self.update_status_bar()
380 self._set_status_msg("OK", 0)
383 def set_gain(self, gain):
384 self.myform['gain'].set_value(gain) # update displayed value
385 self.subdev.set_gain(gain)
387 def update_status_bar (self):
388 msg = "Volume:%r Setting:%s" % (self.vol, self.state)
389 self._set_status_msg(msg, 1)
390 self.src_fft.set_baseband_freq(self.freq)
392 def volume_range(self):
393 return (-20.0, 0.0, 0.5)
396 if __name__ == '__main__':
397 app = stdgui2.stdapp (wfm_rx_sca_block, "USRP WFM SCA RX")