#!/usr/bin/env python # # Copyright 2006,2007,2011 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 this program; if not, write to the Free Software Foundation, Inc., # 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA. # """ Here is a bit of code that will receive SCA analog subcarriers of FM Broadcast Stations using the USRP. It is a modified version of usrp_wfm_rcv.py. Common SCA frequencies are 67 kHz and 92 kHz. SCA is used for Reading Services for the Blind, Background Music, Foreign Language Services, and other services. Remember you may hear static when tuned to a FM station because this code only outputs SCA audio. The USRP gain is critical for good decoding. Adjust for minimum noise. I use the Post FM Demod FFT to check for SCA subcarriers and to adjust the USRP gain for the lowest noise floor. The stereo pilot at 19 KHz, the stereo difference signal around 38 KHz, and RDS at 57 KHz are also displayed on the Post FM Demod FFT if present. The range below 67 kHz is used for SCA only when Stereo is not used. The SCA recieve range is not as far as the main FM carrier receive range so tune in strong local stations first. I tried to comment the code with the various parameters. There seems to be several choices for a couple of them. I coded the common ones I see here. In the local area there are a couple of stations using digital SCA. These look similar to narrow DRM signals and I wonder if they are using OFDM. """ from gnuradio import gr, optfir, audio, blks2, uhd from gnuradio.eng_option import eng_option from gnuradio.wxgui import slider, powermate from gnuradio.wxgui import stdgui2, fftsink2, form from optparse import OptionParser import sys import math import wx class wfm_rx_sca_block (stdgui2.std_top_block): def __init__(self,frame,panel,vbox,argv): stdgui2.std_top_block.__init__ (self,frame,panel,vbox,argv) 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") parser.add_option("-f", "--freq", type="eng_float", default=100.1e6, help="set frequency to FREQ", metavar="FREQ") parser.add_option("-g", "--gain", type="eng_float", default=40, help="set gain in dB (default is midpoint)") parser.add_option("-V", "--volume", type="eng_float", default=None, help="set volume (default is midpoint)") parser.add_option("-O", "--audio-output", type="string", default="", help="pcm device name. E.g., hw:0,0 or surround51 or /dev/dsp") parser.add_option("", "--freq-min", type="eng_float", default=87.9e6, help="Set a minimum frequency [default=%default]") parser.add_option("", "--freq-max", type="eng_float", default=108.1e6, help="Set a maximum frequency [default=%default]") (options, args) = parser.parse_args() if len(args) != 0: parser.print_help() sys.exit(1) self.frame = frame self.panel = panel self.vol = 0 self.state = "FREQ" self.freq = 0 self.fm_freq_min = options.freq_min self.fm_freq_max = options.freq_max # build graph self.u = uhd.usrp_source(device_addr=options.args, stream_args=uhd.stream_args('fc32')) # Set the subdevice spec if(options.spec): self.u.set_subdev_spec(options.spec, 0) # Set the antenna if(options.antenna): self.u.set_antenna(options.antenna, 0) usrp_rate = 320e3 demod_rate = 320e3 audio_rate = 32e3 sca_demod_rate = 64e3 audio_decim = int(demod_rate / audio_rate) sca_chanfilt_decim = int(demod_rate / sca_demod_rate) self.u.set_samp_rate(usrp_rate) dev_rate = self.u.get_samp_rate() nfilts = 32 chan_coeffs = optfir.low_pass (nfilts, # gain nfilts*usrp_rate, # sampling rate 100e3, # passband cutoff 140e3, # stopband cutoff 0.1, # passband ripple 60) # stopband attenuation rrate = usrp_rate / dev_rate self.chan_filt = blks2.pfb_arb_resampler_ccf(rrate, chan_coeffs, nfilts) #Create demodulator block for Main FM Channel max_dev = 75e3 fm_demod_gain = demod_rate/(2*math.pi*max_dev) self.fm_demod = gr.quadrature_demod_cf (fm_demod_gain) # Note - deemphasis is not applied to the Main FM Channel as # main audio is not decoded # SCA Devation is 10% of carrier but some references say 20% # if mono with one SCA (6 KHz seems typical) max_sca_dev = 6e3 # Create filter to get SCA channel we want sca_chan_coeffs = gr.firdes.low_pass (1.0, # gain demod_rate, # sampling rate max_sca_dev, # cutoff freq max_sca_dev/3, # trans. band gr.firdes.WIN_HANN) # filter type self.ddc = gr.freq_xlating_fir_filter_fcf(sca_chanfilt_decim, # decim rate sca_chan_coeffs, # taps 0, # freq translation amount (Gets set by the UI) demod_rate) # input sample rate #Create demodulator block for SCA Channel sca_demod_gain = sca_demod_rate/(2*math.pi*max_sca_dev) self.fm_demod_sca = gr.quadrature_demod_cf (sca_demod_gain) # SCA analog audio is bandwidth limited to 5 KHz max_sca_audio_freq = 5.0e3 # SCA analog deephasis is 150 uS (75 uS may be used) sca_tau = 150e-6 # compute FIR filter taps for SCA audio filter audio_coeffs = gr.firdes.low_pass (1.0, # gain sca_demod_rate, # sampling rate max_sca_audio_freq, # cutoff freq max_sca_audio_freq/2.5, # trans. band gr.firdes.WIN_HAMMING) # input: float; output: float self.audio_filter = gr.fir_filter_fff (audio_decim, audio_coeffs) # Create deemphasis block that is applied after SCA demodulation self.deemph = blks2.fm_deemph (audio_rate, sca_tau) self.volume_control = gr.multiply_const_ff(self.vol) # sound card as final sink self.audio_sink = audio.sink (int (audio_rate), options.audio_output, False) # ok_to_block # now wire it all together self.connect (self.u, self.chan_filt, self.fm_demod, self.ddc, self.fm_demod_sca) self.connect (self.fm_demod_sca, self.audio_filter, self.deemph, self.volume_control, self.audio_sink) self._build_gui(vbox, usrp_rate, demod_rate, sca_demod_rate, audio_rate) if options.gain is None: # if no gain was specified, use the mid-point in dB g = self.u.get_gain_range() options.gain = float(g.start()+g.stop())/2 if options.volume is None: g = self.volume_range() options.volume = float(g[0]+g[1])/2 frange = self.u.get_freq_range() if(frange.start() > self.fm_freq_max or frange.stop() < self.fm_freq_min): sys.stderr.write("Radio does not support required frequency range.\n") sys.exit(1) if(options.freq < self.fm_freq_min or options.freq > self.fm_freq_max): sys.stderr.write("Requested frequency is outside of required frequency range.\n") sys.exit(1) # set initial values self.set_gain(options.gain) self.set_vol(options.volume) if not(self.set_freq(options.freq)): self._set_status_msg("Failed to set initial frequency") self.set_sca_freq(67000) # A common SCA Frequency def _set_status_msg(self, msg, which=0): self.frame.GetStatusBar().SetStatusText(msg, which) def _build_gui(self, vbox, usrp_rate, demod_rate, sca_demod_rate, audio_rate): def _form_set_freq(kv): return self.set_freq(kv['freq']) def _form_set_sca_freq(kv): return self.set_sca_freq(kv['sca_freq']) if 1: self.src_fft = fftsink2.fft_sink_c(self.panel, title="Data from USRP", fft_size=512, sample_rate=usrp_rate, ref_scale=32768.0, ref_level=0, y_divs=12) self.connect (self.u, self.src_fft) vbox.Add (self.src_fft.win, 4, wx.EXPAND) if 1: post_demod_fft = fftsink2.fft_sink_f(self.panel, title="Post FM Demod", fft_size=2048, sample_rate=demod_rate, y_per_div=10, ref_level=0) self.connect (self.fm_demod, post_demod_fft) vbox.Add (post_demod_fft.win, 4, wx.EXPAND) if 0: post_demod_sca_fft = fftsink2.fft_sink_f(self.panel, title="Post SCA Demod", fft_size=1024, sample_rate=sca_demod_rate, y_per_div=10, ref_level=0) self.connect (self.fm_demod_sca, post_demod_sca_fft) vbox.Add (post_demod_sca_fft.win, 4, wx.EXPAND) if 0: post_deemph_fft = fftsink2.fft_sink_f (self.panel, title="Post SCA Deemph", fft_size=512, sample_rate=audio_rate, y_per_div=10, ref_level=-20) self.connect (self.deemph, post_deemph_fft) vbox.Add (post_deemph_fft.win, 4, wx.EXPAND) # control area form at bottom self.myform = myform = form.form() hbox = wx.BoxSizer(wx.HORIZONTAL) hbox.Add((5,0), 0) myform['freq'] = form.float_field( parent=self.panel, sizer=hbox, label="Freq", weight=1, callback=myform.check_input_and_call(_form_set_freq, self._set_status_msg)) hbox.Add((5,0), 0) myform['freq_slider'] = \ form.quantized_slider_field(parent=self.panel, sizer=hbox, weight=3, range=(self.fm_freq_min, self.fm_freq_max, 0.1e6), callback=self.set_freq) hbox.Add((5,0), 0) vbox.Add(hbox, 0, wx.EXPAND) hbox = wx.BoxSizer(wx.HORIZONTAL) hbox.Add((5,0), 0) myform['sca_freq'] = form.float_field( parent=self.panel, sizer=hbox, label="SCA", weight=1, callback=myform.check_input_and_call(_form_set_sca_freq, self._set_status_msg)) hbox.Add((5,0), 0) myform['sca_freq_slider'] = \ form.quantized_slider_field(parent=self.panel, sizer=hbox, weight=3, range=(38e3, 100e3, 1.0e3), callback=self.set_sca_freq) hbox.Add((5,0), 0) vbox.Add(hbox, 0, wx.EXPAND) hbox = wx.BoxSizer(wx.HORIZONTAL) hbox.Add((5,0), 0) myform['volume'] = \ form.quantized_slider_field(parent=self.panel, sizer=hbox, label="Volume", weight=3, range=self.volume_range(), callback=self.set_vol) hbox.Add((5,0), 1) g = self.u.get_gain_range() myform['gain'] = \ form.quantized_slider_field(parent=self.panel, sizer=hbox, label="Gain", weight=3, range=(g.start(), g.stop(), g.step()), callback=self.set_gain) hbox.Add((5,0), 0) vbox.Add(hbox, 0, wx.EXPAND) try: self.knob = powermate.powermate(self.frame) self.rot = 0 powermate.EVT_POWERMATE_ROTATE (self.frame, self.on_rotate) powermate.EVT_POWERMATE_BUTTON (self.frame, self.on_button) except: print "FYI: No Powermate or Contour Knob found" def on_rotate (self, event): self.rot += event.delta if (self.state == "FREQ"): if self.rot >= 3: self.set_freq(self.freq + .1e6) self.rot -= 3 elif self.rot <=-3: self.set_freq(self.freq - .1e6) self.rot += 3 else: step = self.volume_range()[2] if self.rot >= 3: self.set_vol(self.vol + step) self.rot -= 3 elif self.rot <=-3: self.set_vol(self.vol - step) self.rot += 3 def on_button (self, event): if event.value == 0: # button up return self.rot = 0 if self.state == "FREQ": self.state = "VOL" else: self.state = "FREQ" self.update_status_bar () def set_vol (self, vol): g = self.volume_range() self.vol = max(g[0], min(g[1], vol)) self.volume_control.set_k(10**(self.vol/10)) self.myform['volume'].set_value(self.vol) self.update_status_bar () def set_freq(self, target_freq): """ Set the center frequency we're interested in. @param target_freq: frequency in Hz @rypte: bool Tuning is a two step process. First we ask the front-end to tune as close to the desired frequency as it can. Then we use the result of that operation and our target_frequency to determine the value for the digital down converter. """ r = self.u.set_center_freq(target_freq) if r: self.freq = target_freq self.myform['freq'].set_value(target_freq) # update displayed value self.myform['freq_slider'].set_value(target_freq) # update displayed value self.update_status_bar() self._set_status_msg("OK", 0) return True self._set_status_msg("Failed", 0) return False def set_sca_freq(self, target_sca_freq): self.ddc.set_center_freq(-target_sca_freq) self.myform['sca_freq'].set_value(target_sca_freq) # update displayed value self.myform['sca_freq_slider'].set_value(target_sca_freq) # update displayed value self.update_status_bar() self._set_status_msg("OK", 0) return True def set_gain(self, gain): self.myform['gain'].set_value(gain) # update displayed value self.u.set_gain(gain) def update_status_bar (self): msg = "Volume:%r Setting:%s" % (self.vol, self.state) self._set_status_msg(msg, 1) self.src_fft.set_baseband_freq(self.freq) def volume_range(self): return (-20.0, 0.0, 0.5) if __name__ == '__main__': app = stdgui2.stdapp (wfm_rx_sca_block, "USRP WFM SCA RX") app.MainLoop ()