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[Discuss-gnuradio] USRP WFM SCA RX Example
From: |
Eric A. Cottrell |
Subject: |
[Discuss-gnuradio] USRP WFM SCA RX Example |
Date: |
Sat, 13 Jan 2007 22:24:12 -0500 |
User-agent: |
Thunderbird 1.5.0.8 (X11/20060911) |
Hello,
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.
Have fun, I am!
73 Eric
#!/usr/bin/env python
from gnuradio import gr, gru, eng_notation, optfir
from gnuradio import audio
from gnuradio import usrp
from gnuradio import blks
from gnuradio.blksimpl.fm_emph import fm_deemph
from gnuradio.eng_option import eng_option
from gnuradio.wxgui import slider, powermate
from gnuradio.wxgui import stdgui, fftsink, form
from optparse import OptionParser
import usrp_dbid
import sys
import math
import wx
def pick_subdevice(u):
"""
The user didn't specify a subdevice on the command line.
Try for one of these, in order: TV_RX, BASIC_RX, whatever is on side A.
@return a subdev_spec
"""
return usrp.pick_subdev(u, (usrp_dbid.TV_RX,
usrp_dbid.TV_RX_REV_2,
usrp_dbid.BASIC_RX))
class wfm_rx_sca_graph (stdgui.gui_flow_graph):
def __init__(self,frame,panel,vbox,argv):
stdgui.gui_flow_graph.__init__ (self,frame,panel,vbox,argv)
parser=OptionParser(option_class=eng_option)
parser.add_option("-R", "--rx-subdev-spec", type="subdev", default=None,
help="select USRP Rx side A or B (default=A)")
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")
(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
# build graph
self.u = usrp.source_c() # usrp is data source
adc_rate = self.u.adc_rate() # 64 MS/s
usrp_decim = 200
self.u.set_decim_rate(usrp_decim)
usrp_rate = adc_rate / usrp_decim # 320 kS/s
chanfilt_decim = 1
demod_rate = usrp_rate / chanfilt_decim
sca_chanfilt_decim = 5
sca_demod_rate = demod_rate / sca_chanfilt_decim #64 kHz
audio_decimation = 2
audio_rate = sca_demod_rate / audio_decimation # 32 kHz
if options.rx_subdev_spec is None:
options.rx_subdev_spec = pick_subdevice(self.u)
self.u.set_mux(usrp.determine_rx_mux_value(self.u,
options.rx_subdev_spec))
self.subdev = usrp.selected_subdev(self.u, options.rx_subdev_spec)
print "Using RX d'board %s" % (self.subdev.side_and_name(),)
#Create filter to get main FM Channel we want
chan_filt_coeffs = optfir.low_pass (1, # gain
usrp_rate, # sampling rate
100e3, # passband cutoff
140e3, # stopband cutoff
0.1, # passband ripple
60) # stopband attenuation
#print len(chan_filt_coeffs)
chan_filt = gr.fir_filter_ccf (chanfilt_decim, chan_filt_coeffs)
#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, # low pass cutoff
freq
max_sca_dev/3, # width of trans.
band
gr.firdes.WIN_HANN) # filter type
self.ddc = gr.freq_xlating_fir_filter_fcf(sca_chanfilt_decim, #
decimation rate
sca_chan_coeffs, # taps
0, # frequency
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, # low pass
cutoff freq
max_sca_audio_freq/2.5,
# width of trans. band
gr.firdes.WIN_HAMMING)
# input: float; output: float
self.audio_filter = gr.fir_filter_fff (audio_decimation, audio_coeffs)
# Create deemphasis block that is applied after SCA demodulation
self.deemph = fm_deemph (self, audio_rate, sca_tau)
self.volume_control = gr.multiply_const_ff(self.vol)
# sound card as final sink
audio_sink = audio.sink (int (audio_rate),
options.audio_output,
False) # ok_to_block
# now wire it all together
self.connect (self.u, 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, 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.subdev.gain_range()
options.gain = float(g[0]+g[1])/2
if options.volume is None:
g = self.volume_range()
options.volume = float(g[0]+g[1])/2
if abs(options.freq) < 1e6:
options.freq *= 1e6
# 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 = fftsink.fft_sink_c (self, self.panel, title="Data
from USRP",
fft_size=512,
sample_rate=usrp_rate)
self.connect (self.u, self.src_fft)
vbox.Add (self.src_fft.win, 4, wx.EXPAND)
if 1:
post_demod_fft = fftsink.fft_sink_f (self, 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 = fftsink.fft_sink_f (self, 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 = fftsink.fft_sink_f (self, 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=(87.9e6, 108.1e6, 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)
myform['gain'] = \
form.quantized_slider_field(parent=self.panel, sizer=hbox,
label="Gain",
weight=3,
range=self.subdev.gain_range(),
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 = usrp.tune(self.u, 0, self.subdev, 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.subdev.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 = stdgui.stdapp (wfm_rx_sca_graph, "USRP WFM SCA RX")
app.MainLoop ()
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