Hi all
I'm trying to use the USRP1 as a beacon receiver i.e. measure the
amplitude and frequency of a signal then store the detected values to
file. I'm using the DBSRX daughter board to measure satellite beacons.
However I have ran into some problems. When viewing the FFT plot from
USRP_FFT.py I can see amplitude variations of up to several dB when
using a highly stable frequency generator. The amplitude variations
seem to increase with decreasing input power i.e lower C/N. Even with
the averaging function turned on the fluctuations are noticeable at
about 10 dB C/N.
My question is therefore: What is causing this ? And is there a way to
avoid or reduce this effect ?
I have already tried to reduce bin size an added FIR filter to the USRP_FFT.
Thanks in advance.
Eivind
#!/usr/bin/env python
#
# Copyright 2004,2005,2007,2008 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 GNU Radio; see the file COPYING. If not, write to
# the Free Software Foundation, Inc., 51 Franklin Street,
# Boston, MA 02110-1301, USA.
#
from gnuradio import gr, gru, optfir
from gnuradio import usrp
from gnuradio import eng_notation
from gnuradio.eng_option import eng_option
from gnuradio.wxgui import stdgui2, fftsink2, waterfallsink2, scopesink2, form, slider
from optparse import OptionParser
import wx
import sys
import numpy
def pick_subdevice(u):
"""
The user didn't specify a subdevice on the command line.
If there's a daughterboard on A, select A.
If there's a daughterboard on B, select B.
Otherwise, select A.
"""
if u.db[0][0].dbid() >= 0: # dbid is < 0 if there's no d'board or a problem
return (0, 0)
if u.db[1][0].dbid() >= 0:
return (1, 0)
return (0, 0)
class app_top_block(stdgui2.std_top_block):
def __init__(self, frame, panel, vbox, argv):
stdgui2.std_top_block.__init__(self, frame, panel, vbox, argv)
self.frame = frame
self.panel = panel
parser = OptionParser(option_class=eng_option)
parser.add_option("-w", "--which", type="int", default=0,
help="select which USRP (0, 1, ...) default is %default",
metavar="NUM")
parser.add_option("-R", "--rx-subdev-spec", type="subdev", default=None,
help="select USRP Rx side A or B (default=first one with a daughterboard)")
parser.add_option("-A", "--antenna", default=None,
help="select Rx Antenna (only on RFX-series boards)")
parser.add_option("-d", "--decim", type="int", default=256,
help="set fgpa decimation rate to DECIM [default=%default]")
parser.add_option("-f", "--freq", type="eng_float", default=1.45031e9,
help="set frequency to FREQ", metavar="FREQ")
parser.add_option("-g", "--gain", type="eng_float", default=20,
help="set gain in dB (default is midpoint)")
parser.add_option("-W", "--waterfall", action="store_true", default=False,
help="Enable waterfall display")
parser.add_option("-8", "--width-8", action="store_true", default=False,
help="Enable 8-bit samples across USB")
parser.add_option( "--no-hb", action="store_true", default=False,
help="don't use halfband filter in usrp")
parser.add_option("-S", "--oscilloscope", action="store_true", default=False,
help="Enable oscilloscope display")
parser.add_option("", "--ref-scale", type="eng_float", default=13490.0,
help="Set dBFS=0dB input value, default=[%default]")
parser.add_option("", "--avg-alpha", type="eng_float", default=1e-1,
help="Set fftsink averaging factor, default=[%default]")
(options, args) = parser.parse_args()
if len(args) != 0:
parser.print_help()
sys.exit(1)
self.options = options
self.show_debug_info = True
options.freq = options.freq #- 9.75e9
# build the graph
if options.no_hb or (options.decim<8):
#Min decimation of this firmware is 4.
#contains 4 Rx paths without halfbands and 0 tx paths.
self.fpga_filename="std_4rx_0tx.rbf"
self.u = usrp.source_c(which=options.which, decim_rate=options.decim, fpga_filename=self.fpga_filename)
else:
#Min decimation of standard firmware is 8.
#standard fpga firmware "std_2rxhb_2tx.rbf"
#contains 2 Rx paths with halfband filters and 2 tx paths (the default)
self.u = usrp.source_c(which=options.which, decim_rate=options.decim)
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))
if options.width_8:
width = 8
shift = 8
format = self.u.make_format(width, shift)
print "format =", hex(format)
r = self.u.set_format(format)
print "set_format =", r
# determine the daughterboard subdevice we're using
self.subdev = usrp.selected_subdev(self.u, options.rx_subdev_spec)
self.subdev.set_bw(1e6)
fft_size = 16384
adc_rate = self.u.adc_rate() # 64 MS/s
usrp_decim = options.decim
self.u.set_decim_rate(usrp_decim)
chanfilt_decim = 0
#input_rate = adc_rate / (usrp_decim + chanfilt_decim)
usrp_rate = self.u.adc_freq() / (self.u.decim_rate() + chanfilt_decim)
input_rate = adc_rate / (usrp_decim + chanfilt_decim)
if options.waterfall:
self.scope = \
waterfallsink2.waterfall_sink_c (panel, fft_size, sample_rate=input_rate)
elif options.oscilloscope:
self.scope = scopesink2.scope_sink_c(panel, sample_rate=input_rate)
else:
self.scope = fftsink2.fft_sink_c (panel, fft_size, sample_rate=input_rate,
ref_scale=options.ref_scale, ref_level=0.0, y_divs = 10,
avg_alpha=options.avg_alpha)
chan_filt_coeffs = optfir.low_pass (1, # gain
usrp_rate, # sampling rate
25e3, # passband cutoff
30e3, # stopband cutoff
0.01, # passband ripple
60) # stopband attenuation
#self.chan_filt = gr.freq_xlating_fir_filter_ccf (chanfilt_decim, chan_filt_coeffs, self.IF_freq, usrp_rate)
self.chan_filt = gr.fir_filter_ccf (chanfilt_decim, chan_filt_coeffs)
self.avg = gr.single_pole_iir_filter_ff(1,2)
self.connect(self.u, self.avg, self.scope)
self._build_gui(vbox)
self._setup_events()
# set initial values
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.freq is None:
# if no freq was specified, use the mid-point
r = self.subdev.freq_range()
options.freq = float(r[0]+r[1])/2
self.set_gain(options.gain)
if options.antenna is not None:
print "Selecting antenna %s" % (options.antenna,)
self.subdev.select_rx_antenna(options.antenna)
if self.show_debug_info:
self.myform['decim'].set_value(self.u.decim_rate())
self.myform['f...@usb'].set_value(self.u.adc_freq() / self.u.decim_rate())
self.myform['dbname'].set_value(self.subdev.name())
self.myform['baseband'].set_value(0)
self.myform['ddc'].set_value(0)
if not(self.set_freq(options.freq)):
self._set_status_msg("Failed to set initial frequency")
def _set_status_msg(self, msg):
self.frame.GetStatusBar().SetStatusText(msg, 0)
def _build_gui(self, vbox):
def _form_set_freq(kv):
return self.set_freq(kv['freq'])
vbox.Add(self.scope.win, 10, wx.EXPAND)
# add control area at the bottom
self.myform = myform = form.form()
hbox = wx.BoxSizer(wx.HORIZONTAL)
hbox.Add((5,0), 0, 0)
myform['freq'] = form.float_field(
parent=self.panel, sizer=hbox, label="Center freq", weight=1,
callback=myform.check_input_and_call(_form_set_freq, self._set_status_msg))
hbox.Add((5,0), 0, 0)
g = self.subdev.gain_range()
myform['gain'] = form.slider_field(parent=self.panel, sizer=hbox, label="Gain",
weight=3,
min=int(g[0]), max=int(g[1]),
callback=self.set_gain)
hbox.Add((5,0), 0, 0)
vbox.Add(hbox, 0, wx.EXPAND)
self._build_subpanel(vbox)
def _build_subpanel(self, vbox_arg):
# build a secondary information panel (sometimes hidden)
# FIXME figure out how to have this be a subpanel that is always
# created, but has its visibility controlled by foo.Show(True/False)
def _form_set_decim(kv):
return self.set_decim(kv['decim'])
if not(self.show_debug_info):
return
panel = self.panel
vbox = vbox_arg
myform = self.myform
#panel = wx.Panel(self.panel, -1)
#vbox = wx.BoxSizer(wx.VERTICAL)
hbox = wx.BoxSizer(wx.HORIZONTAL)
hbox.Add((5,0), 0)
myform['decim'] = form.int_field(
parent=panel, sizer=hbox, label="Decim",
callback=myform.check_input_and_call(_form_set_decim, self._set_status_msg))
hbox.Add((5,0), 1)
myform['f...@usb'] = form.static_float_field(
parent=panel, sizer=hbox, label="f...@usb")
hbox.Add((5,0), 1)
myform['dbname'] = form.static_text_field(
parent=panel, sizer=hbox)
hbox.Add((5,0), 1)
myform['baseband'] = form.static_float_field(
parent=panel, sizer=hbox, label="Analog BB")
hbox.Add((5,0), 1)
myform['ddc'] = form.static_float_field(
parent=panel, sizer=hbox, label="DDC")
hbox.Add((5,0), 0)
vbox.Add(hbox, 0, wx.EXPAND)
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.tune(0, self.subdev, target_freq)
if r:
self.myform['freq'].set_value(target_freq) # update displayed value
if self.show_debug_info:
self.myform['baseband'].set_value(r.baseband_freq)
self.myform['ddc'].set_value(r.dxc_freq)
if not self.options.waterfall and not self.options.oscilloscope:
self.scope.win.set_baseband_freq(target_freq)
return True
return False
def set_gain(self, gain):
self.myform['gain'].set_value(gain) # update displayed value
self.subdev.set_gain(gain)
def set_decim(self, decim):
ok = self.u.set_decim_rate(decim)
if not ok:
print "set_decim failed"
input_rate = self.u.adc_freq() / self.u.decim_rate()
self.scope.set_sample_rate(input_rate)
if self.show_debug_info: # update displayed values
self.myform['decim'].set_value(self.u.decim_rate())
self.myform['f...@usb'].set_value(self.u.adc_freq() / self.u.decim_rate())
return ok
def _setup_events(self):
if not self.options.waterfall and not self.options.oscilloscope:
self.scope.win.Bind(wx.EVT_LEFT_DCLICK, self.evt_left_dclick)
def evt_left_dclick(self, event):
(ux, uy) = self.scope.win.GetXY(event)
if event.CmdDown():
# Re-center on maximum power
points = self.scope.win._points
if self.scope.win.peak_hold:
if self.scope.win.peak_vals is not None:
ind = numpy.argmax(self.scope.win.peak_vals)
else:
ind = int(points.shape()[0]/2)
else:
ind = numpy.argmax(points[:,1])
(freq, pwr) = points[ind]
target_freq = freq/self.scope.win._scale_factor
print ind, freq, pwr
self.set_freq(target_freq)
else:
# Re-center on clicked frequency
target_freq = ux/self.scope.win._scale_factor
self.set_freq(target_freq)
def main ():
app = stdgui2.stdapp(app_top_block, "USRP FFT", nstatus=1)
app.MainLoop()
if __name__ == '__main__':
main ()
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