Пример #1
0
    def set_folding_params(self):
        if (self.pulse_freq <= 0):
            return

        # Compute required sample rate
        self.sample_rate = int(self.pulse_freq * self.folding)

        # And the implied decimation rate
        required_decimation = int(self.folder_input_rate / self.sample_rate)

        # We also compute a new FFT comb filter, based on the expected
        #  spectral profile of our pulse parameters
        #
        # FFT-based comb filter
        #
        N_COMB_TAPS = int(self.sample_rate * 4)
        if N_COMB_TAPS > 2000:
            N_COMB_TAPS = 2000
        self.folder_comb_taps = Numeric.zeros(N_COMB_TAPS, Numeric.Complex64)
        fincr = (self.sample_rate) / float(N_COMB_TAPS)
        for i in range(0, len(self.folder_comb_taps)):
            self.folder_comb_taps[i] = complex(0.0, 0.0)

        freq = 0.0
        harmonics = [1.0, 2.0, 3.0, 4.0, 5.0, 6.0, 7.0]
        for i in range(0, len(self.folder_comb_taps) / 2):
            for j in range(0, len(harmonics)):
                if abs(freq - harmonics[j] * self.pulse_freq) <= fincr:
                    self.folder_comb_taps[i] = complex(4.0, 0.0)
                    if harmonics[j] == 1.0:
                        self.folder_comb_taps[i] = complex(8.0, 0.0)
            freq += fincr

        if self.enable_comb_filter == True:
            # Set the just-computed FFT comb filter taps
            self.folder_comb.set_taps(self.folder_comb_taps)

        # And compute a new decimated bandpass filter, to go in front
        #   of the comb.  Primary function is to decimate and filter down
        #   to an exact-ish multiple of the target pulse rate
        #
        self.folding_taps = gr.firdes_band_pass(1.0, self.folder_input_rate,
                                                0.10, self.sample_rate / 2, 10,
                                                gr.firdes.WIN_HAMMING)

        # Set the computed taps for the bandpass/decimate filter
        self.folder_bandpass.set_taps(self.folding_taps)
Пример #2
0
    def set_folding_params(self):
        if (self.pulse_freq <= 0):
            return

        # Compute required sample rate
        self.sample_rate = int(self.pulse_freq*self.folding)

        # And the implied decimation rate
        required_decimation = int(self.folder_input_rate / self.sample_rate)

        # We also compute a new FFT comb filter, based on the expected
        #  spectral profile of our pulse parameters
        #
        # FFT-based comb filter
        #
        N_COMB_TAPS=int(self.sample_rate*4)
        if N_COMB_TAPS > 2000:
            N_COMB_TAPS = 2000
        self.folder_comb_taps = Numeric.zeros(N_COMB_TAPS,Numeric.Complex64)
        fincr = (self.sample_rate)/float(N_COMB_TAPS)
        for i in range(0,len(self.folder_comb_taps)):
            self.folder_comb_taps[i] = complex(0.0, 0.0)

        freq = 0.0
        harmonics = [1.0,2.0,3.0,4.0,5.0,6.0,7.0]
        for i in range(0,len(self.folder_comb_taps)/2):
            for j in range(0,len(harmonics)):
                 if abs(freq - harmonics[j]*self.pulse_freq) <= fincr:
                     self.folder_comb_taps[i] = complex(4.0, 0.0)
                     if harmonics[j] == 1.0:
                         self.folder_comb_taps[i] = complex(8.0, 0.0)
            freq += fincr

        if self.enable_comb_filter == True:
            # Set the just-computed FFT comb filter taps
            self.folder_comb.set_taps(self.folder_comb_taps)

        # And compute a new decimated bandpass filter, to go in front
        #   of the comb.  Primary function is to decimate and filter down
        #   to an exact-ish multiple of the target pulse rate
        #
        self.folding_taps = gr.firdes_band_pass (1.0, self.folder_input_rate,
            0.10, self.sample_rate/2, 10, 
            gr.firdes.WIN_HAMMING)

        # Set the computed taps for the bandpass/decimate filter
        self.folder_bandpass.set_taps (self.folding_taps)
Пример #3
0
    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("-R",
                          "--rx-subdev-spec",
                          type="subdev",
                          default=(0, 0),
                          help="select USRP Rx side A or B (default=A)")
        parser.add_option(
            "-d",
            "--decim",
            type="int",
            default=16,
            help="set fgpa decimation rate to DECIM [default=%default]")
        parser.add_option("-f",
                          "--freq",
                          type="eng_float",
                          default=None,
                          help="set frequency to FREQ",
                          metavar="FREQ")
        parser.add_option("-Q",
                          "--observing",
                          type="eng_float",
                          default=0.0,
                          help="set observing frequency to FREQ")
        parser.add_option("-a",
                          "--avg",
                          type="eng_float",
                          default=1.0,
                          help="set spectral averaging alpha")
        parser.add_option("-V",
                          "--favg",
                          type="eng_float",
                          default=2.0,
                          help="set folder averaging alpha")
        parser.add_option("-g",
                          "--gain",
                          type="eng_float",
                          default=None,
                          help="set gain in dB (default is midpoint)")
        parser.add_option("-l",
                          "--reflevel",
                          type="eng_float",
                          default=30.0,
                          help="Set pulse display reference level")
        parser.add_option("-L",
                          "--lowest",
                          type="eng_float",
                          default=1.5,
                          help="Lowest valid frequency bin")
        parser.add_option("-e",
                          "--longitude",
                          type="eng_float",
                          default=-76.02,
                          help="Set Observer Longitude")
        parser.add_option("-c",
                          "--latitude",
                          type="eng_float",
                          default=44.85,
                          help="Set Observer Latitude")
        parser.add_option("-F",
                          "--fft_size",
                          type="eng_float",
                          default=1024,
                          help="Size of FFT")

        parser.add_option("-t",
                          "--threshold",
                          type="eng_float",
                          default=2.5,
                          help="pulsar threshold")
        parser.add_option("-p",
                          "--lowpass",
                          type="eng_float",
                          default=100,
                          help="Pulse spectra cutoff freq")
        parser.add_option("-P", "--prefix", default="./", help="File prefix")
        parser.add_option("-u",
                          "--pulsefreq",
                          type="eng_float",
                          default=0.748,
                          help="Observation pulse rate")
        parser.add_option("-D",
                          "--dm",
                          type="eng_float",
                          default=1.0e-5,
                          help="Dispersion Measure")
        parser.add_option("-O",
                          "--doppler",
                          type="eng_float",
                          default=1.0,
                          help="Doppler ratio")
        parser.add_option("-B",
                          "--divbase",
                          type="eng_float",
                          default=20,
                          help="Y/Div menu base")
        parser.add_option("-I",
                          "--division",
                          type="eng_float",
                          default=100,
                          help="Y/Div")
        parser.add_option("-A",
                          "--audio_source",
                          default="plughw:0,0",
                          help="Audio input device spec")
        parser.add_option("-N",
                          "--num_pulses",
                          default=1,
                          type="eng_float",
                          help="Number of display pulses")
        (options, args) = parser.parse_args()
        if len(args) != 0:
            parser.print_help()
            sys.exit(1)

        self.show_debug_info = True

        self.reflevel = options.reflevel
        self.divbase = options.divbase
        self.division = options.division
        self.audiodev = options.audio_source
        self.mult = int(options.num_pulses)

        # Low-pass cutoff for post-detector filter
        # Set to 100Hz usually, since lots of pulsars fit in this
        #   range
        self.lowpass = options.lowpass

        # What is lowest valid frequency bin in post-detector FFT?
        # There's some pollution very close to DC
        self.lowest_freq = options.lowest

        # What (dB) threshold to use in determining spectral candidates
        self.threshold = options.threshold

        # Filename prefix for recording file
        self.prefix = options.prefix

        # Dispersion Measure (DM)
        self.dm = options.dm

        # Doppler shift, as a ratio
        #  1.0 == no doppler shift
        #  1.005 == a little negative shift
        #  0.995 == a little positive shift
        self.doppler = options.doppler

        #
        # Input frequency and observing frequency--not necessarily the
        #   same thing, if we're looking at the IF of some downconverter
        #   that's ahead of the USRP and daughtercard.  This distinction
        #   is important in computing the correct de-dispersion filter.
        #
        self.frequency = options.freq
        if options.observing <= 0:
            self.observing_freq = options.freq
        else:
            self.observing_freq = options.observing

        # build the graph
        self.u = usrp.source_c(decim_rate=options.decim)
        self.u.set_mux(
            usrp.determine_rx_mux_value(self.u, options.rx_subdev_spec))

        #
        # Recording file, in case we ever need to record baseband data
        #
        self.recording = gr.file_sink(gr.sizeof_char, "/dev/null")
        self.recording_state = False

        self.pulse_recording = gr.file_sink(gr.sizeof_short, "/dev/null")
        self.pulse_recording_state = False

        #
        # We come up with recording turned off, but the user may
        #  request recording later on
        self.recording.close()
        self.pulse_recording.close()

        #
        # Need these two for converting 12-bit baseband signals to 8-bit
        #
        self.tofloat = gr.complex_to_float()
        self.tochar = gr.float_to_char()

        # Need this for recording pulses (post-detector)
        self.toshort = gr.float_to_short()

        #
        # The spectral measurer sets this when it has a valid
        #   average spectral peak-to-peak distance
        # We can then use this to program the parameters for the epoch folder
        #
        # We set a sentimental value here
        self.pulse_freq = options.pulsefreq

        # Folder runs at this raw sample rate
        self.folder_input_rate = 20000

        # Each pulse in the epoch folder is sampled at 128 times the nominal
        #  pulse rate
        self.folding = 128

        #
        # Try to find candidate parameters for rational resampler
        #
        save_i = 0
        candidates = []
        for i in range(20, 300):
            input_rate = self.folder_input_rate
            output_rate = int(self.pulse_freq * i)
            interp = gru.lcm(input_rate, output_rate) / input_rate
            decim = gru.lcm(input_rate, output_rate) / output_rate
            if (interp < 500 and decim < 250000):
                candidates.append(i)

        # We didn't find anything, bail!
        if (len(candidates) < 1):
            print "Couldn't converge on resampler parameters"
            sys.exit(1)

        #
        # Now try to find candidate with the least sampling error
        #
        mindiff = 999.999
        for i in candidates:
            diff = self.pulse_freq * i
            diff = diff - int(diff)
            if (diff < mindiff):
                mindiff = diff
                save_i = i

        # Recompute rates
        input_rate = self.folder_input_rate
        output_rate = int(self.pulse_freq * save_i)

        # Compute new interp and decim, based on best candidate
        interp = gru.lcm(input_rate, output_rate) / input_rate
        decim = gru.lcm(input_rate, output_rate) / output_rate

        # Save optimized folding parameters, used later
        self.folding = save_i
        self.interp = int(interp)
        self.decim = int(decim)

        # So that we can view N pulses in the pulse viewer window
        FOLD_MULT = self.mult

        # determine the daughterboard subdevice we're using
        self.subdev = usrp.selected_subdev(self.u, options.rx_subdev_spec)
        self.cardtype = self.u.daughterboard_id(0)

        # Compute raw input rate
        input_rate = self.u.adc_freq() / self.u.decim_rate()

        # BW==input_rate for complex data
        self.bw = input_rate

        #
        # Set baseband filter bandwidth if DBS_RX:
        #
        if self.cardtype == usrp_dbid.DBS_RX:
            lbw = input_rate / 2
            if lbw < 1.0e6:
                lbw = 1.0e6
            self.subdev.set_bw(lbw)

        #
        # We use this as a crude volume control for the audio output
        #
        #self.volume = gr.multiply_const_ff(10**(-1))

        #
        # Create location data for ephem package
        #
        self.locality = ephem.Observer()
        self.locality.long = str(options.longitude)
        self.locality.lat = str(options.latitude)

        #
        # What is the post-detector LPF cutoff for the FFT?
        #
        PULSAR_MAX_FREQ = int(options.lowpass)

        # First low-pass filters down to input_rate/FIRST_FACTOR
        #   and decimates appropriately
        FIRST_FACTOR = int(input_rate / (self.folder_input_rate / 2))
        first_filter = gr.firdes.low_pass(1.0, input_rate,
                                          input_rate / FIRST_FACTOR,
                                          input_rate / (FIRST_FACTOR * 20),
                                          gr.firdes.WIN_HAMMING)

        # Second filter runs at the output rate of the first filter,
        #  And low-pass filters down to PULSAR_MAX_FREQ*10
        #
        second_input_rate = int(input_rate / (FIRST_FACTOR / 2))
        second_filter = gr.firdes.band_pass(1.0, second_input_rate, 0.10,
                                            PULSAR_MAX_FREQ * 10,
                                            PULSAR_MAX_FREQ * 1.5,
                                            gr.firdes.WIN_HAMMING)

        # Third filter runs at PULSAR_MAX_FREQ*20
        #   and filters down to PULSAR_MAX_FREQ
        #
        third_input_rate = PULSAR_MAX_FREQ * 20
        third_filter = gr.firdes_band_pass(1.0, third_input_rate, 0.10,
                                           PULSAR_MAX_FREQ,
                                           PULSAR_MAX_FREQ / 10.0,
                                           gr.firdes.WIN_HAMMING)

        #
        # Create the appropriate FFT scope
        #
        self.scope = ra_fftsink.ra_fft_sink_f(panel,
                                              fft_size=int(options.fft_size),
                                              sample_rate=PULSAR_MAX_FREQ * 2,
                                              title="Post-detector spectrum",
                                              ofunc=self.pulsarfunc,
                                              xydfunc=self.xydfunc,
                                              fft_rate=200)

        #
        # Tell scope we're looking from DC to PULSAR_MAX_FREQ
        #
        self.scope.set_baseband_freq(0.0)

        #
        # Setup stripchart for showing pulse profiles
        #
        hz = "%5.3fHz " % self.pulse_freq
        per = "(%5.3f sec)" % (1.0 / self.pulse_freq)
        sr = "%d sps" % (int(self.pulse_freq * self.folding))
        times = " %d Pulse Intervals" % self.mult
        self.chart = ra_stripchartsink.stripchart_sink_f(
            panel,
            sample_rate=1,
            stripsize=self.folding * FOLD_MULT,
            parallel=True,
            title="Pulse Profiles: " + hz + per + times,
            xlabel="Seconds @ " + sr,
            ylabel="Level",
            autoscale=True,
            divbase=self.divbase,
            scaling=1.0 / (self.folding * self.pulse_freq))
        self.chart.set_ref_level(self.reflevel)
        self.chart.set_y_per_div(self.division)

        # De-dispersion filter setup
        #
        # Do this here, just before creating the filter
        #  that will use the taps.
        #
        ntaps = self.compute_disp_ntaps(self.dm, self.bw, self.observing_freq)

        # Taps for the de-dispersion filter
        self.disp_taps = Numeric.zeros(ntaps, Numeric.Complex64)

        # Compute the de-dispersion filter now
        self.compute_dispfilter(self.dm, self.doppler, self.bw,
                                self.observing_freq)

        #
        # Call constructors for receive chains
        #

        #
        # Now create the FFT filter using the computed taps
        self.dispfilt = gr.fft_filter_ccc(1, self.disp_taps)

        #
        # Audio sink
        #
        #print "input_rate ", second_input_rate, "audiodev ", self.audiodev
        #self.audio = audio.sink(second_input_rate, self.audiodev)

        #
        # The three post-detector filters
        # Done this way to allow an audio path (up to 10Khz)
        # ...and also because going from xMhz down to ~100Hz
        # In a single filter doesn't seem to work.
        #
        self.first = gr.fir_filter_fff(FIRST_FACTOR / 2, first_filter)

        p = second_input_rate / (PULSAR_MAX_FREQ * 20)
        self.second = gr.fir_filter_fff(int(p), second_filter)
        self.third = gr.fir_filter_fff(10, third_filter)

        # Detector
        self.detector = gr.complex_to_mag_squared()

        self.enable_comb_filter = False
        # Epoch folder comb filter
        if self.enable_comb_filter == True:
            bogtaps = Numeric.zeros(512, Numeric.Float64)
            self.folder_comb = gr.fft_filter_ccc(1, bogtaps)

        # Rational resampler
        self.folder_rr = blks2.rational_resampler_fff(self.interp, self.decim)

        # Epoch folder bandpass
        bogtaps = Numeric.zeros(1, Numeric.Float64)
        self.folder_bandpass = gr.fir_filter_fff(1, bogtaps)

        # Epoch folder F2C/C2F
        self.folder_f2c = gr.float_to_complex()
        self.folder_c2f = gr.complex_to_float()

        # Epoch folder S2P
        self.folder_s2p = gr.serial_to_parallel(gr.sizeof_float,
                                                self.folding * FOLD_MULT)

        # Epoch folder IIR Filter (produces average pulse profiles)
        self.folder_iir = gr.single_pole_iir_filter_ff(
            1.0 / options.favg, self.folding * FOLD_MULT)

        #
        # Set all the epoch-folder goop up
        #
        self.set_folding_params()

        #
        # Start connecting configured modules in the receive chain
        #

        # Connect raw USRP to de-dispersion filter, detector
        self.connect(self.u, self.dispfilt, self.detector)

        # Connect detector output to FIR LPF
        #  in two stages, followed by the FFT scope
        self.connect(self.detector, self.first, self.second, self.third,
                     self.scope)

        # Connect audio output
        #self.connect(self.first, self.volume)
        #self.connect(self.volume, (self.audio, 0))
        #self.connect(self.volume, (self.audio, 1))

        # Connect epoch folder
        if self.enable_comb_filter == True:
            self.connect(self.first, self.folder_bandpass, self.folder_rr,
                         self.folder_f2c, self.folder_comb, self.folder_c2f,
                         self.folder_s2p, self.folder_iir, self.chart)

        else:
            self.connect(self.first, self.folder_bandpass, self.folder_rr,
                         self.folder_s2p, self.folder_iir, self.chart)

        # Connect baseband recording file (initially /dev/null)
        self.connect(self.u, self.tofloat, self.tochar, self.recording)

        # Connect pulse recording file (initially /dev/null)
        self.connect(self.first, self.toshort, self.pulse_recording)

        #
        # Build the GUI elements
        #
        self._build_gui(vbox)

        # Make GUI agree with command-line
        self.myform['average'].set_value(int(options.avg))
        self.myform['foldavg'].set_value(int(options.favg))

        # Make spectral averager agree with command line
        if options.avg != 1.0:
            self.scope.set_avg_alpha(float(1.0 / options.avg))
            self.scope.set_average(True)

        # 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)
        #self.set_volume(-10.0)

        if not (self.set_freq(options.freq)):
            self._set_status_msg("Failed to set initial frequency")

        self.myform['decim'].set_value(self.u.decim_rate())
        self.myform['fs@usb'].set_value(self.u.adc_freq() /
                                        self.u.decim_rate())
        self.myform['dbname'].set_value(self.subdev.name())
        self.myform['DM'].set_value(self.dm)
        self.myform['Doppler'].set_value(self.doppler)

        #
        # Start the timer that shows current LMST on the GUI
        #
        self.lmst_timer.Start(1000)
Пример #4
0
    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("-R", "--rx-subdev-spec", type="subdev", default=(0, 0),
                          help="select USRP Rx side A or B (default=A)")
        parser.add_option("-d", "--decim", type="int", default=16,
                          help="set fgpa decimation rate to DECIM [default=%default]")
        parser.add_option("-f", "--freq", type="eng_float", default=None,
                          help="set frequency to FREQ", metavar="FREQ")
        parser.add_option("-Q", "--observing", type="eng_float", default=0.0,
                          help="set observing frequency to FREQ")
        parser.add_option("-a", "--avg", type="eng_float", default=1.0,
		help="set spectral averaging alpha")
        parser.add_option("-V", "--favg", type="eng_float", default=2.0,
                help="set folder averaging alpha")
        parser.add_option("-g", "--gain", type="eng_float", default=None,
                          help="set gain in dB (default is midpoint)")
        parser.add_option("-l", "--reflevel", type="eng_float", default=30.0,
                          help="Set pulse display reference level")
        parser.add_option("-L", "--lowest", type="eng_float", default=1.5,
                          help="Lowest valid frequency bin")
        parser.add_option("-e", "--longitude", type="eng_float", default=-76.02,                          help="Set Observer Longitude")
        parser.add_option("-c", "--latitude", type="eng_float", default=44.85,                          help="Set Observer Latitude")
        parser.add_option("-F", "--fft_size", type="eng_float", default=1024, help="Size of FFT")

        parser.add_option ("-t", "--threshold", type="eng_float", default=2.5, help="pulsar threshold")
        parser.add_option("-p", "--lowpass", type="eng_float", default=100, help="Pulse spectra cutoff freq")
        parser.add_option("-P", "--prefix", default="./", help="File prefix")
        parser.add_option("-u", "--pulsefreq", type="eng_float", default=0.748, help="Observation pulse rate")
        parser.add_option("-D", "--dm", type="eng_float", default=1.0e-5, help="Dispersion Measure")
        parser.add_option("-O", "--doppler", type="eng_float", default=1.0, help="Doppler ratio")
        parser.add_option("-B", "--divbase", type="eng_float", default=20, help="Y/Div menu base")
        parser.add_option("-I", "--division", type="eng_float", default=100, help="Y/Div")
        parser.add_option("-A", "--audio_source", default="plughw:0,0", help="Audio input device spec")
        parser.add_option("-N", "--num_pulses", default=1, type="eng_float", help="Number of display pulses")
        (options, args) = parser.parse_args()
        if len(args) != 0:
            parser.print_help()
            sys.exit(1)

        self.show_debug_info = True

        self.reflevel = options.reflevel
        self.divbase = options.divbase
        self.division = options.division
        self.audiodev = options.audio_source
        self.mult = int(options.num_pulses)

        # Low-pass cutoff for post-detector filter
        # Set to 100Hz usually, since lots of pulsars fit in this
        #   range
        self.lowpass = options.lowpass

        # What is lowest valid frequency bin in post-detector FFT?
        # There's some pollution very close to DC
        self.lowest_freq = options.lowest

        # What (dB) threshold to use in determining spectral candidates
        self.threshold = options.threshold

        # Filename prefix for recording file
        self.prefix = options.prefix

        # Dispersion Measure (DM)
        self.dm = options.dm

        # Doppler shift, as a ratio
        #  1.0 == no doppler shift
        #  1.005 == a little negative shift
        #  0.995 == a little positive shift
        self.doppler = options.doppler

        #
        # Input frequency and observing frequency--not necessarily the
        #   same thing, if we're looking at the IF of some downconverter
        #   that's ahead of the USRP and daughtercard.  This distinction
        #   is important in computing the correct de-dispersion filter.
        #
        self.frequency = options.freq
        if options.observing <= 0:
            self.observing_freq = options.freq
        else:
            self.observing_freq = options.observing
        
        # build the graph
        self.u = usrp.source_c(decim_rate=options.decim)
        self.u.set_mux(usrp.determine_rx_mux_value(self.u, options.rx_subdev_spec))

        #
        # Recording file, in case we ever need to record baseband data
        #
        self.recording = gr.file_sink(gr.sizeof_char, "/dev/null")
        self.recording_state = False

        self.pulse_recording = gr.file_sink(gr.sizeof_short, "/dev/null")
        self.pulse_recording_state = False

        #
        # We come up with recording turned off, but the user may
        #  request recording later on
        self.recording.close()
        self.pulse_recording.close()

        #
        # Need these two for converting 12-bit baseband signals to 8-bit
        #
        self.tofloat = gr.complex_to_float()
        self.tochar = gr.float_to_char()

        # Need this for recording pulses (post-detector)
        self.toshort = gr.float_to_short()


        #
        # The spectral measurer sets this when it has a valid
        #   average spectral peak-to-peak distance
        # We can then use this to program the parameters for the epoch folder
        #
        # We set a sentimental value here
        self.pulse_freq = options.pulsefreq

        # Folder runs at this raw sample rate
        self.folder_input_rate = 20000

        # Each pulse in the epoch folder is sampled at 128 times the nominal
        #  pulse rate
        self.folding = 128

 
        #
        # Try to find candidate parameters for rational resampler
        #
        save_i = 0
        candidates = []
        for i in range(20,300):
            input_rate = self.folder_input_rate
            output_rate = int(self.pulse_freq * i)
            interp = gru.lcm(input_rate, output_rate) / input_rate
            decim = gru.lcm(input_rate, output_rate) / output_rate
            if (interp < 500 and decim < 250000):
                 candidates.append(i)

        # We didn't find anything, bail!
        if (len(candidates) < 1):
            print "Couldn't converge on resampler parameters"
            sys.exit(1)

        #
        # Now try to find candidate with the least sampling error
        #
        mindiff = 999.999
        for i in candidates:
            diff = self.pulse_freq * i
            diff = diff - int(diff)
            if (diff < mindiff):
                mindiff = diff
                save_i = i

        # Recompute rates
        input_rate = self.folder_input_rate
        output_rate = int(self.pulse_freq * save_i)

        # Compute new interp and decim, based on best candidate
        interp = gru.lcm(input_rate, output_rate) / input_rate
        decim = gru.lcm(input_rate, output_rate) / output_rate

        # Save optimized folding parameters, used later
        self.folding = save_i
        self.interp = int(interp)
        self.decim = int(decim)

        # So that we can view N pulses in the pulse viewer window
        FOLD_MULT=self.mult

        # determine the daughterboard subdevice we're using
        self.subdev = usrp.selected_subdev(self.u, options.rx_subdev_spec)
        self.cardtype = self.u.daughterboard_id(0)

        # Compute raw input rate
        input_rate = self.u.adc_freq() / self.u.decim_rate()

        # BW==input_rate for complex data
        self.bw = input_rate

        #
        # Set baseband filter bandwidth if DBS_RX:
        #
        if self.cardtype == usrp_dbid.DBS_RX:
            lbw = input_rate / 2
            if lbw < 1.0e6:
                lbw = 1.0e6
            self.subdev.set_bw(lbw)

        #
        # We use this as a crude volume control for the audio output
        #
        #self.volume = gr.multiply_const_ff(10**(-1))
        

        #
        # Create location data for ephem package
        #
        self.locality = ephem.Observer()
        self.locality.long = str(options.longitude)
        self.locality.lat = str(options.latitude)

        #
        # What is the post-detector LPF cutoff for the FFT?
        #
        PULSAR_MAX_FREQ=int(options.lowpass)

        # First low-pass filters down to input_rate/FIRST_FACTOR
        #   and decimates appropriately
        FIRST_FACTOR=int(input_rate/(self.folder_input_rate/2))
        first_filter = gr.firdes.low_pass (1.0,
                                          input_rate,
                                          input_rate/FIRST_FACTOR,
                                          input_rate/(FIRST_FACTOR*20),         
                                          gr.firdes.WIN_HAMMING)

        # Second filter runs at the output rate of the first filter,
        #  And low-pass filters down to PULSAR_MAX_FREQ*10
        #
        second_input_rate =  int(input_rate/(FIRST_FACTOR/2))
        second_filter = gr.firdes.band_pass(1.0, second_input_rate,
                                          0.10,
                                          PULSAR_MAX_FREQ*10,
                                          PULSAR_MAX_FREQ*1.5,
                                          gr.firdes.WIN_HAMMING)

        # Third filter runs at PULSAR_MAX_FREQ*20
        #   and filters down to PULSAR_MAX_FREQ
        #
        third_input_rate = PULSAR_MAX_FREQ*20
        third_filter = gr.firdes_band_pass(1.0, third_input_rate,
                                           0.10, PULSAR_MAX_FREQ,
                                           PULSAR_MAX_FREQ/10.0,
                                           gr.firdes.WIN_HAMMING)


        #
        # Create the appropriate FFT scope
        #
        self.scope = ra_fftsink.ra_fft_sink_f (panel, 
           fft_size=int(options.fft_size), sample_rate=PULSAR_MAX_FREQ*2,
           title="Post-detector spectrum",  
           ofunc=self.pulsarfunc, xydfunc=self.xydfunc, fft_rate=200)

        #
        # Tell scope we're looking from DC to PULSAR_MAX_FREQ
        #
        self.scope.set_baseband_freq (0.0)


        #
        # Setup stripchart for showing pulse profiles
        #
        hz = "%5.3fHz " % self.pulse_freq
        per = "(%5.3f sec)" % (1.0/self.pulse_freq)
        sr = "%d sps" % (int(self.pulse_freq*self.folding))
        times = " %d Pulse Intervals" % self.mult
        self.chart = ra_stripchartsink.stripchart_sink_f (panel,
               sample_rate=1,
               stripsize=self.folding*FOLD_MULT, parallel=True, title="Pulse Profiles: "+hz+per+times, 
               xlabel="Seconds @ "+sr, ylabel="Level", autoscale=True,
               divbase=self.divbase, scaling=1.0/(self.folding*self.pulse_freq))
        self.chart.set_ref_level(self.reflevel)
        self.chart.set_y_per_div(self.division)

        # De-dispersion filter setup
        #
        # Do this here, just before creating the filter
        #  that will use the taps.
        #
        ntaps = self.compute_disp_ntaps(self.dm,self.bw,self.observing_freq)

        # Taps for the de-dispersion filter
        self.disp_taps = Numeric.zeros(ntaps,Numeric.Complex64)

        # Compute the de-dispersion filter now
        self.compute_dispfilter(self.dm,self.doppler,
            self.bw,self.observing_freq)

        #
        # Call constructors for receive chains
        #

        #
        # Now create the FFT filter using the computed taps
        self.dispfilt = gr.fft_filter_ccc(1, self.disp_taps)

        #
        # Audio sink
        #
        #print "input_rate ", second_input_rate, "audiodev ", self.audiodev
        #self.audio = audio.sink(second_input_rate, self.audiodev)

        #
        # The three post-detector filters
        # Done this way to allow an audio path (up to 10Khz)
        # ...and also because going from xMhz down to ~100Hz
        # In a single filter doesn't seem to work.
        #
        self.first = gr.fir_filter_fff (FIRST_FACTOR/2, first_filter)

        p = second_input_rate / (PULSAR_MAX_FREQ*20)
        self.second = gr.fir_filter_fff (int(p), second_filter)
        self.third = gr.fir_filter_fff (10, third_filter)

        # Detector
        self.detector = gr.complex_to_mag_squared()

        self.enable_comb_filter = False
        # Epoch folder comb filter
        if self.enable_comb_filter == True:
            bogtaps = Numeric.zeros(512, Numeric.Float64)
            self.folder_comb = gr.fft_filter_ccc(1,bogtaps)

        # Rational resampler
        self.folder_rr = blks2.rational_resampler_fff(self.interp, self.decim)

        # Epoch folder bandpass
        bogtaps = Numeric.zeros(1, Numeric.Float64)
        self.folder_bandpass = gr.fir_filter_fff (1, bogtaps)

        # Epoch folder F2C/C2F
        self.folder_f2c = gr.float_to_complex()
        self.folder_c2f = gr.complex_to_float()

        # Epoch folder S2P
        self.folder_s2p = gr.serial_to_parallel (gr.sizeof_float, 
             self.folding*FOLD_MULT)

        # Epoch folder IIR Filter (produces average pulse profiles)
        self.folder_iir = gr.single_pole_iir_filter_ff(1.0/options.favg,
             self.folding*FOLD_MULT)

        #
        # Set all the epoch-folder goop up
        #
        self.set_folding_params()

        # 
        # Start connecting configured modules in the receive chain
        #

        # Connect raw USRP to de-dispersion filter, detector
        self.connect(self.u, self.dispfilt, self.detector)

        # Connect detector output to FIR LPF
        #  in two stages, followed by the FFT scope
        self.connect(self.detector, self.first,
            self.second, self.third, self.scope)

        # Connect audio output
        #self.connect(self.first, self.volume)
        #self.connect(self.volume, (self.audio, 0))
        #self.connect(self.volume, (self.audio, 1))

        # Connect epoch folder
        if self.enable_comb_filter == True:
            self.connect (self.first, self.folder_bandpass, self.folder_rr,
                self.folder_f2c,
                self.folder_comb, self.folder_c2f,
                self.folder_s2p, self.folder_iir,
                self.chart)

        else:
            self.connect (self.first, self.folder_bandpass, self.folder_rr,
                self.folder_s2p, self.folder_iir, self.chart)

        # Connect baseband recording file (initially /dev/null)
        self.connect(self.u, self.tofloat, self.tochar, self.recording)

        # Connect pulse recording file (initially /dev/null)
        self.connect(self.first, self.toshort, self.pulse_recording)

        #
        # Build the GUI elements
        #
        self._build_gui(vbox)

        # Make GUI agree with command-line
        self.myform['average'].set_value(int(options.avg))
        self.myform['foldavg'].set_value(int(options.favg))


        # Make spectral averager agree with command line
        if options.avg != 1.0:
            self.scope.set_avg_alpha(float(1.0/options.avg))
            self.scope.set_average(True)


        # 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)
        #self.set_volume(-10.0)

        if not(self.set_freq(options.freq)):
            self._set_status_msg("Failed to set initial frequency")

        self.myform['decim'].set_value(self.u.decim_rate())
        self.myform['fs@usb'].set_value(self.u.adc_freq() / self.u.decim_rate())
        self.myform['dbname'].set_value(self.subdev.name())
        self.myform['DM'].set_value(self.dm)
        self.myform['Doppler'].set_value(self.doppler)

        #
        # Start the timer that shows current LMST on the GUI
        #
        self.lmst_timer.Start(1000)