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| From: | Arora_Amit |
| Subject: | [Discuss-gnuradio] Doubts in Gnu-Radio examples of USRP |
| Date: | Sun, 24 Jul 2005 16:34:59 +0530 |
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Hi All, In the gnu-radio-examples0.4 for USRP , kindly provide a theoretical
explanation of the following points: 1. What is the criteria of selecting the IF Frequency (IF_freq) for a
particular application? 2. What is IF_rate , and what is its significance? 3. How do we chose IF_decim and what is its significance? 4. What is quad_rate(IF_rate/ IF_decim)? 5. What is audio_decim and audio_rate? Here is the particular example taken from gnu-radio examples : nbfm_ptt_quick_and_dirty.py ------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------ import math import sys from optparse import OptionParser from gnuradio import gr, eng_notation from gnuradio import usrp from gnuradio import audio from gnuradio import blks from gnuradio.eng_option import eng_option from gnuradio.wxgui import stdgui, fftsink import wx class ptt_graph(stdgui.gui_flow_graph): def __init__(self, frame, panel, vbox,
argv): stdgui.gui_flow_graph.__init__
(self, frame, panel, vbox, argv) self.frame = frame self.space_bar_pressed = False parser = OptionParser
(option_class=eng_option) parser.add_option ("-f",
"--freq", type="eng_float", default=29.325e6, help="set
Tx and Rx frequency to FREQ", metavar="FREQ") parser.add_option ("-N",
"--no-gui", action="" default=False) (options, args) =
parser.parse_args () if len(args) != 0: parser.print_help() sys.exit(1) if options.freq < 1e6: options.freq *= 1e6 self.txpath = transmit_path(self,
options.freq) self.rxpath = receive_path(self,
options.freq) self.build_gui(frame, panel, vbox,
argv, options.no_gui) self.set_transmit(False) def set_transmit(self, enabled): self.txpath.set_enable(enabled)
self.rxpath.set_enable(not(enabled)) if enabled: self.frame.SetStatusText
("Transmitter ON") else: self.frame.SetStatusText
("Receiver ON") def build_gui(self, frame, panel,
vbox, argv, no_gui): hbox = wx.BoxSizer(wx.HORIZONTAL) hbox.Add((10,0), 1.0) #
stretchy space self.status_msg =
wx.StaticText(panel, -1, "Press Space Bar to Transmit") of = self.status_msg.GetFont()
self.status_msg.SetFont(wx.Font(15, of.GetFamily(), of.GetStyle(),
of.GetWeight())) hbox.Add(self.status_msg, 0,
wx.ALIGN_CENTER | wx.EXPAND) hbox.Add((10,0), 1.0) #
stretchy space vbox.Add(hbox, 0, wx.EXPAND |
wx.ALIGN_CENTER) panel.Bind(wx.EVT_KEY_DOWN,
self._on_key_down) panel.Bind(wx.EVT_KEY_UP,
self._on_key_up) panel.Bind(wx.EVT_KILL_FOCUS,
self._on_kill_focus) panel.SetFocus() if 1 and not(no_gui): rx_fft, win1 = \
fftsink.make_fft_sink_c (self, panel, "Rx Input", 512,
self.rxpath.IF_rate, 0, 100) self.connect (self.rxpath.u,
rx_fft) vbox.Add (win1, 1, wx.EXPAND) if 1 and not(no_gui): tx_fft, win1 = \
fftsink.make_fft_sink_c (self, panel, "Tx Output", 512,
self.txpath.usrp_rate, 20, 140) self.connect (self.txpath.amp,
tx_fft) vbox.Add (win1, 1, wx.EXPAND) def _on_key_down(self, evt): # print "key_down:",
evt.m_keyCode if evt.m_keyCode == wx.WXK_SPACE
and not(self.space_bar_pressed): self.space_bar_pressed = True self.set_transmit(True) def _on_key_up(self, evt): # print "key_up",
evt.m_keyCode if evt.m_keyCode == wx.WXK_SPACE: self.space_bar_pressed = False self.set_transmit(False) def _on_kill_focus(self, evt): # if we lose the keyboard focus,
turn off the transmitter self.space_bar_pressed = False self.set_transmit(False) class transmit_path(gr.hier_block): def __init__(self, fg, RF_freq): dac_rate = 128e6 self.usrp_interp = 400 self.usrp_rate = dac_rate //
self.usrp_interp # 320 kS/s self.sw_interp = 10 self.audio_rate = self.usrp_rate
// self.sw_interp # 32 kS/s self.normal_gain = 4000 RF_freq = fold_freq(RF_freq,
dac_rate) self.audio =
audio.source(int(self.audio_rate)) self.fmtx = blks.nbfm_tx(fg,
self.audio_rate, self.usrp_rate) self.amp = gr.multiply_const_cc
(self.normal_gain) self.u = usrp.sink_c (0,
self.usrp_interp) self.u.set_tx_freq(0, RF_freq) fg.connect(self.audio, self.fmtx,
self.amp, self.u) gr.hier_block.__init__(self, fg,
None, None) def set_enable(self, enable): if enable: self.amp.set_k
(self.normal_gain) else: self.amp.set_k (0) class receive_path(gr.hier_block): def __init__(self, fg, RF_freq): adc_rate = 64e6 IF_freq = 40e3 RF_freq = fold_freq (RF_freq, adc_rate) usrp_decim = 125 IF_rate = adc_rate // usrp_decim # 512 kS/s self.IF_rate = IF_rate IF_decim = 8 quad_rate = IF_rate // IF_decim # 64 kS/s audio_decim = 2
audio_rate = quad_rate // audio_decim # 32 kS/s u = usrp.source_c (0, usrp_decim) self.u = u u.set_rx_freq (0, IF_freq -
RF_freq) u.set_pga (0, 20) u.set_pga (1, 20) IF_freq = RF_freq +
u.rx_freq(0) # compute actual IF freq # Create filter to get actual
channel we want chan_coeffs = gr.firdes.low_pass
(1.0, # gain
IF_rate, # sampling rate
11e3, # low pass cutoff freq
4e3, # width of trans. band
gr.firdes.WIN_HANN) # filter type print len(chan_coeffs) # Decimating Channel filter with
frequency translation # complex in and out, float taps ddc =
gr.freq_xlating_fir_filter_ccf(IF_decim, # decimation rate
chan_coeffs, # taps
-IF_freq, # frequency translation amount
IF_rate) # input sample rate # instantiate the guts of the
single channel receiver self.fmrx = blks.nbfm_rx(fg,
audio_rate, quad_rate) self.set_squelch(15) # use mute block to disable Rx
while transmitting self.m = gr.mute_ff(False) # sound card as final sink audio_sink = audio.sink
(int(audio_rate)) # now wire it all together fg.connect (u, ddc, self.fmrx,
self.m, audio_sink) gr.hier_block.__init__(self, fg,
u, audio_sink) def set_enable(self, enable): self.m.set_mute(not (enable)) def set_squelch(self,
threshold_in_db):
self.fmrx.squelch.set_threshold(threshold_in_db) def fold_freq(freq, fs): while freq > fs: freq = freq - fs if freq > fs/2: freq = fs - freq return freq def main(): app = stdgui.stdapp(ptt_graph,
"NBFM Push to Talk") app.MainLoop() if __name__ == '__main__': main() -------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- Thanks and Regards, Amit Arora DISCLAIMER: |
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