Merge commit 'v3.3.0' into upstream

[debian/gnuradio] / docs / exploring-gnuradio / fm_demod_example.xml

diff --git a/docs/exploring-gnuradio/fm_demod_example.xml b/docs/exploring-gnuradio/fm_demod_example.xml
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+<?xml version="1.0" encoding="ISO-8859-1"?>
+<example id="fm_demod_ex"><title>Broadcast FM Receiver</title>
+<programlisting>
+#!/usr/bin/env python
+
+from gnuradio import gr
+from gnuradio import audio
+from gnuradio import mc4020
+import sys
+
+def high_speed_adc (fg, input_rate):
+    # return gr.file_source (gr.sizeof_short, "dummy.dat", False)
+    return mc4020.source (input_rate, mc4020.MCC_CH3_EN | mc4020.MCC_ALL_1V)
+
+#
+# return a gr.flow_graph
+#
+def build_graph (freq1, freq2):
+    input_rate = 20e6
+    cfir_decimation = 125
+    audio_decimation = 5
+
+    quad_rate = input_rate / cfir_decimation
+    audio_rate = quad_rate / audio_decimation
+
+    fg = gr.flow_graph ()
+    
+    # use high speed ADC as input source
+    src = high_speed_adc (fg, input_rate)
+    
+    # compute FIR filter taps for channel selection
+    channel_coeffs = \
+      gr.firdes.low_pass (1.0,          # gain
+                          input_rate,   # sampling rate
+                          250e3,        # low pass cutoff freq
+                          8*100e3,      # width of trans. band
+                          gr.firdes.WIN_HAMMING)
+
+    # input: short; output: complex
+    chan_filter1 = \
+      gr.freq_xlating_fir_filter_scf (cfir_decimation,
+                                      channel_coeffs,
+                                      freq1,        # 1st station freq
+                                      input_rate)
+    
+    (head1, tail1) = build_pipeline (fg, quad_rate, audio_decimation)
+    
+    # sound card as final sink
+    audio_sink = audio.sink (int (audio_rate))
+
+    # now wire it all together
+    fg.connect (src, chan_filter1)
+    fg.connect (chan_filter1, head1)
+    fg.connect (tail1, (audio_sink, 0))
+
+    return fg
+
+def build_pipeline (fg, quad_rate, audio_decimation):
+    '''Given a flow_graph, fg, construct a pipeline
+    for demodulating a broadcast FM signal.  The
+    input is the downconverted complex baseband
+    signal. The output is the demodulated audio.
+
+    build_pipeline returns a two element tuple
+    containing the input and output endpoints.
+    '''
+    fm_demod_gain = 2200.0/32768.0
+    audio_rate = quad_rate / audio_decimation
+    volume = 1.0
+
+    # input: complex; output: float
+    fm_demod = gr.quadrature_demod_cf (volume*fm_demod_gain)
+
+    # compute FIR filter taps for audio filter
+    width_of_transition_band = audio_rate / 32
+    audio_coeffs = gr.firdes.low_pass (1.0,            # gain
+                                       quad_rate,      # sampling rate
+                                       audio_rate/2 - width_of_transition_band,
+                                       width_of_transition_band,
+                                       gr.firdes.WIN_HAMMING)
+
+    # input: float; output: float
+    audio_filter = gr.fir_filter_fff (audio_decimation, audio_coeffs)
+
+    fg.connect (fm_demod, audio_filter)
+    return ((fm_demod, 0), (audio_filter, 0))
+    
+
+def main (args):
+    nargs = len (args)
+    if nargs == 1:
+        # get station frequency from command line
+        freq1 = float (args[0]) * 1e6
+    else:
+        sys.stderr.write ('usage: fm_demod freq\n')
+        sys.exit (1)
+
+    # connect to RF front end
+    rf_front_end = gr.microtune_4937_eval_board ()
+    if not rf_front_end.board_present_p ():
+        raise IOError, 'RF front end not found'
+
+    # set front end gain
+    rf_front_end.set_AGC (300)
+
+    # determine the front end's "Intermediate Frequency"
+    IF_freq = rf_front_end.get_output_freq () # 5.75e6
+
+    # Tell the front end to tune to freq1.  
+    # I.e., freq1 is translated down to the IF frequency
+    rf_front_end.set_RF_freq (freq1)
+
+    # build the flow graph
+    fg = build_graph (IF_freq, None)
+    
+    fg.start ()        # fork thread(s) and return
+    raw_input ('Press Enter to quit: ')
+    fg.stop ()
+
+if __name__ == '__main__':
+    main (sys.argv[1:])
+</programlisting>
+</example>