#!/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:])