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Stereo FM transmitter using gnuradio. Tools needed: *gnuradio 3.2 *grc (gnuradio companion) *mpg123 *USRP In this example we will show how to make a Stereo FM software transmitter. Input is from an mp3 stream for an Internet radio. Look at GRC schema or use directly python code below. Input file is a unix FIFO file that means that we need to feed it externally from the shell using these commands: Creation of the FIFO file (once): mkfifo stream_32k.fifo Decoding of an mp3 Internet radio station stream, conversion and output of raw linear samples to the FIFO: mpg123 -r32000 -s http://maxxima.mine.nu:8000 >stream_32k.fifo "-r32000" perform sample rate conversion to 32kHz. ==GRC Schema== [[Image:FM transmitter stereo.png]] ==Python code== #!/usr/bin/env python ################################################## # Gnuradio Python Flow Graph # Title: FM Stereo Transmitter # Author: Mathias Coinchon # Generated: Sat Jan 2 19:06:07 2010 ################################################## from gnuradio import blks2 from gnuradio import gr from gnuradio.eng_option import eng_option from gnuradio.gr import firdes from gnuradio.wxgui import fftsink2 from gnuradio.wxgui import forms from grc_gnuradio import usrp as grc_usrp from grc_gnuradio import wxgui as grc_wxgui from optparse import OptionParser import wx class FM_stereo_tx(grc_wxgui.top_block_gui): def __init__(self): grc_wxgui.top_block_gui.__init__(self, title="FM Stereo Transmitter") ################################################## # Variables ################################################## self.st_gain = st_gain = 10 self.samp_rate = samp_rate = 32000 self.pilot_gain = pilot_gain = 80e-3 self.mpx_rate = mpx_rate = 160000 self.Mono_gain = Mono_gain = 0.3 self.FM_freq = FM_freq = 107900000 ################################################## # Controls ################################################## _st_gain_sizer = wx.BoxSizer(wx.VERTICAL) self._st_gain_text_box = forms.text_box( parent=self.GetWin(), sizer=_st_gain_sizer, value=self.st_gain, callback=self.set_st_gain, label="Stereo gain", converter=forms.float_converter(), proportion=0, ) self._st_gain_slider = forms.slider( parent=self.GetWin(), sizer=_st_gain_sizer, value=self.st_gain, callback=self.set_st_gain, minimum=0, maximum=100, num_steps=100, style=wx.SL_HORIZONTAL, cast=float, proportion=1, ) self.Add(_st_gain_sizer) _pilot_gain_sizer = wx.BoxSizer(wx.VERTICAL) self._pilot_gain_text_box = forms.text_box( parent=self.GetWin(), sizer=_pilot_gain_sizer, value=self.pilot_gain, callback=self.set_pilot_gain, label='pilot_gain', converter=forms.float_converter(), proportion=0, ) self._pilot_gain_slider = forms.slider( parent=self.GetWin(), sizer=_pilot_gain_sizer, value=self.pilot_gain, callback=self.set_pilot_gain, minimum=0, maximum=1, num_steps=100, style=wx.SL_HORIZONTAL, cast=float, proportion=1, ) self.Add(_pilot_gain_sizer) _Mono_gain_sizer = wx.BoxSizer(wx.VERTICAL) self._Mono_gain_text_box = forms.text_box( parent=self.GetWin(), sizer=_Mono_gain_sizer, value=self.Mono_gain, callback=self.set_Mono_gain, label="Mono signal gain", converter=forms.float_converter(), proportion=0, ) self._Mono_gain_slider = forms.slider( parent=self.GetWin(), sizer=_Mono_gain_sizer, value=self.Mono_gain, callback=self.set_Mono_gain, minimum=0, maximum=1, num_steps=100, style=wx.SL_HORIZONTAL, cast=float, proportion=1, ) self.Add(_Mono_gain_sizer) _FM_freq_sizer = wx.BoxSizer(wx.VERTICAL) self._FM_freq_text_box = forms.text_box( parent=self.GetWin(), sizer=_FM_freq_sizer, value=self.FM_freq, callback=self.set_FM_freq, label="FM Frequency", converter=forms.float_converter(), proportion=0, ) self._FM_freq_slider = forms.slider( parent=self.GetWin(), sizer=_FM_freq_sizer, value=self.FM_freq, callback=self.set_FM_freq, minimum=87500000, maximum=108000000, num_steps=205, style=wx.SL_HORIZONTAL, cast=float, proportion=1, ) self.Add(_FM_freq_sizer) ################################################## # Blocks ################################################## self.Audio_A_resampler = blks2.rational_resampler_fff( interpolation=5, decimation=1, taps=None, fractional_bw=None, ) self.Audio_B_resampler = blks2.rational_resampler_fff( interpolation=5, decimation=1, taps=None, fractional_bw=None, ) self.MPX_upsampler = blks2.rational_resampler_fff( interpolation=4, decimation=1, taps=None, fractional_bw=None, ) self.Pilot = gr.sig_source_f(mpx_rate, gr.GR_SIN_WAVE, 19000, pilot_gain, 0) self.band_pass_filter_0 = gr.fir_filter_fff(1, firdes.band_pass( st_gain, mpx_rate, 23e3, 53e3, 2e3, firdes.WIN_HAMMING, 6.76)) self.blks2_fm_preemph_0 = blks2.fm_preemph(fs=mpx_rate, tau=50e-6) self.gr_add_xx_0 = gr.add_vff(1) self.gr_add_xx_1 = gr.add_vff(1) self.gr_file_source_0 = gr.file_source(gr.sizeof_short*2, "/home/mc/FM_demo/stream_32k.fifo", True) self.gr_frequency_modulator_fc_0 = gr.frequency_modulator_fc(0.98) self.gr_multiply_const_vxx_0 = gr.multiply_const_vcc((32768, )) self.gr_multiply_const_vxx_1 = gr.multiply_const_vff((0.00003, )) self.gr_multiply_const_vxx_3 = gr.multiply_const_vff((0.00003, )) self.gr_multiply_xx_1 = gr.multiply_vff(1) self.gr_short_to_float_0 = gr.short_to_float() self.gr_short_to_float_1 = gr.short_to_float() self.gr_sub_xx_0 = gr.sub_ff(1) self.gr_vector_to_streams_0 = gr.vector_to_streams(gr.sizeof_short*1, 2) self.low_pass_filter_0 = gr.fir_filter_fff(1, firdes.low_pass( Mono_gain, mpx_rate, 15e3, 2e3, firdes.WIN_HAMMING, 6.76)) self.st_38k_carrier = gr.sig_source_f(mpx_rate, gr.GR_SIN_WAVE, 38000, 30e-3, 0) self.usrp_simple_sink_x_0 = grc_usrp.simple_sink_c(which=0, side="B") self.usrp_simple_sink_x_0.set_interp_rate(200) self.usrp_simple_sink_x_0.set_frequency(-FM_freq, verbose=True) self.usrp_simple_sink_x_0.set_gain(0) self.usrp_simple_sink_x_0.set_enable(True) self.wxgui_fftsink2_0 = fftsink2.fft_sink_f( self.GetWin(), baseband_freq=0, y_per_div=10, y_divs=10, ref_level=50, sample_rate=mpx_rate, fft_size=1024, fft_rate=30, average=False, avg_alpha=None, title="Baseband spectrum", peak_hold=False, ) self.Add(self.wxgui_fftsink2_0.win) ################################################## # Connections ################################################## self.connect((self.Audio_A_resampler, 0), (self.gr_add_xx_1, 0)) self.connect((self.Audio_B_resampler, 0), (self.gr_add_xx_1, 1)) self.connect((self.Audio_A_resampler, 0), (self.gr_sub_xx_0, 0)) self.connect((self.gr_multiply_xx_1, 0), (self.band_pass_filter_0, 0)) self.connect((self.st_38k_carrier, 0), (self.gr_multiply_xx_1, 1)) self.connect((self.low_pass_filter_0, 0), (self.gr_add_xx_0, 0)) self.connect((self.gr_add_xx_1, 0), (self.low_pass_filter_0, 0)) self.connect((self.gr_frequency_modulator_fc_0, 0), (self.gr_multiply_const_vxx_0, 0)) self.connect((self.MPX_upsampler, 0), (self.gr_frequency_modulator_fc_0, 0)) self.connect((self.blks2_fm_preemph_0, 0), (self.MPX_upsampler, 0)) self.connect((self.gr_add_xx_0, 0), (self.blks2_fm_preemph_0, 0)) self.connect((self.Pilot, 0), (self.gr_add_xx_0, 2)) self.connect((self.band_pass_filter_0, 0), (self.gr_add_xx_0, 1)) self.connect((self.gr_add_xx_0, 0), (self.wxgui_fftsink2_0, 0)) self.connect((self.gr_sub_xx_0, 0), (self.gr_multiply_xx_1, 0)) self.connect((self.Audio_B_resampler, 0), (self.gr_sub_xx_0, 1)) self.connect((self.gr_multiply_const_vxx_0, 0), (self.usrp_simple_sink_x_0, 0)) self.connect((self.gr_file_source_0, 0), (self.gr_vector_to_streams_0, 0)) self.connect((self.gr_short_to_float_1, 0), (self.gr_multiply_const_vxx_1, 0)) self.connect((self.gr_multiply_const_vxx_1, 0), (self.Audio_A_resampler, 0)) self.connect((self.gr_short_to_float_0, 0), (self.gr_multiply_const_vxx_3, 0)) self.connect((self.gr_multiply_const_vxx_3, 0), (self.Audio_B_resampler, 0)) self.connect((self.gr_vector_to_streams_0, 1), (self.gr_short_to_float_1, 0)) self.connect((self.gr_vector_to_streams_0, 0), (self.gr_short_to_float_0, 0)) def set_st_gain(self, st_gain): self.st_gain = st_gain self.band_pass_filter_0.set_taps(firdes.band_pass(self.st_gain, self.mpx_rate, 23e3, 53e3, 2e3, firdes.WIN_HAMMING, 6.76)) self._st_gain_slider.set_value(self.st_gain) self._st_gain_text_box.set_value(self.st_gain) def set_samp_rate(self, samp_rate): self.samp_rate = samp_rate def set_pilot_gain(self, pilot_gain): self.pilot_gain = pilot_gain self.Pilot.set_amplitude(self.pilot_gain) self._pilot_gain_slider.set_value(self.pilot_gain) self._pilot_gain_text_box.set_value(self.pilot_gain) def set_mpx_rate(self, mpx_rate): self.mpx_rate = mpx_rate self.band_pass_filter_0.set_taps(firdes.band_pass(self.st_gain, self.mpx_rate, 23e3, 53e3, 2e3, firdes.WIN_HAMMING, 6.76)) self.low_pass_filter_0.set_taps(firdes.low_pass(self.Mono_gain, self.mpx_rate, 15e3, 2e3, firdes.WIN_HAMMING, 6.76)) self.Pilot.set_sampling_freq(self.mpx_rate) self.st_38k_carrier.set_sampling_freq(self.mpx_rate) self.wxgui_fftsink2_0.set_sample_rate(self.mpx_rate) def set_Mono_gain(self, Mono_gain): self.Mono_gain = Mono_gain self.low_pass_filter_0.set_taps(firdes.low_pass(self.Mono_gain, self.mpx_rate, 15e3, 2e3, firdes.WIN_HAMMING, 6.76)) self._Mono_gain_slider.set_value(self.Mono_gain) self._Mono_gain_text_box.set_value(self.Mono_gain) def set_FM_freq(self, FM_freq): self.FM_freq = FM_freq self.usrp_simple_sink_x_0.set_frequency(-self.FM_freq) self._FM_freq_slider.set_value(self.FM_freq) self._FM_freq_text_box.set_value(self.FM_freq) if __name__ == '__main__': parser = OptionParser(option_class=eng_option, usage="%prog: [options]") (options, args) = parser.parse_args() tb = FM_stereo_tx() tb.Run(True)

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