FM transmission on many channels using gnuradio

FM transmitter on many channels using gnuradio.

Tools needed:

• gnuradio 3.2
• grc (gnuradio companion)
• USRP

In this example we will show how to make an FM software transmitter broadcasting simultaneously on many channels. The same signal is transmitter on 3 different carriers. Look at GRC schema or use directly python code below.

GRC schema

Python code

Python script can be run directly, without GRC.

#!/usr/bin/env python
##################################################
# Gnuradio Python Flow Graph
# Title: Multiplex frequencies FM transmitter
# Author: Mathias Coinchon
# Generated: Sat Jan  2 19:19:17 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 MF_FM_TX(grc_wxgui.top_block_gui):

	def __init__(self):
		grc_wxgui.top_block_gui.__init__(self, title="Multiplex frequencies FM transmitter")

		##################################################
		# Variables
		##################################################
		self.samp_rate = samp_rate = 32000
		self.quad_rate = quad_rate = 1280000
		self.carrier2_frequency = carrier2_frequency = 300000
		self.carrier1_frequency = carrier1_frequency = -300000
		self.FM_frequency = FM_frequency = 107600000

		##################################################
		# Controls
		##################################################
		_carrier2_frequency_sizer = wx.BoxSizer(wx.VERTICAL)
		self._carrier2_frequency_text_box = forms.text_box(
			parent=self.GetWin(),
			sizer=_carrier2_frequency_sizer,
			value=self.carrier2_frequency,
			callback=self.set_carrier2_frequency,
			label="Carrier 2 Frequency",
			converter=forms.float_converter(),
			proportion=0,
		)
		self._carrier2_frequency_slider = forms.slider(
			parent=self.GetWin(),
			sizer=_carrier2_frequency_sizer,
			value=self.carrier2_frequency,
			callback=self.set_carrier2_frequency,
			minimum=-500000,
			maximum=500000,
			num_steps=100,
			style=wx.SL_HORIZONTAL,
			cast=float,
			proportion=1,
		)
		self.Add(_carrier2_frequency_sizer)
		_carrier1_frequency_sizer = wx.BoxSizer(wx.VERTICAL)
		self._carrier1_frequency_text_box = forms.text_box(
			parent=self.GetWin(),
			sizer=_carrier1_frequency_sizer,
			value=self.carrier1_frequency,
			callback=self.set_carrier1_frequency,
			label="Carrier 1 Frequency",
			converter=forms.float_converter(),
			proportion=0,
		)
		self._carrier1_frequency_slider = forms.slider(
			parent=self.GetWin(),
			sizer=_carrier1_frequency_sizer,
			value=self.carrier1_frequency,
			callback=self.set_carrier1_frequency,
			minimum=-500000,
			maximum=500000,
			num_steps=100,
			style=wx.SL_HORIZONTAL,
			cast=float,
			proportion=1,
		)
		self.Add(_carrier1_frequency_sizer)
		_FM_frequency_sizer = wx.BoxSizer(wx.VERTICAL)
		self._FM_frequency_text_box = forms.text_box(
			parent=self.GetWin(),
			sizer=_FM_frequency_sizer,
			value=self.FM_frequency,
			callback=self.set_FM_frequency,
			label="Central FM frequency",
			converter=forms.float_converter(),
			proportion=0,
		)
		self._FM_frequency_slider = forms.slider(
			parent=self.GetWin(),
			sizer=_FM_frequency_sizer,
			value=self.FM_frequency,
			callback=self.set_FM_frequency,
			minimum=87500000,
			maximum=108000000,
			num_steps=205,
			style=wx.SL_HORIZONTAL,
			cast=float,
			proportion=1,
		)
		self.Add(_FM_frequency_sizer)

		##################################################
		# Blocks
		##################################################
		self.blks2_rational_resampler_xxx_0 = blks2.rational_resampler_ccc(
			interpolation=4,
			decimation=1,
			taps=None,
			fractional_bw=None,
		)
		self.blks2_wfm_tx_0 = blks2.wfm_tx(
			audio_rate=samp_rate,
			quad_rate=320000,
			tau=50e-6,
			max_dev=75e3,
		)
		self.gr_add_xx_0 = gr.add_vcc(1)
		self.gr_multiply_const_vxx_0 = gr.multiply_const_vcc((5000, ))
		self.gr_multiply_xx_0 = gr.multiply_vcc(1)
		self.gr_multiply_xx_1 = gr.multiply_vcc(1)
		self.gr_sig_source_x_0 = gr.sig_source_c(quad_rate, gr.GR_COS_WAVE, carrier1_frequency, 1, 0)
		self.gr_sig_source_x_1 = gr.sig_source_c(quad_rate, gr.GR_COS_WAVE, carrier2_frequency, 1, 0)
		self.gr_wavfile_source_0 = gr.wavfile_source("/home/mc/FM_demo/test_32k_mono.wav", True)
		self.usrp_simple_sink_x_0 = grc_usrp.simple_sink_c(which=0, side="B")
		self.usrp_simple_sink_x_0.set_interp_rate(100)
		self.usrp_simple_sink_x_0.set_frequency(-FM_frequency, verbose=True)
		self.usrp_simple_sink_x_0.set_gain(0)
		self.wxgui_fftsink2_0 = fftsink2.fft_sink_c(
			self.GetWin(),
			baseband_freq=0,
			y_per_div=10,
			y_divs=10,
			ref_level=50,
			sample_rate=quad_rate,
			fft_size=1024,
			fft_rate=30,
			average=False,
			avg_alpha=None,
			title="FFT Plot",
			peak_hold=False,
		)
		self.Add(self.wxgui_fftsink2_0.win)

		##################################################
		# Connections
		##################################################
		self.connect((self.gr_wavfile_source_0, 0), (self.blks2_wfm_tx_0, 0))
		self.connect((self.gr_multiply_const_vxx_0, 0), (self.usrp_simple_sink_x_0, 0))
		self.connect((self.gr_multiply_xx_0, 0), (self.gr_add_xx_0, 0))
		self.connect((self.gr_add_xx_0, 0), (self.gr_multiply_const_vxx_0, 0))
		self.connect((self.gr_add_xx_0, 0), (self.wxgui_fftsink2_0, 0))
		self.connect((self.blks2_wfm_tx_0, 0), (self.blks2_rational_resampler_xxx_0, 0))
		self.connect((self.blks2_rational_resampler_xxx_0, 0), (self.gr_add_xx_0, 1))
		self.connect((self.gr_multiply_xx_1, 0), (self.gr_add_xx_0, 2))
		self.connect((self.gr_sig_source_x_1, 0), (self.gr_multiply_xx_1, 1))
		self.connect((self.blks2_rational_resampler_xxx_0, 0), (self.gr_multiply_xx_1, 0))
		self.connect((self.blks2_rational_resampler_xxx_0, 0), (self.gr_multiply_xx_0, 1))
		self.connect((self.gr_sig_source_x_0, 0), (self.gr_multiply_xx_0, 0))

	def set_samp_rate(self, samp_rate):
		self.samp_rate = samp_rate

	def set_quad_rate(self, quad_rate):
		self.quad_rate = quad_rate
		self.wxgui_fftsink2_0.set_sample_rate(self.quad_rate)
		self.gr_sig_source_x_1.set_sampling_freq(self.quad_rate)
		self.gr_sig_source_x_0.set_sampling_freq(self.quad_rate)

	def set_carrier2_frequency(self, carrier2_frequency):
		self.carrier2_frequency = carrier2_frequency
		self._carrier2_frequency_slider.set_value(self.carrier2_frequency)
		self._carrier2_frequency_text_box.set_value(self.carrier2_frequency)
		self.gr_sig_source_x_1.set_frequency(self.carrier2_frequency)

	def set_carrier1_frequency(self, carrier1_frequency):
		self.carrier1_frequency = carrier1_frequency
		self._carrier1_frequency_slider.set_value(self.carrier1_frequency)
		self._carrier1_frequency_text_box.set_value(self.carrier1_frequency)
		self.gr_sig_source_x_0.set_frequency(self.carrier1_frequency)

	def set_FM_frequency(self, FM_frequency):
		self.FM_frequency = FM_frequency
		self._FM_frequency_slider.set_value(self.FM_frequency)
		self._FM_frequency_text_box.set_value(self.FM_frequency)
		self.usrp_simple_sink_x_0.set_frequency(-self.FM_frequency)

if __name__ == '__main__':
	parser = OptionParser(option_class=eng_option, usage="%prog: [options]")
	(options, args) = parser.parse_args()
	tb = MF_FM_TX()
	tb.Run(True)