FM Radio

FM Reception Decoding

For the FM reception decoding part, the following GRC design is used:

Module parameters:

• Soapy HackRF: Center Freq=100e6
• Range f=96e6~104e6
• Signal Source: Freq=100e6-f
• Low Pass Filter: Decimation=20, Cutoff Freq=80e3, Transition_width=20e3
• WBFM Receive: Quadrature Rate=500e3, Audio Decimation=10
• Rational Resampler: Decimation=25, Interpolation=24
• Range gain=0~3
• Audio Sink: 48e3

Set the ID as fm_recv, and set the saved file as fm_recv.py.

FM Control Panel

We slightly modified the Panel panel from the previous page as follows:

import sys
from PyQt5 import Qt

class Station(Qt.QWidget):

    stations = {
        "ICRT(100.7)": 100.7,
        "Wind City Radio(98.7)": 98.7,
        "International Broadcasting Station(101.1)": 101.1,
    }

    def __init__(self, grc):
        super().__init__() # parent initialization
        self.setWindowTitle("Radio Station") # set title
        self.grc = grc # save the grc instance

        vlayout = Qt.QVBoxLayout(self) # create a vertical layout
        self.setLayout(vlayout) # set the layout
        
        for name, freq in self.stations.items(): # loop items
            btn = Qt.QRadioButton(name) # add a button
            btn.toggled.connect(self.changeFreq) # connect click event
            vlayout.addWidget(btn) # put into the vlayout

    def changeFreq(self):   # event handler
        btn = self.sender() # get sender button
        freq = float(self.stations[btn.text()])
        self.grc.set_f(freq*1e6) # set frequency

The modifications made here include:

1. Changing the radio channel list, which is reset based on the current situation.
2. In the __init__ function, we pass the object generated by GNU Radio and set it as the self.grc attribute.
3. In the changeFreq function, we pass the obtained frequency back to the setting function of self.grc.

Main Program

Write a main program main.py to combine the above two program modules together:

import sys
from PyQt5 import Qt
from fm_recv import fm_recv
from station import Station

qapp = Qt.QApplication(sys.argv)

grc = fm_recv()
grc.start()
grc.show()

fmStation = Station(grc)
fmStation.show()

qapp.exec_()

Execution result:

Exercise 4

1. Execute the above code to ensure it works correctly.
2. Add more radio stations or change the layout.