gnuradio-fm-radio-receiver/fm_radio.py

#!/usr/bin/env python3
#
# SPDX-License-Identifier: GPL-3.0
#
# GNU Radio Python Flow Graph
# Title: FM Radio Receiver

import gnuradio.analog
import gnuradio.audio
import gnuradio.filter
import gnuradio.gr
import osmosdr


class fm_radio(gnuradio.gr.top_block):
    def __init__(self):
        gnuradio.gr.top_block.__init__(self, "FM Radio Receiver", catch_exceptions=True)

        audio_sample_rate_hertz = 48000
        channel_width_hertz = (
            250000 // audio_sample_rate_hertz
        ) * audio_sample_rate_hertz

        rtlsdr_source = osmosdr.source()
        # `rtlsdr_source.get_sample_rates().values()`:
        # > TypeError: Unregistered type : std::vector<double, std::allocator<double> >
        # minimum for raspberry pi 1B:
        rtlsdr_source.set_sample_rate(rtlsdr_source.get_sample_rates().start())
        print(f"RTL-SDR sampling rate: {rtlsdr_source.get_sample_rate():.0f} Hz")
        rtlsdr_source.set_center_freq((98.3 * 1e6), 0)

        resampler = gnuradio.filter.rational_resampler_ccf(
            interpolation=channel_width_hertz,
            decimation=int(rtlsdr_source.get_sample_rate()),
        )
        self.connect((rtlsdr_source, 0), (resampler, 0))

        assert channel_width_hertz % audio_sample_rate_hertz == 0
        wbfm_demodulator = gnuradio.analog.wfm_rcv(
            quad_rate=channel_width_hertz,
            audio_decimation=channel_width_hertz // audio_sample_rate_hertz,
        )
        self.connect((resampler, 0), (wbfm_demodulator, 0))

        audio_sink = gnuradio.audio.sink(audio_sample_rate_hertz, "", False)
        self.connect((wbfm_demodulator, 0), (audio_sink, 0))
        # for raspberry pi 1B:
        # > RuntimeError: check topology failed on audio_alsa_sink(11) using ninputs=1, noutputs=0
        self.connect((wbfm_demodulator, 0), (audio_sink, 1))


def _main():
    top_block = fm_radio()
    top_block.start()
    input("Press Enter to quit: ")
    top_block.stop()
    top_block.wait()


if __name__ == "__main__":
    _main()