fm_rtl_sdr_recever.py

from typing import List

from rtlsdr import RtlSdr

import argparse

import numpy as np

import pyaudio

import scipy.signal as signal



SampleStream = List[float]

AudioStream = List[int]



stream_buf = bytes()

stream_counter = 0



audio_rate = 48000

audio_output = pyaudio.PyAudio().open(format=pyaudio.paInt16, channels=1, rate=audio_rate, output=True)



def process(samples: SampleStream, sdr: RtlSdr) -> None:

    sample_rate_fm = 240000

    iq_comercial = signal.decimate(samples, int(sdr.get_sample_rate()) // sample_rate_fm)



    angle_comercial = np.unwrap(np.angle(iq_comercial))

    demodulated_comercial = np.diff(angle_comercial)



    audio_signal = signal.decimate(demodulated_comercial, sample_rate_fm // audio_rate, zero_phase=True)

    audio_signal = np.int16(14000 * audio_signal)



    audio_output.write(audio_signal.astype("int16").tobytes())



def read_callback(samples, rtl_sdr_obj):

    process(samples, rtl_sdr_obj)



parser = argparse.ArgumentParser(formatter_class=argparse.ArgumentDefaultsHelpFormatter)

parser.add_argument('--ppm', type=int, default=0,

                    help='ppm error correction')

parser.add_argument('--gain', type=int, default=20,

                    help='RF gain level')

parser.add_argument('--freq', type=int, default=92900000,

                    help='frequency to listen to, in Hertz')

parser.add_argument('--verbose', action='store_true',

                    help='mute audio output')



args = parser.parse_args()



sdr = RtlSdr()

sdr.rs = 1024000

sdr.fc = args.freq

sdr.gain = args.gain

sdr.err_ppm = args.ppm



sdr.read_samples_async(read_callback, int(sdr.get_sample_rate()) // 16)