rtl_fm_logger.py

from subprocess import *
import time
import os
from datetime import datetime
import fcntl
import wave


FREQUENCY = 438025000
BANDWIDTH = 20000
SQUELCH = 100
GAIN = 50
SLEEP_TIME = 1 # seconds before creating a new file

FM_COMMAND = ["rtl_fm","-d","port4","-l",str(SQUELCH),"-g",str(GAIN),"-f",str(FREQUENCY),"-M","fm","-s",str(BANDWIDTH),"-E", "deemp", "-"]
SOX_COMMAND = ["sox", "-r", str(BANDWIDTH), "-t", "raw", "-e", "s" ,"-b", "16", "-c", "1", "-V1", "-", 
                "-t", "raw", "-e", "s", "-b", "16", "-c", "1", "-",  "sinc","-n","2048","300-6000", "gain", "6"]

def non_block_read(output):
    fd = output.fileno()
    fl = fcntl.fcntl(fd, fcntl.F_GETFL)
    fcntl.fcntl(fd, fcntl.F_SETFL, fl | os.O_NONBLOCK)
    try:
        return output.read()
    except:
        return ""

file_object = None
with Popen(FM_COMMAND, shell=False, stdout=PIPE, bufsize=0) as rtl_fm:
    with Popen(SOX_COMMAND, shell=False, stdout=PIPE, stdin=rtl_fm.stdout, bufsize=0) as sox:
        while 1:
            buffer = non_block_read(sox.stdout)
            if not file_object and buffer:
                print("openning new log")
                file_object = wave.open(f"rtl-fm-monitor-{datetime.now().isoformat().replace(':','')}.wav", "wb")
                file_object.setnchannels(1)
                file_object.setsampwidth(2)
                file_object.setframerate(BANDWIDTH)
            if file_object and not buffer:
                print("stopped")
                file_object.close()
                file_object = None
            if buffer:
                print("logging")
                file_object.writeframesraw(buffer)
            time.sleep(SLEEP_TIME)