man rtl_fm (1): a simple FM demodulator for RTL2832 based DVB-T receivers

DESCRIPTION

Uses a re-purposed DVB-T receiver as a software defined radio to receive narrow band FM signals and demodulate to audio. Written for and incorporated in the osmocom rtl-sdr project.

Narrowband FM is commonly used by public service agencies and commercial dispatch operations in the VHF and UHF bands. Also can demodulate Wideband FM, as found in the 88-108 MHz FM broadcast band. Experimental options include AM, LSB, USB and DSB demodulation.

Much software is available for the RTL2832. Most of the user-level packages rely on the librtlsdr library which comes as part of the rtl-sdr codebase. This codebase contains both the library itself and also a number of command line tools such as rtl_test, rtl_sdr, rtl_tcp, and rtl_fm. These command line tools use the library to test for the existence of RTL2832 devices and to perform basic data transfer functions to and from the device.

Because most of the RTL2832 devices are connected using USB, the librtlsdr library depends on the libusb library to communicate with the device.

USAGE

With a suitable antenna for receiving the signal attached to the rtl-sdr supported device, this program will output the digital audio data decoded from that signal. The data can be listened to by piping to Sox or aplay applications to play the stream on the computer sound card.

SYNOPSIS

rtl_fm [-f freq] [-options] [filename]

OPTIONS

-f frequency_to_tune_to [Hz]: use multiple -f for scanning, (requires squelch)
ranges supported, -f 118M:137M:25k
[-M modulation (default: fm)]: fm, wbfm, raw, am, usb, lsb
wbfm == -M fm -s 170k -o 4 -A fast -r 32k -l 0 -E deemp
raw mode outputs 2x16 bit IQ pairs
-s sample_rate (default: 24k)
-d device_index (default: 0)
-g tuner_gain (default: automatic)
-l squelch_level (default: 0/off)
-o oversampling (default: 1, 4 recommended): for fm squelch is inverted
[-o oversampling (default: 1, 4 recommended)]
-p ppm_error (default: 0)
[-E enable_option (default: none)]: use multiple -E to enable multiple options
    edge:   enable lower edge tuning
    dc:     enable dc blocking filter
    deemp:  enable de-emphasis filter
    direct: enable direct sampling
    offset: enable offset tuning
filename ('-' means stdout): omitting the filename also uses stdout

Experimental options

[-r resample_rate (default: none / same as -s)]
[-t squelch_delay (default: 10)]: +values will mute/scan, -values will exit
[-F fir_size (default: off)]: enables low-leakage downsample filter
size can be 0 or 9. 0 has bad roll off
-A std/fast/lut choose atan math (default: std)
filename: (a '-' dumps samples to stdout)
(omitting the filename also uses stdout)

EXAMPLES

Produces signed 16 bit ints, use Sox or aplay to hear them.

rtl_fm ... - | play -t raw -r 24k -es -b 16 -c 1 -V1 -: | aplay -r 24k -f S16_LE -t raw -c 1
-M wbfm | play -r 32k ...
rtl_fm ... -s 22050 - | multimon -t raw /dev/stdin

AUTHOR

This manual page was written by Maitland Bottoms for the Debian project (but may be used by others).

COPYRIGHT

This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 2 of the License, or (at your option) any later version.

This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details.