rtl_fm - Online in the Cloud

PROGRAM:

NAME

rtl_fm - 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

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