SoftFM - Software decoder for FM broadcast radio with RTL-SDR

SoftFM is a software-defined radio receiver for FM broadcast radio. It is written in C++ and uses RTL-SDR to interface with RTL2832-based hardware.

This program is mostly an experiment rather than a useful tool. The purposes of SoftFM are

• experimenting with digital signal processing and software radio;
• investigating the stability of the 19 kHz pilot;
• doing the above while listening to my favorite radio station.

Having said that, SoftFM actually produces pretty good stereo sound when receiving a strong radio station. Weak stations are noisy, but SoftFM gets much better results than rtl_fm (bundled with RTL-SDR) and the few GNURadio-based FM receivers I have seen.

SoftFM provides:

• mono or stereo decoding of FM broadcasting stations
• real-time playback to soundcard or dumping to file
• command-line interface (no GUI, no visualization, nothing fancy)

SoftFM requires:

• Linux
• C++11
• RTL-SDR library (http://sdr.osmocom.org/trac/wiki/rtl-sdr)
• supported DVB-T receiver
• medium-fast computer (SoftFM takes 25% CPU time on my 1.6 GHz Core i3)
• medium-strong FM radio signal

For the latest version, see https://github.com/jorisvr/SoftFM

Installing

The Osmocom RTL-SDR library must be installed before you can build SoftFM. See http://sdr.osmocom.org/trac/wiki/rtl-sdr for more information. SoftFM has been tested successfully with RTL-SDR 0.5.3.

To install SoftFM, download and unpack the source code and go to the top level directory. Then do like this:

$ mkdir build $ cd build $ cmake ..

CMake tries to find librtlsdr. If this fails, you need to specify

the location of the library in one the following ways:

$ cmake .. -DCMAKE_INSTALL_PREFIX=/path/rtlsdr

$ cmake .. -DRTLSDR_INCLUDE_DIR=/path/rtlsdr/include -DRTLSDR_LIBRARY_PATH=/path/rtlsdr/lib/librtlsdr.a

$ PKG_CONFIG_PATH=/path/rtlsdr/lib/pkgconfig cmake ..

$ make

$ ./softfm -f <radio-frequency-in-Hz>

( enjoy music )

License

SoftFM, copyright (C) 2013, Joris van Rantwijk

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.

You should have received a copy of the GNU General Public License along with this program; if not, see http://www.gnu.org/licenses/gpl-2.0.html

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