NGSoftFM

NGSoftFM is a command line software decoder for FM broadcast radio with stereo support

Introduction

NGSoftFM is a software-defined radio receiver for FM broadcast radio. Stereo decoding is supported. It is written in C++. It is a derivative work of SoftFM (https://github.com/jorisvr/SoftFM) with a new application design and new features. It also corrects wrong de-emphasis scheme for stereo signals.

Hardware supported:

• RTL-SDR based (RTL2832-based) hardware is suppoeted and uses the librtlsdr library to interface with the RTL-SDR hardware.
• HackRF One and variants are supported with libhackrf library.
• Airspy is supported with libairspy library.
• BladeRF is supported with libbladerf library.

The purposes of NGSoftFM 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.

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

NGSoftFM 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)

NGSoftFM requires:

• Linux
• C++11
• RTL-SDR library (http://sdr.osmocom.org/trac/wiki/rtl-sdr)
• HackRF library (https://github.com/mossmann/hackrf/tree/master/host/libhackrf)
• Airspy library (https://github.com/airspy/host/tree/master/libairspy)
• supported RTL-SDR DVB-T receiver or HackRF Rx/Tx
• medium-fast computer (NGSoftFM takes 25% CPU time on a 1.6 GHz Core i3, ~12% of one core of a Core i7 5700HQ @ 2.7 GHz)
• medium-strong FM radio signal. However the R820T2 based dongles give better results than the former R820T based dongles. HackRF, Airspy or BladeRF are usually even better but you have to spend the buck for the bang.

For the latest version, see https://github.com/f4exb/ngsoftfm

Branches:

• master is the "production" branch with the most stable release
• dev is the development branch that contains current developments that will be eventually released in the master branch

Prerequisites

Base requirements

• sudo apt-get install cmake pkg-config libusb-1.0-0-dev libasound2-dev libboost-all-dev

RTL-SDR support

The Osmocom RTL-SDR library must be installed before you can build NGSoftFM. See http://sdr.osmocom.org/trac/wiki/rtl-sdr for more information. NGSoftFM has been tested successfully with RTL-SDR 0.5.3. Normally your distribution should provide the appropriate librtlsdr package. If you go with your own installation of librtlsdr you have to specify the include path and library path. For example if you installed it in /opt/install/librtlsdr you have to add -DRTLSDR_INCLUDE_DIR=/opt/install/librtlsdr/include -DRTLSDR_LIBRARY=/opt/install/librtlsdr/lib/librtlsdr.a to the cmake options

To install the library from a Debian/Ubuntu installation just do:

• sudo apt-get install librtlsdr-dev

HackRF support

For now HackRF support must be installed even if no HackRF device is connected.

If you install from source (https://github.com/mossmann/hackrf/tree/master/host/libhackrf) in your own installation path you have to specify the include path and library path. For example if you installed it in /opt/install/libhackrf you have to add -DHACKRF_INCLUDE_DIR=/opt/install/libhackrf/include -DHACKRF_LIBRARY=/opt/install/libhackrf/lib/libhackrf.a to the cmake options.

To install the library from a Debian/Ubuntu installation just do:

• sudo apt-get install libhackrf-dev

Airspy support

For now Airspy support must be installed even if no Airspy device is connected.

If you install from source (https://github.com/airspy/host/tree/master/libairspy) in your own installation path you have to specify the include path and library path. For example if you installed it in /opt/install/libairspy you have to add -DAIRSPY_INCLUDE_DIR=/opt/install/libairspy/include -DHACKRF_LIBRARY=/opt/install/libairspy/lib/libairspy.a to the cmake options.

To install the library from a Debian/Ubuntu installation just do:

• sudo apt-get install libairspy-dev

BladeRF support

For now BladeRF support must be installed even if no Airspy device is connected.

If you install from source (https://github.com/Nuand/bladeRF) in your own installation path you have to specify the include path and library path. For example if you installed it in /opt/install/libbladerf you have to add -DBLADERF_INCLUDE_DIR=/opt/install/libbladerf/include -DBLADERF_LIBRARY=/opt/install/libbladerf/lib/libbladeRF.so to the cmake options.

To install the library from a Debian/Ubuntu installation just do:

• sudo apt-get install libbladerf-dev

Note: for the BladeRF to work effectively on FM broadcast frequencies you have to fit it with the XB200 extension board.

Installing

To install NGSoftFM, 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 .. -DRTLSDR_INCLUDE_DIR=/path/rtlsdr/include -DRTLSDR_LIBRARY_PATH=/path/rtlsdr/lib/librtlsdr.a
• PKG_CONFIG_PATH=/path/to/rtlsdr/lib/pkgconfig cmake ..

Compile and install

• make -j8 (for machines with 8 CPUs)
• make install

Running

Examples

Basic usage:

• ./softfm -t rtlsdr -c freq=94600000 Tunes to 94.6 MHz

Specify gain:

• ./softfm -t rtlsdr -c freq=94600000,gain=22.9 Tunes to 94.6 MHz and sets gain to 22.9 dB

All options

• -t devtype is mandatory and must be rtlsdr for RTL-SDR devices or hackrf for HackRF.
• -c config Comma separated list of configuration options as key=value pairs or just key for switches. Depends on device type (see next paragraph).
• -d devidx Device index, 'list' to show device list (default 0)
• -r pcmrate Audio sample rate in Hz (default 48000 Hz)
• -M Disable stereo decoding
• -R filename Write audio data as raw S16_LE samples. Uuse filename - to write to stdout
• -W filename Write audio data to .WAV file
• -P [device] Play audio via ALSA device (default default). Use aplay -L to get the list of devices for your system
• -T filename Write pulse-per-second timestamps. Use filename '-' to write to stdout
• -b seconds Set audio buffer size in seconds

Device type specific configuration options

RTL-SDR

• freq=<int> Desired tune frequency in Hz. Accepted range from 10M to 2.2G. (default 100M: 100000000)
• gain=<x> (default auto)
  • auto Selects gain automatically
  • list Lists available gains and exit
  • <float> gain in dB. Possible gains in dB are: 0.0, 0.9, 1.4, 2.7, 3.7, 7.7, 8.7, 12.5, 14.4, 15.7, 16.6, 19.7, 20.7, 22.9, 25.4, 28.0, 29.7, 32.8, 33.8, 36.4, 37.2, 38.6, 40.2, 42.1, 43.4, 43.9, 44.5, 48.0, 49.6
• srate=<int> Device sample rate. valid values in the [225001, 300000], [900001, 3200000] ranges. (default 1000000)
• blklen=<int> Device block length in bytes (default RTL-SDR default i.e. 64k)
• agc Activates device AGC (default off)

HackRF

• freq=<int> Desired tune frequency in Hz. Valid range from 1M to 6G. (default 100M: 100000000)
• srate=<int> Device sample rate (default 5000000). Valid values from 1M to 20M. In fact rates lower than 10M are not specified in the datasheets of the ADC chip however a rate of 1000000 (1M) still works well with NGSoftFM.
• lgain=<x> LNA gain in dB. Valid values are: 0, 8, 16, 24, 32, 40, list. list lists valid values and exits. (default 16)
• vgain=<x> VGA gain in dB. Valid values are: 0, 2, 4, 6, 8, 10, 12, 14, 16, 18, 20, 22, 24, 26, 28, 30, 32, 34, 36, 38, 40, 42, 44, 46, 48, 50, 52, 54, 56, 58, 60, 62, list. list lists valid values and exits. (default 22)
• bwfilter=<x> RF (IF) filter bandwith in MHz. Actual value is taken as the closest to the following values: 1.75, 2.5, 3.5, 5, 5.5, 6, 7, 8, 9, 10, 12, 14, 15, 20, 24, 28, list. list lists valid values and exits. (default 2.5)
• extamp Turn on the extra amplifier (default off)
• antbias Turn on the antenna bias for remote LNA (default off)

Airspy

• freq=<int> Desired tune frequency in Hz. Valid range from 1M to 1.8G. (default 100M: 100000000)
• srate=<int> Device sample rate. list lists valid values and exits. (default 10000000). Valid values depend on the Airspy firmware. Airspy firmware and library must support dynamic sample rate query.
• lgain=<x> LNA gain in dB. Valid values are: 0, 1, 2, 3, 4, 5, 6, 7, 8 ,9 ,10, 11 12, 13, 14, list. list lists valid values and exits. (default 8)
• mgain=<x> Mixer gain in dB. Valid values are: 0, 1, 2, 3, 4, 5, 6, 7, 8 ,9 ,10, 11 12, 13, 14, 15, list. list lists valid values and exits. (default 8)
• vgain=<x> VGA gain in dB. Valid values are: 0, 1, 2, 3, 4, 5, 6, 7, 8 ,9 ,10, 11 12, 13, 14, 15, list. list lists valid values and exits. (default 0)
• antbias Turn on the antenna bias for remote LNA (default off)
• lagc Turn on the LNA AGC (default off)
• magc Turn on the mixer AGC (default off)

BladeRF

• freq=<int> Desired tune frequency in Hz. Valid range low boundary depends whether the XB200 extension board is fitted (default 300000000).
  • XB200 fitted: 100kHz to 3,8 GHz
  • XB200 not fitted: 300 MHZ to 3.8 GHz.
• srate=<int> Device sample rate in Hz. Valid range is 48kHZ to 40MHz. (default 1000000).
• bw=<int> IF filter bandwidth in Hz. list lists valid values and exits. (default 1500000).
• lgain=<x> LNA gain in dB. Valid values are: 0, 3, 6, list. list lists valid values and exits. (default 3)
• v1gain=<x> VGA1 gain in dB. Valid values are: 5, 6, 7, 8 ,9 ,10, 11 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, list. list lists valid values and exits. (default 20)
• v2gain=<x> VGA2 gain in dB. Valid values are: 0, 3, 6, 9, 12, 15, 18, 21, 24, 27, 30, list. list lists valid values and exits. (default 9)

License

NGSoftFM, copyright (C) 2015, Edouard Griffiths, F4EXB

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