multimon-ng

multimon-ng

multimon-ng is the successor of multimon. It decodes the following digital transmission modes:

• POCSAG512 POCSAG1200 POCSAG2400
• FLEX FLEX_NEXT
• EAS
• UFSK1200 CLIPFSK FMSFSK AFSK1200 AFSK2400 AFSK2400_2 AFSK2400_3
• HAPN4800
• FSK9600
• DTMF
• ZVEI1 ZVEI2 ZVEI3 DZVEI PZVEI
• EEA EIA CCIR
• MORSE_CW
• DUMPCSV X10 SCOPE SDL_SCOPE
• GSC (Golay Sequential Code)

Building

multimon-ng is built using CMake.

Prerequisites

Required:

• A C compiler (GCC or Clang)
• CMake 3.15 or newer
• make (or another CMake-supported generator)

Optional (auto-detected):

• libpulse-dev — enables PulseAudio live audio input
• libx11-dev — enables the X11 scope display
• SDL3 — enables the SDL3 digital phosphor scope

If none of the audio libraries are found, multimon-ng is built with file/stdin input only (DUMMY_AUDIO). This is fine for processing recorded samples or piped input from tools like rtl_fm.

Example (Debian/Ubuntu):

sudo apt-get install build-essential cmake libpulse-dev libx11-dev

Build

cmake -S . -B build
cmake --build build --parallel 4
sudo cmake --install build

The default install prefix is /usr/local. To install elsewhere (for example, system-wide at /usr or into your user directory), pass CMAKE_INSTALL_PREFIX:

cmake -S . -B build -DCMAKE_INSTALL_PREFIX=/usr

Windows MinGW Builds

On Windows (MSYS2/MinGW)

Install MSYS2, then from the MinGW64 or MinGW32 shell:

cmake -S . -B build
cmake --build build --parallel 4

Cross-compiling from Linux

Install the MinGW cross-compiler, then use the provided toolchain files:

# For 64-bit Windows
cmake -S . -B build-mingw64 -DCMAKE_TOOLCHAIN_FILE=cmake/toolchain-mingw64.cmake
cmake --build build-mingw64 --parallel 4

# For 32-bit Windows
cmake -S . -B build-mingw32 -DCMAKE_TOOLCHAIN_FILE=cmake/toolchain-mingw32.cmake
cmake --build build-mingw32 --parallel 4

Supported Environments

So far multimon-ng has been successfully built on:

• Arch Linux
• Debian
• Gentoo
• Kali Linux
• Ubuntu
• macOS
• Windows (MSYS2/MinGW, Cygwin, and VisualStudio/MSVC)
• FreeBSD

Examples

Wav to raw

Files can be easily converted into multimon-ng's native raw format using sox. e.g:

sox -R -t wav pocsag_short.wav -esigned-integer -b16 -r 22050 -t raw pocsag_short.raw

GNURadio can also generate the format using the file sink in input mode short.

Pipe sox to multimon-ng

You can also "pipe" raw samples into multimon-ng using something like:

sox -R -t wav pocsag_short.wav -esigned-integer -b16 -r 22050 -t raw - | ./multimon-ng -

[!NOTE] Note the trailing dash, means write/read to/from stdin

Pipe rtl_fm to multimon-ng

As a last example, here is how you can use it in combination with RTL-SDR:

rtl_fm -f 403600000 -s 22050 | multimon-ng -t raw -a FMSFSK -a AFSK1200 /dev/stdin

Flac record and parse live data

A more advanced sample that combines rtl_fm, flac, and tee to split the output from rtl_rm into separate streams. One stream to be passed to flac to record the audio and another stream to for example an application that does text parsing of mulimon-ng output

rtl_fm -s 22050 -f 123.456M -g -9.9 | tee >(flac -8 --endian=little --channels=1 --bps=16 --sample-rate=22050 --sign=signed - -o ~/recordings/rtlfm.$EPOCHSECONDS.flac -f) | multimon-ng -v 0 -a FLEX -a FLEX_NEXT -t raw /dev/stdin

1. You can pass -l to rtl_fm for the squelch level, this will cut the noise floor so less data gets encoded by flac and will significantly reduce the file size but could result in loss of signal data. This value must be tuned!
2. Flac uses -8 here, if you run an a resource constraint device you may want to lower this value
3. The Flac -o argument value contains $EPOCHSECONDS to make unique files when this gets restarted

To replay the recorded flac file to multimon-ng (requires sox):

flac -d --stdout ~/recordings/rtlf/rtlfm.1725033204.flac | multimon-ng -r -v 0 -a FLEX_NEXT -t flac -

Packaging

To stage an install into a packaging directory (typical for distribution packaging), use the standard DESTDIR variable:

cmake -S . -B build -DCMAKE_INSTALL_PREFIX=/usr
cmake --build build --parallel 4
DESTDIR=/path/to/pkgroot cmake --install build

DESTDIR is prepended to the install paths, so files land under /path/to/pkgroot/usr/bin/multimon-ng, etc.

Testing

After building, run the test suite:

./test/run_tests.sh

[!NOTE] Testing non-raw sample files (flac, wav) requires SoX to be installed.