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qt-dab is a software dab decoder for use with sdrplay, dabstick, airspy, limeSDR or hackrf for RPI and PC
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Qt-DAB-3.x Build Status

Qt-DAB-3.x is software for Windows, Linux and Raspberry Pi for listening to terrestrial Digital Audio Broadcasting (DAB and DAB+). It is the successor of both DAB-rpi and sdr-j-DAB, two former programs by the same author.

Table of Contents

Qt-DAB with sdrplay input


  • DAB (mp2) and DAB+ (HE-AAC v1, HE-AAC v2 and LC-AAC) decoding
  • MOT SlideShow (SLS)
  • Dynamic Label (DLS)
  • Both DAB bands supported:
    • VHF Band III
    • L-Band (only used in Czech Republic and Vatican) (see "obsolete properties")
  • Spectrum view (incl. constellation diagram, impulse response, TII spectrum)
  • Scanning function (scan the subsequent channels in the selected band until a channel is encountered where a DAB signal is detected)
  • Detailed information for selected service (SNR, bitrate, frequency, ensemble name, ensemble ID, subchannel ID, used CUs, protection level, CPU usage, program type, language, 4 quality bars)
  • Detailed information for other services by right-clicking on their name (bitrate, subchannel ID, used CU's protection level, program type)
  • Automatic display of TII (Transmitter Identification Information) data when transmitted
  • Presets for easy switching of programs in different ensembles (see Presets)
  • Dumping of the complete DAB channel (Warning: produces large raw files!) into * sdr files and playing them again later
  • Saving audio as uncompressed wave files
  • Saving aac frames from DAB+ services for processing by e.g. VLC
  • Saving the ensemble content (description of audio and data streams, including almost all technical data) into a text file readable by e.g LibreOfficeCalc
  • Supports inputs from
    • SDRplay (both RSP I and RSP II),
    • Airspy, including Airspy mini,
    • SDR DAB sticks (RTL2838U or similar),
    • HACKRF One,
    • limeSDR,
    • Soapy (experimental, Linux only), and
    • prerecorded dump (*.raw, *.iq and *.sdr)
    • rtl_tcp servers
  • Clean interface to add other devices, see below.

Not (Not yet or partly) implemented:

  • DMB (Audio and Video)
  • TPEG: when configured, TPEG messages are being sent to a TCP port; sources for a simple client are part of the source distribution.
  • EPG: when configured, the EPG decoding will generate so called EHB files.
  • Journaline (an untested Journaline implementation is part of the sources).
  • ip output: when configured the ip data - if selected - is sent to a specificied ip address (default:
  • Other bands than used for terrestrial broadcasting in Europe (like DAB over cable)


Qt-DAB-3.x is an implementation of a DAB decoder for use on Linux and Windows based PC's, including some ARM based boards, such as the Raspberry PI, both 2 and 3.

Some other programs are derived from the sources of Qt-DAB, a "light" version dabradio, an SDRPlay-specific version sdrplayDab, a command-line based version and a stand-alone server version dab-server. The versions with a GUI are implemented in C++, using the Qt framework for the implementation of the GUI. The command-line version dab-cmdline and the dab-server are implemented using C++, and do not depend on Qt.

The dab-server can be installed to run as a "service" on an RPI, with control - over a bluetooth connection - from an "app" on an Android tablet.

Furthermore, for DX purposes, a dab-scanner is implemented that allows for a continuous scanning of selected channels in a given band. Results are written in a txt file, formatted for use with LibreOffice Calc and comparable programs.

dabradio, sdrplayDab, the Qt-free version dab-cmdline, the dab-server and the dab-scanner have their own repository on Github.

Qt-DAB-3.x also supports input from an rtl-tcp server (see osmocom software) and from pre-recorded files (*.sdr, *.iq and *.raw). Obviously there is a provision for dumping the input into an (*.sdr)-file.

Note that if the rtl_tcp server is used as input device, the connection needs to support the inputrate, i.e. 2,048,000 I/Q samples (i.e. 2 * 2,048,000 bytes/second).

Since the Qt-DAB program has to run on a headless RPI 2/3 using the home WiFi, the resulting PCM output can be sent - if so configured - to a TCP port (Sources for a small client are part of the source distribution).

For further information please visit

Widgets and scopes

The picture below shows Qt-DAB's main window and the other 5 optional widgets

  • a widget with controls for the attached device,
  • a widget showing the technical information of the selected service as well as some information on the quality of the decoding,
  • a widget showing the spectrum of the received radio signal and the constellation of the decoded signal,
  • a widget showing the spectrum of the NULL period between successive DAB frames,
  • and a widget showing the response(s) from different transmitters in the SFN.

While the main window is always shown, the others are only shown when pushing a button on the main window (touching the button again will cause the widget to disappear from the screen).

Qt-DAB with SDRplay input

The buttons and other controls on the main widget are equipped with tool tips briefly explaining the (in most cases obvious) function of the element.

The elements in the left part of the widget are concerned with selecting a channel and a service.

To ease operation the channel selector is augmented with a "-" and a "+" button for selecting the previous resp. next channel.

To ease selection of a service, a second pair of "-" and "+" buttons is available, now for selecting the previous resp. the next service on the list.


A preset selector is available to store and retrieve "favorit" services, note that the services are encoded as "channel:serviceName" pair, it sometimes happens that a service appears in more than one ensemble (see as example the "Omroep West" service, appearing in channels 5B and 8A.

Different from previous versions is that now some information, previously shown on the "technical data" widger is now shown on the main widget.

Qt-DAB with sdrplay input

Some data on the selected service - if any - is to be found on a separate widget. This widget will show where the data for the service is to be found in the DAB frames, and how it is encoded.

Furthermore, if the service is accompanied by a logo, that logo will be shown here.

The further selectors are concentrated on the bottom part of the right side of the widget. Buttons to make scopes visible, to store input and or output into a file, to select input device and the audio and to scan and store a description of the ensemble are in that section.


Qt-DAB-3.x saves data on all services found. Pairs Channel:serviceName will be made (in)visible when touching the appropriate button.

The data in stored in a file in xml format.

Comment on some settings

Some settings are preserved between program invocations, they are stored in a file .qt-dab.ini, to be found in the home directory. Settings maintained between program invocations are typically the name of the device used, the channel that was used, the name of the service last used etc.

The presets are stored in an xml file, `.qt-dab-presets.xml'.

Some settings are not influenced by buttons or sliders of the GUI, they will only change by editing the .ini file.

Two settings have an impact on the speed and accuracy of the synchronization,

threshold_1=x' threshold_2=x'

Detecting whether a channel might contain a DAB signal is essentially by looking at the amplitude of the signal and by correlating the signal with the signal as it should be. Of course detecting the existence of a signal is important, however, a speedy detection that no signal is available is also important, especially when stepping though the channels.

The threshold_x=y' setting is a value used in determining whether or not the correlation is sufficiently strong to assume the existence of DAB data in the channel. 'threshold_1=x" is used on start up of the channel, threshold_2=x' is used when running. To avoid false positives, threshold_2' ususally holds a higher value. Default values are 3 and 5. diff_length=x'

Once the existence of DAB data is established, an attempt is made to estimate the frequency offset of the incoming signal. Again, this is done by correlating a fragment of the (processed) incoming signal with a predefined signal. The length of the segment (length interms of samples) used is defined by the settings for `diff_length'. If no value is given, the default value of 40 is used

saveSlides=1 when set to 0 the slides that are attached to audio programs will not be saved. If set to 1 the slides will be saved in a directory /tmp/qt-pictures (Linux) or in %tmp%\qt-pictures (Windows).

picturesPath defines the directory where the slides (MOT slideshow) should be stored. Default is the home directory.

showSlides=1 when set to 0 the slides will not be shown.

has-presetName=1 when set the name of the selected service - that is selected when closing down the program - is kept and at the next invocation of the program, an attempt is made to start that particular service. The name of the service is kept as presetname=xxxx

The background colors of the spectrum can be changed by setting


If one uses the rtl_tcp handler, the default value for the "port" is 1234, a port can de set in the "ini" file by setting


Obsolete properties

The recent DAB standard eliminated the support for Modes other than Mode 1 and Bands other than VHF Band III. The Qt-DAB implementation still supports these features, however, since they are obsolete, there are no controls on the GUI anymore (the control for the Mode was already removed from earlier versions).

Explicitly setting the Mode and/or the Band is possible by including some command lines in the ".qt-dab.ini" file.

For the Mode, one will add/set a line

dabMode=Mode x, where x is either 1, 2 or 4

For the Band, one will add/set a line

dabBand=band, where band is either VHF Band III or L_Band

Since the control for the dab band is now removed from the GUI, this GUI could be made slightly smaller.


For windows an installer is to be found in the releases section, The installer will install the executable as well as required libraries. The installer will also call the official installer for the dll implementing the api for getting access to the SDRplay devices.

Ubuntu Linux

If you are not familar with compiling then please continue reading by jumping to chapter appImage which is much easier for Linux beginners.

Ubuntu 16.04 (and on) have good support for Qt5 and qwt (compiled for Qt5). For generating an executable under Ubuntu (16.04 or newer), you can put the following commands into a script. (For Ubuntu 14.04 look into the package manager for Qt4 packages)

  1. Fetch the required components

    sudo apt-get update
    sudo apt-get install qt5-qmake build-essential g++
    sudo apt-get install libsndfile1-dev qt5-default libfftw3-dev portaudio19-dev 
    sudo apt-get install libfaad-dev zlib1g-dev rtl-sdr libusb-1.0-0-dev mesa-common-dev
    sudo apt-get install libgl1-mesa-dev libqt5opengl5-dev libsamplerate0-dev libqwt-qt5-dev
    sudo apt-get install qtbase5-dev
  2. Fetch the required libraries

a) Assuming you want to use a dabstick (also known as rtlsdr) as device, fetch a version of the library for the dabstick

 git clone git://
 cd rtl-sdr/
 mkdir build
 cd build
 sudo make install
 sudo ldconfig
 cd ..
 rm -rf build
 cd ..

b) Assuming you want to use an Airspy as device, fetch a version of the library for the Airspy

sudo apt-get install build-essential cmake libusb-1.0-0-dev pkg-config
cd airspyone_host-master
mkdir build
cd build
sudo make install
sudo ldconfig

Clean CMake temporary files/dirs:

cd host-master/build
rm -rf *

Note that in order for the libraries to be effective, ensure that

a) the path /usr/local/lib is in the load library paths (i.e. it is named in one of the .conf files in the etc/ directory

b) a file exists in the /etc/udev/rules.d directory describing the device, allowing "ordinary" users to access the device.

  1. Get a copy of the Qt-DAB sources
git clone
cd qt-dab
  1. Edit the file for configuring the supported devices and other options. Comment the respective lines for devices that you do not have or do not want to support out.

4.a. Check the installation path to qwt. If you were downloading it from please mention the correct path in file (for other installation change it accordingly):

INCLUDEPATH += /usr/local/include  /usr/local/qwt-6.1.3

4.b. If you are compiling on/for an RPI2/3 device, you might want to uncomment the line DEFINE+=__THREADED_BACKEND. This will cause a better load balance on the cores of the processor.

  1. Build and make

You could also use QtCreator, load the file and build the executable.

Remark: The executable file can be found in the sub-directory linux-bin. A make install command is not implemented.

Configuring using the file

Options in the configuration are:

a) select or unselect devices

b) select the output: soundcard or TCP connection

c) select defines related to performance

Adding or removing from the configuration is in all cases by commenting or uncommenting a line in the configuration file.

Comment the lines out by prefixing the line with a # in the file (section "unix") for the device(s) you want to exclude in the configuration. In the example below, rtl_tcp (i.e. the connection to the rtlsdr server) won't be used.

CONFIG          += dabstick
CONFIG          += sdrplay
CONFIG          += lime
CONFIG          += rtl_tcp
CONFIG          += airspy
CONFIG          += hackrf
#CONFIG         += soapy

In the Windows configuration one may also choose, however soapy is not supported.

CONFIG		+= extio

for use with (appropriate) extio handlers

Remark: Input from pre-recorded files (8 bit unsigned *.raw and *.iq as well as 16-bit wav *.sdr files) is configured by default.

Audio samples are - by default - sent to an audio device using the portaudio library. Two alternatives are available:

For selecting the output to be sent to a TCP port, uncomment

#CONFIG         += tcp-streamer         # use for remote listening

Note that on default audio output is handled by the portaudio library. Other options are using Qt audio or audio through an TCP port.

The source tree contains a directory sound-client, that contains sources to generate a simple "listener" for remote listening.

For selecting the output to be handled by the Qt system (default device only) uncomment

#CONFIG		+= qt-audio

The CPU load of running the Qt-DAB program can be divided over more CPU cores by uncommenting


This causes the backend to run in a separate thread.

For choosing between single and double precision floats one can comment out or uncomment the line


Note that with HIGH_PRECISION defined, the load on an RPI3 will rise to app 60 %, while with HIGH_PRECISION not defined, the load will remain app 42 %.

Configuring using CMake

The CMakeLists.txt file has all devices and the spectrum switched off per default. You can select a device (or more devices) without altering the CMakeLists.txt file, but by passing on definitions to the command line.

An example:


will generate a makefile with support for

a) the RTLSDR (dabstick) device,

b) for the remote dabstick (using the rtl_tcp connection) and

Other devices that can be selected (beside dabstick and rtl_tcp) are sdrplay, HackRF and airspy. Use -DHACKRF=ON, -DSDRPLAY=ON, or -DAIRSPY=ON after the cmake command if you want to configure them.

The default location for installation depends on your system, mostly /usr/local/bin or something like that. Set your own location by adding

-DCMAKE_INSTALL_PREFIX=your installation prefix

For other options, see the CMakeLists.txt file.

Important: Note that CMakeLists.txt file expects the appropriate Qt version (and - if configured - the qwt library) to be installed.


The current set of sources provides support for both the RSP-I and the RSP-II. Due to an incompatibility between libraries 2.13 and older versions, be certain to have at least 2.13 installed.


The software uses the Qt library and - for the spectrum and the constellation diagram - the qwt library.

The CMakeLists.txt assumes Qt5. If you want to use Qt4, and you want to have the spectrum in the configuration, be aware of the binding of the qwt library (i.e. Qt4 and a qwt that uses Qt5 does not work well).

Raspberry PI

The Qt-DAB software runs pretty well on the author's RPI-2 and 3. The average load on the 4 cores is somewhere between 50 and 60 percent.

One remark: getting "sound" is not always easy. Be certain that you have installed the alsa-utils, and that you are - as non-root user - able to see devices with aplay -L

In arch, it was essential to add the username to the group "audio".

The most recent distributions, Raspbian Stretch and Raspbian Buster supports both Qt5 and a qwt compiled against Qt5.

Since Raspbian Stretch is a Debian derivate, the description for creating a version under Ubuntu applies, a script to download all required packages, compile and build a full executable for qt-dab is part of the source tree.

appImage for x64 Linux systems contains a generated appImage, Qt-DAB-x64.Appimage, which is created on Ubuntu 16.04 (Xenial).

Different from previous versions, this version assumes you have installed the support library for the devices you want to use.

If you want to run with an SDRplay, follow the installation instructions for the library from . All further dependencies are included.

If you want to run an RTLSDR based dabstick, please note that the appImage may complain with some Linux distros with a "" pre-installed that the kernel module has to be blacklisted. Depending on the distribution, blacklisting is in /etc/modprobe.d/local-blaclist

For compiling and installing a support library for an RTLSDR device, follow the instruction on

For compiling and installing a support library for an AIRspy device, find the sources on

The appImage itself is just a self-contained single file which you have to make executable in order to run.

For more information see

Interfacing to another device

There are - obviously - more different devices than supported here. Interfacing another device is not very complicated, it might be done using the "Soapy" interface, or one might write a new interface class.

The device handlers are implemented as a class, derived from the class virtualInput. Only a few functions have to be implemented, to set and get the VFO frequency, to inspect the number of samples available and to get a number of samples, to start and stop operating the device and to report on the number of bits per sample. This last function, is used to scale the various spectrum scopes.

A complete description is given in the file "interfacing.txt", in the sourcetree


Copyright (C)  2013, 2014, 2015, 2016, 2017, 2018, 2019
Jan van Katwijk (
Lazy Chair Computing

The Qt-DAB software is made available under the GPL-2.0.
The SDR-J software, of which the Qt-DAB software is a part, 
is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
GNU General Public License for more details.
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