MATLAB SigDigger User manual

User’s Manual
Version 0.3.0
Gonzalo José Carracedo Carballal
June 27, 2022

Contents
1 Introduction 5
About SigDigger ................................. 5
About this manual ................................ 5
About the author ................................. 6
2 Installing SigDigger 7
GNU/Linux .................................... 7
macOS ...................................... 8
Microsoft Windows ............................... 8
Building from sources .............................. 9
Fully-automated build using BLSD (GNU/Linux only) .......... 10
Manual compilation (all systems) .................... 11
3 Basic operation 13
Interface overview ................................ 13
Configuring the signal source .......................... 14
SDR device ................................. 15
File source ................................. 16
Source parameters ............................ 17
Starting a capture ................................ 18
Real-time source tweaks ............................ 22
Adjusting the FFT ................................ 24
Listening to the radio: audio preview ...................... 26
Defining a channel ............................. 26
Minor tweaks ................................ 28
Saving audio ................................ 29
4 Channel inspection 31
Deferred inspection: the time window ..................... 32
Opening the Time window ........................ 33
Display controls .............................. 34
Basic measurements ........................... 36
Measurements over selected data .................... 37
Periodic selection ............................. 38
Saving samples .............................. 39
Carrier recovery .............................. 40
Transforms ................................. 42
3

4CONTENTS
Sampling and decision .......................... 43
Real-time inspection: inspection tabs ..................... 49
DSP chain .................................. 49
Inspection tabs ............................... 52
Using the Generic Channel Inspector tab ................ 52
Spectrum sources ............................. 55
Fine-tuning ................................. 56
Parameter estimation ........................... 57
Demodulator controls ........................... 59
Data forwarding .............................. 62
5 Panoramic spectrum 65
Interface overview ................................ 65
Strategy and partitioning ............................ 66
Saving data .................................... 67

1
Chapter
Introduction
Thank you for choosing SigDigger. The following chapters attempt to cover all the
relevant functions from the perspective of a user with minimal knowledge on digital
signal processing and radio signals. It also includes practical examples for many real-
world applications, including blind demodulation of radio signals and data acquisition
from amateur satellites.
About SigDigger
SigDigger is a free
1
graphical digital signal analyzer. Its main use case is the reverse
engineering of radio signals, in which some (or all) parameters of the signal of interest
are unknown. This is achieved by a set of features that enable interactive measuring
and guessing of the unknown parameters.
SigDigger is compatible with most SDR receivers in the consumer market thanks to
the SoapySDR
2
support library. It also supports record and playback of RF/IF sample
data to and from multiple file formats, including WAV and raw complex float I/Q.
In addition to the reverse engineering-related features, it can be used as a regular
spectrum analyzer with multiple visualization functions. It also support real-time audio
demodulation of FM, AM and SSB signals.
About this manual
This manual intends to be a continuous effort on documenting existing features of
SigDigger as thoroughly as possible. Unfortunately, as I write in English considerably
slower than in C, many of the most interesting features of the software have been left
uncovered (for now). Take this manual as a draft I will be updating from time to time.
The cover picture is a Peter de Jong attractor
3
, generated with Fyre
4
. This particular
1https://www.gnu.org/philosophy/free-sw.html
2https://github.com/pothosware/SoapySDR/wiki
3http://paulbourke.net/fractals/peterdejong/peterdejong.pdf
4https://en.wikipedia.org/wiki/Fyre_(software)
5

6CHAPTER 1. INTRODUCTION
realization of the attractor is a fractal
5
, and depicts (in words of Iban EB3FRN
6
) the
fractal nature of amateur radio as a hobby.
About the author
Gonzalo José Carracedo Carballal
7
(BatchDrake) is a software engineer with a back-
ground in cybersecurity, mathematical engineering and astrophysics. He has been in
love with radio and radioastronomy since he first watched Contact
8
circa 1997. He
likes coding for fun in his spare time and maintains a number of free software projects
in his public GitHub account9.
5https://es.wikipedia.org/wiki/Fractal
6https://www.eb3frn.net/
7https://actinid.org
8https://www.imdb.com/title/tt0118884/
9https://github.com/BatchDrake

2
Chapter
Installing SigDigger
SigDigger is designed to work in most Unix-like operating systems. Nonetheless,
official support with precompiled binaries is only available for x86-64 based modern
GNU/Linux and macOS systems.
Precompiled releases can be downloaded directly from the GitHub page
1
. Usually, two
types of releases are available:
•Development builds, containing the latest features with minimal testing.
• Stable releases, with the latest bug-fixes and ready for inclusion in 3rd-party
repositories.
GNU/Linux
Precompiled binaries in AppImage
2
format exist for x86-64 GNU/Linux systems with
glibc version 2.27 and newer. AppImage files are self-contained executables and
therefore easy to run. Open a terminal, change to the directory in which the AppImage
file was downloaded and give execute permissions to it (this is something that needs
to be done only once):
$ chmod a+x SigDigger-0.3.0-x86_64-full.AppImage
Now you can execute by typing:
$ ./SigDigger-0.3.0-x86_64-full.AppImage
Pro Tip: The AppImage file is a container not only for SigDigger but also for suscli and
RMSViewer
a
. Depending on the file name of the AppImage, one of these tools is exe-
cuted. Some users find it handy to have these tools available from the command line
by creating symbolic links to them in directories of their $PATH variable. Assuming that
/usr/local/bin is in your $PATH and the AppImage file is in $PWD, run:
$ sudo ln -s $PWD/SigDigger-0.3.0-x86_64-full.AppImage
1https://github.com/BatchDrake/SigDigger/releases
2https://appimage.org/
7

8CHAPTER 2. INSTALLING SIGDIGGER
/usr/local/bin/SigDigger
$ sudo ln -s $PWD/SigDigger-0.3.0-x86_64-full.AppImage
/usr/local/bin/RMSViewer
$ sudo ln -s $PWD/SigDigger-0.3.0-x86_64-full.AppImage
/usr/local/bin/suscli
This will let you run SigDigger , suscli and RMSViewer from anywhere in the command
line.
ahttps://batchdrake.github.io/suscli/
macOS
Precompiled bundles are distributed in .dmg image files for x86-64 processors only.
Although there is no official support for M1 processors (yet), x86-64 bundles can still
be executed in newer computers by installing Rosetta3.
Once you have downloaded the .dmg file, opening SigDigger is straight-forward. Just
open the .dmg file and double-click the SigDigger icon to start it.
Note: SigDigger bundles are not currently being signed. You may need to authorize the
execution of SigDigger explicitly by enabling running software from unidentified developers
a
.
ahttps://support.apple.com/guide/mac-help/mh40616/mac
Microsoft Windows
Experimental builds of SigDigger for x64 Microsoft Windows systems exist, in the
form of a redistributable ZIP file containing the main SigDigger executable, along
with all its dependencies. This build was possible thanks to Ángel Fernández
4
, who
managed to port most of the Unix-specific code and linked SigDigger (along with all
its dependencies) against MinGW-w64
5
libraries. Alas, as of March 2022, only local
analyzers are supported (which is what most people normally use), with out-of-the-box
RTLSDR support. Remote analyzers (which allow sharing SDR devices in a network
with reduced bandwidth usage) will not work, partly due to the chaotic nature of
Windows polling mechanisms.
If you happen to be interested in the gory details of this limitation: any sane (and modern)
operating system provides mechanisms for programmers to put their applications to sleep
until certain event of a given set (like activity in a socket or data in a pipe) occurs. In
normal operating systems (like GNU/Linux, macOS or any Unix in general) this mechanism
is provided by a system call named poll() , which enables simultaneous monitoring of
miscellaneous objects like sockets, files, pipes, events, timers and so on. In Windows,
3https://en.wikipedia.org/wiki/Rosetta_(software)
4https://github.com/arf20
5https://www.mingw-w64.org/

BUILDING FROM SOURCES 9
however, there is a myriad of different, mutually incompatible polling mechanisms that do
not work for all types of objects. In particular, the Windows equivalent of poll() (named
WaitForMultipleObjects ) will not work with Winsock sockets, which has its own polling
function (named WSAPoll which, on the other hand, is slow and only works with sockets).
Additionaly, MinGW-w64 has its own poll implementation which has been flawed for years
and whose behavior is not compatible with the one you would expect in Unix. This is
catastrophic for the remote analyzer support, which needs to mix sockets and certain
anonymous pipe to know when to cancel certain blocking operations (like hitting "Stop" in
the middle of a connection).
The solution to this issue is hard. It is hard, because it involves multiple threads using the
corresponding implementation of poll that works for each possible subset of objects. If you
are interested in this subject and want to provide a better solution (or do some progress in
this direction), feel free to contact me at BatchDr[email protected].
Building from sources
SigDigger has been designed to be easily built in Unix-like systems. Nonetheless, the
following dependencies are required:
•A modern C/C++ compiler (GCC or clang)
•Git
•CMake (version 3.5.1 or newer)
•libsndfile
•libfftw3
•volk (version 1.0 or newer)
•SoapySDR (version 0.5 or newer)
•libxml 2.0
•PortAudio 2.0
•Qt 5 (at least 5.15)
•cURL
•ALSA libraries (for GNU/Linux targets only)
Any mainstream GNU/Linux distribution should maintain packages for these depen-
dencies in their public repositories, under one name or another. In the particular case
of Debian-based systems (like Ubuntu), all of these dependencies can be installed
with a single command:

10 CHAPTER 2. INSTALLING SIGDIGGER
$ sudo apt install build-essential cmake qtbase5-dev libsndfile1-dev
libvolk1-dev libcurl4-openssl-dev libfftw3-dev
soapysdr-module-all libsoapysdr-dev libxml2-dev portaudio19-dev
libasound2-dev
In macOS systems with brew , the procedure is a bit more complicated as it involves
installing Qt 5 manually and preparing SoapySDR taps.
The first step is installing –in this order– Xcode (available from Apple’s developer
website6) and Qt 5.15 (tutorial here7).
Once both Xcode and Qt are installed, run the following commands as regular user:
$ brew install libsndfile volk curl fftw
$ brew tap pothosware/homebrew-pothos && brew update
$ brew install pothossoapy
$ rm -f /usr/local/lib/libSoapySDR.0.8.dylib
$ brew install soapyrtlsdr soapyhackrf soapybladerf soapyairspy
soapyairspyhf soapyredpitaya soapyiris limesuite soapyplutosdr
$ brew install libxml2
$ brew install portaudio
Once all dependencies have been satisfied, the user can choose one of the following
ways to compile SigDigger:
Fully-automated build using BLSD (GNU/Linux only)
BLSD (short for Build Latest SigDigger from Develop) is a shell script that builds
SigDigger from development branch and installs it inside a subdirectory of the current
working directory. This is an option for users that do not want to install files in system-
wide locations or have no root access to their system.
The resulting directory (named blsd-dir ) contains a folder named SigDigger that
can be placed anywhere in the system. Inside the SigDigger folder two executable
launcher scripts can be found: SigDigger and suscli . The user may run any of
these directly from the command line.
Running BLSD is straight-forward. You can download the script from here
8
, give
execute permissions to it and run it as regular user:
$ chmod a+x blsd
$ ./blsd
A variety of options can be passed to blsd ’s command line, instructing it to enable / dis-
able support for specific features. In particular, –disable-alsa can be used to disable
ALSA support in Linux targets (which is known to cause sound issues in Raspberry Pi 4).
6https://developer.apple.com/download/
7https://doc.qt.io/qt-5/gettingstarted.html
8http://actinid.org/blsd