Fldigi - Kambing UI

Recognitions
This software would not have been possible without the contribution of many programmers who have given their
best to the open source community. The application is built upon the foundation of the Fast Light Tool Kit
(http://www.fltk.org), a wonderfully fast and efficient graphical user interface design library. Many have asked
what the Fast Light means. There are probably as many answers as there are programmers using the toolkit. I
prefer to think of it as lightning fast and light on the code size. Take a look at the size of the executable for fldigi
and then compare it with similar applications. I think you will be surprised by how small it is for what it does.
The current development team consists of:
• Dave Freese - W1HKJ
• Stelios Bounanos - M0GLD
• Leigh Klotz - WA5ZNU
• Stephane Fillod - F8CFE
FldigiContents Recognitions
Several authors have placed their digital modem code and signal processing code in the public domain and their
source was either an inspiration or in some cases formed the backbone of the code used in Fldigi.
• AE4JY - WinPsk - a windows application
• Takuya OOURA - a generic Fast Fourier Transform for real valued data streams -
http://momonga.t.u-tokyo.ac.jp/~ooura/fft.html
• Tomi Manninen, OH2BNS - gmfsk - a great digital modem program for Linux
• Hamish Moffatt, VK3SB - dominoEX code originally for gmfsk
• Joe Veldhuis, KD8ATU - Olivia 2 tone and other mods.
• Dr. Steven W. Smith - author of "Digital Signal Processing", who has kindly placed an entire book on
digital signal processing on the internet. (http://www.dspguide.com)
If you make a side-by-side comparison between gmfsk and fldigi source code you will see that they follow the
same general structure. The primary difference is that gmfsk is written in the C language and uses the gnome/gtk
libraries for the user interface. Fldigi is a C++ application that uses the Fast Light Tool Kit (Fltk) gui library. The
design of Fldigi puts emphasis on separating the user interface from the sound card and transceiver input/output
operations. Nearly all modern digital modem programs use a programming paradigm called "threads." Threads
are light weight processes that share the same memory space, but each has its own stack. The use of threads
makes the program look and feel responsive to the user while a lot of code is being executed in the background.
Many of the modem source code files are C to C++ rewrites from the gmfsk application. They say that copying is
the best form of flattery and gmfsk simply had the best explanations and the easiest source code to read and
understand. The author had also spent several months creating improvements and fixing bugs in the original
gmfsk application. That exercise was the impetus to create Fldigi. Gmfsk was becoming too difficult to modify
without great effort. I also wanted to learn more about coding with threads ... fools rush in.
The Fast Fourier Transform used by Fldigi is a rewrite of Takuya Ooura's C code. The rewrite is in C++ but you
will see the strong resemblence to Takuya's original if you study both. Takuya's FFT code was also used in the
Winpsk program. Some of the signal processing algorithms used in Fldigi are from Dr. Smith's book. His on-line
publication is sufficient to allow you to become fluent in fft analysis and the creation of digital filters. I printed
the relevant pdf files and then purchased the hard bound copy. Improvements to the original gmfsk signal
processing algorithms can all be attributed to this excellent source.
Recognitions 3