Initial release 2007 | Written in Fltk (GUI), C, C++ | |
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Developer(s) Dave Freese (W1HKJ) Stelios Bounanos (M0GLD), RemI Chateauneu (F4ECW), John Douyere (VK2ETA), Stefan Fendt (DL1SMF), Leigh Klotz (WA5ZNU), John Phelps (KL4YFD),Andrej Lajovic (S57LN) Stable release 3.23.21 / 28 January 2017; 41 days ago (2017-01-28) Operating system | ||
Fldigi, the Fast Light Digital modem application, is a free and open-source program which allows an ordinary computer's sound card to be used as a simple two-way data modem. The software is mostly used by amateur radio operators who connect the microphone and headphone connections of an amateur radio SSB transceiver or an FM two way radio to the computer's headphone and microphone connections, respectively.
Contents
- Portability
- Sound Systems
- Features
- The Fldigi Suite
- RSID
- Community Extension Programs
- Awards and Recognitions
- In The News
- Notable users
- Decodeable Broadcasts
- References
This interconnection creates a "soundcard defined radio" whose available bandwidth is limited by the soundcard's samplerate and the external radio's bandwidth.
Such communications are normally done on the shortwave amateur radio bands in modes such as PSK31, MFSK, RTTY, Olivia, and CW (morse code). Increasingly the software is also being used for data on VHF and UHF frequencies.
Using this software, it is possible for amateur radio operators to communicate worldwide while using only a few watts of RF power.
Fldigi software is also used for amateur radio emergency communications when other communication systems fail due to natural disaster or power outage. Transfer of small files, emails, and ICS forms are possible using inexpensive radio hardware.
Portability
Fldigi is based on the lightweight portable graphics library FLTK and the C/C++ language. Because of this, the software can be compiled to run on many different operating systems such as:
Additionally, Fldigi is designed to compile and run on any POSIX compliant operating system that uses an X11 compatible window system / graphical user interface.
The software is also written to be highly portable and can be used on many CPU architectures.
Sound Systems
Multiple sound systems are supported by Fldigi, allowing the program to abstract the soundcard hardware across differing hardware and operating systems.
Features
The Fldigi Suite
The "Fldigi Suite" consists of the Fldigi modem and all extension programs released by the same development group. These extensions add more capabilities to Fldigi such as verified file transfer and message passing. Interconnecion between these programs and the Fldigi modem is made over TCP/IP port 7322.
RSID
To identify the mode being transmitted a signal called an RSID, or Reed-Solomon Identifier, can be transmitted before the data. Using this identifier the receiving software can automatically switch to the proper mode for decoding. The assigning of these identifiers to new modes is coordinated to ensure inter-operation between programs. Currently 7 soundcard-digital-modem programs support this standard.
RSID operates by sending a short burst of a specific modulation before the data signal, which can be used to automatically identify over 272 digital modes. This burst consists of a 10.766 baud 16-tone MFSK modulation where 15 tones/symbols are sent. The burst occupies 172Hz of bandwidth and lasts for 1.4 seconds.
Community Extension Programs
Fldigi allows external programs to attach and send / receive data by connecting to port 7322/ARQ or 7342/KISS. When used this way, Fldigi and the computer's soundcard are acting as a "softmodem" allowing text or data sent on one computer to be transferred using the wireless radio link in-between. The following programs have a history of use with Fldigi as the underlying modem:
Awards and Recognitions
At the 2014 Dayton Hamvention the project lead, Dave Freese (W1HKJ), was recognized with the Technical Excellence Award "for his development and distribution of the Fast Light Digital Modem Application (fldigi) family of programs for use in amateur and emergency communications."
In The News
In 2014 the group Anonymous released a communications tool named AirChat, which used Fldigi as the underlying modem. This provided a low speed yet reliable data connection using only moderate radio hardware. The AirChat software allows for anonymous transmissions of both encrypted and unencrypted messages over unencrypted channels.
Notable users
Following the successful tests by the Voice of America's VOA Radiogram program, international and government shortwave broadcasters began testing and experimenting with digital data over shortwave broadcast channels using the Fldigi software. These tests led to regular weekly digital broadcasts by the broadcasters listed below.
The Fldigi suite of programs has become popular within the U.S. Army and U.S Air Force Military Auxiliary Radio System.
The software is also utilized by some organizations for both routine and disaster/emergency relief services.
Decodeable Broadcasts
The broadcasts listed below are transmitted on a regular schedule and can be decoded using Fldigi.