Fldigi

Fldigi, the Fast Light Digital modem application,^[2] 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.^[3][4]

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, RTTY, Olivia, and CW (morse code). Increasingly the software is also being used 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.^[5][6][7]

Digital Modes Supported

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:

• Microsoft Windows
• macOS
• Linux
• FreeBSD.^[9]

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.

• Open Sound System(OSS)
• Portaudio
• Pulseaudio

Features

• NBEMS: The narrowband emergency messaging system ^[10][11]
• Is the underlying modem for PSKmail ^[12]
• Support for transmitting and receiving in all languages by using UTF-8 character encoding (some modes)
• Rig control
• Connection to external programs via TCP/IP port (7322 and 7342) ^[13]
• DTMF encode / decode
• Soundcard oscillator frequency/skew correction
• Measure soundcard oscillator's skew to atomic clock: WWV or WWVH
• Measure frequency skew to atomic clock: WWV or WWVH
• Transmit a WWV-like time signal as a calibration reference

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.^[14] Currently 7 soundcard-digital-modem programs support this standard.

• PocketDigi
• FDMDV
• DM780
• Multipsk
• FLdigi
• AndFlmsg
• TIVAR

External Programs

Fldigi allows external programs to attach and send / receive data by connecting to port 7322 or 7342. 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:

• Flamp
• Flarq
• Flmsg
• Flwrap
• Flics
• Flnet
• D-Rats
• PSKmail
• jPSKmail
• Bitcoin Armory
• Fldigiattach
• UIChat
• LinkUP

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."^[15]

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.^[16][17][18]

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. ^[19] These tests led to regular weekly digital broadcasts by the broadcasters listed below.

• VOA Radiogram
• DigiDX
• Radio Havana Cuba
• Radio Moscow
• Radio Australia ^[20]
• Radio Miami International
• Italian Broadcasting Corporation ^[21]
• WBCQ (SW) ^[22]
• Mighty KBC ^[23]

The Fldigi suite of programs has become popular within the U.S. Army and U.S Air Force Military Auxiliary Radio System.^[24][25]

The software is also utilized by some organizations for both routine and disaster/emergency relief services.

• W1AW (ARRL) ^[26]
• Amateur Radio Emergency Services (ARES)^[27]
• Radio Amateur Civil Emergency Service (RACES)^[28]
• Civil Air Patrol^[29]
• Skywarn^[30]

Decodeable Broadcasts

The broadcasts listed below are transmitted on a regular schedule and can be decoded using Fldigi.

• SITOR text forecasts and storm warnings
• WEFAX visual weather fax
• SYNOP surface synoptic observations
• NAVTEX warnings, forecasts, and safety information broadcasts
• VOA Radiogram Broadcasts
• W1AW Broadcasts

See also

• Amateur Radio
• Shortwave Radio
• PSK31
• RTTY
• VOA Radiogram
• WACM (AM)
• American Radio Relay League
• Sights and sounds of digital modes

External links

• Linux Fldigi group
• Windows Fldigi group
• NBEMS group
• Fldigi Download Link

References