Fldigi

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.

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 the Narrowband Emergency Messaging System (NBEMS) software and inexpensive radio hardware.