fldigi is designed to help amateur HAM radio operators quickly calibrate sound cards to a specific time signal as well as perform frequency measurement tests and more.

It allows an ordinary computer's sound card to be used as a simple two-way data modem. It is mostly used by amateur radio operators that need to 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.

Using fldigi will be possible for amateur radio operators to communicate worldwide with limited power consumption. It can also be used as a stand-in for radio emergency communications when other communication systems fail due to a natural disaster or power outage.

During setup, you have the option to include flarq (same author), an ARQ specification, K9PS to transfer emails, text files, images, and binary files over the radio. This protocol is unicast and connection-based and seamlessly integrates with existing email clients such as Microsoft Outlook, Mozilla Thunderbird, and Sylpheed. It is not needed to run fldigi, which is why we included the Ad-Supported notice.

Fldigi supports CW, PSK, MFSK, RTTY, Hell, DominoEX, Olivia, and Throb.