FLdigi (FLdigi Development Team / David A. Freese, W1HKJ)

FLdigi (Fast, Light Digital Modem Application) is an open-source digital modem program primarily used in the amateur (ham) radio community. It was developed and is maintained by David A. Freese (callsign W1HKJ) and contributors collectively known as the FLdigi Development Team. FLdigi provides a graphical interface and a wide range of implemented digital modes (PSK, MFSK, RTTY, Olivia, Hellschreiber, and many others), making it a versatile tool for keyboard-to-keyboard contacts, automated message passing, contesting, and experimenters working with digital signal processing on shortwave and VHF/UHF bands.

The project is cross-platform (Windows, macOS, Linux) and historically has been hosted and distributed via SourceForge, with a longstanding user community and integrations with related tools in the FL suite (for example flrig for rig control, flamp/flmsg for file/message handling). FLdigi is distributed under an open-source license and is widely used in emergency communications, conte...