Part of our Getting On The Air: Modes, Operations, and Making Contacts guide.
If you spend time in digital modes or emergency communications, you will run into a family of programs whose names all start with “fl”: Fldigi, Flrig, Flmsg, and several others. They are all free, they are all developed by the same team (the W1HKJ group), and they are designed to work together. Here is a tour of what each one does.
Fldigi (the flagship)
Fldigi (Fast Light digital) is the centerpiece. It is a multi-mode digital software modem that lets your computer and radio send and receive a huge range of keyboard-to-keyboard digital modes: PSK31, RTTY, Olivia, MFSK, CW, Contestia, Thor, and many more. You type, it transmits; other stations transmit, it decodes and displays the text.
Unlike FT8 (which uses fixed automated exchanges), the modes in Fldigi are conversational, so it is popular for ragchewing, nets, and traffic handling. It is the digital-mode workhorse that the rest of the suite supports.
Flrig (rig control)
Flrig is a rig-control program. It handles CAT control of your radio, meaning it reads and sets your frequency, mode, power, and other settings, and provides transmit keying. It pairs tightly with Fldigi: run them together and Fldigi can control your radio through Flrig, so changing bands or modes on screen actually moves the radio. It also gives you a handy on-screen control panel for your rig. Many people use Flrig as their rig-control layer even alongside other software.
Flmsg (structured messages)
Flmsg handles formatted messages. It is built for emergency communications and traffic handling, where you need to send standardized forms like ICS-213 general messages, radiograms, weather reports, and other official templates. Flmsg lets you fill out these forms and send them over the air through Fldigi, so the message arrives properly formatted on the other end. For served-agency and ARES/RACES work, this is a key tool.
Flamp (file and message broadcasting)
Flamp (Amateur Multicast Protocol) is for sending files and messages to many stations at once. It breaks a file into blocks and transmits it, and receiving stations can collect the blocks (even across multiple transmissions) and fill in any missing pieces. This makes it possible to reliably distribute a document to a group over radio, which is again very useful in emcomm scenarios.
The rest of the family
- Flwrap wraps files with error-checking so you can confirm a file arrived intact.
- Fllog is a simple logging program that other FL apps can share log data with.
- Fllog and the built-in logbook let you keep and share contacts across the suite.
- Flnet is a net-control tool for managing check-ins during on-air nets.
- Flcluster and others round out the ecosystem for more specialized needs.
Why they matter
The strength of the FL suite is that it is free, cross-platform (Windows, macOS, and Linux), and modular. You can run just Fldigi to play with PSK31, or combine Fldigi, Flrig, and Flmsg into a capable emergency communications station that controls your radio and sends official forms. Because the programs are designed to talk to each other, they form a flexible toolkit that scales from casual digital chatting to serious traffic handling.
If you are getting into conversational digital modes or emcomm, downloading Fldigi and Flrig is a great first step, and you can add Flmsg and Flamp as your needs grow.