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Fldigi FAQ

Here you can find answers to some of the most frequently asked questions about Fldigi.

You are invited to edit this page and add FAQs on topics that you are familiar with or have answered yourself. However, please do not add unanswered questions and try to keep the answers brief. Long answers should be in separate pages and linked to below.

General information

What is fldigi?

Fldigi (Fast Light Digital Modem Application) is a program for transmitting and receiving signals via a radio transceiver. It includes support for most digital modes used on the amateur radio bands, as well as many related functions (logging, transceiver control, sound card calibration and frequency analysis).

Is fldigi free software?

Fldigi is Free Software and can be modified and redistributed under the terms of the GNU license.

How do I obtain fldigi?

Fldigi can be found at the main web site.

Installing Fldigi

Set Up

What are the minimum hardware requirements for fldigi?

We recommend at least a 1.2 GHz processor for most digital modes, and at least a 1.6 GHz processor for CPU-intensive modes like DominoEX and Thor. A faster CPU may be needed for multiple PSK decoding.

Fldigi can interface with many transceiver models via Hamlib, RigCAT, or using the peer application flrig.

Which operating systems does fldigi run on?

Fldigi should run on all POSIX/X11 systems (*BSD, Linux, Solaris, etc.). It has also been ported to Mac OS X (10.4 or newer) and Windows (2000 or newer).

I want to run the Linux version of fldigi. Do I need to build it from source?

Fldigi is available as a pre-compiled binary from various Linux distributions. Note that this might not be the most current version. It is highly recommended that Linux users learn to build fldigi and it's peer applications from source.

Where can I find the alpha (test) releases?

Source and binaries for the latest alpha release can be found at Alpha releases may have bugs; we advise you to make a backup copy of your fldigi configuration files. You can also use the fldigi command line parameter –config-dir to specify a directory in which to test a new installation.

Where can I find flmsg custom forms?

Custom forms for flmsg, including Red Cross custom forms can be downloaded from

Installation Issues

See Linux User group configuration for serial ports and remember to logout and login again.

Upgrade Issues

fldigi crashes after upgrading

Seems to be a common complaint - see here.

Using fldigi

How can I toggle transmit and receive without using a macro?

Press Ctrl-T/Ctrl-R or the Pause key inside the transmit text area.

Why does fldigi access the Internet?

Short answer: it doesn't unless you tell it to.

Users of certain “personal firewall” programs for Windows (e.g., Zone Alarm) may see alerts about fldigi's network usage. While fldigi does open several network sockets, they are all bound to the localhost address and therefore only accessible by programs running on the same machine. The sockets are used for:

The latter means that fldigi will generate network traffic on the localhost loopback interface even when no other programs are using fldigi's network servers.

Note that fldigi also has features that involve actual internet access (e.g., the PSK Reporter module), but those are activated by the user.

How can I receive (and decode) SYNOP and SHIP Weather reports ?

SYNOP (Also called FM-12) is a numerical code used for reporting weather observations. These reports, along with FM-13, i.e. SHIP data, are also transmitted are transmitted in RTTY by the Deutscher Wetterdienst (German Meteorological) at regular times.

This is discussed here and more information is available in the Fldigi Manual here: SYNOP reports in Fldigi


Is there any material I can use to present fldigi at my club meeting?

faq/main.txt · Last modified: 2017/07/11 08:08 by m0ift