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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

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).

fldigi crashes after upgrading on Windows

Seems to be a common complaint and usually caused by trying to upgrade and skip several version changes. fldigi maintains it's configuration (long term settings) and status (state on last execution) files in it's own files folder.

Operating System folder / directory
XP C:\Documents and Settings\<login_name>\fldigi.files\
W2K C:\Documents and Settings\<login_name>\fldigi.files\
Vista/Win7/Win8/Win10 C:\User\<login_name>\fldigi.files\
OS X /home/<login_name>/.fldigi
Linux /home/<login_name>/.fldigi

On Linux and OS X you can can create a link to the hidden “.fldigi” folders:

$ cd
$ ln -s fldigi.files .fldigi

Delete these two files located in the files folder: fldigi_def.xml and fldigi.prefs

It is not necessary to delete any other files or folders. If you do then you will probably lose your macro and logbook files.

Start the new fldigi and you will be presented with the start-up wizard.

You should disable all Windows power saving features, including

* USB devices * Disk drives * Serial devices * Keyboard / Mouse i/o

All versions of Windows will disable idle devices (or devices the OS thinks are idle) from XP on, but Windows 7, Windows 8 and Windows 10 are notorious for this dis-service. You should recheck these device settings whenever the OS is updated. Someone in Redmond should be neutered.

Where can I find flmsg custom forms?

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

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.

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 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.

It is necessary to click on the fldigi Rv (Reverse) button on the bottom menu bar, lower right corner of the Fldigi screen. That is, the signal must be inverted and the mark and space put at the right place.

The ( mode and frequencies ) in F1B are, in LSB with 50 Bauds:

147,300 kHz+/- 42,5 HertzDDH 47
4583,000 kHz+/- 225 Hertz DDK 2
7646,000 kHz+/- 225 Hertz DDH 7
10100,800 kHz+/- 225 Hertz DDK 9
11039,000 kHz+/- 225 Hertz DDH 9
14467,300 kHz+/- 225 Hertz DDH 8

SYNOP reports look like sequence of words, mostly group of five numbers, such as:

SMPO60 LPMG 241200 CCA
AAXX 24121
08522 32570 49902 10250 20176 30131 40199 52002 82200 222// 00240
 314// 40301 333 82820 83099 555 50004 60005=

Because RTTY code represent letters and numbers with shift code, it might happen that a transmission error unexpectedly shifts numbers to letters. It is possible to turn this behaviour off in the RTTY configuration by turning off the “Unshift on Space”, these spaces being the ones between group of words. That way, it keeps the numbers displayed in all circumstances.

How do I decode SYNOP weather reports ?

Fldigi contains a SYNOP decoder, software which translates these cryptic codes into clear weather reports. When these reports can be associated to a longitude/latitude pair, the report is written in a KML file which can be displayed in Google Earth.

During installation of fldigi, you were prompted to download a couple of data files: There are necessary for decoding many reports.

Much more information available here: SYNOP reports in Fldigi


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

faq.txt · Last modified: 2017/03/13 13:39 by admin