fldigi(1) digital modem program for hamradio operators


fldigi [OPTIONS]


Fldigi is a cross-platform multi-modem program for most of the digital modes used by radio amateurs today: CW, PSK, MFSK, MT-63, RTTY, Hellschreiber, DominoEX, Olivia, THOR and Throb are all supported. It can also help calibrate a sound card to a time signal and do on-air frequency measurement tests. Fldigi features basic rig control, logging, and contest operation, "panoramic" PSK decoding, a PSK Reporter client, and remote control via XML-RPC.


Long options begin with two hyphens and are handled by fldigi. The option names may be abbreviated to any unambiguous substring, and the option argument may be separated from the name by a space or equals sign, as per getopt(3).

Short options begin with a single hyphen and are passed directly to FLTK. They may be abbreviated only as indicated.

--config-dir DIRECTORY

Look for and store configuration files in directory DIRECTORY, which is created if it does not exist. Defaults to "$HOME/.fldigi".

--rx-ipc-key KEY

Set the receive message queue key. May be given in hex if prefixed with "0x". Defaults to "9876" or "0x2694".

--tx-ipc-key KEY

Set the transmit message queue key. May be given in hex if prefixed with "0x". Defaults to "6789" or "0x1a85".

--arq-server-address HOSTNAME

Set the ARQ TCP server address. Defaults to "". HOSTNAME may be any node name string accepted by getaddrinfo(3).

--arq-server-port PORT

Set the ARQ TCP server port. Defaults to "7322". PORT may be any service name string accepted by getaddrinfo(3).


The --xmlrpc-* options are only available if fldigi was built with XML-RPC support.

--xmlrpc-server-address HOSTNAME

Set the XML-RPC server address. Defaults to "".

--xmlrpc-server-port PORT

Set the XML-RPC server port. Defaults to "7362".

--xmlrpc-allow REGEX

Allow only the methods whose names match REGEX. REGEX is a POSIX extended regular expression.

--xmlrpc-deny REGEX

Allow only the methods whose names do not match REGEX.


List all available XML-RPC methods and exit. May be preceded by the --xmlrpc-allow or --xmlrpc-deny options to verify their effect.


Perform the CPU speed test that is normally done when fldigi is run without an existing configuration directory. Results are shown in the event log and options may be changed to the recommended values for the measured CPU speed.


Unhide controls for adding noise to the transmitted signal.


Hide all main window widgets except the menu bar and waterfall (with its associated controls). Meant to be used with external programs that control fldigi with XML-RPC.

--debug-level LEVEL

Set the event log verbosity. LEVEL is clamped to the range [0,5]; for Quiet, Error, Warning, Info, Verbose and Debug. Defaults to "3" (Info).


Print version information and exit.


Print build information and exit.


Print options summary and exit.

Standard FLTK options

-bg, -background COLOUR

Set the background colour.

-bg2, -background2 COLOUR

Set the secondary (text) background colour.

-di, -display DISPLAY

Specifies the X server to connect to; see X(7).

-dn, -dnd or -nodn, -nodnd

Enable or disable drag and drop copy and paste in text fields.

-fg, -foreground COLOUR

Set the foreground colour.

-g, -geometry GEOMETRY

Set the initial window size and position. Fldigi may not honour this option.

-i, -iconic

Start fldigi in iconified state. Fldigi may not honour this option.

-k, -kbd or -nok, -nokbd

Enable or disable visible keyboard focus in non-text widgets.

-na, -name CLASSNAME

Set the window class. Defaults to "Fldigi".

-ti, -title WINDOWTITLE

Set the window title. Defaults to "fldigi - <callsign>".

Additional UI options

--font FONT[:SIZE]

Set the widget font and (optionally) size. Defaults to "sans:12".

Options useful to developers


The --benchmark-* options are only enabled if fldigi was built (exclusively) for benchmarking and batch decoding.

--benchmark-modem ID

Specify the modem. Defaults to "25" ("BPSK31").

--benchmark-frequency FREQ

Set the modem frequency in Hz. Defaults to "1000".

--benchmark-afc BOOLEAN

Enable or disable modem AFC. Defaults to "false".

--benchmark-squelch BOOLEAN

Enable or disable modem squelch. Defaults to "false".

--benchmark-squelch-level LEVEL

Set the modem squelch level (1---100%). Defaults to "0.0".

--benchmark-input INPUT

Specify the input. Must be a positive integer indicating the number of samples of silence to generate as the input, or, if fldigi was linked with libsndfile, the name of the input audio file. The filename must contain non-digit characters.

--benchmark-output FILE

Specify the output data file. Non-textual output (i.e. Hellschreiber or MFSK images) cannot be saved. Default: decoder output is discarded.

--benchmark-src-ratio RATIO

Specify the sample rate conversion ratio. Defaults to "1.0" (input is not resampled).

--benchmark-src-type TYPE

Set the sample rate conversion type. TYPE is an integer in the range [0,4]. Defaults to "2" ("Fastest SINC Interpolator").


The following options should not be relied upon. They are listed here only for the sake of completeness, and may be replaced by GUI settings or removed altogether in a future version.

--wfall-width WIDTH

Set the waterfall width.

--wfall-height HEIGHT

Set the waterfall height.

--window-width WIDTH

Set the minimum window width.

--window-height HEIGHT

Set the minimum window height.

--exit-after SECONDS

Run for approximately SECONDS seconds.

--frames-per-buffer FRAMES

Set frames per buffer option to FRAMES when creating PortAudio streams. Defaults to "0" (let PortAudio choose).


Fldigi uses several environment variables, mainly set for child processes created by the <EXEC> macro and the notifier.

General variables


The web browser to use for http and file URIs. Overrides $BROWSER and xdg-open(1).

Macro variables

The following variables are created in the environment of the child process that is forked by the <EXEC> macro. They are empty if values are not available.


The receive message queue key.


The transmit message queue key.


The XML-RPC server address string.


The XML-RPC server port string.


The ARQ server address string.


The ARQ server port string.


The version string.


The process ID of the parent fldigi process.


The configuration directory.


The operator's callsign.


The operator's name.


The operator's IARU (Maidenhead) locator.


The short modem name.


The long modem name.


The rig (radio) frequency.


The modem (audio) centre frequency.


The actual receive/transmit frequency, i.e. the sum of rig and modem frequencies taking into account the rig sideband.


The text (frequency in MHz) contained in the QSO Freq log field.


The text (QSO start time) contained in the (time) On log field.


The text (QSO end time) contained in the (time) Off log field.


The text (other station's callsign) contained in the Call log field.


The text (other station's name) contained in the Name log field.


The text (received RST) contained in the (RST) In log field.


The text (sent RST) contained in the (RST) Out log field.


The text (other station's QTH) contained in the QTH log field.


The text (other station's Maidenhead locator) contained in the Loc log field.


The text (free-form notes) contained in the Notes log field.


The text (azimuth in degrees to other station) contained in the Az log field.

Notifier variables

The following variables are created in the environment of child processes created by the notifier.


These variables (i in [0,9]) contain substrings matched by capturing groups in the event's regular expression. 0 contains the whole matched text.


The number of substrings available.


Builtin event types that match callsigns will place the callsign in this variable.


The complete string that matched the event's regular expression.


The modem frequency.


The event type.


The station's country name (for events of type "station heard twice").

Debugging variables

The following variables are only used if fldigi was built with debugging support (--enable-debug), or they are only useful when debugging specific modules.


If set, this variable disables glibc's malloc debugging, which fldigi enables by default when built for debugging.


Traces Fl::lock() calls.


Initialises hamlib in debug mode.


Fldigi is licensed under the GNU GPL, which grants you the right to run the program for any purpose (freedom 0). However, permission to use it for the transmission of radio signals can only be obtained from the communications authority of your country. When given, this permission almost always comes in the form of an amateur radio license.

If you do not have an amateur radio license you can still have fun using fldigi as a shortwave listener. One way to do so is by using the builtin PSK Reporter client to submit realtime spots of transmitting stations; see RESOURCES below. All you need is a computer, homebrew SDR receiver, and simple wire antenna!


Various files and subdirectories are created in $HOME/.fldigi. Some of the most interesting ones are listed below.


The main settings file.


The "status" file. Stores window geometries, button states, current modem, current audio frequency, squelch level, and so on.


The event log.


The default macro file.


This directory contains waterfall palettes.


This directory is added to the PATH environment variable of the child process that runs <EXEC> macros.


This directory contains logged received and sent text (when such logging is enabled), including the default logbook database, logbook.adif.


Received MFSK images are automatically saved in this directory.


This file is written by the frequency analysis modem. The fields are dial frequency, audio frequency, and offset. See documentation for details.


The following files are used if present. They must be downloaded and copied to ~/.fldigi/ by the user.


List of DXCC entities and callsign prefixes; used to display tooltips in the received text buffer, and also to auto-fill the Country, Locator and Azimuth log fields. Available at http://www.country-files.com/cty/.


List of known LOTW users (one callsign per line); used for the received text tooltips. Available at http://www.hb9bza.net/lotw/.

AGMemberList.txt or eqsl.txt

List of "Authenticity Guaranteed" eQSL users (one callsign per line); used for the received text tooltips. Available at http://www.eqsl.cc/QSLcard/Programming.cfm.


fldigi --wfall-height 144 --font sans:11 -fg "#c0c0c0" -bg "#5f5f63" -bg2 "#19213b"

This is how the author of this document invokes fldigi.

fldigi --xmlrpc-deny "main.(tx|tune|run_macro)"

Unregister XML-RPC methods that may transmit.

ssh -L 7362:localhost:7362 remote-host xvfb-run fldigi -display :99

Start fldigi on remote-host under a "fake" X server. (The xvfb-run(1) utility is available on Debian systems). The remote "headless" fldigi is then controlled via XML-RPC on port 7362, i.e from flrig, flamp etc.

fldigi --benchmark-input 480000 --benchmark-modem 1

Benchmark the DominoEX-4 modem with 480K audio samples.

fldigi --benchmark-input audio.wav --benchmark-modem 25 --benchmark-frequency 1500 --benchmark-afc 1 --benchmark-squelch 1 --benchmark-squelch-level 5.0 --benchmark-output out.txt

Read audio.wav (whose sample rate must be 8000Hz in this case) and decode BPSK-31 signals at 1500Hz. AFC is enabled and the squelch is set to 5%. Decoded text is saved to out.txt.




Main web site: http://www.w1hkj.com/Fldigi.html

Sourceforge project page: http://sourceforge.net/projects/fldigi/

Wiki and bug tracker: https://fedorahosted.org/fldigi/

More information on MFSK16, DominoEX and other digital modes can be found at http://www.qsl.net/zl1bpu/ and http://www.w1hkj.com/FldigiHelp/Modes/index.htm

The PSK Automatic Propagation Reporter site can be found at http://www.pskreporter.info/


Fldigi was written by

• David Freese, W1HKJ.

• Stelios Bounanos, M0GLD.

• Leigh L. Klotz, Jr., WA5ZNU.

Fldigi also includes code written by others. Among them are

• Tomi Manninen, OH2BNS.

• Pawel Jalocha, SP9VRC.

• Hamish Moffatt, VK3SB.

This manual page was written by Stelios Bounanos <sb[at]enotty(dot)net>.


License GPLv3+: GNU GPL version 3 or later.