2.7.6 Digital - Fldigi for Sound Card Modes

1. The Fldigi interface

The Fldigi sound card interface is based on the fldigi code by Dave Freese, W1HKJ.

Fldigi supports a wide variety of digital modes, including not only AFSK RTTY and PSK, but also other less common modes such as MFSK, MT63, Olivia, Throb, etc.

Fldigi is a stand alone application, so you can also use it separately from N1MM Logger. Note that the configurations for Fldigi stand-alone and within the Logger are separate, i.e. changes made to the stand-alone configuration will not be applied to the configuration within the Logger, and vice versa.

Fldigi does not support keying outputs on serial or parallel ports, as used by N1MM Logger for CW and FSK keying. Fldigi can be used from the Logger for AFSK RTTY or for PSK31 or other digital modes, but not for transmitting RTTY using FSK. It can also be used as a CW receive-only decoder, but not for transmitting CW. For transmitting CW, use one of the CW interfacing methods detailed in the "Basic Interfacing - Radio, CW, PTT" chapter. You must not check the Digital check box on a port that will be used for CW keying while the DI window or the CW Reader window is open.

2. Download and Configure Fldigi

2.1. Download Fldigi

  • Download the current release of fldigi from the W1HKJ website at http://www.w1hkj.com/ . You can find a copy of the full installer for the current version of fldigi at that website. This file is a self-extracting executable, similar to the N1MM Logger installer. Download the installer file to a temporary folder and then execute it. It is recommended that you install fldigi in its own program folder and not in the N1MM Logger+ program folder. By default, the installer will install fldigi to C:\Program Files\Fldigi-x.xx.xx\, where x.xx.xx is the fldigi version number. If you are using Windows Vista, 7 or 8, and you want to run fldigi from inside N1MM Logger+, you must use a copy of fldigi.exe that is installed in its own folder outside the Program Files (or Program Files(x86)) folder. You can, for example, create a folder for fldigi inside your N1MM Logger+ user files area and install a copy of fldigi.exe into that folder.

2.2. Fldigi Initial Configuration

After fldigi has been downloaded and installed, open the Configurer and set up the path to fldigi.exe under the Digital Modes tab. After closing the Configurer, choose a contest in N1MM Logger that supports digital modes, select the Logger's Window > Digital Interface menu item, and then in the Digital Interface window, select the Interface > Fldigi menu item.

When you first open the fldigi interface from the Logger, and also any time you install fldigi into a different location, such as separate locations for the two digital interface windows or for the DI window and the CW Reader window, you will be prompted to fill in some configuration information by the fldigi configuration wizard, as follows:

  • Operator information - You do not need to fill in any of this information; N1MM Logger+ handles logging and all related information
  • Audio devices - Under the Devices tab, check the PortAudio box and select the sound card input and output you are using for Capture and Playback. Click Next
  • Transceiver control - Select the XML-RPC tab, check the Use XML-RPC Program box, and click the Initialize button. Do NOT select RigCAT, Hamlib, or MemMap for rig control; none of those will work with N1MM Logger+
  • You can let N1MM Logger handle PTT, in which case you do not need to configure PTT in fldigi. However, if you do not use PTT in other modes and you want to use hardware PTT controlled by the digital interface (e.g. fldigi), you can select the Hardware PTT tab, check the Use separate serial port PTT checkbox, select the appropriate COM port in the Device: window, and check either Use RTS or Use DTR, depending on which one your hardware setup uses. If the label on the Initialize button is red, click on the button. Note that a COM port that is used by fldigi cannot be used simultaneously by the Logger for other purposes. If you are time-sharing a serial port between fldigi in digital modes (not including CW) and the Logger in CW or SSB, check the Digital check box beside the COM port in the Configurer to ensure that the Logger will not try to use this port while the Digital Interface is open
    • If you intend to use fldigi as a receive-only CW decoder, be aware that you cannot use fldigi to transmit CW. Also, you cannot control PTT from fldigi on the same port that N1MM Logger+ uses for CW keying; do not check the Digital check box beside this port, and do not configure it within fldigi as a PTT port
  • Click Finish

The fldigi configuration wizard does not automatically save its settings. After you have exited the configuration wizard and the main fldigi interface window has opened, you must save the configuration settings using the fldigi Configure > Save Config menu item. If you don't do this, then every time you open the fldigi window you will have to go through the configuration wizard steps again. Similarly, any time you make a subsequent change to the fldigi configuration you must explicitly save the new configuration if you want the change to be remembered.

3. The Fldigi Interface Window


  • Menu
    • File
      • Exit - closes the Fldigi window
    • Op Mode
      • CW - This configures Fldigi to decode CW (receive-only)
      • PSK - select BPSK-31 for normal PSK31, BPSK-63 for PSK63, etc.
      • RTTY - select RTTY-45 for normal 45 baud AFSK RTTY
      • Other selections can be used for other modes - see the fldigi help for details
    • Configure
      • Waterfall - under the Display tab, you can select whether to show audio or RF frequencies in the scale at the top of the waterfall, and whether to display transmitted as well as received signals
      • Rig control - XML-RPC should have been selected during the initial configuration. You can use the Hardware PTT tab to change the PTT settings for a separate hardware PTT port
      • Sound card - you can select the sound card to be used by Fldigi under the Devices tab
      • Modems - this is where you make configuration changes that apply to specific modes only (e.g. PSK-specific changes, or RTTY-specific changes)
      • Save Config - use this to save the new configuration any time you make changes
    • View
      • PSK Browser - opens a browser window that can display up to 30 signals within the waterfall simultaneously (PSK only). To configure this browser window, use Fldigi's Configure > Modems > PSK > Viewer configuration window to set the number of channels, the starting (lowest) audio frequency (channel separation is 100 Hz), and various other parameters

Most Fldigi menu items not mentioned above are either not used by N1MM Logger, or perform advanced functions that are not needed for basic operation. See the fldigi help at the W1HKJ web site for more details (there is a link to the Fldigi-Help page from the download page at

Note also that when the Fldigi engine is selected, additional buttons appear in the Logger's Digital Interface window:

  • Align - for retuning the radio so that the desired signal is aligned on a pre-configured frequency
  • Lock - to lock the transmit frequency at the present position in the waterfall while allowing the receive frequency to vary (for operating split)
  • Rev - in sideband-sensitive modes like RTTY, reverses the tones

warningSO2V/SO2R Limitation
There is a basic limitation in the Fldigi engine which can make it harder to use in dual-receiver situations (SO2R and SO2V). Fldigi always receives in mono mode. If you are using a stereo sound card to decode two receivers, with one receiver in the left channel and the other receiver in the right channel, Fldigi will combine the two receivers in its waterfall. It doesn't matter whether Fldigi is the interface engine in DI1 or DI2, it will see the audio from both receivers.

Therefore, if you want to use Fldigi with both receivers in a two-receiver setup, you will need to use two separate sound cards for the two receivers. You will also need to install two copies of Fldigi in two separate program folders in order to allow a different sound card to be configured in each copy.

Last Modification: 13 November 2014 21:08:14 EST by VE3KI.