Yaesu FT-991A and MMTTY how-to

Condensing the material available on the web.   This is the least “intrusive” set of edits to your FT-991A settings to work RTTY, using the 991A’s USB connectivity.   We assume that you are familiar with the operation of the rig and any software on the PC/laptop.   We believe the instructions here will do no harm but we are not responsible for any damage that may arise from following these steps!


  • Install the Yaesu factory recommended USB driver onto your (Windows) PC/laptop.   Make a note of the COM port number that Windows has assigned to the Standard and to the Enhanced ports.   Typically the Enhanced port will be one lower than the COM port number for the Standard port.
  • Connect an appropriate antenna or dummy load to the rig.   This will prevent accidental damage in case the PC/laptop connection, or MTTY or any other conflicting software keys up the rig’s transmitter during setup.
  • Connect the rig and PC/laptop, power up the PC/laptop and then the rig.  The power-up order should not matter but doing it this way gives Windows a chance to get the USB driver ready.
  • Install MMTTY onto your PC/laptop.

FT-991A menu settings

Menu xxx set to yyy


MMTTY options setup (connect to PC/laptop part of setup)

  • Open MMTTY’s Options, Setup screen.
    • Demodulator tab – leave all settings at default
    • AFC/ATC/PLL tab – leave all settings at default
    • DECODE tab – leave all settings at default
    • TX tab – several things to do here:
      • Put your call sign in the Macro window
      • PTT&FSK section, Port should be EXTFSK64, click on Radio Command
        • Frequency offset zero
        • DTR/RTS – tick the PTT  box
        • Group (of rigs) – select Yaesu FT9000, 2000, 991,… from the drop-down menu that should fill in the RX, TX strings
        • Click OK
    • Font/Window tab – leave all settings at default
    • Misc tab – in the Tx port section, select Sound+COM-TxD(FSK)
    • SoundCard tab – select the USB audio connections for Mic and Speaker.  (These will only appear if the rig is connected and powered on.)
  • Finally, there should have appeared a small window EXTFSK 2.0e
    • In here select the COM port corresponding to the Enhanced driver port.   The status indicator should show ON.   If it is red and shows NG then the port is incorrect or the rig is not connected.   Fix it before the next step is possible.
    • FSK Output should be set to DTR
    • PTT Output should be set to RTS
  • Back in the main Setup window click OK to go to the MMTTY screen.

MMTTY operational setup (get ready to go on air)

  • Make sure that a suitable antenna or dummy load is attached to the rig.   Set lowest power level just in case.
  • Click the TX button.   The rig’s Tx LED should come on.   Click the Tx OFF button and the rig’s Rx LED should come back on.
  • If this does not happen re-check the above setup for both the rig menu and for the MMTTY setup.
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