Setting Up MMTTY FSK: A Beginner’s Guide to RTTY Transmission
Radioteletype (RTTY) is one of the oldest and most reliable digital modes in amateur radio. While you can operate RTTY using Audio Frequency Shift Keying (AFSK), true Frequency Shift Keying (FSK) is the gold standard. FSK produces a cleaner signal, prevents accidental over-modulation, and utilizes your transceiver’s dedicated internal filters.
The undisputed champion for decoding and transmitting this mode is MMTTY, a free software program developed by Mako Mori (JE3HHT). This step-by-step guide will walk you through setting up MMTTY for true FSK transmission. Prerequisites: What You Need
Before diving into the software configuration, ensure you have the necessary hardware and driver components ready:
An FSK-Capable Transceiver: Most modern HF radios have a dedicated “RTTY” or “FSK” mode. A Hardware Interface: Devices like a Tigertronics SignaLink (with FSK module), a West Mountain Radio RIGblaster
, or a microHAM interface. Many modern radios with built-in USB ports can also handle FSK directly via a virtual COM port.
EXTFSK Plugin: Windows cannot natively handle the precise timing required for FSK via standard virtual serial ports. You will need the EXTFSK.dll or EXTFSK64.dll plugin file to bridge MMTTY to your serial port. Step 1: Install MMTTY and EXTFSK
Download the latest version of the software from the official MMTTY Help Page.
Run the installer and choose your installation directory (e.g., C:\MMTTY). Download the EXTFSK zip file from the same page.
Extract EXTFSK.dll (or the 64-bit version depending on your OS) and drop it directly into your main MMTTY installation folder. Step 2: Configure MMTTY TX Settings Open MMTTY. In the top menu, click Option and select Setup MMTTY. Click on the TX tab.
In the PTT Port dropdown menu, do not select a standard COM port. Instead, scroll down and select EXTFSK.
Look at the Radio command section on the same tab. Ensure your specific radio control (CAT) port is mapped correctly if you want MMTTY to control your radio’s PTT via CAT, though EXTFSK will handle the keying. Step 3: Configure the EXTFSK Extension
Once you select EXTFSK and hit close (or apply), a separate small window titled EXTFSK will pop up on your screen. This window tells MMTTY exactly where to send the FSK data.
Port: Select the actual COM Port number associated with your interface’s FSK/UART driver.
FSK Output: Set this to TXD or DTR depending on your hardware interface requirements (check your interface manual; TXD is standard for many virtual ports).
PTT Output: Set this to RTS or DTR to handle the push-to-talk switching.
Minimize this window. Do not close it, or FSK transmission will fail. Step 4: Configure the Misc Tab Go back to the Setup MMTTY window. Click on the Misc tab.
In the Tx Port section in the top right, select the radio button for COM-TxD(FSK). This tells the software to output a true on/off digital FSK stream rather than an audio signal. Click OK to save all settings and exit the setup menu. Step 5: Adjusting Your Transceiver
Your software is now ready, but your radio needs to be configured to look for the FSK signal:
Change your transceiver’s mode to RTTY or RTTY-R (Reverse), not USB or LSB.
Set your RF power to a safe continuous-duty level. RTTY is a 100% duty-cycle mode. If you have a 100W radio, turn it down to 50W or less to protect your finals.
Turn off your speech processor and your microphone gain; true FSK bypasses the mic circuit entirely, so you do not need to worry about audio overdrive. Step 6: Testing the Transmission Find a clear frequency on the air.
Click the TX button in the lower-right corner of the MMTTY main screen (or press your designated transmit hotkey). Your radio should immediately click into transmit mode.
Type a few characters in the transmit window. You should hear your radio emit the classic, rhythmic two-tone warble of RTTY. Click RX to return to receive mode.
Congratulations! You are now configured for flawless, razor-sharp FSK RTTY transmission.
To tailor these instructions more specifically to your setup, please share: What model of transceiver are you using?
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