Hi QRZers and FT-991/A owners; I would like to share here a step by step setup guide in order to use the native RTTY encode mode of the 991/A, using RTTY-LSB instead of the Data-LSB. The mode RTTY-LSB works by a serial port pin (or the SHIFT pin on the rear port) 'tickle' the radio so the radio can actually 'modulate' the RTTY signal. For correctness, shift the signal. This is named FSK mode. I choose to use the RTTY native (FSK) mode due mainly to not having to take care of the audio control/loudness feed to keep ALC in reins - this is all taken care by the radio itself. AA5AU gives an great explanation describing AFSK and FSK advantages and pitfalls. An tl;dr by me describing each mode is: AFSK - You feed the audio to your computer, modulated and ready to be transmitted; FSK - You "tickle" the Shift/Serial pin and then the radio will modulate it. Advantages, verbatim: I prefer FSK because it’s straight on/off keying into the FSK input of my radio. I don’t have to worry about the audio level or whether I forgot to turn the speech processor off. I can then use the FSK mode on my radio along with the narrow 250 and 500 hz filters. When I switch from SSB to RTTY, I only have to change the mode on my radio. In the end, the resulting transmitted signal will be (almost) just the same. I went the FSK route to give some use to the Standard COM Port and use the native RTTY-LSB mode - and I do agree with AA5AU's opinions too. So without further ado: 1. First thing, identify what's your Standard COM port (not the Enhanced!!!!!). Open the Windows' Device Manager. In the below example, it is COM5. Write it down. 2. Download and install MMTTY (link) 3. After installing, open MMTTY. Go to menu "Option", select "Setup MMTTY" 4. Go to the SoundCard tab. In "Reception", choose the interface that contains "USB Audio CODEC". No need to choose an "Transmission" audio card. Do not click OK yet. 5. Go to the TX tab. In the "PTT & FSK" "Port" clause, scroll all way down to the bottom and select EXTFSK64. Do not click OK yet. 6. Now, move to the "Misc" tab. In "TX Port", select "COM-TxD(FSK)". Now, click OK and you are all set. 7. Now, let's configure the EXTFSK. Click the RTTY icon in the task bar, select the below EXTFSK program. 8. In "Port", select the COM port that you found in Step #1. In FSK Output, select DTR. In PTT Output, select RTS. Click the trace next to the OK status to minimize. 9. Now, to the radio. Go to the Configuration Clause "060 - PC Keying" - Choose RTS 10. Scroll down to the configuration "096 - RTTY SHIFT PORT" - choose DTR 11. Hit the MODE button on the radio, select RTTY-LSB 12. You are all set!! Tune to the proper RTTY frequency in the band, hit the MMTTY's CQ2 button and enjoy!