For anyone struggling with FT-991A CAT control on Windows 11: Just spent two hours troubleshooting why WSJT-X couldn't connect to my rig. For Windows 11 need install USB driver manually - the automatic driver installation doesn't work properly. Download the FT-991/ SCU-17 USB Driver (Virtual COM Port Driver) from Yaesu and follow the directions to install them on your computer. You will end up installing: TWO (2) COM ports. One is an ENHANCED COM port (in my case COM 4) the other is a Standard COM port (in my case COM 5). Use the Enhanced port for CAT control in your logging software.

Thanks for this! I was having the same exact problem with Ham Radio Deluxe. I'm using Ham Radio Deluxe. I've followed the settings to use Rig Control, as the "radio" via a USB cable. Doing the test in the configuration screen I can test rig control and get a green light, if I push the PTT test it lights red and the radio goes to test mode.

Good info - I maintain a club station with three 991As and had to deal with this on all the computers. Pro tip: Some users might have a USB to serial converter based on the chips (Prolific, FTDI). These drivers will not work with the 991/991a. You need to download and install the Yaesu drivers. Don't mix up your driver installs!

Excellent timing on this post! Setting up FT8 for the first time on my 991A. CAT control as well as PTT via one USB cable from the computer to the radio. SWEET! The built-in sound card interface really makes this radio shine for digital modes. No external interfaces needed.