A At least with past versions of FlDigi you had to run with Vox enabled and dataport set to the Vox input when using the SCU-17 interface, which is the interface that Yaesu has built into their radios with USB Ports. You need Vox mode because FlDigi does not (at least in the past when I last tried) support CAT control on one Com (serial) port and PTT on another Com port, it wants to do both on the same serial port but enabling such on the CAT port tends to enable the microphone input and not the data audio port. In the interests of full disclosure I run an FT-950 with the SCU-17 (the SCU-17 having the same chipset built into their USB radios), so the implementation should be very similar for us both. On those who get transmit on their radios but no power output, you will have a problem somewhere with your audio settings. It may be that the wrong audio output device has been selected or that the audio level has been set way too low in either the windows audio mixer (for the FT-991 soundcard interface) or, in the case of WSJT-X the left-hand power slider bar may be set too low and need adjustment upwards. It may also be that your radio is not configured to look at the digital audio port and is expecting audio from your microphone (you can test this by speaking into the mic to see if you get transmit output) or that the digital data audio input volume level is set too low in the radio menus (I know my FT-950 allows menu adjustment of input and output audio levels on the data port, so the 991 may also). Also, be aware that if you are running a rig control application, such as HRD, then that application will own the CAT serial port and all CAT control must be through the rig control application and not direct to the serial CAT port by the digital modes software. If your digital mode software does not know how to communicate with your rig control application directly then you may need to resort to Vox mode to enable transmit or you may need to close your rig control software so that it can surrender the CAT serial port to the digital modes application. The reason this is so is because serial ports, even virtual USB ones, are exclusively owned by the first application to claim them and may only be accessed by one application at a time (i.e. exclusive ownership by the application on a first come first serve basis). These are a few of the possibilities to check out and will hopefully get you up and running. I always tell people that the greatest challenge in working digital modes is not the mastering of the mode or software but figuring out the optimal and correct setup for your HF rig the very first time as each is a bit different and there are several different solutions on the market which do similar things but which are also setup somewhat differently. But the biggest challenge is getting your computer, the digital modes interface (which is embedded with your radio), and the radio all talking to one another properly and the more things there are to make work in the chain the more opportunities there are for something to be setup wrong or suboptimally. Just do not give up as you will get there!