As it turns out, you can connect a USB cable from a PC to an IC-7300, and run some free software, and instantly enjoy a bunch of HF digital modes. The IC-7300 appears to the PC as two separate USB devices – an audio interface, and the remote CI-V (CAT) serial interface, so no additional hardware is required. Pretty sweet!
So the two softwares are fldigi and WSJT-X.
WSJT-X software handles FT8, JT4, JT9, JT65, QRA64, ISCAT, MSK144, and WSPR, and Echo.
But, I haven’t tried out WSJT-X yet. I’m struggling to understand fldigi. Also there may be some IC-7300 settings that aren’t optimal as well. I can see the audio on the waterfall and oscilloscope displays, and the frequency and radio knob are synced, so both the USB interfaces are working and fldigi is configured correctly. I think the RX levels might not be optimal, because it decodes garbage. PTT works (radio transmits), but I don’t want to transmit until I know receive is working correctly and I have a better understanding of everything.
This link may help me understand the basics of fldigi: