Some time ago I already built some "loose" interfaces for my FT-817. I used these later on my FT-891. The CAT, respectively the FTDI USB to serial converter I needed at the FT-8x7, I don't need at the FT-891 anymore, because it already has CAT via USB integrated. The FT-891 simply uses a Silicon Labs CP2105-F01 USB/Serial UART converter internally. As with many other TRXs, this is not galvanically isolated, but the engineers thought of something. Apparently it works well anyway. I have had no problems at least in the last 2 years. In this article I show you my solution for this problem.