Step 2: set up COM port links & test
Using Com0Com, make at least 1 virtual COM port pair on both PC's. In this example, the server PC will have the pair set as COM2 & COM3, the radio PC will have COM4 & COM5.
Run this command in a CMD window on the server PC (alternatively , make a match file for each command, to make setup easy.)
> com2tcp-rfc2217 COM3 41000
This will link COM3 to a telnet session on TCP port 41000.
Run this command on the radio PC:
> com2tcp-rfc2217 \\.\COM4 192.168.xxx.xxx 41000
This will link the radio PC's COM 4 port to the server PC's COM3 port via TCP. Open a PuTTY window on both PC's, and link them to the open COM port on the PC (COM2 and COM5). Anything you type into one PuTTy session should appear in the other. If you can do that, the link is working.
Connect the radio laptop back to the VPN on the hotspot like in Step 1 to verify the link still works over the internet.