For radio amateurs
the three-antenna changeover PC's using a single antenna cable.
The antenna cable HF signala and DC control
The program can select the antenna 1, 2 or 3 locally ,using an intranet or via the Internet.
Remote application program is the same as the local program.
Control takes place via the serial port (RTS and DTR)
You need the relay hardware to operate the software in the picture to do actual control