External Com.G@te (part number HB6915)
You could either connect it with a 3 m cable (part number HB16160), or alternatively use a shorter cable and a bracket to mount it on the unit (different part numbers for different Huber models).
Internal Com.G@te (part number HB31217)
Remove the RS232 plate from the Huber unit (4 screws), and disconnect the cable on the back. There is another cable inside (which may be slightly hidden; it’s labelled -WVL3) that connects to the back of the internal Com.G@te plate.