How do I add a [email protected] to my existing Huber unit? External [email protected] (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 [email protected] (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 [email protected] plate.