Hi
This is my point of view : Z--> option does not change the physically pot2 impedance , it remaine always at 50 Ohm +/- 1 ohm value, just firmware by computing way can display S11 or S21 as its at 75 ohm or 300 ohm , for example seting it at the accurate physically port2 50.45 ohm will gives more accurate S11 S21 displayed results , but if DUT does not run smoothly on physically 50 Ohm load , computing compensation will loos sens , so its rather to have the two Z port option one for port1 and second for port2 .
73s Nizar.
