Modifying frontend for 75 ohm Z0

[goscickiw]

This is, in a way, a continuation of #42. I have upgraded to SAA2 recently, but I still want to make use of my NanoVNA-H, and I thought of converting it to a 75 ohm VNA. I assume that the bridge resistors have to be replaced, but to what values? Do I have to replace any other parts? Also, in the code I found several variables declared as float z0 = 50;. I assume that I'd have to change that to float z0 = 75; and compile the firmware? Would I have to change the code in any other way?

[DiSlord]

Now you can use DISPLAY->Port-Z and set value. Now NanoVNA recalculate measured impedance to this value