Thanks Erik.
I read the slides from the link but did not notice mention of another protection method that I've seen using zener diodes.
Referring to the attached image, drawing A is mentioned in the slides.
However, I have also seen the use of back-to-back zener diodes in series as shown in drawing B that I think would provide a higher input range.
Lastly, I wonder how the use of a two-color LED as in drawing C would work, with its higher forward voltage. (and visual indication?)
The original aim of the diode protection was to limit input voltage to 0.6V at the radio's sensitive front-end.
The VNA uses a resistance bridge - how much signal can it tolerate before physical damage or actually modifying what you're trying to measure?
