VNA Damaged Front-End Characteristics?

[fourierpwn]

Hi all,

A general question, what would one typically expect to see on the display (ports floating) if the input section of a VNA was blown due to being overdriven? I am trying to pre-diagnose a faulty VNA before potentially committing to the purchase but I'm quite cautious of what the fault may be. There is a warning message on the display which says that the test ports are overloaded yet both ports are floating and S11 has a few notches across the sweep.

Thanks!

[joeqsmith]

I bought a few things over the years that had damaged front ends.  Looking at the inputs, they no longer measure 50 ohms.   Then you take them apart and see the carnage.   I had an SA that they must have locked out the attenuator and actually took out the mixer.   I always envision some amateur radio or CBer thinking they are a EE, trying to measure their output power or response of their new Japanese gear.     

The last VNA I bought had been damaged.  It was hot enough to discolor some of the metal.  Depending what you bought,  if it was sold "working"  I would just return it.  You may find the costs to repair it are very high or you just can't get parts.   If you do decide to keep it and pull it down, take a few pictures.  If you decide to open it up, I would check with the seller first.  You may not be able to return it if you open it.    Of course, if we are talking $100 or $50,000 it makes a difference.   So does your skill, education, tools available and aversion to risk.   

[Bud]

If you have access to the VNA in question and another VNA, measure the Return Loss of the test ports.
You are not indicating the damaged VNA model. Industrial high frequency VNAs have custom parts in the test ports which you will unlikely be able to repair unless the entire test port assembly is replaced.

[thinkfat]