Hi Manfred,
You note that you cannot use NanoVNA Saver under Windows XP.
I inherited a laptop running Windows XP from my daughter.
I just tried that if I copy the NanoVNA-App to the C: / root directory, it will log in without further ado.
I remembered that the creator of the program mentioned this, but I never tried it.
You may also want to update the firmware because the program and firmware were developed together.
So one cannot be used without the other.
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*** If you are not part of the solution, then you are the problem. ( ) ***
Gyula Molnar