4NEC2 plots of STL VSWR II

At 4NEC2 plots of STL VSWR I explained a method of working around a limitation of 4NEC2 values for Zo that can be applied using the Settings menu.

I asked the developer to consider a change, but I gathered that he regarded 4NEC2 to be at End Of Life.

It appears that 4NEC2 enforces a requirement that Zo>=0.1, so having discovered that by trial and error, one wondered if it was possible to change that threshold by hacking the exe file.

The IEEE754 Double representation of 0.1 is 0x3FB999999999999A, and of course it would be stored backwords in the exe file. Searching for 0x9A9999999999B93F found only one occurrence, offset 0x1490. That was changed to 0xfca0f1d24d62503f (the backwords representation of 0.001) and the exe tested. (It might be tempting to set it so zero, but that would permit entering zero which may cause run time errors).

To my delight, it now permits directly changing Zo down to 0.001Ω.

There is a side effect of this change, it appears that the literal constant is used by (at least) one other function, and current graphs on the geometry window need to be scaled up with the page up key to be useful.

If you want to use this you can:

  • edit 4NEC2.exe directly with your favourite hex editor (don’t forget to take a backup), or
  • an xdelta3 patch file is available for 4NEC2 v5.8.16: 4NEC2-5.8.16-ZoPatch, the xdelta3 command is : xdelta3 -d -s 4nec2.exe patch.xd3 .