On Sat, 19 May 2012 02:55:38 +0000 (UTC),
(Myron A. Calhoun) wrote:

I've been playing with several programs (tunehalf.exe, endfeed.exe,
and EZNEC). All ask these questions:
(...)
Among other things, both calculate the antenna impedance.

HOW DO THEY DO THIS? I'd like to write some programs of my own.
What is the formula or equation for estimating/calculating antenna
impedance given the above inputs?

If you want to see how a program works, it's often best to go to the
source code. Most of the major programs are user friendly front ends
to the Fortran or C NEC "engine" that actually grinds the numbers.
However, there is a C version of the code available:
http://5b4az.chronos.org.uk/pages/nec2.html
http://www.si-list.net/NEC_Archives/nec2c.tar.gz
There are other source code versions that might help:
http://www.si-list.net/swindex.html
http://www.qsl.net/m5aiq/nec.html
etc...


--
Jeff Liebermann
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558