I've been playing with several programs (tunehalf.exe, endfeed.exe,
and EZNEC). All ask these questions:
* Height of vertical portion of wire
* Length of horizontal portion of wire
* Wire diameter
* Frequency

Endfeed.exe also asks these questions:
* Number, length, & diameter of buried radial wires
* Length of strap from radio to radial connection

Tunehalf also asks these questions:
* Transmitter output impedance
* Length * diameter of coil
* Parallel and serial capacitance
* Estimated ground loss resistance

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?

--
-- Myron A. Calhoun.
Five boxes preserve our freedoms: soap, ballot, witness, jury, and cartridge
NRA Life Member & Certified Instructor for Rifle, Pistol, & Home Firearm Safety
Also Certified Instructor for the Kansas Concealed-Carry Handgun (CCH) license