Richard Clark wrote:
. . .
I will add a proviso in that the Source represented by EZNEC, and
presumably by extension NEC, has no characteristic Zc; or rather I am
not aware of its value. . .

I'm not sure what Zc is, but NEC sources have a definite, well-defined
internal impedance: Zero. EZNEC gives you the choice of voltage sources,
which are the same as NEC sources, with an impedance of zero; and
current sources, which have an impedance of about 10^15 ohms --
infinite, for practical purposes.

Roy Lewallen, W7EL