[TowerTalk] oddities in NVIS model

[Jim Lux]

As Tom pointed out, my quick and dirty model of a NEC antenna didn't 
comport well with the usual wisdom on antennas (i.e. low antennas are 
inefficent).  It showed virtually the same gain at 50cm as 10m.

A bit of investigation has found the reason.

I did all the models with exactly the same length of wire and the wire was 
lossless.

When it's only 50 cm off the ground, the feedpoint impedance gets highly 
reactive (because of the dielectric loading of the earth). (we're talking a 
few ohms resistive and hundreds of ohms reactive).

If you actually built such an antenna you'd
a) need a (lossy) matching network
b) even if the network were lossless, the resistive losses in the wire 
would be huge (low Z = high IR losses)

I'm running some more models.