[TowerTalk] oddities in NVIS model

[Michael Tope]

----- Original Message ----- 
From: "Jim Lux" <jimlux at earthlink.net>
>
> 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)
>

That was my experience with a 80 meter dipole 10 feet off the
ground, Jim. It had a very pathological input Z. With "reasonable"
mistmatches my T antenna network tuner easily handles the ~1.2
KW output of my Drake L-7. When I had that low 80 meter
dipole, it was arcing with just the 100 watt exciter driving it. The
net result was a very poor antenna system. On the air performance
was dismal with consistently poor signal reports on NVIS paths.
When I raised the center to 27' and the ends to about 20', the
antenna behaved conventionally (reasonable input Z) and I started
getting consistenly good reports from the locals on 75 meters.

73 de Mike, W4EF...............................