[TowerTalk] 16om vertical and the number of radials

[Brian Beezley]

Paul, W9AC: "Isn't the measured probe result only useful for near-field 
system efficiency analysis?  By near-field I mean to obtain system 
efficiency within a wavelength or so of a vertical radiator.

But for skywave propagation field strength, don't we also need to know 
more about the ground conductivity much further out to more than 1km on 
160m?"


Paul, I don't know how distant ground affects 160m specifically. But if 
you're on a hilltop, at low elevation angles your signal may reflect or 
diffract from ground miles away. Its permittivity and conductivity might 
be quite different than that of the ground beneath your antenna.

I think the main usefulness of knowing your ground characteristics is to 
predict antenna efficiency. That could easily determine your choice 
between a horizontal and vertical antenna on 80m or 40m.

If you have some idea of the ground quality far away, you could create a 
separate model with that value to study low-angle effects. You could 
take a drive and go measure distant ground. But you'd probably have to 
take a number of measurements to satisfy yourself that you had a 
representative sample. My ground probe calculator includes a utility 
that will average probe measurements. I had in mind making multiple 
measurements near the antenna, but you could use it to create an average 
of far-away ground for a low-angle model.

Brian