[TowerTalk] 16om vertical and the number of radials

[Leeson]

My thought on this is that the very shallow angle grazing reflection 
from the dielectric discontinuity at the distant ground surface is 
pretty much 100%. The ground permittivity and conductivity variability 
would have a bigger effect for higher radiation angles.

For fire protection and layout reasons, I have only two elevated radials 
on my full-size quarter-wave vertical, and it seems competitive enough. 
Because the SWR is low without any matching, I assume there's some 
ground loss, but my 12° sloping foreground seems to make up for it. From 
modeling, I expect a little gain to the northeast from the 140' tower 
reflector behind it.

We used two full-size half-wave verticals above a sloping foreground in 
our HC8 station, with very good results. One was always a little better, 
but it was hard to predict which one by direction alone. "Person with 
one watch knows what time it is; with two, never quite sure."

Dave

On 12/3/22 10:21 AM, Brian Beezley wrote:
> 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
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