[TowerTalk] 160 meter vertical on sloping ground

[Brian Beezley]

"Today, with DEMs available to generate the "tiles" for a full 3d model 
would be straightforward. That was one of the challenges when Breakall 
did his work."


Jim, the data I would need are measured 3D patterns to validate a 3D 
modeling program. I thought a drone might generate them, now I don't 
think so. There are many sources of error with a drone, some rather 
subtle. It might work in certain limited terrain, but not in general. 
There's no way one would work at my QTH.


"I'm not sure an ever increasing model fidelity is useful."


The issue with a radial-only model is that it can be entirely wrong, not 
just off a bit. Worse, it gives no indication that the result is 
unreliable. I think it's possible to use a radial-only model under 
certain circumstances, but you need to carefully vet the terrain. It 
definitely wouldn't work in most directions at my QTH. And while some 
directions look benign, I'm not sure they really are. It's tricky!


"My understanding is that HFTA is horizontal pol only (the reflection 
model is simpler)."


I don't know what HFTA does, but TA used specified ground constants with 
Fresnel reflection coefficients for both horizontal and vertical 
polarization at all reflection points. Vertical is no more difficult 
than horizontal. The equations are just a little different.

Incidentally, after months of making innumerable errors of all kinds, I 
think I finally have an accurate stratified ground model. Its 
application is rather limited, as is the available stratified ground 
data. But it provides some insight into the accuracy of surface ground 
probes:

http://ham-radio.com/k6sti/sg.htm

My writeup on the Hagn generic curves, which yield ground constants much 
more appropriate at HF than the figures antenna analysis programs 
suggest, is here:

http://ham-radio.com/k6sti/hfgc.htm

Brian