On 3/4/12 9:00 AM, David Gilbert wrote:
>
>
> If you have the patience you can draw a line on Google Earth and
> manually pick the numbers directly from that to load into any text
> editor. A bit tedious, but simple and effective. I've done it myself,
> although I generally find it quicker to manually pull the numbers from
> the terrain profile that DeLorme's 3D Topo software generates. I've
> used HFTA a lot, both for my QTH and for a few friends, and I've never
> used Microdem. I don't bother to generate files every five degrees
> azimuth or anything like that. I just pick the key locations I want to
> hit (Europe, Japan, Central Asia, South America, Central Africa, etc)
> and even in the mountainous terrain around my QTH about six or eight
> terrain files suffice to tell me what I want to know.
>
Yes, because HFTA doesn't do any calculations for "sideways"
propagation. It models the surface as a set of plates that don't slope
left or right.
Jim Breakall (W3FET, I believe) and his colleagues did a similar
sophisticated analysis a few decades ago, using a real "surface model",
published in IEEE Trans on Ant and Prop.
The modeling and measurement of HF antenna skywave radiation patterns in
irregular terrain
Breakall, J.K. Young, J.S. Hagn, G.H. Adler, R.W. Faust, D.L.
Werner, D.H.
This paper appears in: Antennas and Propagation, IEEE Transactions on
Issue Date: Jul 1994
Volume: 42 Issue: 7
On page(s): 936 - 945
There's tons of stuff out there recently on using a variety of methods
to look at VHF and UHF propagation over terrain models ingested from one
source or another. There are companies that actually do this as a
business (finding databases, building modeling codes, having useful user
interfaces, generating reports to tell you where to put your antennas).
I suspect that one might be able to find something that would be
adaptable to HF (after all, the physics is the same).. One thing that
HFTA doesn't do is deal with vertical polarization, for instance.
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