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Re: [TowerTalk] Modelling a basic stack

To: "Jim Lux" <>,"Towertalk" <>
Subject: Re: [TowerTalk] Modelling a basic stack
From: Pete Smith <>
Date: Mon, 10 May 2004 13:51:36 -0400
List-post: <>
At 09:17 AM 5/10/2004, Jim Lux wrote:
The desktop computer might be powerful enough (especially if you're willing
to wait overnight), but I think you're also looking for a modeling
program/system that is reasonably inexpensive and doesn't take hundreds of
hours to use effectively.

There are a number of approaches, none cheap in either time and money, that
exist today.  Ohio State's NEC-BSC has been used (10-20 years ago?) to model
HF and VHF propagation over real terrain with real dielectric properties.
Companies like EDX provide tools for very accurate propagation analysis in a
variety of environments (they'll even sell you a database of buildings in
some cities).

Of course, once you have the terrain model, you still need the earth
properties for that model.

Thanks for the info. Yes, I was thinking in terms of something that "we" (amateurs) could both afford and put to reasonable use.

I had heard of NEC-BSC, but had the impression that it was principally used for problems like antennas placed in the superstructure of ships, rather than above real ground. A quick Googling found only that sort of application.

Jim speculates about the effects of earth properties on the modeling fidelity. I tend to rely on Dave Leeson on this. If I understand what he writes on page 10-2ff of "Physical Design of Yagi Antennas," this is relatively unimportant. He writes, "The reflection is from the conductive or dielectric discontinuity between the air and the surface of the ground (giving effect to skin depth), not from some magical underground water layer."

Jim also comments (in part of his message I did not quote) on the potential usefulness of data from Landsat Thematic Mapper. HFTA's 2-D terrain profiles are generated from USGS's seamless data server. Its 1 and 3-meter resolution data are derived from Thematic Mapper and Shuttle radar mission data, if I understand correctly. In any case, a whale of a lot better than drawing pencil lines on a topo map.

73, Pete N4ZR
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