[TowerTalk] HFTA Question

[Máximo EA1DDO_HK1H]

Hi Bill,

It seems that terrain model is not realistic, according to you.
At my home country, Spain, we can download DEM up to 5m resolution, very high. Usually 25m is enough.
For worldwide coverage there are a couple of options.
You can visit my web site talking about that>
https://translate.google.com/translate?sl=es&tl=en&u=http%3A%2F%2Fwww.ea1ddo.es%2Fdem%2Fdem.html

Worldwide DEM servers I know:

ASTER  https://wist.echo.nasa.gov/wist-bin/api/ims.cgi?mode=MAINSRCH&JS=1

SRTM  http://srtm.csi.cgiar.org/SELECTION/inputCoord.asp

ATDI   http://www.atdi.com/cartography/
<http://foro.ea1ddo.es/>


Remember you can edit manually your data. I use to do it because HFTA only accepts 150 points, so i use to edit manually in a logaritmic way. The closer the points are, I take smaller separation, increasing when distance to antenna is larger. For example, I can leave one point every 5m from antenna up to 500m away, then every 25m, then every 50m, up to 150 points.
It depends on your terrain profile, you need more detail where disrruptions are, less detail on flat land.

73, Maximo



________________________________
De: TowerTalk <towertalk-bounces at contesting.com> en nombre de Bill via TowerTalk <towertalk at contesting.com>
Enviado: jueves, 24 de septiembre de 2020 23:43
Para: towertalk at contesting.com <towertalk at contesting.com>
Asunto: [TowerTalk] HFTA Question

I've used N6BV's HFTA for over 15 years, love it and found it very useful.
Recently I downloaded the terrain from K6TU for a new planned station in V31 and found some strange numbers.  All latitude and longitude numbers were double checked so that is not an issue.  From being in the area where the station will be located and from the Google Earth terrain numbers, things don't agree.  I'm talking about 50 foot hills that don't exist.  From observation, I know there is a steady slow slope to the ocean from an elevation of 45 feet to ocean level 2500 ft away.  No hills, and Google Earth confirms this, but the terrain numbers from K6TU claims there is one
I manually downloaded the numbers for several different directions and compared the output between the numbers from K6TU and the ones from Google and there are differences.  No gross changes, but enough to change the output by 3 or more dB in many cases.  I'm not badmouthing  K6TU and appreciate his work, but this is quite puzzling.  I've never had this happen before.  In low flat sugar cane areas, Google gives numbers that conform, but the numbers I got from K6TU  show rises of almost 40 ft.
My guess is that the numbers outside the US are not quite as accurate and perhaps  thick jungle gives an artificial height.  Any thoughts?
Bill K4XS/KH7XS
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