How far you should go out is strictly a function of what your particular
terrain looks like. In my case, I live on a hillside and the land
slopes significantly downward to the east (toward Europe) for about
seven miles, then gradually rises for another several miles before
hitting a mountain range about 15 miles away. The strongly downward
slope gives me a VERY low takeoff angle to Europe (check out
http://www.ab7e.com/HFTA/AB7E_HFTA.html ) and I can most definitely see
the impact of that distant mountain range. If the land within a few
miles of my house was flatter that almost for certain would not be the case.
Regarding what increments you should use, HFTA simply plots straight
lines between the terrain file points, so if you have sharp terrain
features you may want to use smaller increments ... or larger increments
if the terrain changes smoothly. The increments don't need to be
uniform within the file, so I look at the terrain profile and use
smaller increments where the terrain is ragged and larger increments
where it is smooth.
The best thing is to do some editing of the terrain file and see if
there is any impact on the results. If there is, use a longer reach or
more precision. The file format is simply two columns of text and can
be easily edited with any text editor.
73 es take care,
Dave AB7E
On 6/2/2015 9:46 PM, Matt wrote:
My experience with changing units in the options tab results in changing
units for BOTH the terrain input and antenna elevations. I have also
observed that the antenna heights displayed in the main window do not
consistently convert automatically when the program is first started,
however, once new antenna height values are input, the units appear to
remain consistent and it causes no problems. Regarding the radius of your
terrain profile, I would suggest extending your profile out to at least
10,000 ft. HFTA results at really low angles seem to be more accurate (at
least at my QTH) when I extended my terrain profiles to around 30,000 ft.
My QTH is on a hilltop, however, and this may not be of benefit for flatter
terrain ?? You may want to experiment with increasing the profile radius
incrementally until the changes in output results become negligible.
Hope this information is of use to you and good luck on your modeling.
73
Matt
KM5VI
-----Original Message-----
From: TowerTalk [mailto:towertalk-bounces@contesting.com] On Behalf Of LY2KZ
Sent: Tuesday, June 02, 2015 2:09 PM
To: towertalk@contesting.com
Subject: [TowerTalk] units in HFTA
Hello guys,
I wish to model some antennas in my location. Got one question about units
in terrain file. I prepared terrain file in my favorite directions. 100ft
step under 3000feet and 200feet step untill 4000ft.
Hope its enough for relatively flat terrain and 15m, 20m bands.
There is option to switch meters - feets in the otions tab in HFTA. Does it
changes only tower height or terrain file units too? Should terrain files
always be in feets?
-----------------
Vytenis LY5T
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