[TowerTalk] FW: units in HFTA

[David Gilbert]

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 at contesting.com] On Behalf Of LY2KZ
> Sent: Tuesday, June 02, 2015 2:09 PM
> To: towertalk at 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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