Since I manually generate my own files I just jump to the next distance
that represents a noticeable difference in height. HFTA simply assumes
a linear incline/decline between data points so instead of creating data
pairs (distance, terrain height) for fixed increments of distance I
create data pairs for roughly fixed increments of height (although I
generally use finer increments within a few wavelengths of the tower).
I've never hit the 150 data point limit that way so I didn't even know
that it existed.
I assume by "default 4400 meter range" you are referring to some
characteristic of Microdem or equivalent because there is no such
default within HFTA that I am aware of. I've edited the heck out of
various .pro files (creating some totally imaginary ones) just to see
what effect various terrain features might have and it simply uses them
as if they were real.
73,
Dave AB7E
On 3/5/2012 8:58 PM, Steve W3AHL wrote:
> Date: Mon, 05 Mar 2012 16:14:58 -0700
> From: David Gilbert<xdavid@cis-broadband.com>
>
>> HFTA will, as far as I know, work with almost any distance you choose.
>> There seems to be a tacit belief that terrain points out beyond 5,000 or
>> 6,000 meters are not worth bothering with, but I believe that to be an
>> erroneous assumption. ..snip..73,
>> Dave AB7E
> HFTA is limited to a total of 150 data points in the .pro file, including
> the tower base location. You can increase the total profile distance, but
> at the expense of also increasing the interval between sampling points along
> the profile. What I have done is generate radials for longer distances when
> there are relevant features beyond the default 4400 meter range, then
> manually edit out the "flat" spots in the profile to fit what I feel is
> relevant into the 149 elements of the array.
>
> This has been a purely intellectual experiment, since I never had a way to
> validate the model. Nor is there much you can do to the antenna design or
> placement usually as a result of such distant geographical features.
>
> Steve, W3AHL
>
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