As I read this I now wonder about TA distance from vertical base. Im kinda on a
knob but then about 2000 feet the hill's in all directions are back at the same
level as vertical. So ai guess the question is whats the area that one should
be concered about if any at all.
Ron
Sent from my iPhone
> On Jan 14, 2025, at 4:34 PM, Brian Beezley <k6sti@att.net> wrote:
>
> "A good way to think about this kind of 'antenna on the side of a hill' is
> to rotate the pattern for flat ground to the angle of the hill."
>
> That's how I think of it, too, Jim. It's a good first approximation, but
> there's more to it. In the simplest case, the far field includes a direct
> ray, one from sloping ground, one from flat ground after the slope quits, and
> diffraction from the bottom of the slope. There might also be a secondary
> bounce from sloping to flat. Although sloping ground can certainly
> concentrate power at low angles, you never get power right at the horizon due
> to the inevitable phase cancellations. W6NL has an old photo me of explaining
> this very geometry to W7EL by drawing rays in the dirt with a stick at his
> hilltop QTH!
>
> My TA program will calculate the resulting pattern for a vertical antenna at
> the edge of a slope, including all possible reflections and diffractions. But
> I don't have a working copy.
>
> One thing to note about these ray-tracing programs is that they all do a
> one-dimensional analysis along a given bearing. For mountainous terrain, this
> is often inadequate. Power can easily reflect or diffract from terrain to the
> right or left and wind up on the bearing of interest. The magnitude of these
> off-bearing paths can be quite large. This really restricts terrain for which
> results are accurate.
>
> I've been thinking of resurrecting TA for Windows. If I do, it will only be
> for a full 2D analysis. That should be possible in a reasonable amount of
> time with modern computers, especially with multiple processors gnawing away
> at all of the potential paths. But the main problem is getting reliable data
> to check the calculations. What I used for TA was the original WA3FET IEEE
> article. I had to extract data by hand from the curves. But as I recall, the
> helicopter that took the data flew directly over a hill with the RF source so
> it is not a good test of 2D terrain. I would not write a 2D program without
> having reliable data to check it with. There are just too many ways to make
> ray-tracing errors.
>
> Brian
>
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