On 1/19/19 11:08 PM, David Gilbert wrote:
"Certainly the topography of adjacent radials affects the true
performance on one radial that won't show up in the HFTA model. No?"
I'm pretty certain that N6BV himself has pointed that out as a
limitation of HFTA. It's a complicated world.
HFTA assumes that (for each direction) the profile is infinite in extent
in the "cross range" direction.
It's a 2D ray tracer with N slices in aziumth.
It's sort of like how most folks do ionospheric models (e.g. VOACAP) and
assume there's no cross range propagation, although there actually is.
One can do a full 3d model, but it's computationally expensive ( a lot
more than just running radial at finer steps), and it's unclear if it
would be useful for antenna planning.
73,
Dave AB7E
On 1/19/2019 8:33 PM, Paul Christensen wrote:
"There are folks who claim that a few thousand meters or so is all
the further anyone should have to collected data points, but that's a
garbage generalization. I have
another mountain range about 15 miles east of me and by editing the
terrain file to either include it or not I can see definite differences."
And that brings me to this point: consider a case where a radial is
analyzed in HFTA and extends to 14,000 ft. At that distance, each 1
deg radial is approx. 244 ft apart.
From what I can determine, HFTA is calculating the radiation profile
from data on only one radial. But since terrain often changes on
adjacent radials, sometimes dramatically, then doesn’t the model
really need data that's spliced and factored from adjacent radials to
get a true picture of the profile? If the antenna beamwidth is
say...40 degrees, then don’t we really need a more comprehensive
analysis of radials within the swath just to determine the profile of
one radial?
Performance as actually measured on one radial could be undermined (or
enhanced) by adverse terrain characteristics from adjacent radials.
Certainly the topography of adjacent radials affects the true
performance on one radial that won't show up in the HFTA model. No?
Paul, W9AC
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