[CQ-Contest] Contest QTH, hilltop or seaside?

[shristov]

HFTA is a great tool, no doubt about it.

But there are certain preconditions that must be met if HFTA results are to be trusted.
Attempts to use HFTA outside of its domain are a waste of time.

The following preconditions are due to HFTA using a geometrical optics (GO) approximation:
  * the wave incident on the terrain must be a plane wave;
    this translates to the wave source (antenna or a diffraction point)
    being many wavelengths away from the observation point;

  * each reflection point must be surrounded by a large enough area (Fresnel zone)
    in order to result in a reflection that obeys the geometrical "law of reflection";
    this translates to the terrain being composed of flat planes large compared to wavelength

The following precondition is due to the use of UTD to augment GO:
  * the distance between successive diffraction points must be many wavelengths.

The following precondition is due to HFTA using discrete ray-tracing:
  * your terrain must be smooth enough because HFTA only uses
    about 100-200 sampled points from your profile;
    if the profile is not smooth, then the sampled points will not be
    representative of the surrounding terrain, and you'll get random results.

The following precondition is due to HFTA using 2D representation of the terrain:
  * your terrain must be representable well enough as a series of wide flat plates ("stairs")
    i.e. parallel terrain profiles taken in the same direction, but laterally displaced, must be identical.

If your terrain profile satisfies ALL of the above conditions,
then you'll get a reliable result from HFTA.

If not, you must look for another tool,
such as experimentation, 3D EM software, or hope.

In addition, HFTA does not address the question of horizon obstructions,
which is at least as important as ground reflections.


73,

Sinisa  YT1NT, VE3EA