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

David Siddall hhamwv at gmail.com
Sun Jan 4 13:49:00 EST 2015

Professional software equivalents to HFTA include consideration of
buildings as well as geography, but seem to be limited to line-of-site
considerations at 30 MHz and up.  One example widely used is EDXSignalPro
but designed for 30 MHz up.

Does anyone know of a similar software package that covers 1.8 MHz and up
for HF?  Seems as though engineers designing AM and HF stations would have
something similar to EDX SignalPro with which to work?

Also, how do the methods used by EDX SignalPro or other similar
professional packages compare to those used by HFTA?

73, Dave K3ZJ

On Sat, Jan 3, 2015 at 8:34 PM, shristov <shristov at ptt.rs> wrote:

> 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

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