[Towertalk] Low-Angle Scattering

[Steve Miller]

N4ZR wrote:

> At the very-low-angle peak, the modeled signal is 17.8 dBi at 1.75 degrees 
> above the real horizon.  At the same elevation angle above flat terrain, 
> the same antenna shows approximately 1.8 dBi.


Pete,

These low angle 'inflated gains' are modeling artifacts.  I saw similar 
behavior after entering a rather detailed topography for my location.  

To check the model, I took the original terrain profile and broke it up 
into smaller segments (interpolating between the original data points). 
This should have provided the same pattern, however the interpolated data 
set also showed inflated gain behavior at low angles.  Too bad, I could 
have used another 16 dB! ;)

73,
Steve  N8SM

P.S. Many scattering/diffraction algorithms become numerically tricky 
at 'near-grazing' incidence angles.