Topband: Skywaves from Monopole Surface Waves

[Tom W8JI]

> As W8JI pointed out, this is nothing new.  Academics like Terman, BL&E, 
> et. al. were teaching it back in the early 1930s.  But we've become firm 
> believers in the typical vertical profile field plots when the only 
> accurate vertical profile result from a vertical radiator is produced from 
> a vertical over a super-conductive surface like salt water.  There's 
> nothing wrong with the far field plot, but we should realize its 
> limitation in the context of the vertical profile, especially on topband.


If we model a vertical wire or a small tuned loop with a load, some distance 
from the antenna (say around five or ten wavelengths) we'll find the load 
power decreases as the height of the distant "sample antenna" is moved up 
away from earth.

Move out further and we'll eventually find where the groundwave signal 
starts to become weaker than the signal at higher angles.

With better soil, the radial distance out where groundwave exceeds elevated 
field strength increases.

This shows how in close, even in the programs said to not calculate 
groundwave, the program shows the antenna does not really have a null at 
zero elevation. The null we see is because of the large distance involved to 
the pattern calculation point, which allows the earth to attenuate the field 
to zero.

If the field really was zero at zero degrees, why does the model show more 
energy at or near ground level than angles that are in the "main lobe"? The 
model can call itself a liar.

73 Tom