[BC] Directional Antenna Proofs - Ground systems.

[Richard Fry]

>A large number of missing radials on one side of the ground system can of 
>course cause some pattern distortion (non-directional).

Having finally acquired a license for NEC-4.2, I modeled a 1/4-wave, 
series-fed monopole (1500 kHz), driven against just two 1/4-wave  horizontal 
radials 90 degrees apart, and buried 1 meter in 6 mS/m dc 13 earth.  The 
model was constructed per the rules for NEC4, and had no geometry or 
segmenting errors.  The calculated h-plane pattern was perfectly 
omnidirectional.

At first I was skeptical, but now I'm thinking that result might be 
correct -- because all of the useful radiation from this system still 
originates from the r-f current that flows along the vertical conductor, 
which radiation would be omnidirectional in the horizontal plane.

The loss in the ground plane within about 1/2 wavelength of the monopole 
controls the amplitude of the displacement/conduction currents in that 
region that return to the transmit system  That loss is relatively high in 
this 2-radial case, and antenna system efficiency is reduced.  But that 
would not produce any directional effects in the horizontal plane.

Just wondering what others might think about this.  Have real-world 
measurements of the groundwaves of single monopoles shown directional 
effects within a few kilometers from the site due to buried radials missing 
over large sectors?

RF