RadioBanter - View Single Post - Quad loop supported by single tower

Roy Lewallen · December 8th 07, 10:42 PM posted to rec.radio.amateur.antenna

wrote:
Thanks Roy!

I guess I was confused about the obvious connection the tower base has
to the ground. Will this have any addition affect?

Yes, the tower's connection to ground can have quite a profound effect
on how it interacts with the antenna. And unfortunately, that can be the
most challenging part to model.

If you put the bottom of the tower at Z = 0 when using any kind of
ground except perfect, you'll get the equivalent of a ground connection
with an unpredictable resistance (or an open circuit, depending on the
GE "card" parameter). About the best you can do is to use Sommerfeld
type ground and put some radials just above the ground. Of course, the
problem then becomes estimating the actual tower ground system
resistance and the resistance of the modeled radial system. You'll
probably end up trying a number of configurations which hopefully
include something representing reality, and assuming that the actual
system will behave somewhere within the range of the results you get.

There's a fair amount of information about ground system modeling in the
EZNEC manual, available in the free demo version. EZNEC's "High
accuracy" ground is the same as NEC Sommerfeld ground.

Roy Lewallen, W7EL