Steve K0SR wrote:
...As I stand at the base of my mighty Butternut, I look in any direction
and see obstructions. Cars, trucks, garages, hills, telephone poles, sheds,
trash cans. The very base of my vertical can "see" about 40 feet away. What
does that do to the radiation pattern of this antenna? ... My gut tells me
I need higher angles of arrival or I'm out of business.
Probably the only objects in your list that would have a significant affect
on radiation patterns would be telephone/power poles, if they have a wire
running down the side of the pole connecting to a ground rod. Such
scenarios are rather easy to model in NEC software to get some idea of their
net effect.
On the lower bands, especially 160m, wavelengths are usually quite a bit
larger than the vertical dimensions of even house-sized obstructions, so
they don't have much affect on low-angle radiation from a monopole. The
link below shows a fairly extreme example of this.
The groundwave fields of AM broadcast stations in the "expanded band"
(1610-1700 kHz) can cross entire cities and still have very nearly the same
value on the far side of them as if the cities weren't there. So
radiation/reception by a monopole at elevation angles below 10 degrees also
won't be much affected by those obstructions.
http://i62.photobucket.com/albums/h85/rfry-100/Part-15_AM_WhipElevated_Frame.gif
_______________________________________________
Remember the PreStew coming on October 20th. http://www.kkn.net/stew for more
info.
|
