RadioBanter - View Single Post

Jerry Stuckle · January 25th 14, 11:54 PM posted to rec.radio.amateur.antenna

On 1/25/2014 6:34 PM, wrote:
On Saturday, January 25, 2014 9:43:57 AM UTC-6, Jerry Stuckle wrote:

And radials on a ground mounted vertical go (preferably) UNDER the ground.

Actually, for a given number of radials, slightly above ground is
better than under ground. But not by too much.
Most would probably not notice the difference, but there is a bit..
Elevated radials really need to be a good ways up in wavelength
to really live up to their potential.
Four radials at 1/4 wave up is equal to about 50-60 in the ground.
At 1/8 wave up, you need at least 20 or so to equal 50-60 on the ground.
At one foot up, you probably need 50-55 to equal 60 in the ground.
So really, the real advantage to burying them in such a case is less to
trip over when walking across the yard. :|

Not necessarily. Above ground, the radials provide only a (very low)
capacitive link to the ground. Below ground, they provide a direct link
to the soil. The effect creates a better ground plane for the antenna(s).

But an even more important point here is maintenance. It's very hard to
cut the grass when radials are above ground. Also, the exposure to the
elements will change the characteristics of the radials.

These are the main reasons why AM radio stations bury their radials.
It's not unusual for a station to have 360 radials per tower, at one
degree intervals. Then there are rings spaced every one to three feed
apart, around the tower. These rings are then soldered (often silver
soldered) to the radials at the points they cross. The result is a very
effective ground system for the antennas. But can you imaging trying to
mow if these were above ground?

A station I worked part time for in Iowa had such a system; so does the
one in my back yard.

--
==================
Remove the "x" from my email address
Jerry, AI0K

==================