On 3/9/2012 9:58 AM, dave wrote:


I don't think a ground screen is needed if you are 1/2 wave.

It's not required to provide the lower half of the antenna, but
they will still reduce ground losses if the antenna is ground mounted.



If you elevate a short vertical you only need a few "ground" radials
(think CB groundplane antenna), btw. My whole transmit antenna system
floats on my roof. The only "ground" is the panel where the RF goes
through the wall. I receive on a balanced 30m horizontal loop, also
floating except for the point of entry. I have an automatic tuner at the
feedpoint under the eave by my kitchen window. (FWIW) I have lived here
14 years and have never seen lightning at the shack.

The number of elevated radials needed to equal certain number on
the ground will depend on the wavelength above ground.
IE: to equal 120 1/4 WL radials on the ground, at 1/8 WL, you will need
appx 60 of them. At 1/4 WL, appx 8-10.. At 1/2 WL, 3-4..
And if the radiator is short, the radial system is a bit more
critical than with a full size 1/4 wave radiator.