[Antennas] Ground Mounted Vertical Radials

Fri Aug 22 02:49:12 EDT 2008

Hi all.
A good radial/counterpoise/ground is necessary to catch the return 
currents from the radiator. Bad ground/radial/counterpoise equals high 
resistance equals low current. So a good current return path is 
absolutely necessary for high efficiency i.e. for the power from the 
transmitter to be actually radiated. Antennas above ground cause less 
currents in the soil, where they anyway have nothing to do.
But that is unfortunately not the entire story. Conductivity and 
capacitance of the surrounding terrain up to about 100 wavelengths 
away also play a very important role. For vertically polarised 
antennas a very, Very, VERY low lobe requires good ground 
conductivity, with salt water being ideal. If on the edge of a salt 
water ocean (or perhaps even in it) you get both 1) exceptional ground 
conductivity and 2) "quite a large" flat surrounding, which in turn 
gives you several S-units increase - and that is a lot for a vertical.
What I want to say is that only a good ground (while a good thing) 
does not automatically give phenomenal performance. Of course a good 
ground increases the chances of getting your signal out - all else 
being equal.
Also not that low lobes for verticals are best achieved when close to 
ground. Lobe splitting in the vertical plane begins being a problem 
when the vertical is mounted too high up. in short: Mount it as low 
as is possible (in terms of wavelength) but not too low as the 
currents stray into ground where they get lost:(
/Micke