[Antennas] Ground Mounted Vertical Radials

[Michael Josefsson]

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