[BC] Elevated Grounds

[Cowboy]

On Monday 13 February 2006 09:05 pm, Stanley Adams wrote:
>Thanks for all the replies fellows.  Appreciate it.  Conceptually, I would
>think that there would not be much difference, yet on the other hand, we are
>attempting actually to transmit one half of the total RF current through the
>medium of the earth.

 Um.....
 In the very near field, yes.....

>In the MW band, this is critical because most of the  
>coverage is by means of the ground wave.

 Um....
 No. ( depending on which school you went to )
 Ground wave is theoreticly induced onto the surface of the ground
 by extracting energy from the direct wave passing above the surface.
 Launching the wave is important, but attempting to transmit a wave
 through the ground pretty much futile.

>Now, I would think that an 
>elevated counterpoise would be better than driving ground rods in the rocks
>of Vermont where the ground conductivity is extremely poor.

 Ground rods have little to nothing to do with RF radiation and are primarily
 a lightning thing, so in that ( any ) case, any counterpoise at all to form
 the ground plane will be better than ground rods !

>On the other 
>hand, in the great state of Illinois, or in the low lands of many places
>where water is in abundance or traces of minerals, then the transfer effect
>to the more conductive ground situation would be better then the elevated
>remainder of what is practically a buried half of a dipole.  

 Perhaps, but I doubt it.
 One theory is that higher conductive ground requires that less energy
 be extracted from the direct wave passing overhead to be dissipated in
 the ground.

 What we know is that the wave needs to be launched as efficiently as possible.
 How that is done varies for many reasons.

 Witness any FM facility.
 It's just a matter of scale.

-- 
Cowboy

http://cowboys.homeip.net

Experience varies directly with equipment ruined.