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[aprssig] What a diffeence an antenna makes

Stephen H. Smith wa8lmf2 at aol.com
Mon Oct 31 20:04:13 UTC 2005


scott at opentrac.org wrote:

>> A 1/4 wave whip over a suitable ground-plane is a reasonable
>> compromise.
>
>
> Does the Pacific Ocean count as a ground plane?  In marine 
> installations, is electrical ground connected to the hull?
>

Only if the base of the 1/4-wave antenna is within inches of the water's 
surface.     A ground isn't a ground at RF (for purposes of influencing 
antenna radiation patterns) unless the connection is a tiny fraction of 
the wavelength at the frequency of interest.  The conductive salt water 
becomes a significant extension of the ground plane/counterpoise 
provided by the hull of a ship at HF where wave lengths are many 10's of 
feet or greater.  


At VHF, any conductive surface that is over a few inches away from the 
antenna base simply won't be a ground for RF purposes.   Which is why 
one creates an artificial ground plane in the form form of horizontal 
radials directly  at the base of VHF or UHF whips when they are at the 
top of a pole or tower.




Stephen H. Smith    wa8lmf (at) aol.com
EchoLink Node:      14400    [Think bottom of the 2M band]
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