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[TowerTalk] vertical antenna ground loss

To: towertalk@contesting.com
Subject: [TowerTalk] vertical antenna ground loss
From: Dennis OConnor <ad4hk2004@yahoo.com>
Reply-to: ad4hk2004@yahoo.com
Date: Thu, 11 Dec 2008 06:58:41 -0800 (PST)
List-post: <towertalk@contesting.com">mailto:towertalk@contesting.com>
The word picture (and diagrams) of the 'missing half 'of a dipole antenna going 
down into the ground is a device to help visualization of how the induced 
ground currents act to complete the return current flow for a quarter wave 
monopole (vertical)... It is not what is actually happening in the generated EM 
field underneath the vertical...  I can assure you that a 160 meter quarter 
wave monopole does not have an image 130 feet down into the dirt and rocks,...
An elevated ground plane antenna also has radials just like a ground mounted 
vertical yet we do not see authors repeatedly claiming that there is an image 
of half a dipole forming below the radials - though some do, must be what they 
are smoking...
 
Next, the 'poor performance' of vertical antennas is grounded in the lack of 
knowledge of those making such claims...  
Lets us discuss two antennas for 40 meters... A half wave DIPOLE hung 
horizontally a quarter wave above ground - and a quarter wave MONOPOLE 
(vertical), ground mounted...  
Now, the dipole has that wonderful 4dB of reflection gain (or whatever your 
favorite fantasy dB number is) giving is something in the 6dBi range...... 
And the poor, tired vertical has a ground loss of xxx dB (pick your favorite 
fantasy dB number) and no reflection gain so it is struggling along at 1.25 dBi 
(or some such - you pick it)...
So now, Joe Ham wants to talk to his friend Bob, 175 miles away.... On the 
dipole Joe is booming in at Bob's qth, and on the vertical Bob can barely hear 
him... Yup, it just proves that verticals radiate equally poorly on all 
directions...
Later that day Joe hears a DX station on a tiny rock in the middle of that 
antarctic ocean exactly half way around the world from his shack (the 
antipode)...
He calls on the dipole... The DX goes CQ back in his face... He calls and calls 
and calls... No joy... Finally, in frustration and about to give up he 
switches to the inferior, radiates equally poorly in all directions, vertical - 
and gets an answer on his first call...
 
So, which antenna is inferior?

denny / k8do


      
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