[Elecraft] OT: Vertical antenna ground systems

[George Badger]

Al
The worst length for a raised radial is a resonant quarter wave. Two together form a half wavelength. The problem is that the ground on one side of the "dipole" is not exactly the same as the ground on the other side so the "dipole" has a life of it's own and becomes a slightly off-center driven resonant dipole.
It will radiate some of your energy because of it's stored energy. Energy will be wasted because it will be radiated so close to ground.
 The radials should be shorter or longer than a quarter wave so they do not form resonant dipoles. Bring the overall antenna system to resonance by adjusting the length of the monopole or adding appropriate reactance.
This is very well covered by Moxon [SK] in his book 'HF Antennas For All Locations' and elsewhere in the amateur press.
73
Good luck on your project.
George Badger                     W6TC


----- Original Message ----
From: Alan Bloom <n1al at cds1.net>
To: Ken Kopp <k0pp at rfwave.net>
Cc: elecraft at mailman.qth.net
Sent: Wednesday, November 5, 2008 8:47:39 AM
Subject: Re: [Elecraft] OT: Vertical antenna ground systems

N6LF has done some wonderful experimental work on vertical antennas.

He found that a radial laid on the ground experiences a velocity factor
similar to coax cable.  A quarter wavelength is only about 60% of its
free space value.  If you make the radials a physical quarter wavelength
long, they are actually closer to a half-wave electrical length
(anti-resonant).

With 4 radials he actually got about a 3 dB improvement by making them
SHORTER!

For my next vertical I will definitely plan to tune the radials.  I
think I'll try laying out a 1/2-wave dipole on the ground and then trim
it to resonance.  Then cut all the radials to equal the length of one
half of the dipole.

Al N1AL


On Tue, 2008-11-04 at 19:10, Ken Kopp wrote:
> Of potential interest to those who use verticals with their Elecraft 
> rigs.
> 
>          http://www.antennasbyn6lf.com/
> 
> 
> 73!  Ken Kopp - K0PP
>      ElecraftCovers at rfwave.net 
> 
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