[Antennas] Tower Installation

Thu Oct 1 14:21:20 EDT 2009

An inverted V with 90 degree apex angle is still a dipole ! And it is mostly
horizontally polarized. The bending down of the legs just affects radiation
elevation (with respect to the horizon) and makes it more omnidirectional.
The impedance is also lowered.
Given that the construction is symmetrical,- also with respect to the ground
below, it is also a balanced dipole-
The elevated radial "hype" is at best a misunderstanding,- very widespread 
in
the amateur community. It is based on computations using early NEC code.
The results showed that the NEAR FIELD was equal to 120 buried 1/4 radials
at a given distance and in the same height as the antenna feedpoint.
It says nothing about the far field that we always almost use.
Remember then that the wave is attenuated far more very close to the ground 
than
it is at say 10 feet above. The model used this height if I remember right. 
Broadcast
AM stations designed to cover local areas focus on covering the area with a 
direct wave
rather than an ionospheric wave...meaning that even if the elevated system 
seems to
perform very well for local AM broadcast,- it may not be that efficient for 
refracted
(ionospheric) waves. When all that is said: If you can not lay out 120 
buried radials..
by all means, go for the elevated system. It works fairly OK. And it is 
physically and
electrically UNBALANCED.
But if you chose to go elevated, then do it properly. The original article 
described a
system using four RESONANT radials in a perfect square. It also assumed that 
the ground below
the system was 100% uniform over the antenna's area, and well beyond. AND a 
current choke
near the feedpoint is mandatory. The coax also had to be run away below the 
penetration depth
of the specific ground under the system, at the TX frequency.
Sorry to kill one of todays most popular ham myths :-(
But the elevated system is still very useful if constructed properly :-)
Peter
----- Original Message ----- 
From: "Joe" <nss at mwt.net>
To: "Chris Boone" <Cboone at earthlink.net>
Cc: <antennas at mailman.qth.net>
Sent: Thursday, October 01, 2009 7:23 PM
Subject: Re: [Antennas] Tower Installation
>>>>>> Then what is an inverted VEE with a 90 degree apex angle. balanced or
> un balanced? It's a vertical with one radial elevated above ground and
> semi up side down,
>>>> the 120 is to try to remove the ground losses, it has nothing to do with
> the antenna itself, the exact same antenna if it was raised so that the
> radials were like 10 to 20 feet above the ground, it would be just as
> effective or even better than the 120 radial version but with only 4
> radials.
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