[TowerTalk] More single elevated radial

[i4jmy@iol.it]

When radials are elevated, the ground plane loses its original meaning 
and becomes a (resonant) counterpoise.
When the counterpoise is close to the ground or to other objects, it 
couples with them and the losses increase.
When the counterpoise is farther from ground, the counterpoise losses 
decrease. 
The lower angles radiation of a vertical antenna whose radiating 
portion is raised (or simply far) from ground is generally worsened . 
(the higher angles are instead enhanced)
A single radial is already an (unsymmetrical) counterpoise. (pattern is 
not omnidirectional)
Only two, but opposed radials is already a symmetrical counterpoise (if 
their current is the same).
A vertical antenna with a single elevated radial effectively behaves 
like a dipole with one of the legs parallel to ground.
If  a vertical has a canonical ground plane and a also a counterpoise, 
the result (pattern) is the combination of the two different modes 
(ground plane & low leg dipole) with the benefit, on both modes, of  an 
inherent high efficiency .
Unless ground plane radials extend much farther than the typical 
quarter wavelenght, lower angle efficiency depends by the point (angle) 
were the ground diffraction acts in reversing the phase between real 
and so called image antenna.
Efficiency at lower angles with relatively short radials depends if 
a “farther” ground that approaches a perfect screen exist or not. 
This situation is best for a ground plane antenna over (or close to) a 
media like salt water where the diffractions occur only for angles 
below 1°.
The best ground plane screen (what's below the antenna in a confined 
area) is helpful to maximize the inherent antenna efficiency, but an 
antenna only 60% (few radials) efficient when placed close to sea 
water “recovers” a consistent gain (several dBs) even if compared to a 
99% efficient vertical below the point were the latter starts to suffer 
its ground phase reversal.

73,
Mauri I4JMY






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