Topband: How much ground independence?

[Tom W8JI]

> On 80 meters wonder if you, at low TX power, have checked the RF at the 
> end of your radials with a field strength meters ?
>
> Do you have a perimeter wire around the ends of you radials ?
>

Fellows,

This is a complex issue. Despite what we hear or imagine an antenna or 
ground does, there actually isn't an antenna in the world that is really 
ground independent in the true literal meaning of those words.

"Ground independent" is most commonly used to mean the antenna does not need 
an earth terminal. That does not mean it is insensitive to ground, earth, or 
ignores things we might call grounds.

There are occasions where "ground independent" is used to mean an antenna or 
counterpoise not being influenced by earth or coupled to earth, but that 
pretty much is always "quack science" unless the antenna is many wavelengths 
above earth.

Fields are mathematical or theoretical descriptions of force on charges by 
other charges. There are three fields, electric, magnetic, and 
electromagnetic. If we use a field strength meter in an attempt to quantify 
intensities in the near field, the measurement is critically dependent on 
the type (field impedance) of the FS meter. If you have a little probe with 
a detector, it primarily sniffs out the electric field. If it is a closed 
loop, it sniffs out the magnetic field.

An antenna always responds to both fields, although it responds as a ratio. 
If you really took either the magnetic or electric field to zero, the 
antenna would go stone dead. An antenna always has a certain "field 
impedance", because it always has both electric and magnetic fields in some 
proportion. Of course radiation always has a certain proportion of electric 
to magnetic field that is never extreme, and depends on the media the wave 
propagates through. This all means we can measure close to an antenna or 
instrument with something we call a field strength meter until we are blue 
in the face, and we almost always wind up with no idea what the measurement 
means in relationship to coupling between two things, like an antenna and a 
radial. It pretty much is a waste of time.

The way we can measure coupling is to actually measure coupling. Then we are 
actually measuring the effects we want to know, and not looking at a small 
part of a big picture and not knowing what it really means.

Interactions here at my house with my antennas in the near field means 
nothing to anyone else, unless we have the very same installations with all 
the same spacings and even the same surroundings.

Not understanding this is generally behind why some antennas make promises 
impossible to keep as a blanket statement or guideline. Someone reads 
something, thinks it applies to every case or to most cases, when it only 
applies to a specific case.

I can't think of a single receiving antenna that can be placed within a few 
wavelengths of other structures or systems and be guaranteed to not 
interact, let alone interact with something .05 wavelengths away. Small 
closed loops, including flags and pennants, are "ground independent" in the 
sense of not requiring a ground connection to function, but in order to be 
"ground independent" in the sense of not coupling to earth, nearby radials, 
things 1 wavelength away, and on, they would also have to not radiate 
(receive). If it receives, it will receive from the mess of things all 
around it from the dirt below it to the wires down the road.

The only way we know is to actually build it, or put it out by itself a long 
distance from anything else.

73 Tom