[TowerTalk] Guy wire interaction - the devil is in the details

[Tom Rauch]

Hi Terry,

> validity of modeling, it is certainly true that having an insulator right
> under the antenna at the top of the tower results in a high-impedance
> point probing a location with maximum RF - thus tending to maximize any
> potential problems whereas with connected guy wires there will tend to be
> at least partial cancellation of the fields caused by the three guy wires
> and the tower.   

If I understand what you are saying, it is not true.

There is no "impedance match" between a high-Z
end in an area dominated by the antenna's current. A high-Z probe 
is actually less likely to sap energy from the antenna than a low Z 
probe, under nearly any coupling condition.

As an example, what do you suppose would couple energy from an 
antenna end more and detune an antenna more... a garbage can 
six inches from the element tip or a pop can?

Same thing with end-to-end dipoles, or end-to- center dipoles. A lot 
of capacitance means more coupling....not less. 

The problem is very complex in the near field. It is certainly one of 
resonance as well as the way the electric and magnetic fields 
interact with the antenna. 

One thing for certain, continuing the guyline to the tower past the 
antenna would most likely make things a lot worse. In that case, 
for an equal resonant condition, the guylines would couple tighter 
to the element because they would be nearly parallel to the 
element. If the guylines are symmetrical in length and resonant, 
the tower would have little effect on coupling.

You also add another can of worms. The tower AND guyline can be 
resonant, a bit like an inverted L. 

Grounding the guylines to the tower is a bad idea.

73, Tom W8JI
w8ji@contesting.com

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