Topband: Feeding a vertical

[Tom W8JI]

> I have a hypoth--er hipoth--oh, alright, a theory, question for all. Take 
> a grounded, 1/4 wave vertical (pick your band/freq of interest) made of 
> tower sections. You're going to feed it with a gamma match. Could the 
> gamma match rod go on the inside of the tower sections for protection?? 
> And, yes, I know, you could insulate the tower from ground and series feed 
> it. BUT, after all this is a hypoth....er hipoth....theory question.
>

Jake,

If the tower was a solid cylinder, you would be feeding it on the inside. 
The walls would isolate the current inside from the outside; it would not 
radiate any practical amount at all. It would be just like loading putting a 
pin through a piece of coax to short the center to the shield inside the 
cable and thinking we were gamma matching the outside of the coax shield.

Since the tower is a less-than-perfect cylinder (or coaxial line), the 
system would radiate some small amount when gamma matched on the inside. The 
amount of outside current would depend on how imperfectly it behaved as a 
cage or cylinder.

I remember taking the time to learn why this happened when I tried to use 
the fall arrest safety line of a large tower (it had a ladder on the inside) 
as a way to shunt feed the tower. It was the deadest 350-foot tall antenna 
imaginable!!

Also, some engineer at Phelps Dodge suggested I mount a repeater antenna 
inside a wide face tower, to get a nearly omni pattern. I took his advice. 
You can imagine how well that worked out!!

73 Tom