Topband: Shortend Vertical model questions

[Tom Rauch]

> couple of questions. I've noticed if I have the loading coil at the
> base the current goes to zero at the top like a full size vertical
> model. If I move the loading coil to near the top of the vertical the
> current shows it stays at maximum for the full length. It also seems
> to take more inductance to resonate the vertical if I place it at the
> top. Is this normal or an effect of EZNEC ? The Radiation resistance

You ALWAYS want to use some sort of "hat" at the top of a 
vertical. If you make the capacitance of the hat large compared to 
the distributed capacitance in the vertical, the current will be 
uniform no matter where you locate the inductor. 

Bandwidth will be greater, efficiency higher, and feedpoint 
resistance higher with a hat.  

> is around 15 ohms and the 2 to 1 bandwidth is about 20khz. Anyone have
> a suggestion for broadening it out abit short of making it taller. The
> tophat is already 10 feet in diameter, so I don't think I can deal
> structurally with much more than that

If you have a ten foot diameter hat, the current can't possibly be 
going to zero at the top. Check the model again! That still is a 
small hat, and you might want to consider using the guy wires as a 
form of a hat.
73, Tom W8JI
W8JI@contesting.com