Topband: Shortend Vertical model questions

[Phil Duff]

At 07:57 2/12/2002 -0500, Tom Rauch wrote:

>If you use a hat, use a large enough element to support the system
>mechanically. Don't worry about the common myth that making the
>vertical element thicker somehow makes a noticeable difference in
>bandwidth in hat-loaded elements. As a matter of fact, a thicker
>vertical section will actually reduce the radiation resistance in
>some cases, and reduce system efficiency!
>
>Use a big wire hat, put the coil where convenient (at ground level),

There was an article some years ago in QST I believe that gave some
efficiency numbers of top hat loaded low band verticals with different top
hat loading configurations.

I seem to recall that a couple of the examples used were with top hat 
loading that did
not droop towards ground (horizontal) and another with the top hat wires 
sloped down
towards ground typical of using the hat wires as guy wires.   The examples 
seemed to show
that sloping top hat wires were considerably less efficient than with them 
horizontal from the
top of the vertical.

My question is if sloping top hat wires truly significantly decrease top 
loaded vertical
efficiency versus non-sloped hat wires?  And how significant is the 
efficiency decrease?
Is it enough of a decrease to make it worthwhile to attempt to keep the top 
hat wires
up in a horizontal plane as much as possible?

And how does a 30-40 ft top hat loaded vertical compare to say a 70 ft 
shunt fed tower
(with beams on top for loading) in terms of efficiency if the ground 
systems were equivalent?

73 Phil NA4M



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Phil Duff NA4M     na4m@arrl.net   Georgetown, Texas