Topband: Short, Fat Vertical

[Richard (Rick) Karlquist]

> inverted L,  but I 
> also wonder if I can achieve a greater effective height by using  
> a fatter 
> radiating element, primarily using wires that are spread apart.
>  
> I've seen antennas that use a sharp V configuration or an 
> apex-down  triangle 
> to apparently achieve greater bandwidth and perhaps more 
> electrical  height.  
> I would imagine that increasing the angle of the apex would  eventually 
> create diminishing returns, as ground losses would eventually  increase.
> 
> Any thoughts here?  I was thinking of combining this fat vertical 
>  element 
> with some type of top loading wire (either an L or a T),  that 
> could also be fat 
> if that would be advantageous.  I've got a  few trees that would 
> enable me to 
> hide this structure, but I can't get too  fancy.
> 
> Any thoughts are appreciated!  Paul, K5AF

I've done a lot of modeling related to this issue and my
conclusions are that (1) you want maximum radiation resistance
to minimize ground loss (2) this is maximized by making the
antenna tall and skinny and (3) the only non-skinny thing
you should do is put on a top hat.  The top hat should not
extend below 2/3 of the antenna height if the wires slope
downward (IE using guys as top loading).  You can model
this and determine the point of maximum radiation resistance.
In conclusion, you want a lot of metal on the ground, a 
skinny wire to the top hat, and a lot of metal up top.
This is why irrigation tubing verticals are better than
verticals made from towers.  Self supporting towers are the
worst.

Making the antenna "fat" will lower the radiation resistance
and increase ground loss.  It will also lower the conductor
loss and will increase bandwidth.  However, the conductor loss
is negligible and I would rather have dB than kHz.

If you model an L vs a T, the L will show a higher radiation
resistance.  However, if you compare vertically polarized 
field strength of the L vs the T, the T wins.  This is explained
by the L warming the clouds.  However, even an L is better than
a bare vertical.

Rick N6RK