Topband: Re: Short Vertical...

[Tom Rauch]

Hi Roy,

> Sorry, there is no way that a 31 foot vertical on 160 M  works out
> enjoying a 50 ohm radiation resistance!! The old folded element feed
> myth for increasing radiation resistance is once again 
perpetuated here.

Exactly. It is a myth. 

The only thing in the Unihat that raises radiation resistance is the 
large hat. When hat capacitance is large compared to the 
distributed capacitance of the vertical section in a short vertical, 
current will be uniform and radiation resistance will be maximized.

Radiation resistance is about four times higher in a short vertical 
with a large hat compared to a no-hat base loaded vertical. If the 
structure size is the same, radiation resistance is exactly the 
same in a folded element as a non-folded element. Feedpoint 
impedance is the only thing that changes.

The skirt wires in the Uni-hat actually reduce radiation resistance 
slightly because they add undesired distributed capacitance below 
the top, Roy Lewallen conformed this by modeling the antenna.

The bottom line is the Unihat is well built and will work much better 
than other non-hat poor radial system short verticals, even though it 
would be better with a good radial system. K0CKD Dennis is a 
good example of how much better that antenna plays with a decent 
ground system. Ask Dennis how much louder he got after he 
added radials to his Unihat!!!

By the way, a patent doesn't mean something works as claimed. 
The patent office, long ago, quit investigating theory or confirming 
operation of an "invention".

73, Tom W8JI
w8ji@contesting.com



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