The capacity hat should only be placed at the top of the vertical element.
Placing the hat any lower on the element essentially chokes off any current
flow above the hat making the antenna electrically shorter. The amount of
choking will depend on the capacitance of the hat.
Force 12 successfully uses small "hats" that act as traps in some of their
multiband antenna designs. There was a 20/15/10 meter design a few years
back that used this technique. They now employ the same concept in the
144/440 Ruby II, VHF/UHF antenna.
'73, Thomas - AC7A - Tucson
----- Original Message -----
From: "Bill" <email@example.com>
Sent: Saturday, June 05, 2004 2:39 AM
Subject: Topband: Tophat? Does it have to be at the top?
> I would like to operate 160m using a shortened vertical. I have read
> alot about "Tophats" and
> I know what they do and why but, have never had an opportunity to put
> what I learned about them
> into practice. Now I would like to.
> My question is: Does a tophat always have to be at the top? Or could
> it be a "Collar", half way
> up the vertical and maybe called a "Scarf"?
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