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Topband: Antennas

To: <topband@contesting.com>
Subject: Topband: Antennas
From: W8JI@contesting.com (Tom Rauch)
Date: Mon, 27 Aug 2001 18:07:47 -0400
Hi Mario,

I'm nearly out of time for this, but I'd hate to see anyone sell an 
idea that has merit short.
 
> Obviously, with a radiator that's shorter than 50 ft problems get even
> more evident

While no one can dispute long hat wires near ground are a 
problem, we should not neglect comparing a vertical with a sloped 
hat to with NO HAT, to see if the hat is a help.

We are after the very best we can do, not perfection in one number.

For example, a 50 foot vertical with 4- 28 foot 45-degree angle hat 
wires has an almost identical loop radiation resistance to a 50 foot 
center loaded vertical. Before tossing the baby out with the bath 
water, it is useful to add the inductor.

When a Q=500 inductor is added the hat vertical has noticeably 
higher efficiency, very much larger bandwidth, and uses a 
convenient BASE coil location.

The center loaded vertical, even with very slightly more loop 
radiation resistance, has less bandwidth, a coil that is hard to 
reach, and less efficiency.

So we can say a 50 foot center loaded vertical has about the same 
loop radiation resistance as a 50 foot vertical with a hat that comes 
down to 30 feet all around the vertical...yet the hat vertical works 
better in every possible thing we care about even with a nearly 
impossible coil Q of 500!  With less Q the difference is 
exaggerated more!

If I can get significantly more bandwidth, much more efficiency, and 
a more convenient coil location than can use a less difficult to build 
coil, I will take all of that even if radiation resistance did not change 
enough to make others happy.

The key is always to plan a design, and not make mistakes or poor 
assumptions based on only one parameter. But the hat works so 
well, I did not even have to plan this for two minutes!

Any vertical you can build without a hat, I can build better with 
one.... even if I have to fold the hat down.
73, Tom W8JI
W8JI@contesting.com 

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