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[TowerTalk] How high should my Tower be for 10-20 Meters?

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Subject: [TowerTalk] How high should my Tower be for 10-20 Meters?
From: (Bill Coleman)
Date: Thu, 26 Jul 2001 14:42:09 -0400
On 7/26/01 12:19 PM, Nathaniel Gates at wrote:

>I am considering erecting a 30' tower of either
>American (Dill) or Rohn 25G.  First, is 30' tall

That depends. If 30' is as high as you can go, so be it.

Practically speaking, 30' is just barely 1/2 wave on 20m. That is about 
as low as you want to mount a yagi, since the proximity to ground really 
starts to distort the patern. (Although there are plenty of folks who use 
40m yagis at 50 feet -- not the most optimum height, but you do what you 

>I live in Trotwood, Ohio (not far from where
>the Dayton Hamvention is held) and have been given a
>mandate by my wife... "No Guy Wires"!  To my
>understanding, Rohn 25 does not need to be guyed if
>shorter than 40'.  That's my second question.  Did I
>understand the spec correctly.  Thanks in advance for
>your responses.

According to the Rohn catalog, Rohn 25G is self-supporting to 70 mph, 
no-ice conditions, with only 1.6 square feet (projected round) of 
antenna. I'm not sure what the wind category is for Trotwood, OH, and you 
have to figure that any small tribander is going to be at least 4 square 

Another thing to consider is -- do you want to CLIMB 40 feet of unguyed 
Rohn 25? I'm just getting started with my tower, and I know I feel 
uncomfortable on top of 25' of Rohn 25 that's bracketed at 9'. 
(Hopefully, as I gain climbing experience, I'll feel more comfortable)

An alternative is to consider a bracketed tower. Put the tower base 
within a foot or two of your house or garage, and then bracket to the 
structure as high as you can manage. Rohn specs a 40 foot tower, 
bracketed at 30 and 15 feet as carrying 15.3 square feet (projected 

You can't practically go more than about 20 feet or so above the bracket 
(remember you still have to climb it...), and you'll have to reinforce 
your building structure to distribute the bracket loads. But it is just 
as good as having guy wires at the same height.

Bill Coleman, AA4LR, PP-ASEL        Mail:
Quote: "Not within a thousand years will man ever fly!"
            -- Wilbur Wright, 1901

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