[TowerTalk] Rotator Placement Question

[Madison Jones]

Dunno about your R25 pointy, but I now know (after pulling the mast, rotor
and plate from the bottom of the section, with attendant effort last
Saturday) that my Ham IV won't fit in the opening just below the pointy.  At
least I was no longer faced with your dilemma.

Regards,

Madison
w5mj
----- Original Message -----
From: "Bill Coleman AA4LR" <aa4lr@radio.org>
To: <towertalk@contesting.com>
Sent: Wednesday, October 04, 2000 12:40 PM
Subject: [TowerTalk] Rotator Placement Question


>
>
> I'm in the process of putting up a bracketed Rohn 25 tower of 45 feet,
> with the bracket at 26 feet. I have a 25AG3 top (the pointy top), which
> permits me to place the rotator either near the top of the top section,
> or I can put it at the base of the top section.
>
> I wonder about the tradeoff:
>
> 1) At the top, this allows a much shorter mast, which presents less wind
> loading. However, the antenna torque is applied only a couple of feet
> from the top of the tower. With a bracketed design, this torque will
> cause twisting of the top two sections. (In a guyed design, the torque
> would be transferred to the top guys)
>
> 2) At the bottom of the top section, the mast is longer, so it presents a
> larger wind load. But the torque from the antenna will be applied 9 feet
> down from the top, which has better rigidity, since the top section won't
> twist at all.
>
> Which is better? Rotator at the top, or bottom?
>
> In this installation, the antenna is just a simple A3S, perhaps with a
> 40m kit. Cushcraft rates this antenna at 5 square feet (flat plate
> equivalent). My calculations indicate this installation should withstand
> 75 MPH winds with a safety margin of 75%.
>
> Bill Coleman, AA4LR, PP-ASEL        Mail: aa4lr@radio.org
> Quote: "Boot, you transistorized tormentor! Boot!"
>             -- Archibald Asparagus, VeggieTales
>
>
> --
> FAQ on WWW:               http://www.contesting.com/FAQ/towertalk
> Submissions:              towertalk@contesting.com
> Administrative requests:  towertalk-REQUEST@contesting.com
> Problems:                 owner-towertalk@contesting.com
>
>


--
FAQ on WWW:               http://www.contesting.com/FAQ/towertalk
Submissions:              towertalk@contesting.com
Administrative requests:  towertalk-REQUEST@contesting.com
Problems:                 owner-towertalk@contesting.com