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Re: [TowerTalk] Rotator Choice for Larger Yagi

To: towertalk@contesting.com
Subject: Re: [TowerTalk] Rotator Choice for Larger Yagi
From: jimlux <jimlux@earthlink.net>
Date: Tue, 26 Apr 2016 12:13:38 -0700
List-post: <towertalk@contesting.com">mailto:towertalk@contesting.com>
On 4/26/16 11:46 AM, Máximo EA1DDO_HK1H wrote:
PST-61D has 39sqft.




The one thing that still concerns me about the Orion, however, is that it's
only rated to 35 sqft. The OB17-4 is 27 sqft, so there's not a lot of
margin there.




It's not clear to me what a "square foot" rating for a rotator would be.. Inertia loads would be in some sort of mass *length^2.

Square foot would be for wind drag forces: Unless you're talking about the "side" (radial) load on the bearings (which depends a LOT on the mast length and whether there's other bearings or mounting points.

But for "turning in the wind", you'd need to know an area and a radius from the axis of rotation to turn that into a torque (e.g. will it overpower the brake or rip the teeth off the gears).


Maybe they're using "square feet" as a shorthand for "size of antenna and polar moment of inertia". Square feet cross section is given for most antennas, polar moment is not. Since most antennas are fairly similar in construction, knowing cross sectional area (square feet) probably correlates well with overall size and mass.

(unless you use solid steel bar as your boom, and silver plated steel bars for the elements. <grin>)



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