Towertalk
[Top] [All Lists]

Re: [TowerTalk] Rotator Choice for Larger Yagi

To: <john@kk9a.com>, <towertalk@contesting.com>
Subject: Re: [TowerTalk] Rotator Choice for Larger Yagi
From: "Steve Baughn" <baughn@centurylink.net>
Date: Tue, 26 Apr 2016 21:02:21 -0400
List-post: <towertalk@contesting.com">mailto:towertalk@contesting.com>
Agreed John. The one down side (I use PP's also) is the cost to have them rebuilt if necessary. Last I checked K7NV was getting in the range of $3k to rebuild them but considering the amortization over its lifespan isn't so bad which brings me to another point-back in the August 1971 edition of QST a good friend W8ZCQ (SK) wrote a pretty good article on rebuilding them. While it takes a bit of work it is not insurmountable. I rebuilt one off the article and have had no problems with it. If anyone would like a scanned copy I'd be glad to furnish it. It is nice if you can mount them where you can get to them in the event you have to replace a reed switch for the controller.

73,
Steve, WD8NPL

-----Original Message----- From: john@kk9a.com
Sent: Tuesday, April 26, 2016 7:36 PM
To: towertalk@contesting.com
Subject: Re: [TowerTalk] Rotator Choice for Larger Yagi

Square feet is not a good way to pick a rotator.  A 5' x 5' piece of sheet
metal on the mast is going to be much easier to turn than a 25 sq ft 80'
boom 20m beam.  Also many beams, including my homebrew ones are not
balanced. Some rotator manufactures use a k-factor.  Finding a rotator with
enough torque to turn a large antenna is easy, but finding one that holds up
over time is the challenge. Most ham rotators are toys. A couple of decades
ago I bought two of Hy-Gain's largest rotator - HDR-300.  Each one HDR-300
needed to be taken down for repair it every year or so. I have never seen a
sq ft rating for a prop pitch motor, but they definitely hold up well.

John KK9A


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.




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>)

_______________________________________________



_______________________________________________
TowerTalk mailing list
TowerTalk@contesting.com
http://lists.contesting.com/mailman/listinfo/towertalk
_______________________________________________



_______________________________________________
TowerTalk mailing list
TowerTalk@contesting.com
http://lists.contesting.com/mailman/listinfo/towertalk

<Prev in Thread] Current Thread [Next in Thread>