Towertalk
[Top] [All Lists]

Re: [TowerTalk] Tribander on a TIC ring

To: Herb Krumich <wa2fgk@yahoo.com>, "towertalk@contesting.com" <towertalk@contesting.com>
Subject: Re: [TowerTalk] Tribander on a TIC ring
From: Grant Saviers <grants2@pacbell.net>
Date: Mon, 13 Feb 2017 20:21:02 -0800
List-post: <towertalk@contesting.com">mailto:towertalk@contesting.com>
The need for static weight balance of a boom always has seemed a bit suspect to me if the boom to mast plate is well designed. I removed the weights inside some custom very large yagis (48' x 3" booms) when they were installed on K0XG rings. These rings have a V shaped mounting system with about the same length as the 24" TIC length. The K0XG rings are totally bearing constrained and will operate with reasonable unbalance.

My arguments against adding mass at the end of a boom: 1. makes the antenna heavier, 2. increases the moment of rotational inertia, thus increasing the load on the rotator, 3. increases the chance that the two cantilevered boom sides have the same resonant frequency, 4. increases the stress on the boom making it more susceptible to ice loading failure.

Leeson doesn't mention weighting for static balance (at least in the index or IIRC) in Physical Design of Yagi Antennas and he does cover boom designs for antennas with asymmetrical booms.

I'd like to hear why boom weights are a good idea, except for when an antenna is trammed up, then it is very helpful on single cable tram carriages. If there is enough headroom for two slings then that need goes away. A crane with two slings doesn't need a balanced boom. Likewise if a boom lift is used.

For an A4S the center element is pretty close to center of the boom. So I think the A4S will be off center mounted in the plate. I'd recommend boom guys and if they are a bit unequal I don't think there is much downside. Having two A4S, I suggest you make some reinforcements of the boom and element clamps. See the thread http://lists.contesting.com/archives//html/Towertalk/2016-10/msg00064.html

Grant KZ1W


On 2/13/2017 17:52 PM, Herb Krumich via TowerTalk wrote:
Has anyone put a tribander on a TIC ring ?
I'm thinking in the lines of a Cushcraft A4S.  The mounting plate on the TIC is 
24 inches long.
Someone mentioned a three element and offsetting the center, and adding weight 
to the one endI would rather not do that.Any thoughtsThanks Herb K2LNS
_______________________________________________



_______________________________________________
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>