[TowerTalk] Tribander on a TIC ring

[Grant Saviers]

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
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