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[TowerTalk] 40 m quad arm material

Subject: [TowerTalk] 40 m quad arm material
Date: Sat, 20 Aug 2005 23:43:55 EDT
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Despite my windy QTH, I am seriously thinking of erecting a two element 
30/40M quad on a 20' boom.  The spreaders would, most likely, be in four 
8' sections tapering from 2" diameter at the spider end to 1-1/4" at the 
far end.  If I were to fabricate my own spiders from, say, 1-1/2" 
aluminum angle stock, I wonder what would be the optimum arm length to 
obtain a balance between reasonable weight and strength.  If anyone has 
any practical experience with such a beast, I would appreciate hearing 
about it.
I don't think you will get very satisfactory results using the fiberglass 
dimensions above if it is Pultrusion material.  First ending with 1-1/4" tip 
as very large,and very heavy.  Having this much weight out at the end will 
cause it to "flop" around under windy conditions with all that mass stressing 
the element wire.  You should end up with no larger then 3/4" diameter.  To cut 
weight use short sleeving pieces to reduce diameter at each joint.   Even this 
approach will result in a very heavy and floppy arm as that is the nature of 
1/8" wall pultrusion fiberglass tubling.   The best material is fiberglass 
tubes made from fiberglass material that is tape wound.  It is strong, 
"stiff" as the weight to diameter is low.

Pole vaulting poles are a good source.   Also Cubex has available 13ft 1-1/2" 
diameter poles as well as tapered 13ft extensions to make up a 26ft arm.

The spider construction using at least 1/4" wall can be made to work well.

Norman W4QN
Cubex Sales

"The Power of a Cubex Quad"

See:  for "Self Supporting Towers", "Wireless Weather 
Stations", and lot's more.  Call Toll Free, 1-800-333-9041 with any questions 
and ask for Sherman, W2FLA.

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