[TowerTalk] 40m BEAM BOOM

[donovanf at starpower.net]

Dave,

Why wouldn't you use the entire 47 foot boom?  Guy attachments five feet from each end of the boom will work well with your heavy 0.25 inch wall boom.

It sounds like you're planning on full sized 40 meter elements, they will be about 75 feet long with your severe taper.  Irrigation tubing only has only 0.040 inch wall, I expect it to fail in the first strong breeze.

Its surprising that you plan to use such a strong boom, an excellent choice for this large antennam, but you plan unreasonably thin wall elements that would be marginal even for a 20 meter Yagi.

My full size 3L 40M Yagis have been installed for nearly 40 years.  They've been beefed up a few times, mainly because of severe ice loads on the 200 foot towers at this QTH.   My 40 meter elements are 2 inch o.d. x 0.25 inch wall at the center, more than six times stronger than irrigation tubing.

73
Frank
W3LPL


---- Original message ----
>Date: Sat, 25 Apr 2009 17:39:15 -0400
>From: "WA3GIN" <wa3gin at comcast.net>  
>Subject: [TowerTalk] 40m BEAM BOOM  
>To: <TOWERTALK at contesting.com>
>
>
>Hi folks,
>
>This year we got the garden done early and I'm having time to work on the 3 ele 40m beam project.
>
>Today I assembled a boom that is about 47ft long. The boom material is .250" wall 3" OD.  
>
>The plan calls for a 41ft boom with the equal spaced elements spaced 21ft from the driven elelment.
>
>The question is how far from the mast should the truss cable be iconnected to the boom; half way between the mast and element, about 10ft; from the mast to the element 21ft?
>
>The elemlents are 2" OD irrigation tubing the first 20ft either side of the boom, then 1.250" OD swagged down to .250" (old 204BA 20 m elements with homebrew donuts to couple to the 2"OD tubing. The element will be guyed at the donut coupling point. or 20ft down the element.
>
>I was planning to have the beam mount just above the thrust bearing with about 10ft of mast extending beyond the boom. I presume the higher up the mast the guy point is installed the better.
>
>Thoughts are welcome and very much appreciated.  Feel free to answer direct.
>
>73,
>dave
>wa3gin
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