Date: Thu, 2 Nov 2017 07:08:44 -0400
From: "john@kk9a.com" <john@kk9a.com>
To: towertalk@contesting.com
Cc: andresskurt@gmail.com
Subject: Re: [TowerTalk] Subject: Wind survival + load ratings... vs,
<I own several smaller 40m OptiBeam antennas which have held up fine and
from an RF viewpoint they are fantastic however I have heard the horror
stories about their 80m beams from other tower installers. OptiBeam also
makes a massive full sized 4el 40m which may have the same issues. I asked
Tom once what aluminum he uses and I seem recall a non specific answer
like aircraft aluminum or something like that. It is interesting that high
strength tubing may not be available in EU. Also metric tubing does not
telescope nicely, I wonder how that effects the strength of the joint.
Imperial sized tubing with a .058 wall fits together perfectly making it
easy to homebrew. For my homebrew antennas I only use 6061-t6, I see most
ham suppliers sell 6063-t8. What is the difference?
John KK9A
## 6063-T832 is 39 ksi yield strength. Done in an air bath. Comes out
shiny. Cheap to buy
## 6061-T6 is 40 ksi yield strength. Oil quenched, done in an oil bath.
Cost between double and triple, vs 6063-T832..at least in small sizes.
In bigger sizes, like 2 inch OD and bigger..and with the bigger wall
thickness, like .125 or .120, there is hardly any difference in price.
## You can now buy 6061-T8 ( T8 not T6) for boom material. Its .120
wall vs the .125 wall u get with 6061-T6. .120 wall is superb, since it
telescopes nicely into the next sized tubing. DX eng sells it, as does
others. Like 1.5 1.75 2.0 2.25 2.50 2.75 3.00
## problem with .125 wall stuff, is u have to turn it down by .05 inches in a
lathe....which is a pita for us back yard folks.
# f12 used a lot of .049 wall stuff on their yagis...which makes for a sloppy
fit. So they do a very light swedge where eles join. another pita for us
back yard folks..if u dont have a swedging tool.
.375 OD tubing comes in .027 wall, and also .035, .049 and .058 wall
.5 od and up will typ come in .049, .058, .065 and also .083 wall. F12 used
a lot of .083 wall in their yagis, like 40m arrays etc, but that too requires
swedging.
## I heard that european tubing and esp optibeam al was as little as 25 ksi
when they 1st started out.... then swapped to stronger al. I cant even fathom
using 23 to 25 ksi yield tubing for anything.
My biggest complaint with eu tubing is its metric...pita. Non standard wall
thickness mean non of it telescopes, so it all has to be swedged. Try finding
metric tubing in the usa or canada.... near unobtainium.
A buddy finally did find a supplier in the usa that carried metric tubing.
## real aircraft tubing is stuff like 2024..which is typ heat treated to
aprx 44 ksi. 2024 has a lot of copper in it....and cant be welded afaik.
7075 al tubing is stupid strong, like 70 ksi... but is cost prohibitive for ham
applications.
Local buddy obtained a bunch of scrap 2024 at the local airport. used it for
15M eles....and they all bent. Turns out what he got was 2024- T0...which is
really soft. When they build ribs and stuff for small aircraft, they are
formed in
jigs, etc. Then sent off to be heat treated... which is a max of T3 for
2024. Ok, then its strong. So much for dumpster diving.
## small tubing, like .375 up to 2 inch od.... in 6061-T6 is now priced
into the stratosphere. F12 and tenedyne both used it. Everybody else uses
6063-T832, including Mosely, m2, old kln, jk ants etc.
## One 2 el 80m optibeam just south of me. ssb + cw switch box was a gong
show, design defect..... later fixed. Then the wrap around square boom to ele
clamp assy disintegrated. The els were dangling below the boom,
left hanging only by the overhead ele truss lines ! It all got sorted out in
the end.... just more crane trips and more $$.
Jim VE7RF
_______________________________________________
_______________________________________________
TowerTalk mailing list
TowerTalk@contesting.com
http://lists.contesting.com/mailman/listinfo/towertalk
|