In my opinion, this is very small tubing for a full sized 40m element. My
homebrew 20m beams use 1 1/4 diameter tubing tapered to 1/2 tips. I suggest
that you start by looking at the element taper schedules in the ARRL antenna
handbook.
John KK9A
To: towertalk@contesting.com
From: terry burge <ki7m@comcast.net>
Date: Tue, 14 Aug 2018 13:11:18 -0700 (PDT)
Hi Jim and group,
Hell of a way to wake up in the morning. Anyway, here are the dimensions.
DX Engineering aluminum tubing all 0.058" wall thickness
1.250" X 6'
1.125" X 6'
1.00" X 6' Spit on the end allowing adjustment with 1/2 - 1 1/4" SS Hose
clamp
0.875" X 6'
0.750" X 3'
0.625" X 3'
0.500" X 6'
Truss 1" X 1" X 0.125" X 3' aluminum angle 'iron' from Lowes. Holes drilled
to
also add a muffler clamp on the vertical truss if necessary to the mast.
Center 'boom to mast' insulating clamp from SSS Solutions for 1.25" element.
A
little small but I figure it will work for my purposes with the trussing.
Comtek 1:1 Current Balun at feed point.
Because of Jim's thoughts about horizontal wind load I will also add another
horizontal truss like I did with my quad array of something like 6' long
aluminum angle 'iron' with 3/16" Dacron truss lines. Hope this won't cause
too
much difficulty reaching the adjustment positions at the 1" to 0.875" slip
joint when rotating the vertical. Will do initial resonance dipping in on
test
support lower to the ground to get the SWR near where I need it around 7150
Khz. Not sure how much of a difference this will be at 124' versus my Comtek
4-Square ground mounted. Interesting experiment but since I have always felt
lacking on 40 meters with 'knowing' I could work more stations in contest on
40
meters with a better antenna system.
I have not modeled this in Nec2 or whatever. Window 10 raises it's ugly head
preventing that from operating. I know there are ways to deal with it but
I'm
not even sure the ARRL Antenna Book disk will run on my windows. And
programming computers is not one of my great accomplishments to say the
least!
I have found when I build something like this I learn more in the building
and
seeing just how big and how much of a load things will be. Might say I try
to
go by feel and try to 'over built' to handle stresses like wind load. Not
always of course but I do think this will work here in Oregon.
Terry
KI7M
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