[TowerTalk] antenna material

[Jim Thomson]

Date: Tue, 9 Feb 2016 09:38:16 -0500
From: "john at kk9a.com" <john at kk9a.com>
To: towertalk at contesting.com
Subject: Re: [TowerTalk] antenna material

I use 6061-T6 for everything however 6063-T8 may be similar and DX
Engineering sells this with a .120 wall for easier telescoping.

The ARRL antenna book also has element taper scheduled for various wind
speeds.  I have been using their 120MPH element designs for years.

John KK9A

##  Both  6061-T6  and also  6063-T832  both are 40 ksi yield strength.
Section modulus X yield strength =  bending moment..which is all you care about. 

##  Dx eng sells the larger diam Al  in .120 wall...which is   6061-T8   ( not T6).
This stuff is slick, since it has a .120 wall.....and the pieces just slide together.... no 
more requirement to machine the ends in a lathe etc...pita.  Steel  tubing has been 
available in .120 wall for years now.... dunno why it took so long to do the same 
with al tubing.    

##  EG:   1.75 inch OD x .120 wall  will slide  right into  2.0 inch OD  x .120 wall.
1.5 inch OD  x .120 wall, will slide right into 1.75 OD.   1.25 will slide right into
1.5 etc, etc. 

##  IF  building a full size 40m eles,  reduce the tips right down to .0375 inch OD.   ( .058 wall  material).

##  ON4UN  ‘forgot’  to tell you his 3 el 40m yagi weighs  350 kg =   770 lbs. 
He also forgot to tell you he spliced the inner sections of the ele halves with a 9 ft long
piece of chromolly steel tubing.   No wonder the damned thing is so heavy. 

##  2 inch OD  is way too small a diam for the center section of a  full size 40m yagi... well maybe not.
Splice the inner 2 inch OD sections with an internal sleeve made from 1.75 OD.   Then the 
inner  12 ft  would be .240 inch thick.   IE:  use  2 x 12 ft sections of  2.0 OD  x .120 wall...and splice
em together   with a 12 ft section of  1.75 x .120 wall.   Then start tapering down from there.  

##  If u design it right, you wont require swedges, machined inserts, etc. 

##  id use channel aluminum to make each  ele to boom bracket.  The wide portion of the channel is called
the ...web.    The web is typ available in both .181 thick..and also .281  thick.  The short vert sides on the channel
are typ .25 inch thick. 

##  IMO, Id  use al rivets  for the ele construction...using .125 diam for the outer sections...and .187 and also 
.250 diam rivets for the heavy wall inner  sections.   Use  SS  bolts and SS nylocks  for the inner most splices. 

##  design it using software..for the mech portion.  Then you will know  exactly what wind speed it will be good for,
with or with out ice.   Then also factor in sag...and design any truss  for each ele at the same time.  Done right,
you can chop a lot of weight out of each ele...and still end up with a robust ele that will survive. 

Jim   VE7RF

Ji