[TowerTalk] Force 12 loading coils

[Jim Thomson]

Date: Sun, 3 Jan 2016 10:23:43 -0800
From: Robert Harmon <k6uj at pacbell.net>
To: towertalk at contesting.com
Subject: [TowerTalk] Force 12 loading coils


I found this interesting article (below) on the evolution of Force 12's 
current Tornado loading coil design from
the beginning with the Tom Schiller, N6BT original design to their final 
Tornado version.   I put this post on the EHAM antenna reflector but no 
interest yet.
I was surprised that in the last part of the article they say that they 
wont disclose the Q of their new Tornado coil.  Huh ???
Reading thru the article it indicates they went away from Tom's original 
design to a smaller dia, smaller inductor,
loading coil design, and now they have gone to their new Tornado design 
which looks very similar to Tom's
original design. hmmmmmmmm
I have surmised from this that they developed a piece of #### loading 
coil, then went back to a slight variation,
original design, higher Q, more efficient coil they named Tornado. It 
bugs me that they wont divulge the Q,
my guess is that they dont want us to  compare the Q's of the loading 
coil evolution from Tom's original design
to the current Tornado.  I think we know why they dont want us to 
compare  :-)
Anyway I am trying to figure out the Q of the different coils.

here is the article:

http://www.force12inc.com/content/Application%20Note%20-%2040m%20Delta%20Coils%20Overview%20DRAFT%202.pdf



73,
Bob
K6UJ

##  If u look at F12s  application notes in ur above  url..... they still havent done it right with their new seco coils.   They used
1/4 inch al tubing, but with a whopping 3/8 inch spacing between turns.   Whats  required is just  1/4 inch spacing between turns.

##  end result with the excess spacing between  turns is the uh of the coil  will drop like a rock.   Hence the tips  on the 40m eles  have to be 
a mile longer than the oem tips, when the new coils  are retrofitted.   The new  ( exposed portion) tips  are between  51-70 inchs long, which 
is  absurd for 3/8”  tubing..     70 inch long tips,  using .375  diam tubing tips, even if  .058 inch wall material used  is fubar.  A 6 foot length
of 3/8” od tubing is only 72 inches long, and you need at least a 3 inch overlap. 

##  what they shoulda done was used .25 inch spacing between turns, that alone would have increased the uh  by a bunch, and tips  would end 
up being the same as oem.  The coil assy would also be shorter.   If they insist on using 3/8 inch spacing, then the number of turns in each coil
has to be increased. 

##  ken at jk ants  used  1/4 inch solid  al, and wound the 40m coils on a  fixture in the lathe.  Then welded each end to the al  stand off support.
With solid 1/4 material, the coil assy is rigid as heck, and the delrin spacers are not required.   I cant weld al rod, so opted to use my  1/4-20
or  1/4-28  SS bolts.   3/8 inch OD tubing, either  al or cu, when end flattened,  will handle a 1/4-20 easily.  If 1/4 inch tubing used,  a 10-32
is about the biggest  SS  screw you can get to fit the flattened 1/4 inch tubing. 

## al tubing, that comes in 15-25-50 foot rolls is usually made from 3003-t0 alloy, which is really soft material, and easy to wind.  f12 used it
to make the hairpins  for its yagi ants. The problem with that alloy is its  too soft for hairpin use, esp when snow or birds land on it, it bends
easily.   I had to support my hairpins with 3 ty raps between far end of hairpin..and the boom.... to prevent sagging. 

##  Cu tubing, also in 15-25-50 foot rolls, is easy to form into a coil, albeit, its one helluva lot more rigid.   I silver plated mine with the cool-amp glop..1st,
then wound each coil.   Coil placement is yet another issue.  If the coil is placed  half way out each side, its uh has to be aprx double, vs the coil being at the boom.
A good compromise is aprx  1/4 way out on each side.   Then the coils don’t have to be huge.   F12 placed the oem LL rod insulator  7 ft 9 inch out from the
boom on their 340N  style els.   The els on the 340N  range from 52 to 59 foot long.  If the oem LL rods are replaced with coils located in the same place as 
the oem LL insulator, the uh of each coil is real small, like 2.8 uh.   That’s like  7 turns on a 4 inch ID, with a length of aprx 5 inchs....using 3/8 inch tubing. 
Still. each ele  has to have its tips tweaked to resonate on the same freqs  as the oem LL rods..which is no big deal.   I replaced the 3/8 inch  x .035 wall tips,
with new 3/8 inch  x .058 wall material.  The tips on the 340N director are only just a few inchs long, so the coils on the dir are a hair on the small side, so new
tips are a hair longer than oem.    Opposite for the 340N  REF.   Coils are a hair bigger, and tips are  a hair shorter. 

##  other material that could be used for coils is  ribbon stock, like used on roller coils in amplifiers and tuners.   3/8 inch x .072  ribbon is the same as using 
1/4 inch od tubing.  But ribbon does require spacers to maintain turn to turn spacing.   Usually stuff like micarta etc is notched   for each turn.  The ribbon
format would make for the most compact coil assy.... as far as length of coil assy.   It would probably be cost prohibitive for coils on a yagi..but doable. 
You can also get ribbon in  1/4 inch  and also  1/2 inch..and from aprx .072 thcik..to  .125 thick. 

##  VE6WZ made his own  1/4 inch hb cu tubing coils for his 80m yagi.   Ditto with his  3/16  al  tubing coils for his 40m yagi. 

Jim   VE7RF