Date: Sun, 3 Jan 2016 10:23:43 -0800
From: Robert Harmon <k6uj@pacbell.net>
To: towertalk@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
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