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[TowerTalk] Replacing the LL in 340N ele's with coils

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Subject: [TowerTalk] Replacing the LL in 340N ele's with coils
From: "Jim Thomson" <>
Date: Thu, 16 Dec 2010 06:52:50 -0800
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Ok, has anybody tried retrofitting the stock  3/16"  solid LL wires in a F-12  
340N  [3 el 40m yagi]  with coils ?? 
On paper, this looks fairly straight forward.  To save weight, and still keep 
the UN loaded Q of the coils high,
I was thinking of either 3/16"  or  1/4"  AL  wound coils.   Per K6STI's   coil 
software, a  typ coil  for  a 40m  yagi,
using  3/16"  AL tubing  [ all air wound]   has an UN loaded Q of aprx  767.   
IF the same  3/16" coil was made from
CU tubing, the Un loaded Q  would be aprx  1200.      If the coil was made from 
1/4"  AL  tubing, the UN loaded 
Q would still be sky high, [ > 1250]... but a lot lighter than 3/16" CU tubing. 

My concern is... where will the 40m yagi resonate on it's  aprx 3rd harmonic ?? 
  As is, stock, the F-12  340N 
does NOT resonate on 15m.  Rather it resonates at aprx  24.3 mhz.  [which 
screws up 12m].  I don't operate
10+12 that is not an issue.   However I do operate 17 +15m.   The only 
thing I can think of, is to try 
retrofitting just the DE... and install it at a reasonable height...and see if 
resonates  any where near 15m. 

The thought here is... stock, the  REF-DE-DIR  are all different tip to tip 
lengths..ranging from 51' to 53' to 59'.
IE: the resonant point on each ele is done by tweaking the tip lengths.  That 
being the case, if coils are retrofitted,
all 6 x coils would have identical uh.   The ele lengths  would still  be 

Has anybody  done a similar retrofit ?    I dunno if it would buy much..since 
the ele's  are  pretty long anyway to start with.
The stock LL consists of  aprx 52" long  x 3/16"  solid al rods.  They start at 
the solid 1"  fiberglass insulator..and then extend
OUT  towards the tips, then across 10", then back 48"   to the other side of 
the same insulator.  Any coil  would not weigh
any more than the existing  9'  of solid rod.  The replacement coils would just 
straddle the existing insulator.  It looks 
'doable'..... but has anybody 'done it' ?     If  AL coils are used, then no 
dissimilar metal problems either.   Each end of the
AL coil could be flattened, and then bolted to some thick AL bar stock, that is 
then in turn, bolted to the AL ele...with
1/4-20 SS bolts and SS nylocks. 

Tnx....... Jim   VE7RF

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