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[TowerTalk] Can capacity hats be installed inboard of a coil or LL ??

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Subject: [TowerTalk] Can capacity hats be installed inboard of a coil or LL ??
From: "Jim Thomson" <>
Date: Sun, 5 Dec 2010 06:51:11 -0800
List-post: <">>
I have a an ongoing project with my F-12 EF-180B.    [68' long 80m  rotary 

I scrapped the stock LL wires.   I added a 17.5' long ....'T-bar' [capacity 
hat]  15'  out on either side of the feed-point.
This is similar to the newer F-12  sigma 180-S  loading scheme.
The stock 1" solid fiberglass  insulator's   are about  2.5'   past [out board] 
 of the  the  new T bars.
The stock 1" insulator's  will  have to  have a shorting strap  placed across 
each of them.

Then it occurred to me that either an AL coil  could be placed across those 1" 
solid insulator's...OR
the LL scheme as used in the F-12 40M  'N'  style  eles  could also be used at 
those points. 

I have a F-12  3-el  40m yagi already  [340N]..and that loading scheme F-12 
uses, would be real easy to
add to the 80m rotary dipole.   That would effectively add another 8'  to 9'   
to each end.

The pair of T bar  capacity hats should add another 8.75'  to each end.  Total 
effective length should
be aprx 101.5'     OK, the trick is, the T bar capacity hats  would be INBOARD 
of the LL scheme. 
Even if large diam AL tubing coils were used instead of the N style loading 
scheme, the T bar
capacity hats would still  be inboard of the coils. [ by 30"]

Now will my proposed scheme work?   The F-12  40m 'N'  loading scheme uses  
3/16"  solid AL rod.
The rod starts  on the inboard side of the insulator..and goes OUT, towards the 
ele tips,   for about
5-6', then does a 90 deg angle..for about 10-12", then comes back on itself, 
terminating on the outboard
side of the same insulator.   IE: the LL  heads towards the ele tips..and NOT 
towards the  feedpoint, like 
the original 12 ga alumoweld wires  did. 

Part of the plan is to use the Tornado drive [made by seco systems] at the 
feedpoint to do the balance of the
loading.   The tornado drive is just a pair of motor driven  compressible  
coils inside a 5"  diam pvc tube. They
use  1/4" cu  or al  tubing coils, and they can be made in any size.

The new F-12 sigma  180-S  80m rotary dipole is  54'  long...and also uses a 
pair of 18'  long T bar  capacity hats,
[albeit, they are 18' on either side of the feedpoint, vs my 15'  on either 
side of the feedpoint].   When the sigma
180-S  is used in conjunction with the model 80-D tornado drive, the swr is 
flat from 3190 khz  to  4090 khz  [ 900 khz wide]

The idea with my conversion proposal is  to minimize the required uh  for the 
pair of coils inside the tornado drive. IE:
do as much loading out on the ele, and the least at the feedpoint.   That 
should  increase the feedpoint Z.
With less coil being used at the feedpoint, the peak V  drop across each coil 
at the feedpoint  would be way less. 
Also, with a higher feedpoint Z, the RF current through the pair of coils  
inside the tornado drive  would be way less. 

The stock F-12  180-B  80m rotary dipole used aprx 44'  of  12 ga  AL wire  on 
each ele  half....and  feedpoint Z  was 18 ohms. 
On paper, after the conversion, the feedpoint Z  should be aprx 30 ohms. 

I was going to just add the 17.5'  T bars, one per side... and add the 
compressible motor driven coils..and call it a day. But
after looking at it closer, extra loading, 18'  on either side of the 
feedpoint, could easily be added, [hb al coils  made of  3003
alloy, or N syle LL  loading].   However,  I see no reference made to using 
capacity hats  inboard of either LL  or  a coil.
On paper, I see no reason why it shouldn't work.    It  would sorta amount to a 
 coil / LL loaded stinger on each end...past the
capacity hat  T bars. 

In any event, the peak V  across the compressible coils at the feed point is 
just wicked. [ longitudaly]  On either side of the center
insulator, the insulation will have to be beefed up.  I will place a disc dead 
center in the stock insulator,  to increase
the peak v  breakdown.  I'll also  wrap the inner ends of the 2" al tuning with 
teflon sheeting, before sliding the grey
pvc slotted  tubes over the 2"  al  tubing.    When the compressible  coils are 
added, the balun/hairpin/coax then goes to
the center of the pair of compressible coils.  The stock, single original  
insulator is no longer used as the feedpoint, however, it still
has to remain.   

Does anybody have experience with placing capacity hat bars  INboard of coils / 
LL ?? 

Tnx... Jim    VE7RF      

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