[TowerTalk] new-to-me Force12 EF-180B rotary dipole

[Grant Saviers]

I rebuilt the larger version, EF180C 86' tip to tip, with a Tornado dual 
variable L at the feedpoint.  It covers the full 80m band in 50KHz steps 
using a MFJ screwdriver controller.  A 50:25 ohm transmission line 
transformer provides the broadband low loss impedance match.

The linear loading wires were replaced with a dual Phillystran truss. 
YagiMech from DX Eng was used to do the mechanical modeling and EZNEC to 
find the inductance values.  The stock EF180C would not survive >65mph 
so internal sleeving was added where needed and that yielded about a 
90mph survival. The tubing was bent a bit where YagiMech predicted 
failure, so that needed replacing to permit sleeving. The factory ABS 
foam core pipe used as the feedpoint insulator crushed over time (DUH) 
and was replaced with custom machined UV resistant nylon saddles on a 
new 1/2" thick 6061 mast plate.

The Tornado reed switch used to drive the MFJ turns counter failed.  My 
guess is a QRO transmission with the antenna mis-tuned caused the 
failure.  A tricky job, but SECO was helpful in getting it done and an 
added choke will hopefully prevent future problems. Otherwise, the mods 
have held up for the past 6 years @ 102'.  I don't think I've much more 
than 75mph wind @ 102', and did have one 1"+ ice storm.

Grant KZ1W

On 1/11/2019 7:00 AM, George Dubovsky wrote:
> I just acquired a used F12 80 meter dipole with the linear-loading wires. I
> have read everything I can find online about this design (mostly in Tower
> Talk) and I have a few questions.
> 
> Has anyone modeled this antenna with the linear loading? I am curious as to
> how much L the linear loading wires present.
> 
> I have read reports of folks using coils instead of the LL wires. Has
> anyone published real details of the modification, including any necessary
> element reinforcing or trussing?
> 
> Is there a source of the Alumoweld wire if I should put it back up using
> the original design? The existing wires appear to be in usable shape, but
> all of the clamps are rusted and I don't know what  I will find when I
> remove them.
> 
> Any and all advice concerning this antenna is cheerfully solicited... ;-).
> 
> 73,
> 
> geo - n4ua
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