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
_______________________________________________
_______________________________________________
TowerTalk mailing list
TowerTalk@contesting.com
http://lists.contesting.com/mailman/listinfo/towertalk
_______________________________________________
_______________________________________________
TowerTalk mailing list
TowerTalk@contesting.com
http://lists.contesting.com/mailman/listinfo/towertalk
|