I bought a used EF180C (F12) LL loaded 86' rotary 80m dipole, tossed the
LL wires, coils, and relays, modeled it with YagiMech (DXEng) and
upgraded it mechanically for 90mph (was maybe 65mph). The LL wires were
replaced with two Phillystran guys to a longer crossbar.
Plugged the stock mechanical dimensions into EZNEC and found the
resonating center inductances for 3.5 and 4.0. Then worked with Mike at
Seco/Tornado drive to get a split coil variable Tornado, as it took
about a 2:1 L range for full band coverage. It's been in use about 7
years at 102'.
A few years ago I talked to a CO ham who was going to build a Tornado
based 80m 3L yagi, full band coverage. Not sure it got built.
JKantennas sells a 55ft 80m Tornado tuned dipole. No sliding contacts
or relays.
My MFJ screwdriver controller has 10 presets every 50KHz and it seems to
repeat well against the home microswitch. So if an inductance vs turns
calibration was done, then a Tornado tuned yagi could cover all of 80m
and do all the fancy stuff a steppir yagi can do with a similar controller.
Grant KZ1W.
On 4/28/2020 12:52, Mike & Becca Krzystyniak wrote:
Greetings All,
I was considering a similar approach, by taking the existing design and
changing the linear loaded elements into center loaded dipoles. Start with
coil placement at LL insulator and tune to that elements current natural
resonant frequency. Has anyone modeled it like this?
Mike K9MK
-----Original Message-----
From: TowerTalk [mailto:towertalk-bounces@contesting.com] On Behalf Of
john@kk9a.com
Sent: Tuesday, April 28, 2020 1:35 PM
To: towertalk@contesting.com
Subject: Re: [TowerTalk] 40m 4el KLM - replacing linear loading with coils
Rather than try to duplicate a design that is decades old, I think it
would make more sense to redesign the antenna using loading coils.
VE6WZ has some loading coil information on:
https://www.qsl.net/ve6wz/index.html
John KK9A
Richard (Rick) N6RK wrote:
The problem is that you don't know the required inductance
of the coils. It would be difficult to determine this
for anyone but M2. At one time, W6ANR used to sell
coils for 40 meter Yagis. Perhaps he has the values
and would be willing to give them to you.
The recent TT thread about determining the resonant frequency
of Yagi elements would help you. You could find the 4
resonant frequencies of the 4 elements of the unmodified
Yagi, and then use trial and error to tune the inductors
to get the same element frequencies. Seems like a lot
of work.
Rick N6RK
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