The main motivation of changing to coils would seem to be the
increased Q and decreased loss. But a non-obvious benefit is
a broadening of the band width. Any linear loading scheme has
the drawback that the effective loading inductance is directly
proportional to frequency; exactly what you don't want. OTOH,
a lumped coil's inductance is relatively constant with frequency,
as long as you don't operate too close to the self resonant
frequency. This could happen if you make the coils too large
(physically) in a single minded quest to maximize the Q.
Rick N6RK
On 4/28/2020 12:52 PM, 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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