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Re: [TowerTalk] 30m/40m Yagi Ideas? (Oops! It got sent before it was fin

To: Dan Hearn <>
Subject: Re: [TowerTalk] 30m/40m Yagi Ideas? (Oops! It got sent before it was finished.)
From: Rob Frohne <>
Date: Wed, 12 Mar 2008 12:45:47 -0700
List-post: <">>
Oops!  Somehow my message got sent before I was done with it!

I would also encourage you to get familiar with NEC2 in some form (if
you are a windows person 4NEC2 is an easy way to get started, and if you
are a Mac or Linux person, there are other GUIs to use with NEC2).
Modeling is easier than doing it in the real world, though perhaps not
as much fun.


Rob, KL7NA 

Anyway, I think your project should be an interesting one.  
On Wed, 2008-03-12 at 12:06 -0700, Dan Hearn wrote:
> I am in the process of building a 2 element 2 band yagi for 30/40m. It will
> use some 20m elements, which I have, extended to full size on 30m. The
> elements will be coil loaded for 40m and the coils will be shorted with vac
> relays, which I have a good supply of, on 30m. Matching will be done using a
> 50/25 ohm balun/xfmr as available from DX engineering. My thought is to use
> coils at the center of each element but I realize the 40m efficiency would
> probably be greater if the coils were further out on the elements, probably
> at the junction between the 17 ft tips and the center tubing section.
>   I plan to mount this antenna on the 2 7/8 mast above my 6 el 20m yagi.
> Spacing will probably be 10-12 ft. Height will probably be 142 ft on my 131
> ft crankup.
>   I would appreciate any comments on this proposed design. I realize that a
> lot of my questions can be answered by modeling the design but I have no
> experience in that area. I am using the Taper program to come up with the
> element lengths and would rather spend my time building the antenna and
> putting it up, Hi. I will ultimately ask for help in determining the
> inductance values for element loading.
> 1. Would putting the coils out on the elements vs. at the center improve the
> gain enough to be worth the extra effort?
> 2. What would be a good compromize element spacing on the boom?
> 3. What do you think of using the 2:1 xfmr for matching? Seems to work for
> SteppIR.
> 4. Is there any place I can buy large type 31 ferrite cores, as used in
> K9YC's great balun designs on his web page, in small quanties? I might wind
> the 2:1 balun xfmr myself.
> Thanks, Dan, N5AR
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Rob Frohne <>
Walla Walla University


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