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Re: [TowerTalk] 20m yagi with dual-driven element

To: "Tower and HF antenna construction topics." <>
Subject: Re: [TowerTalk] 20m yagi with dual-driven element
From: "David Thompson" <>
Reply-to: David Thompson <>, "Tower and HF antenna construction topics." <>
Date: Sun, 28 Feb 2010 21:54:00 -0500
List-post: <">>

Years ago I had a 5 el KLM Big Stick on a 42 foot boom.  At the same time 
K4JPD had the 6 el KLM on a 57 foot boom.  The dual driven elements gave the 
beams the wide band width and are a log cell as designed by the developer 
Oliver Swan.  According to Swan's work (years ago modeled on VHF) the log 
cell does provide some gain.

Tennedyne also has a 6 El 20 with dual driven elements.  His literature says 
the dual log cell provides a wide bandwidth and some forward gain.

The Oliver Swan model shows dual nulls for low SWR with one on the low end 
and another toward the mid top of the band.  This is in the two KT-34XA 
manuals I have.  The max SWR is between 1.3 and 1.4 on the three bands with 
the higher SWR in the mid band.

As to 40, KLM made a 4 el dual driven beam on as I recall a 42 foot boom. 
The weakness of this beam was the short elements.  I feel full size elements 
would add a lot to performance.

Hope this helps.

73 Dave K4JRB

----- Original Message ----- 
From: "Stein Roar Brobakken" <>
To: "'Tower and HF antenna construction topics.'" <>
Sent: Sunday, February 28, 2010 7:25 PM
Subject: [TowerTalk] 20m yagi with dual-driven element

> Hi
> I have plans to make a 4 to 6 element yagi for 20 or 40m since I have 
> pretty
> lot of aluminum tubes and parts in stock.
> Have any other made a mono-band yagi with dual-driven element like the 
> such
> like:
> * KLM  KT34XA ? KLM use 55" / 140 cm spacing about 0.065 wavelength on 20 
> m.
> *KLM 40m 4 el with dual driven element. I don't what spacing they use this
> one, but it works super from OH8X in stack 1/2 wl spacing.
> *The 2 el dual driven element 40m yagi from 
> which using 0.11 wavelengths.
> The Dual driven element is nothing new as it is almost the same as HB9CV 
> and
> ZL-special which use about 0.125 wavelength spacing between "the front and
> rear" element.
> What do you think is the good optimized setup to use in a 4 to 6 el yagi ? 
> I
> am just familiar with old Quickyagi and not familiar with Eznec, but I am
> wondering if anyone have calculated or tested this things??
> I planned just to use same configuration as a 3 element yagi with same
> spacing to reflector and director, BUT with dual-driven elements..... I
> cannot model it in quickyagi...
> 73 LA6FJA Rag
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