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Re: [TowerTalk] 40 m 2 el Yagi bandwidth very narrow

To: "'Kari Dx Supply'" <>, <>
Subject: Re: [TowerTalk] 40 m 2 el Yagi bandwidth very narrow
From: "Tim Duffy K3LR" <>
Date: Fri, 16 Nov 2012 12:50:32 -0600
List-post: <">>
Hello Kari:

This narrow VSWR is a limitation of the design of the antenna you are using.

A possible solution to your problem, is the W6NL Moxon two element 40 meter
Yagi design.

You can view some VSWR models and the construction of the W6NL antenna here:

Refer to the three papers on Moxon design posted there.

Tim K3LR

-----Original Message-----
From: TowerTalk [] On Behalf Of Kari
Dx Supply
Sent: Friday, November 16, 2012 4:42 AM
Subject: [TowerTalk] 40 m 2 el yagi bandwidth very narrow

I just recently built a 2 el 40 m shorty with linear loading. I have reused
Hy- gain parts. Boom is 23 feet long and 0.17 wl spacing. Element length
like most shortys. After some adjustment with a hair pin coil I got it well
matched at 7040 (1.12:1). The feed point impedance was like theory  predicts
- z= 17 ohms - j23.
But the 2:1 SWR bandwidth is very narrow only about 80-90 kHz. I have not
adjusted reflector more then made it  abt 4% longer. The reflector element
is electrically in contact with the boom ( driver is isolated). According to
theory the SWR bandwidth should be greater with this spacing or? Looking at
reflector on similar threads also supports much broader bandwidth.
How can I achieve a greater bandwidth? Is it that the relector is a little
bit to short and influences the driver to much? Again doing the practical
way by using a signal source some distance away and adjusting reflector for
actually the best F/B and hoping this improves the SWR is a feasible way.
What says theory in this respect? Thanking for valubale tips. I have tried
to read  the Yagi design book and see what is says but I can not get hold of
a copy.
73s Kari SM0HRP

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