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[TowerTalk] 40 m 2 el yagi bandwidth very narrow

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Subject: [TowerTalk] 40 m 2 el yagi bandwidth very narrow
From: Kari Dx Supply <>
Date: Fri, 16 Nov 2012 11:42:14 +0100
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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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