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Topband: Inverted L matching problem

Subject: Topband: Inverted L matching problem
From: Dennis W0JX <>
Date: Fri, 5 Dec 2008 13:10:12 -0800 (PST)
List-post: <">>
Your tower with beam is interacting with the inverted L. My 80 foot tower and 
TH6 is resonant right around 1875 Khz and I think your setup is resonant 
somewhere near the 160 meter band.
Your SWR results suggest that you should not connect the braid to the tower 
base. The tower's ground rods do little for your ground loss issues under the 
vertical portion of the antenna. That is affected mostly by the number and 
length of radials you put out under the vertical portion of the "L."
There was a recent article in QST that did an extensive job of analzing the 
inverted L. It suggested that a 70 foot vertical height produced a better 
outcome than a 90 foot vertical run. You will need some kind of tuning network 
to get the match closer to what you want. Put out at least another two radials 
out and your efficiency will still only be in the 25% range.
Lastly, why bother with an inverted L when you have that beautiful tower 
arrangement just waiting to be shunt fed? It will require that you ground the 
40 meter beam elements but that is easy to do with coils.
73, Dennis W0JX/8

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