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Re: Topband: Tophat? Does it have to be at the top?

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Subject: Re: Topband: Tophat? Does it have to be at the top?
From: "Ford Peterson" <>
Date: Tue, 8 Jun 2004 19:19:07 -0500
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My 42' tower and SteppIR 3 element beam at 45' are shunt fed at the thrust 
bearing.  A single 120' horizontal loading wire is also attached to the thrust 
bearing plate.  

Very clearly, tuning the elements of the SteppIR effectively changes the 
feedpoint impedance of the tower on 160M.  Even though the SteppIR elements are 
electrically 'floating' above the boom, changing their length does change the 
feedpoint.  The 20M position on the SteppIR places the 'sweet spot' at about 
1825.  The 15M position places the sweet spot at about 1860.  Retracting the 
elements completely is not useful as the 'effect' of the elements is nil once 
retracted to the 10M position or so.

While the system is far from ideal for a number of reasons, it does work.  And 
the configuration illustrates that the 'loading' can take place in spots other 
than the top of the vertical, which in my case is an inverted L arrangement.  
It is apparent to me that I do not fully understand the workings of the 
system--discovered using serendipitous methods.  A similar stunt is performed 
on 80M using a separate shunt (tap at 33' instead of 42') and a horizontal hat 
wire of only 20', but the position of the SteppIR elements has no effect on 
feedpoint impedance on 80M.  Go figure...

Your mileage WILL vary...


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