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[TowerTalk] Linear loading

To: <>
Subject: [TowerTalk] Linear loading
From: (Tom Rauch)
Date: Thu, 17 Jun 1999 14:15:07 -0400
From:                   "Rod Brink" <>
To:                     <>
Subject:                [TowerTalk] Linear loading
Date sent:              Thu, 17 Jun 1999 08:57:15 -0700

> Recently heard a guy on 40M say that he was operating with a
> "linear-loaded loop".  What is that?  My antenna books are in storage, but
> as I remember, linear loading refers to electrically extending radiating
> elements by folding them back on themselves at the endpoints, right?  How
> would you apply this to a loop??

Hi Rod, 

You are basically correct on the definition, but the one point 
throwing you is the folding does not have to be at an "end". It can 
be anywhere along an element. If you consider that, then you will 
see he could "linear load" a loop.

The advantages of linear loading are mostly imagined, rather than 
practical. This is especially true if the loading is folded in towards 
the feedpoint.

Linear loading is really just a simple inductor that has been 
stretched out of optimum shape so mutual coupling is less. Of 
course this effect increases resistive loss for a given conductor  
size and material because it takes more wire length to produce the 
same amount of reactance when mutual coupling is reduced. 

Linear loading also has more distributed capacitance because the 
a high voltage difference (strong electric field) appears between 
close spaced conductors. This effect increases the effective 
inductance, but at the expense of additional loss. Loss increases 
because current bunches at the inside edges of the wires (reducing 
surface area that carries current) and because circulating currents 
increase. Capacitance across a loading inductor (or stub) is 
ALWAYS a bad thing for efficiency, even if it reduces the number of 
turns and narrows the measured bandwidth.

The last effect of linear loading is it radiates. The radiation changes 
efficiency depending on the direction the loading wires are folded. 
Many antennas fold the linear loading the wrong way, with the 
result that replacing the linear load with a conventional load 
improves performance quite a bit. Folding the linear loading IN 
towards the feedpoint is the WRONG way to fold linear loading, 
when compared to an inductor placed at the same point where the 
element is "loaded".

73, Tom W8JI

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