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Date: Fri, 21 Apr 2006 14:52:01 -0400
From: Dexter McIntyre W4DEX <dmcintyre@att.net>
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Subject: Re: LF: Top load coil at ground level?
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Peter Martinez wrote:
> 
> Incidently, Dex, have you thought about removing the wire you have 
> labelled 'tower grounding wire' and returning the feed to the base of 
> the tower instead? There should be no voltage between the bottom of the 
> tower and the bottom of this grounding wire, so you might as well use 
> the tower to 'ground itself'.  Maybe you cannot rely on the tower to 
> conduct current!
> 

Peter,

I initially used this antenna with a single vertical wire and the coil 
grounded to the base of the tower ground system.  I think this is what 
you described above.  There was some discussion about the capacitance 
between the vertical wire and tower shunting the antenna current to 
ground so I went looking for a way to feed a short grounded tower.  So I 
found the balanced feed method on Rik's site and give it a try.

I tried to make some meaningful field strength measurements between the 
two methods of feeding the antenna but gave up when I figured out I 
didn't know what I was doing.  Seems I never found a place far enough 
away from power lines that I could repeat the same levels from day to 
day with the same antenna.  I could even see as much as a 6 db change in 
signal strength while watching a SLM receiving a steady carrier.  These 
changes could usually be associated with a click or pop which I assume 
was load changed on the power grid.  Conquering this problem is on my 
list of things to do but right now it's microwave season :)

 From the signal reports I received with both feeds I could not tell 
that one way was better than the other.

The idea of using coax up the center of the tower is a possibility here. 
  I have a spare rung of 7/8" Heliax that would probably handle the 
voltage.  The tower is well bonded from top to bottom with multiple runs 
of Heliax and wave guide.

Always open for suggestions,

Dex,
W4DEX / WD2XKO