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How much "gap" for lightning ?

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Subject: How much "gap" for lightning ?
From: (Ed J Hughes)
Date: Mon, 22 Jul 1996 22:24:30 EDT
Working on  "feedpoint fabrication" on  4
verticals where the vertical itself is Rohn 25
and the radials are "elevated" and "floating".
The  "feedpoints" are elevated and  the 
insulation between the grounded (bottom
sections of  Rohn 25) & the ant is accomplished
with the Rohn "insulated joint" sections.

I am going to use pieces of aluminum yardstick
(sharpened) as "lightning bleed-off" devices.
Will have one "set of points" protecting the 
floating radials and anouther set protecting 
the ant itself.  All bleeding charge off to the 
Rohn 25 (grounded) below the insulated

Question is, how much gap should one leave
between the "points" ?

My "gut feeling" would be to have the gap protecting
the radials be about  1/4 inch & the gap protecting
the ant itself be about 1/2 inch. Wonder if anyone 
out there has experience/info regarding this ?  I've
never been involved with it before.  This is a 160 mtr
system, so the radials are abt 131 ft long (QTY 4) per
vert & the antennas are full size with the feedpoints
ranging from 35 to 10 feet above the ground.


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