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Re: [TowerTalk] Grounding base slab and pier tower bases

To: "Roger D Johnson" <>, <>,"Jim Lux" <>
Subject: Re: [TowerTalk] Grounding base slab and pier tower bases
From: "Michael Tope" <>
Date: Tue, 4 Jul 2006 17:58:04 -0700
List-post: <>

----- Original Message ----- 
From: "Jim Lux" <>
To: "Roger D Johnson" <>; <>
Cc: <>
Sent: Tuesday, July 04, 2006 1:36 PM
Subject: Re: [TowerTalk] Grounding base slab and pier tower bases

> Now, let's look at the reactance of that C, at, say, 100 kHz (a standard
> lightning impulse is 2 microsecond rise and 50 microsecond fall, so let's
> say that it's like 100 kHz). X=1/(2*pi*100E5*80E-9) = 1/(2*pi*8000E-4) =
> 1/(6*0.8) = 1/5 -> 0.2 ohms....  That's pretty low.. MUCH lower than the
> resistive impedance to the earth from a ground rod (5-20 ohms).  With that
> 20 kA impulse, you're looking at a 4 kV voltage drop, which isn't all that
> huge.  Given that the rise time is actually much faster, and the reactance
> lower,  the voltage will be less.

Here is a practical question you UFER guys. I am planning to
have some front yard hardscaping done in the next month or
so (concrete retaining wall, steps, pilasters, etc). My thought
was that following excavation and prior to the pour for the
new concrete, I would lay down a fairly dense radial field for
my short 160 meter vertical. The radials would start at the base
of the vertical and then fan out into the front yard:'s-Ham-Radio-Page/Radial_Project/Radial.htm

Originally I was planning to have the existing driveway slab
demo'd and replaced but due to cost constraints, I've decided
to keep it as is. Unfortunately, if I keep the existing driveway slab
as planned, the front yard radials for the 160 meter antenna will
have to be cut short about 20 feet of reaching all the way across
the front yard (see illustration above).

The UFER discussion got me to thinking that perhaps I could
somehow tie the ends of the front-yard radials into the edge of
the existing driveway slab so that could get some additional RF
grounding benefit as compared to letting the front-yard radials
stop just short of the slab.

So the question is, how would I go about attaching the ends
of the radials wires to the edge of the slab in a way that would
provide a low resistance/reactance connection to the slab? I
have a bunch of 3/8 diameter "Red Hat" concrete anchors left
over from another project, so one thought was to use these to
provide the connection. The Red Hat's wouldn't provide much
actual contact area, however, as the only place where there is
significant contact force between the metal and the concrete
would be under the head of the hex-nut/washer and the wedge
on the end of the anchor.

Anyway, I would be interested in suggestions on how best to make
these connections (or if its even worth bothering with). BTW,
I should mention that my main goal for the radial system is to
lower the losses of the radial system in order to raise the
antenna efficiency. I am on dry rocky soil here with a less than
ideal radial field arrangment (antenna on side of house), so I am
looking for every last drop of efficiency that I can squeeze out of
the system. As far as lightning protection goes, I am in Southern
California, so this isn't a big concern.


Mike W4EF............................................ 


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