[TowerTalk] B olted connections to concrete

[Michael Tope]

----- Original Message ----- 
From: "Nick Pair" <daweezil2003 at yahoo.com>
To: <towertalk at contesting.com>
Sent: Wednesday, July 05, 2006 3:32 PM
Subject: Re: [TowerTalk] B olted connections to concrete


> No form of connection directly to the concrete will give you any 
> additional radial length or ability to dissipate any currents. You would 
> need a low impedance connection to any( a lot of driveways don't have 
> rebar or mesh reinforcing in them) metallic items in the original pour. 
> Your really out of luck on existing slabs. Prestressed slabs are a whole 
> new category and not really pertinent to this thread but usually have some 
> method of grounding any structural steel contained, and sometime cathodic 
> protection for tendons.

Okay, I see what you mean, Nick. My train of thought really jumped
the track on this one. There's nothing magic about the conductivity
of concrete. The conductivity of the concrete is probably on par
with dirt (perhaps a little better, but nothing remotely approaching
even a poor metal conductor), the idea being that an electrode
buried in concrete can serve as a ground more or less the same
way that an electrode buried in dirt serves as a ground, but
bolting radials to concrete would be no better than bolting radials
to dirt.

>Most antenna radials are part of the antenna tuning and therefore need to 
>be a tuned length to be as effective as possible.

In the case of radials laying on the ground, I disagree, Nick.
Radials very close to the ground generally don't require tuning to
be effective. What counts is density of coverage. Ideally you are
trying to shield the fields generated by the antenna from reaching
the lossy earth underneath the radials.

73, Mike W4EF....................................................




>  73
>  Nick
>  WB7PEK
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