[Ham-Mac] Ground for new shack

[David Kelly]

On Dec 16, 2003, at 2:18 PM, Brian Short wrote:

> Hello,
>
> This is a good question that you ask and my answer will probably
> not be as good.
>
> My suggestion is that you look at this as you might a tower base.
> The idea comes up about attaching a ground at the bottom of
> a deep base, but discharging lightning through the cement can
> (as I understand it) cause it to explode through nearly instantaneous
> expansion of moisture.
>
> This is (evidently) why all of my towers have an 8' copper ground rod
> installed next to the tower base and attached to the tower.
>
> I don't think you want a strike to conduct through the re-bar structure
> of the home's foundation.

All well and good, but lighting is not the reason you ground your 
shack. The primary reason is to hold all stray "static" potential 
(voltage) as low as possible so as to minimize the chance of shock to 
the operator. Generating RF can build up static charges.

The primary reason for grounding an antenna and tower is to *prevent* 
lightning strikes. Wind blowing over an antenna will induce a static 
charge. Once enough static charge is built up a spark jumps from both 
up the charged item and down from the sky. Keep your antenna and tower 
discharged with good grounding and you prevent lightning. Usually.

Good antenna switches ground both sides of the coax or wire of unused 
antennas because often one or both sides lack a DC path to ground. 
During windy conditions that feedline will spark across the easiest 
point, usually the connector if disconnected.

Lightning rods were originally put on buildings as conduits for 
lightning but then it was found the lightning rods served to prevent 
lightning strikes.

--
David Kelly N4HHE, dkelly@HiWAAY.net
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