[TowerTalk] Conductive Concrete and Grounding
w8ji at contesting.com
Thu Jan 27 08:09:38 EST 2005
> Although lightning is DC (static electricity) is does tend
to "ring" with a
> strike consisting of both positive and negative current
Even when flowing in one direction a waveform can contain
multiple high frequency components and act just like AC.
Lightning can never be treated like DC.
> The latest, or at least one of the latest theories is the
super strikes are
> a downward current flow receiving power from sprites which
cover a wide
> area. Strangely enough these are a higher percent of cold
> lightening than that associated with warm, or hot weather.
That's when it hit here. During an ice storm.
> Supposedly the regular strikes of a strength that can be
managed, while the
> super strikes are a tad beyond our abilities at present.
> So, taking precautions should mitigate damage from the
lesser strikes, but
> with the super strikes you can only hope for the best.
Not true. I had a strike that hit my 300 ft tower. It melted
the shield on 7/8th inch heliax and melted the telephone
wires from the street to the house. It did not damage my
modems or anything else inside any building, including a
GAsFET preamp on a repeater that was on that 7/8th inch
cable AND I don't have a single Polyphaser or other
lightning protection device on any feedline.
> > I've always heard even from lightning experts that there
is little one can
> > do to stop or even minimize the affects of a direct hit.
That's just nonsense, as Roger already pointed out.
My tall tower takes several direct hits a year. Other than a
sizzle and loud crack, I'd never notice. Go to an AM BC
station and have a look at the pits in the lightning gap, or
look at the highest point of the tower and you'll see deep
burns. A properly installed station, even long before the
days of fancy lighting protection devices, will almost
always survive multiple hits without damage.
I would certainly never depend on a ground through concrete.
It would be that good of a ground, no matter what you did to
the concrete. Concrete grounds are only meant to augment the
main ground, not replace it.
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