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[TowerTalk] Porcupines

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Subject: [TowerTalk] Porcupines
From: (Larry McDavid)
Date: Sun, 16 Nov 1997 06:40:45 -0800
At the risk of raising yet another controversial topic, I want to ask
for members' experiences with static charge dissipators atop towers.

The kind I refer to are are often called, "porcupines." I saw one at
Pacificon that was made of a one-inch diameter bundle of perhaps
0.015-inch diameter stainless steel wires sticking about a foot out of a
heavy-wall stainless steel tube. Each individual wire was flattened over
a one-inch length near the end of the wire. Before installing, each wire
was to be cut at a shallow angle in the flattened area to produce a
sharp point on the end. Each wire was then bent out and down to form the
final hemispherical shape. I don't know the manufacturer of this one,
but I sure would like to find out. Anyone familiar with this product?

Some folks swear by these porcupines and anecdotally report marked
reduction is loss of repeater equipment on mountain tops. Others claim
they are worthless. I would like to hear from list members about real

Press Jones sometimes does a demo using a van de Graf generator in which
the generator static charge is essentially dissipated by a single
grounded pin point nearby, even though no arc is created. This seems
convincing. For us, the implication is that if you can drain to ground a
static charge before it builds to lightning-bolt magnitude, there will
be a reduced probability of the bolt.

Now, folks, this may not be effective in Florida where lightning
abounds, but here in Los Angeles we have very little lightning. I think
I saw some last year. Or, was it the year before....? In my case, my
tower mast is the highest thing (by far) around my residential
neighborhood for at least a half-mile radius. So, I have some concern.

Proper grounding and supression to survive a lightning strike is a
different subject, and not the topic of this inquiry. Rather, what about
these porcupines?

A related topic is the desired shape of the end of each wire in the
porcupine. I believe the sharper the point the better to "attract" the
static charge and ground it. Others have suggested the ball shape often
found on mobile antennas. My opinion is that the spherical or smooth
shape on these antennas may reduce the static buildup resulting from air
motion over the antenna end. But, if you want to dissipate that charge
into ground, the point is better. What say you?

The sailboat crowd often places a porcupine atop their tall masts. The
typical sailboat porcupine I have seen is much smaller than I described
above and is made of a brush of very fine stainless wire swaged in a
3/8-inch diameter aluminum rod; the brush is only about four inches
long. Kinda springs open but looks kinda dinky atop a 2-inch steel mast.

So, what say you, fellow TowerTalkians? I welcome your comments and
Best wishes,

Larry McDavid W6FUB
Anaheim, CA  (20 miles southeast of Los Angeles, near Disneyland)

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