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Re: [TowerTalk] Vertical antennas and lightning

Subject: Re: [TowerTalk] Vertical antennas and lightning
From: "Roger (K8RI)" <>
Date: Sun, 01 Aug 2010 17:49:39 -0400
List-post: <">>

On 8/1/2010 4:02 PM, Tommy Alderman wrote:
> This then, means that ICE lightning protectors, with their center conductor
> at DC ground, are really not good protectors to use? Doesn't it also bring
> in to question the advice to connect coax shields to both the top and bottom
> of a tower?
> To me, what Dave says, answers the age old question about antennas of any
> kind: 'To ground or not to ground?".

When charged clouds pass overhead, there is an equal and opposite 
"charged area" (more or less) following along under the cloud on the 
ground. That includes all objects such as homes, cars, people, and 
towers whether they are grounded or not.

What you do to the tower has very little effect on whether it's going to 
get struck or or not.  What you do *does* affect what happens when the 
tower does get struck and the results of that strike in the ham shack or 
house. Grounding the coax to the top and bottom of the tower keeps the 
coax at what ever potential the tower is at those points.  Antennas that 
keep the center conductor at DC ground potential may or may not help, 
BUT it will certainly help with the many thousands of volts generated by 
precipitation static. Also that center conductor possesses inductance 
and capacitance to the shield. So on longer runs the two will tend to 
move to the same potential. That is why we put the Polyphaser of Ice 
protector at the grounded bulkhead.  Coax that is not grounded to the 
tower at the top and bottom can actually have more voltage induced into 
it while at the same time the tower is dumping the current into the 
ground system. I have seen "snow static" create a big fat arc that 
actually extended out away from the PL-259 before reaching the shield 
and sounding like a balloon popping every 5 to 10 seconds. So instead of 
a half inch spark it was an inch or two long and far fatter than any 
spark I ever saw from an ignition coil. Had that 40 meter vertical been 
grounded it would not have had that build up.

This is one of the reasons when you disconnect the coax from the rigs 
before a thunderstorm, you need to get the end of that coax out of the 
house/ham shack. Ideally the end of the coax should be terminated on a 
grounded connector before it enters the shack.  If that antenna is 
struck by lightning, or even has an induced voltage from a nearby 
strike, that cable laying on the floor may have hundreds of thousands of 
volts on it. That voltage is likely to jump to the nearest object or 
lesser potential, or grounded objects.  That could be a person or the 
rig and it could create an electrical shock or fire.   Hence the reason 
for the grounding bulkhead where the coax enters the house. If the coax 
is not grounded where it enters the house, throw it out. You are 
repeating Franklin's experiment with much better conductors than wet 
string. Of course by what we know now, Franklin was extremely lucky not 
to have been killed.]

For those who just run the coax through an ungrounded bulkhead under the 
window, I know the thought of throwing the coax out into the elements 
where the end is likely to get wet and dirt in it is a terrible thought, 
but not doing so is like playing "Russian Roulette" with your house and 
body at risk.

I've said it on here many times, but the first 5 years I had the tower 
up it was struck by lightning an average of 3 verified times per summer 
or a total of 17 times the first 6 years.  It has not been stuck  at all 
(that I know of) over the past two summers nor so far this summer.

One additional point is that a good and adequate ground system enables 
the tower to sink all (or most)of  that current and voltage from a 
strike, into the ground instead of having it run down the coax and into 
the house.


Roger (K8RI)
> Tom - W4BQF
> Subject: Re: [TowerTalk] Vertical antennas and lightning
> Unfortunately in this case the 'bleeding' when there is a charged cloud over
> head is putting charge ONTO the antenna from the ground to equalize it with
> the rest of the charge being attracted to the base of the cloud.  So it make
> it MORE likely to start the upward streamer that completes the path.
> David Robbins K1TTT
> e-mail:
> web:
> AR-Cluster node: 145.69MHz or telnet://
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