[Antennas] Dumb question?

Mon May 18 17:01:12 EDT 2009

.snip>..... Here's what I mean. If you have a system that is effective in 
allowing Nature to balance dissimilarly charged patches of atmosphere and 
earth, then you dang well better have a wonderful way to handle the 
resulting strike that you will be likely to attract........</snip...
I would look at this another way : If you have a system that is likely to 
attract lightning, then you dang well better make it able to balance the 
charges
without getting blown up or lead the energy into your home or other unwanted 
paths..
This is a question of using Ohms law... The lower the resistance, the lower 
the energy dissipation will be. and less destruction is usually the result.
Be aware that we can not think pure DC here !! A lightning strike has a 
steep pulse front and radiates plenty of electromagnetic energy. It must be 
taken
into consideration that voltages/currents of lethal or damaging levels can 
and will be induced in any nearby conductor ! This means that even if
you manage to keep 100 percent of the strike current in your lightning 
"downlead" you may still suffer damage nearby caused by em fields !!
This may well happen several tens or hundreds of feet away.... Another 
result of the RF nature of the pulse front is that all downleads/groundwire 
etc
should have the lowest possible reactances...in other words ohm law for 
reactances...to say it in a simple language.
***I want to stress that it is IMPOSSIBLE to insulate any tower system to 
make it less attractive to lightning ! The idea that having no ground may 
make it less
attractive is dangerous ! You could be understood this way, at least by 
readers with less perfection in english
 I want to add another story to the many other I have read about strange 
lightning strikes : Near my home I have a 100 foot tower and a 60 foot 
tower.
VERY well grounded according to the professionals, and attached to a large 
underground RF and lightning ground system... These belong to contest
station LA8W/LN8W , and are located within 40 feet of the house at either 
side. A little further away..abt 120 feet is a 160m vertical attached to the
same underground system. Each tower also has a system of interconnected 
ground rods tied in to the rest of the ground system and the towers.
In the middle, that is inside the triangle formed by the three towers 
is...or sadly was a very nice tree that I loved to sit under enjoying a cold 
beer in a
summer night. The tree was abt 35 feet tall... Lucky for me I did not sit 
there that night last year when a direct hit to the tree took away more than 
half of it....
stripped the roots more or less out of the ground, and killed the tree... 
There was not a single wire in that tree.... No towers had any evidence of
having been hit ! And no damage to the station or my home. The latter was 
probably the result of my knowledge of the RF nature of a strike ;
I had plenty of in house protection devices, very fast ones capable of 
reacting in nanoseconds, which is important. Simple MOV devices or
gas-dicharge devices found in many supply stores at bargain prices are 
seldom fast enough....
And again : Make sure that you do not lead anyone to believe that you can 
make anything less attractive to a strike by leaving it "insulated" from
ground !
This was my story
73's de PETER
LA/SL
----- Original Message ----- 
From: <don_keith at bellsouth.net>
To: <Antennas at mailman.qth.net>
Sent: Monday, May 18, 2009 5:25 PM
Subject: [Antennas] Dumb question?
> Joe K2XX:
>> The URL of the article you mention is:
>> http://www.lightningsafety.com/nlsi_lhm/magic.pdf
>> It is, as you note, very well written. Nature seeks balance in 
> everything. That is why water runs to the lowest level, the strong eat 
> the weak, and lightning takes the best path it can find to equalize the 
> charge when it strikes. I sometimes wonder if lightning protection should 
> be either extremely well done or very poorly done to be successful.
>> Here's what I mean. If you have a system that is effective in allowing 
> Nature to balance dissimilarly charged patches of atmosphere and earth, 
> then you dang well better have a wonderful way to handle the resulting 
> strike that you will be likely to attract.
Antennas at mailman.qth.net>
> 73,
> Don N4KC
> www.n4kc.com
> www.donkeith.com
> www.n4kc.blogspot.com
> (An open blog about rapid technological change and its effect on society,
> media, and amateur radio)
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