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[TowerTalk] Lightning question

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Subject: [TowerTalk] Lightning question
From: (Guy L. Olinger)
Date: Fri, 12 Jun 1998 00:40:05 -0400 wrote:
> In a message dated 98-06-11 19:36:07 EDT, writes:
> << Also, you might compare the total square feet of land that you
>  have antennas on to the total square feet of land encompassing
>  the area where you have seen the lightning hitting.  It just
>  might not have been your turn yet. >>
>        Ouch! The cold slap of reality strikes again (no pun intended).
> Cheers,  Steve  K7LXC

I keep seeing these (apparently) contractory anecdotes. Assuming noone
is telling bald-faced lies, any theory must include *all* the anecdotal
material to count.

I suspect that there is a real reason that certain towers never get hit,
and others get hit all the time. 

Remember the story I told about my 70 ft tower at K4VDL topped by a 33'
vertical that was never hit and a 12 foot mimosa tree 70 feet away
converted to toothpicks by a strike. Do folks *really* want to ascribe
that to random behavior? By some opinions here, the tower should have
been 100 feet more attractive than the mimosa.

My elmer was the head engineer at WCTT (AM & low end of the band).
Lessons were at the transmitter house out at a place lovingly called
"the swamp". I think the tower was 450 foot or so quarter wave. Also
think the swamp was 10% copper. Many summer nights watched the lightning
gap at the bottom of the tower arc with an almost metronome regularity.
Now and then lightning would hit the top of the tower and throw sparkles
fifty feet from the gap balls. The gap balls got quite pitted and had to
be replaced a couple times a summer. Lightning never took transmitter
off the air while I was there.

*HOW* do both stories fit under the same theory?

My own personal >*guess*< is that towers gain strike attractiveness in a
manner proportional to their height. On the other hand, effective
bleeding of charge in the region, by points, beams, whatever, creates a
*fixed* deterence to strikes, the bled-off zone of ionization, whose
extent is limited by laws of physics. This fixed deterence will balance
an attractiveness which then equates to a certain height. Above this
height, the attraction less deterence is still attractive, and strikes
will jump the bled-off zone anyway.

The WCTT tower was way over this height, and the K4VDL tower was below.
I would speculate that a porcupine works FB under this height, and gets
blown into lethal darts above this height (someone else's story). It
would also say that lightning rods work fine on barns and houses, and
get melted above the critical height.

In the fireball story I told, where lightning came in the telephone
line, he *did* have a small tower & a beam, which was not struck. He was
on a mild knob with flat area around, and the knob took a lot of
strikes. Why not his tower? This would fit with the theory above.

If the theory is true, I sure would like to know what the balance height
is, or what it depends on. It's above 100 feet and below 450 feet. 

I also would *guess* that ground conditions underneath the tower could
raise or lower this height, and so could local geographic features, such
as the ridge in one account. A local ridge would raise the critical
height in an adjoining valley. Being on an isolated knob in otherwise
flat territory would lower the critical height. 

As you can hear on HBO, "That's just my opinion, I could be wrong."

73, y'all


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