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Lightning Safety - Not concerned? Look Here!
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by KI4NVK on June 14, 2009
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A timely article. Here is a new video that all Hams should view. Last night Jim Bailey of East Palatka, Florida found out the dangers of a Lightning Strike. Jim had a bird feeder strung up in the tree in his front yard, and happened to be video taping when it hit the chain on the tree.
This is a good reminder to all Hams out there. Disconnect before the storm hits, and be safe. Jim's chain wasn't near as attractive to a strike as YOUR antenna's are!
http://www.firstcoastnews.com/news/local/news-article.aspx?storyid=139798&provider=rss
vr,
David Grimes
KI4NVK
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RE: Lightning Safety
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by K5END on June 14, 2009
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Alan,
What you witnessed was very rare. You're fortunate to have seen it. I'd catalog that in the "memory scrapbook."
What I call a "memory scrapbook" is the collection of rarest of events, personally witnessed.
The centerpiece of mine is the zodiacal light I observed with the naked eye in November 1985, and recall it like it was last night.
I was observing the early stages of Halley's comet in the constellation Taurus, and further West along the ecliptic there was the zodiacal light, all the way down to the horizon. I'll remember it much longer than I will having observed the comet.
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RE: Personal Lightning Safety
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by K7BAB on June 14, 2009
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I was living in the high desert of Central Nevada when this incident happened.
There were very few thunder storms, but we did have something people called “heat lightning.” Out of a sky with few clouds, a flash would be seen and a thunderclap heard.
A teenager was standing somewhere in town and was struck by lightning and killed. No rain, no clouds to speak of.
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RE: Lightning Safety
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by WA8MEA on June 14, 2009
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>>"Can anyone at all tell me why some Old Timers put their PL-259's in glass jars after disconnecting their antennae????"
>I guess they want to get themselves in a pickle.
Goodness! Gracious! Great balls of fire!!
Bill
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RE: Lightning Safety
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by WA8MEA on June 14, 2009
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A teenager was standing somewhere in town and was struck by lightning and killed. No rain, no clouds to speak of.
----------------------------------------------------
On a more serious note, this is where the phrase "out of the clear, blue sky" comes from.
There are scientific disagreements on this phenomena. Some meteorologists claim that blue sky might have been overhead, but dark skies were off in another direction.
Others claim it is the result of winds and low humidity causing static build-up to the point of discharge.
However, there seems to be enough documented cases that show that lightning can/will "come out of the clear, blue sky."
Now excuse me while I go spontaneously combust....
Bill
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RE: Lightning Safety
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by QRZDXR2 on June 14, 2009
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Good article..
Arizona State has done lots of studies on lightening and safety. Their bottom line.. GOOD LUCK.
As any static charge develops you just can't predict all the discharge points.
We know that a sharp object pointing skyward and above all the other items will normally be the discharge point.
As to being safe in a car.. what makes you think that 6 or 8 inches of wet rubber tires is going to keep you safe after all the bolt just came through how many feet of dry/wet air and you think them little tires are going to save you? Faraday showed that enclosing yourself in a metal cage would keep you safe. Well Arizona state put that one to bed when the bolt jumped from the top of the cage to the ground plate in the bottom. Guess the steel was not put togeather as good as the copper cage that Faraday used.
But some protection is better than none if you build the system.
A Faraday Cage Lightning Protection System consists of Strike Termination Devices (air terminals) along the ridges, flat-roof portions and perimeters, interconnected with specialized lightning protection conductor coursed throughout the building, terminating at grounding locations.
The air terminals are spaced out at 20'-25' intervals around the perimeter and peaked ridges of structures and 50' intervals across mid-roof areas. The specialized conductors consist of many small gauge wires interwoven in a rope braid to maximize the surface area.
Each 100' of perimeter requires a downlead. A downlead is a cable connecting the roof-top lightning protection to a grounding location. The grounding location is typically a ground rod or a series of ground rods, but it can also be a ground plate. The grounding system can also include a counterpoise, which is basically a buried ground wire that interconnects all grounding locations and helps to make all grounding systems common.
Now whay the many small guage wires interwoven into a rope braid... Well as some now know lighting is not just a single DC discharge. Instead the new research has proven it is a HIGH FREQUENCY AC DISCHARGE. Thus like our UHF microwave stuff it only is conserned with the surface conduction. (which now is well known and accepted)
So when you see that lightening bolt your really seeing a rapid charge/discharge osc taking place.
Alen...
I too have seen the ball lightening run across the the ground... going from blue to a yellow.. it moves in strange ways. Most things it doesn't come in contact with due to the repulsion charges but indeed it will kill any living thing that gets in its way as we saw with the ground hogs. Getting a picture of it is difficult. I tried to get several and they never turned out on the film. Just a white blotch.
how they form is interesting. Mostly right after a ligtening bolt hits. They only last for about 5-20 seconds.. and float around like a beach ball on invisable water surface. \
The research contenues as now the guys in spacelab are saying a shaft or plumes shoots up from the cloud as the lightening discharges. could there be more to this than meets the eye. Do sunspots promote lightening? Where do the charges come from... if they are all like charges then why doesn't the cloud repell and disapate. We know air movement and friction can develop static charges. What conditions are ripe for it to happen. Why doesn't it happen to other clouds than the Q's ? What is so special about them than others?
And now the experts tell us that if you have a ham antenna up, its better to leave it un-grounded than to ground it so as to remain somewhat uniform with the charge around it. Grounding it could upset the field and actually cause the lightening to emulate from your antenna. anything pointie concentrates the charge-discharge point due to the potential/air breakdown densenty. Remember its surface charge we dealing with here. (think of the surface charge as a drop of oil in a glass jar of water.. its always moving around. But, why doesn't it (the charge) disapate. Tulsa was the expert here. To find out why you need to read his works. Thus we have the cloud which has potential to itself or the ground. We have ground which has potential to the cloud and itself (as allen has said) and we have the density of the charge with repect to the clouds size and distance from the ground. All of these combinations have unlimited variances that one has to contend with to be safe and not a number in the dead zone. (by the way you can get lightening on a clear day with the wind blowing too... makes surface charge like skuffing across the carpet and then touching the door knob.)
Oh and never stick you finger up in the air to give mother nature the international peace sign when its stroming above you... one documented case showed that happened. Blew the guys finger away.. but he lived to tell about it.
Another documented case was a ranger rick who has been hit at least 3 times by lightening ... setting in his truck...
And of course you always get some from the gene pool that want to go outside and get a closer look at the storm. Lucky those sometime become statics and keep the rest safe from sudden death.
Most interesting article... thanks for stemulating the hams who have lots of wire things up in the air too.
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RE: Lightning Safety
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by QRZDXR2 on June 14, 2009
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By the way lightening does have a resonace frequency. Somewhere around 3.5 mc so they are saying... gee right in the 80 mtr ham band where the nut hang out. go figure
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RE: Lightning Safety
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by KL7EDK on June 14, 2009
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Check this web site in the evenings during the summer months. We get a few good storms...certainly nothing like the folks in Florida.
http://afsmaps.blm.gov/imf/imf.jsp?site=lightning
Jerry
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RE: Lightning Safety
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by K5END on June 14, 2009
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KL7EDK,
Yes, Alaska gets lightning, but in comparison to the lower 48 the incidence is what I call "rare" in terms of strikes, per square mile, per year.
In fact, I understand, lightning causes the lion's share of the forest fires in Alaska.
Long before the other 49 states even knew who she is, Sarah Palin was pointing out the hazards and consequences of lightning in Alaska.
When my family lived in Alaska, in Anchorage and along the Kuskokwim, we hardly ever saw lightning. I personally don't recall ever once seeing lighting in Alaska. But it does happen. We had a bear in our front yard who wanted to come inside the house, but never had lightning visit us.
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RE: Lightning Safety
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by K5END on June 14, 2009
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>
"Somewhere around 3.5 mc"
Close.
That figure is close to what they call the "plasma frequency" of the ionosphere. Anything below that frequency will always be reflected back, even in the lowest solar activity.
So that component of the lightning signature will always be "reflected" back down to the surface (the ionosphere is much, much, much higher in altitude than the lightning activity.)
Anything higher than the plasma frequency happens to be in conditions at the time will either pass on through to outer space or will be "refracted" back to the surface where your antenna sits.
But that reflection/refraction of the ionosphere layers is an article for another day.
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