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Old 11-07-2019, 02:05 PM
johnmcd johnmcd is offline
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Default Lightning protection for vehicle antenna



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I'm in the process of setting up my first serious radio rig in my vehicle, and I was looking for some suggestions to reduce the impact of a lightning strike on my antenna(s). I've found a lot of info on lightning protection for base station antennas, but I can't find much on protecting antennas on vehicles. My thought was to use an inline gas lightning arrestor, grounded to the body or frame with a reasonably thick cable, but would that even make a difference? I realize that something's going to take a bad hit if I get a strike on my antenna, but I'd like to minimize the damage as much as possible (especially damage to me!)

Thanks
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Old 11-07-2019, 02:15 PM
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Interesting problem. The truck is isolated by the tires so no real good path to ground. Airplanes get struck all the time and yet they fly.

I suggest you take down or tie down the whip when the storm is imminent.

Here at home I leave the am radio on almost 24/7 just because I can hear the lightning on the radio far sooner than thunder. I unplug my computer and refrigerator for the storm - never for longer than a few hours.
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Old 11-07-2019, 04:58 PM
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Quote:
Originally Posted by charliemeyer007 View Post
Interesting problem. The truck is isolated by the tires so no real good path to ground. Airplanes get struck all the time and yet they fly.

I suggest you take down or tie down the whip when the storm is imminent.

Here at home I leave the am radio on almost 24/7 just because I can hear the lightning on the radio far sooner than thunder. I unplug my computer and refrigerator for the storm - never for longer than a few hours.
Thanks - I'm actually designing my antenna mount so it can be easily rotated between vertical and horizontal, so I have that option. I was just wondering if I could do anything for an unexpected situation where I don't get it down in time and the worst-case occurs.
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Old 11-07-2019, 07:56 PM
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Statistically speaking, chances are low that your vehicle will be struck. Yes, I was once driving behind a vehicle that was hit by lightning, and lightning struck close to my parked truck once, without damaging the radios.

But you can use a Polyphaser type protector and bond it to the vehicle body. That would be as sufficient as protection.

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Old 11-08-2019, 08:43 AM
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Quote:
Originally Posted by charliemeyer007 View Post
Interesting problem. The truck is isolated by the tires so no real good path to ground.
Years ago vehicles used to have straps or even chains that used to drag on the ground to eliminate static electricity. I don't see as many of them now as I used to.
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Old 11-08-2019, 10:27 AM
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In sailing, I asked the marina owner about whether sailboat masts should be grounded.

he replied that the ones that were grounded are the ones that got struck by lightning. He pointed to a beautiful boat that was on the hard, being repaired from it's lighting strike.

An ungrounded mast is waaay less likely to get hit. But in the rare chance that it does get hit, you would like the bolt to go to ground and not through your body.

So a few wraps around the mast with INSULATED wire, which is taken then to ground provides the best of both worlds. If the wire electrically contacts with the mast, then charge flows up the mast (from the magnetic interaction with the overhead storm cloud) and puts a few million volts at the top, attracting the strike, so it needs to be insulated.

it doesn't need to be super heavy wire either. Whatever wire you use, will of course overheat immediately during a strike, and establish a super-conducting air plasma pathway, which will carry the energy of the bolt. You just need the wire to start the air plasma. If you watch a Jacob's ladder experiment or watch a 138 kV disconnect switch operate, you will see the same effect.

Lightning will breach that little bit of insulation on the wrapped wire, and go safely to ground (via a dragging ground strap in the case of a road vehicle.

Another sailor (Arlyn Stewart) wrote a research paper on his website about 20 yrs ago, covering the topic rather well.
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Old 11-09-2019, 12:04 PM
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I had no idea sailboat masts were not grounded to a keel plate or anode. It seems one would want static to dissipate and a lightning bolt (which can occur in clear sky) to pass directly to the ocean. I will think twice about helping with the rigging!
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Old 11-09-2019, 12:48 PM
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Quote:
Originally Posted by Central Scrutinizer View Post
I had no idea sailboat masts were not grounded to a keel plate or anode. It seems one would want static to dissipate and a lightning bolt (which can occur in clear sky) to pass directly to the ocean. I will think twice about helping with the rigging!
Most books advocate a fully "bonded" system. Connecting the mast and the battery ground to a copper grounding about a foot square submerged in the water.

this can result in 2 things.

1) The boat WILL GET HIT BY LIGHTNING. You might not be killed by the lightning, but your boat will likely have all kinds of damage. Demagnetized compass, most all electronics fried, including the radio, and scorched and melted bits along the path.

When the charged cloud moves overhead, this will draw charge up from the ground and make the top of the mast a attractive target.

if it is ungrounded, minimal charge accumulation occurs at the top, and it likely will not be struck. It isn't so much that you have an aluminum mast in the air, but whether you have a couple million volts on the tip. A bronze static dissipation brush should be fitted to the top of all masts as another means of protection.

2) Bonding the electrical system to ground can turn the boat's charging system into a galvanic destruction device. (my term). All of the metal through-hull fittings dissolve off the boat while charging, unless it is fitted with an isolation transformer. Then the boat may lose those fittings at sea in rough weather, resulting in a boat heading for the bottom without your consent. I probably saved a guy's life by observing that his through-hulls had dissolved. He had just sailed up the Atlantic coast in late November, was getting supplies to continue his journey. We put his boat on the lift and I told him to go inside and tug on the through-hull fitting hoses. When he was looking through a large hole in the bottom of his boat at me, he realized how lucky he was to be alive.
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Old 11-09-2019, 12:54 PM
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I've never heard of a vehicle antenna getting struck by lightning. If that was a potential problem, any vehicle with an AM/FM antenna would be a target for lightning.

A vehicle is likely safe because it doesn't have an earth ground.
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