The AM Forum

This subject may or may not be obvious, or it may even prevent people from enjoying radio when it shouldn't. Or maybe keeps their stuff from being hit by lightning.

There is a 55FT tower with dipole, and there are throughout the neighborhood in the city, many very old 70FT trees.

It's overcast, and every 20 minutes or so, there is some rather quiet and far away sounding thunder in the clouds, from where it is not possible to say but probably high up. It is not raining and probably won't, and there have been no visible strikes to ground.

Is it really unsafe to use the antenna? How can I tell, because today might be a good day to get on the air at some point.

Just unplugged all my stuff. Lightning and storm for real here this evening.

Caveat Hamoniae.

Nothing you do will change the chances of the antenna being struck.

The only question is what are the chances of the radio being damaged by near strikes.

Nothing? Not even lowering it, perhaps all the way to the ground?

If you can't lower it, then your best solution would be to put a lightning rod on the tower a few feet above the highest part of the dipole, the theory being (and I recall seeing this in one of the ARRL's publications) that the lightning will be most likely to hit the rod than the antenna, and anything below the highest point should be safe.

Lightning is very unpredictable. Even if you had 10 lightning rods on the top of your tower (I'll assume metal tower), it won't offer much protection. If you took a direct hit, the lightning surge can propagate down the tower and into anything that's connected to it or near it. If the tower is not grounded properly at the base, it's conceivable you could even blow the concrete base apart. When lightning storms are nearby, to protect your equipment, disconnect all your incoming cables as a somewhat safe measure, but in reality, there are no guarantees.

Back when I was young and crazy, I had a 50 foot metal telescoping mast on my roof as a center support for my 160, 80, and 40 dipoles. Every time a lightning storm came through, I'd be in a sweat, even though the base of the mast had four, #8 ground wires attached to it. It lasted through many a lightning storm and several hurricanes, but a December ice storm eventually took it down.

You were pretty fortunate Pete.  I guess most hams these days put there towers up away from the house with good grounding and maybe radials at the base if they have the room.

I'm lucky to have very tall trees around three sides of the house. I've had lightning hit a tree about 75 ft. From house and split the bark from top to roots on two sides.  The oak still lives but I wonder how long before the bugs kill it.  Seems to have self-healed so far.

So I guess we pick our poison. Trees so close a hurricane remnant, drecho or whatever could get me, but meanwhile they're nice wire antenna supports.

Fwiw,Top of my wires far below tree tops.

There was a thunderstorm here last week....Lightning struck a Ponderosa Pine tree across the field from my house...I was sitting on the porch watching...That tree burned its full length almost immediately...the needles burned off very fast and then the bark was burning...It was raining so hard that the rain put the fire out in about 20 minutes....The sky was filled with lightning flashes that didn't seem to originate from or go to the earth.....Smell the ozone...feel the hair on your neck raise up...Tower was cranked down, cables all disconnected (but not grounded)......I have a beam on the tower and lots of wire in the trees around the shack...I forgot to disconnect the rotator wires....Nothing was damaged except my wireless phones...They were not disconnected and they got fried.....I don't know if they got fried thru the phone line or if their electronics are fragile enough to be zapped just be being in the presence of such a strong electrical storm...My rotary dial wall phone (Western Electric.12lbs) survived....More thunderstorms predicted this week.... certainly hear a lot of lightning crashes on the bands...

Don't take a chance. If you can hear thunder, then you are at peril.

I'm still off the air due a strike on July 31, 2013.

Some of my broadcast associates have told me that on some mountain top sites, they get lightning strikes on the side of the towers, not only the top/tip.  Now a 500+ foot tower on a mountain is somewhat outside of a typical ham installation, of course, it still shows that lightning doesn't always strike the top of a tower.

One of the most effective devices that reduce the chance of a direct strike on broadcast towers is a dissipation array on the tower top.  Those are devices that look like a "porcupine", with hundreds of pointed needles that bleed off the static charge.  If you look up "stati-cat" (an old name but should still produce results in a search engine) you can see what the device looks like.

Now, for sure, broadcast towers are not ham towers, but we can often glean some ideas from other users that have metal in the air.

73
Ted W8IXY

Regarding 'porcupines' there does not seem to be agreement among engineers that they can actually reduce lightning strikes.

The FAA placed them on a tower, which was later hit by lightning.  During repairs they found the ground system was installed in a faulty manner.  Unfortunately, they terminated the experiment, leaving the question unanswered.

I know of a few hams who never ground their antennas and seemingly never get hit?

I always unhook my antennas and still get hit. I posted this a few years back. The is for the telephone line which is underground. I had the open wire line laying on the ground not grounded and it sparked over to the black ground system and blew a little bark off the wire.  As you can see, it also destroyed the ground fault telephone system.  I wasn't there when it happened and I am happy about that because that may have blown my Depends off or caused me to start wearing them!