Proper way to disconnect a station for thunderstorm.

srd · Nov 3, 2024

Hi,

I am trying to understand a bit about lightening protection, specifically, what is the proper way to disconnect an antenna from station equipment? I am currently working the grounding and bonding of the station, and have LMR400 going to an SPGP on the exterior wall where, as I understand it, I need to put in an arrestor which connects the "unprotected" side to the station "protected" side.

What I don't get is, should I have to open up the panel each time a thunderstorm comes and unscrew the LMR400 from the arrestor at that point? Aside from being tedious, seems like I would wear out the threads and thought there must be a better way.

Thanks,

Crawdad · Nov 4, 2024

No, you don't have to but replacing a worn out PL259, it seems to me, is a hell of a lot cheaper and easier than replacing radios, tuners, power supplies and anything else in your shack that can get cooked. Myself, I disconnect the coax that runs into the shack leaving my HexBeam connected to ground via the ground wire/rod. So far so good after a busy lightning season this past summer. I also disconnect the rotator control cable on both ends. It all takes just a couple minutes and hopefully protects my investment as much as possible. My $0.02

7 3

ClaimJumper · Nov 5, 2024

Yeah. That's probably the safest thing to do. Disconnect is best. I've heard tell of people putting the end of the coax in a glass jar, and leaving it in the shack. I made my shack with an easy to pull through conduit just for that reason.

brandon7861 · Nov 5, 2024

Here I go again. I just wanted to add my $0.02 on glass jars.

IMO, a glass jar is only good for the charge that builds up between the center conductor and shield. That might be ok for a nearby strike or charge buildup from a passing storm, but for a direct strike without a tower ground or other grounding setup (like if you had a dipole in a tree with no grounded lightning arrestor where it enters your house), having the coax in a glass jar would absolutely terrify me. To a mile long lightning bolt, a glass jar is nothing. The arc will simply jump out of that jar and find the nearest ground, and when it does, chances are that jar shatters sending glass everywhere. If your antenna setup is ungrounded, a glass jar is not just false comfort, it's potential shrapnel. Some form of outside grounding is a must!

To my knowledge, good lightning arrestors fire at a voltage just over their rated RF voltage. Lets say an arrestor is rated at 200w RF. Sqrt(200w*50Ω)=100v RMS or 142v peak. Even if it were designed to fire at that exact voltage, that's still enough to kill a radio's front end in receive.

The best protection is lightning rods, several of them, on a good ground network. Take away lightnings chance to strike in the first place. My antenna is 60' lower than the highest point in MN and I have never had a lightning strike. It strikes all around us, but not there. We have three lightning rods all tied into a ground network of 3 ground rods around the cabin. The tower has its own ground too, and thanks to my base loaded sirio827 also being at DC ground potential, the radials and antenna tip can also serve as lightning rods dissipating charge before it can build up to the point of a strike. Lightning rods are not a guaranteed solution, but they sure do shift the odds in your favor.

If your tower and coax shield are grounded, then by all means, save the money on the arrestor and just use the jar. But if your antenna is in a tree, best to do something else.

Shockwave · Saturday at 4:24 AM

brandon7861 said:
Here I go again. I just wanted to add my $0.02 on glass jars.

IMO, a glass jar is only good for the charge that builds up between the center conductor and shield. That might be ok for a nearby strike or charge buildup from a passing storm, but for a direct strike without a tower ground or other grounding setup (like if you had a dipole in a tree with no grounded lightning arrestor where it enters your house), having the coax in a glass jar would absolutely terrify me. To a mile long lightning bolt, a glass jar is nothing. The arc will simply jump out of that jar and find the nearest ground, and when it does, chances are that jar shatters sending glass everywhere. If your antenna setup is ungrounded, a glass jar is not just false comfort, it's potential shrapnel. Some form of outside grounding is a must!

To my knowledge, good lightning arrestors fire at a voltage just over their rated RF voltage. Lets say an arrestor is rated at 200w RF. Sqrt(200w*50Ω)=100v RMS or 142v peak. Even if it were designed to fire at that exact voltage, that's still enough to kill a radio's front end in receive.

The best protection is lightning rods, several of them, on a good ground network. Take away lightnings chance to strike in the first place. My antenna is 60' lower than the highest point in MN and I have never had a lightning strike. It strikes all around us, but not there. We have three lightning rods all tied into a ground network of 3 ground rods around the cabin. The tower has its own ground too, and thanks to my base loaded sirio827 also being at DC ground potential, the radials and antenna tip can also serve as lightning rods dissipating charge before it can build up to the point of a strike. Lightning rods are not a guaranteed solution, but they sure do shift the odds in your favor.

If your tower and coax shield are grounded, then by all means, save the money on the arrestor and just use the jar. But if your antenna is in a tree, best to do something else.

Your lightning protection advice, is spot on. The only thing I will add is that the S-827s DC grounded loading coil will protect you from nearby lightning strikes however, it most certainly will open right up under a direct strike. I've got one that took a direct strike and the coil burned open and came unwound like a spring. The resulting fireworks almost burned the fiberglass insulator to the point where the radiator folded right over.

brandon7861 · Saturday at 5:20 AM

I kind of assumed the coil would be shredded during a direct strike, which is why I bypass mine with an old welding clamp and heavy cable if I am here to do so.

The reason I even mentioned it is because of the lightning rod effect, which I fugured should help to prevent the strike from happening. But knowing it didn't help in your case is making me rethink my reasoning. Severe storm?

Those vandegraff generator videos that demonstrate the function of a lightning rod, where adding a pointy object to the ball stops the arc in that area, was my basis. Maybe I have been getting lucky or maybe the other lightning rods here make up the difference. I don't know now. My confidence in the system I have here just got a warm shower lol. Thanks!

Edit: I know sometimes lightning happens with opposite polarity, and I suppose in that situation, a lightning rod isn't discharging electrons...

Shockwave · Saturday at 6:03 AM

brandon7861 said:
I kind of assumed the coil would be shredded during a direct strike, which is why I bypass mine with an old welding clamp and heavy cable if I am here to do so.

The reason I even mentioned it is because of the lightning rod effect, which I fugured should help to prevent the strike from happening. But knowing it didn't help in your case is making me rethink my reasoning. Severe storm?

Those vandegraff generator videos that demonstrate the function of a lightning rod, where adding a pointy object to the ball stops the arc in that area, was my basis. Maybe I have been getting lucky or maybe the other lightning rods here make up the difference. I don't know now. My confidence in the system I have here just got a warm shower lol. Thanks!

Edit: I know sometimes lightning happens with opposite polarity, and I suppose in that situation, a lightning rod isn't discharging electrons...

In the case of this particular S-827, we sold it to a school bus company in Florida. We cut them down and tuned them for VHF low band. I can only assume because of the area that it was a severe lightning storm. The customer sent the antenna back to me claiming that only the coil was damaged and asking if it could be rebuilt. Unfortunately the insulator was also severely damaged and loaded with carbon trails. I couldn't even begin to tell you what it did to the radio at the other end of the coax. They purchased that from Motorola.

I will mention that points do not repel lightning, they attract it. That's why lightning rods are pointy and Communications Towers have round wire brushes attached to the top that look like stainless steel whiskers to attract lightning first.

When I use the term "attract", I don't mean they draw lightning in like a magnet. That just means if lightning was going to strike in this general area, you can pull it towards a protected target rather than having it hit your antennas.

brandon7861 · Saturday at 9:53 AM

Mixed opinions I guess... Hard to argue with a demonstration like that IMO. And there are many videos demonstrating this in various ways too.

Heres another one

and another one

and another one

My point is that there are videos of people telling you that lightning rods attract lightning with absolutely no evidence to support the claim, and then there are videos that actually demonstrate the opposite is true.

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Proper way to disconnect a station for thunderstorm.

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