Antenna height?

[SteveShannon]

1 hour ago, Lscott said:

I wouldn't recommend that. Lighting strikes are very high voltage and current. Chances are the RF switch would have the internals destroyed, melted contacts and so on, and the current will take whatever path to ground it can find, including jumping any gaps inside of the switch. Your best bet, provided you know a storm is coming, is disconnecting the coax from any equipment and keeping the ends away from anything conductive. A few people claim they put the ends in thick glass jars.

Even near strikes can induce high voltages in the cable ruining to equipment, similar to an EMP event. A lighting arrestor won't guarantee no damage will occur but will go a long way in reducing any that does.

One thing that people don't think about is build up of static electricity, even on bright sunny days. If there is no way to bleed it off the voltage that builds up can destroy RF front ends in radios. You may have seen it mentioned in the specifications but never really thought much about it, some antennas are built with a DC ground, due to the driven element(s) would otherwise be isolated, for exactly the above reason.    

Keep in mind that the grounded coax switch ii recommended was already secondary to a good lightning arrester.  Paths to ground before entering the house in the first place provides more protection than a glass jar, which I believe is more myth than fact.  Pretty sure NEC and ARRL don’t make such recommendations. 

[Lscott]

19 minutes ago, Sshannon said:

Keep in mind that the grounded coax switch ii recommended was already secondary to a good lightning arrester.  Paths to ground before entering the house in the first place provides more protection than a glass jar, which I believe is more myth than fact.  Pretty sure NEC and ARRL don’t make such recommendations. 

Lighting arresters do fail. How many people check to see if their arrester is any good? I didn't want to imply not to use an arrester, but disconnecting the coax is additional protection. 

While having the arrester tied to an earth ground is required no mention of the quality of that earth ground was mentioned. One could sink a 10 foot rod in the ground only to later discover the earth around the rod is mostly dry with a fairly high resistance between it and a ground rod sunk in a patch of soil with high conductivity. In fact some installations they even put salt crystals in the ground around the rod down a bit to improve the soil conductivity. A ground rod where the resistance is too high is basically useless.

https://iaeimagazine.org/electrical-fundamentals/the-5-ft-ground-rod-and-its-little-known-use-in-the-nec/

https://electrical-inspector.blogspot.com/2013/05/verifying-ground-rod-installation.html

https://handtoolsforfun.com/how-to-measure-ground-rod-resistance-with-a-multimeter/

[SteveShannon]

The thing is there are literally tens of thousands of communication sites that rely on high quality lightning arresters and and grounding systems with all grounds bonded.  They ride through massive lightning storms.  Not one of them relies on someone disconnecting a chunk of coax and placing it in a jar. 

A direct strike certainly introduces some uncertainty, but forcing the lightning to take an unknown path by disconnecting a conductor and placing it in a glass container rather than providing a path to ground is worse.  It’s voodoo engineering and we shouldn’t perpetuate such ideas.  

This document has lots of information (chapter 4 I believe) and also lists many other references. 

https://www.blm.gov/sites/blm.gov/files/Lands_ROW_Motorola_R56_2005_manual.pdf

An even more succinct one is the document I linked earlier in the thread, but this one is the most comprehensive I’ve found yet, establishing minimum distances between the antenna tower and any radio buildings, showing how to protect antennas mounted laterally on towers with lightning rods, and many other situations.

 

[marcspaz]

I disconnect my cable and toss it on the ground outside when there is lightning around because I'm lazy and a cheapskate who doesn't want to do it right... but it's not the best recommendation. LoL

[SteveShannon]

43 minutes ago, marcspaz said:

I disconnect my cable and toss it on the ground outside when there is lightning around because I'm lazy and a cheapskate who doesn't want to do it right... but it's not the best recommendation. LoL

Disconnected outside the house and left on the ground with significant separation from the house will work. It’s not terrible. I just have a problem with the whole “put it in a glass jar” in the house. A spark that travels thousands of feet through the air won’t even blink once when it comes to a glass jar. I’d love to see that tested at a lightning lab! ️
Ionized metal, vaporized cable dielectric, and air plus explosively expanding plasma in a glass container. What could go wrong?

[axorlov]

2 hours ago, Sshannon said:

I just have a problem with the whole “put it in a glass jar” in the house. A spark that travels thousands of feet through the air won’t even blink once when it comes to a glass jar.

I see the comment is a sort of jesting and tongue in cheek, but let's be fair. Spark will blink in a glass jar, with both eyes. The ionization properties of air and glass are very different. Another thing to consider, when lightning comes inside, it's already weakened by being bled off by a proper grounding and lightning protectors [hopefully] installed. Leaving cable in a jar vs not leaving it in a jar may mean burned-up radio vs not burned-up radio. Of course, when we are talking direct hit, everything is off the table. One can get a coolest scar ever vs going to the other side of the grass.

[Lscott]

3 hours ago, Sshannon said:What could go wrong?

Just about everything. Don’t bet against Murphy either.

[SteveShannon]

2 hours ago, axorlov said:

I see the comment is a sort of jesting and tongue in cheek, but let's be fair. Spark will blink in a glass jar, with both eyes. The ionization properties of air and glass are very different. Another thing to consider, when lightning comes inside, it's already weakened by being bled off by a proper grounding and lightning protectors [hopefully] installed. Leaving cable in a jar vs not leaving it in a jar may mean burned-up radio vs not burned-up radio. Of course, when we are talking direct hit, everything is off the table. One can get a coolest scar ever vs going to the other side of the grass.

I’m glad you got that my description was over the top; it was meant to be. As you pointed out a properly grounded system with a quality lightning arrester will greatly weaken the energy delivery. I think it’s fine to disconnect the coax also. That’s also why a grounded coax switch is better than a loose coax end inside a glass jar. Of course disconnecting on the antenna end is even better, but may be more challenging. 
 

[Lscott]

On 1/25/2022 at 3:40 PM, Sshannon said:

The thing is there are literally tens of thousands of communication sites that rely on high quality lightning arresters and and grounding systems with all grounds bonded.  They ride through massive lightning storms.  Not one of them relies on someone disconnecting a chunk of coax and placing it in a jar. 

A direct strike certainly introduces some uncertainty, but forcing the lightning to take an unknown path by disconnecting a conductor and placing it in a glass container rather than providing a path to ground is worse.  It’s voodoo engineering and we shouldn’t perpetuate such ideas.  

This document has lots of information (chapter 4 I believe) and also lists many other references. 

https://www.blm.gov/sites/blm.gov/files/Lands_ROW_Motorola_R56_2005_manual.pdf

An even more succinct one is the document I linked earlier in the thread, but this one is the most comprehensive I’ve found yet, establishing minimum distances between the antenna tower and any radio buildings, showing how to protect antennas mounted laterally on towers with lightning rods, and many other situations.

 

You made some invalid assumptions.

I simply mentioned what other people have done, cable end in a glass jar. It’s fair to debate the merits of the practice. I’m not advocating the idea. Perhaps that wasn’t made crystal clear in my post. If I’ve stumbled across this then it’s assured others will. It needs to be addressed. 

The second one is nowhere was there mention of not using a lighting arrester in place of the cable in a glass jar either.

http://www.na0tc.org/lib/exe/fetch.php?media=technical:dissipation_of_lightning_energy_dayton_050908.pdf

This is a good read on the topic.

https://www.w5nor.org/presentations/PolyphaserGuide.pdf