Lightning Arrestor?

[Brales60]

Newb question, but I've seen don't be afraid to ask on here. I live in SW FL, and we get a ton of T-Storms in the summer. I have a outside antenna that can be raised from 10' to about18'. All that said, what are y'all using for lightning?
I was looking at the Poly Phaser, but see a ton of cheaper options on Amazon. Those seem to use a gas tube to blow, and not really sure how this stuff works.
Thanks

 

[mmckenna]

Polyphaser is well respected in the industry. That's what I use at work.

For hobby type use, there may be cost savings in the less expensive models, but the needs/requirements are the same. I don't use anything but the Polyphaser brand, so I wouldn't even try recommending anything else. But, consider it a safety item, and spend accordingly. Lightning isn't something you want to gamble with. Amazon usually has a ton of cheap Chinese products. Even some of the 'name brand' stuff is just a sticker stuck on a cheap product.

Remember, it's not just the direct strikes you need to be concerned with. Even a nearby strike and induce enough energy into the antenna and/or coax to cause major issues.

 

[Brales60]

Thank you sir. That's what I'm going to get when I order my new cables and put it in a weather proof enclosure.

 

[Ronnierozier2]

Thank you sir. That's what I'm going to get when I order my new cables and put it in a weather proof enclosure.

Typically Polyphasers are connected just inside the structure where your coax comes in and runs to a ground bar. Don't put it outside of your home.

 

[W4EMS]

If you can access them the ARRL has several good articles on lightning protection.
Lightning Protection (arrl.org)

I agree polyphaser one of if not the best, alpha delta also very good. This is an area you do not want to skimp on including the grounding rods (plural) and tying into your home power ground. The perfect site is probably not achievable after the home is finished but you can get really close and should.
Lastly be aware some cities/counties may require a permit.

 

[Brales60]

Typically Polyphasers are connected just inside the structure where your coax comes in and runs to a ground bar. Don't put it outside of your home.

Curious, why not outside? My grounds are all outside on my pole. No ground wire on the poly phaser that I can see. Besides the pole, I have a 8' rod running into the ground that everything is tied into.

 

[mmckenna]

Curious, why not outside? My grounds are all outside on my pole. No ground wire on the poly phaser that I can see. Besides the pole, I have a 8' rod running into the ground that everything is tied into.

You can place them outside if you weather seal everything really well.
Preferred location is indoors where they are protected from the environment. Also, in a commercial application, it's common to transition from the larger coax coming down the tower to a small coax to connect to the equipment. Better to have that inside than an additional connection just inside.

 

[Brales60]

You can place them outside if you weather seal everything really well.
Preferred location is indoors where they are protected from the environment. Also, in a commercial application, it's common to transition from the larger coax coming down the tower to a small coax to connect to the equipment. Better to have that inside than an additional connection just inside.

Noted, and actually makes it easier. Thanks again.

 

[W8HDU]

Polyphaser is good, but in actual practice, if lighting is going to jump several miles across the sky, there is no guarantee it won't jump across the polyphaser or come into the shack. As a rule of thumb, you can't prevent lightning, but you can discourage it from ingress to your equipment. In my line of work the tower is well grounded. My home tower, Rohn 25 has two woven braided straps off the legs, out 6' from the tower where the ground rods are driven in deep. Antennas are grounded at the antenna attachment, 6' above where they transition horizontally to the house/shack, and just before they line goes inside through the mounting plate after going through 6 raps of coax on a 9" form. The line should also be afixed to a leg mount of the leg. Don't use isolated standoffs.

I've taken 2 hits while I've lived here, 9 hits in the neighborhood because of our conductivity. But in both times the line was trashed by the lightning, but there was no damage to the inside or the house, or equipment. Only casualty was the line on the tower as lightning egresses the line to the ground points. (Easiest path to earth).

 

[W4EMS]

mmkenna, any thoughts on coiling the coax? I know some installers who do this for the AC cords and swear by it with anecdotal experience (i.e. DC likes a straight line path), wondering if same holds true for coax, all other things being equal.

 

[WA0CBW]

They are NOT lightning protectors, the are lightning surge arrestors. They are designed to shunt to ground induced voltages on the coax center conductor caused by a nearby lightning strike. Nothing will prevent or protect you from a direct lightning strike.
BB

 

[mmckenna]

mmkenna, any thoughts on coiling the coax? I know some installers who do this for the AC cords and swear by it with anecdotal experience (i.e. DC likes a straight line path), wondering if same holds true for coax, all other things being equal.

The loop is something I've seen some ham operators do.
I've never seen it at a commercial site.
But at commercial sites, things are done quite a bit differently than you'd find in most hobby installations. DC grounded antennas, lightning air terminals, very serious grounding, coax is grounded at several points coming down the tower.

The art of doing this isn't something that can be compressed into a paragraph or two on a chat board like this. If you want it right, you hire an engineer who designs the system.

You should look at the National Electric Code:

https://www.mikeholt.com/instructor2/img/product/pdf/17LED-1498-sample.pdf

And Motorola R56 document is pretty much the industry bible on grounding. It takes NEC and goes several steps farther. It's out there on the web, just do a search on it.

 

[amcferrin90]

In working with alarms we would tie knots in the phone cable. Where transients would come in through phone lines, they would literally blow the solder off the back of the boards where the phone line plugged in. Once we started using the knots, the phone wire would blow out and take the damage. Something about lightning and transients not being capable of following sharp bends. Just for reference. Not sure how tight of a knot you could put in antenna cable, depends on what you're using I guess. Also depending on the Polyphaser you're using, they may not have a noticeable ground connection but if you look at the install sheet there's extra parts to buy for a bracket that one of the threaded ends mounts to. Such as the NSX-TFF or similar devices.

 

[MUTNAV]

mmkenna, any thoughts on coiling the coax? I know some installers who do this for the AC cords and swear by it with anecdotal experience (i.e. DC likes a straight line path), wondering if same holds true for coax, all other things being equal.

NAMB (Nobody asked me, but)...

correct lightning protection usually isn't ever run with anything but curves and direct runs.

IEEE also has good info, as does the mil handbook on grounding and shielding. The N.E.C. is usually what is required though.

A person that coils up an antenna cable is either experimenting with some novel ideas (which is fine with me), or just not wanting to cut the cable to size. Which I've done also, but I don't claim that it improves).

This isn't talking about drip loops, but actual coils of wire.

This is from the FAA handbook on their sites.

3.7.7 Conductor Routing
Roof and down conductors shall maintain a horizontal or downward course. No bend or
connection in a roof or down conductor shall form an included angle of less than 90 degrees, nor
shall it have a bend radius of less than 8 in. (203 mm). Conductors shall be routed external to
buildings and 6 ft. (1.8 m) or more from power (including obstruction lighting power cables) or
signal conductors. T-connectors shall not be used to interconnect main conductors. All main
conductor transitions shall be swept so as to maintain the 8in or greater bend radius.
Thanks
Joel

 

[mmckenna]

Using multiple loops of something like RG-8/LMR-400, etc. is fine for HF or VHF use where cable loss isn't as critical and the cable will handle a relatively small bend radius. Also, not as critical in hobby applications.

Higher frequencies, cable loss becomes a concern. Coiling up 20-30 feet of cable on UHF, 700MHz, 800MHz, or 900MHz, that becomes an issue because you are introducing additional loss. That loss has to be designed into the system, and accounted for, or made up somewhere else in the system.
If you size up to larger cable, like 7/8" Heliax or 1-5/8" Heliax, the bend radii get really large, and you'll waste cable and add loss.

In commercial applications, the system of proper grounding, grounding the coax at several points, and using lightning protectors/suppressors, it all works pretty well.

Lightning strikes can have an enormous amount of energy, and man thinking they can control it is usually met with laughter. I think Ms. @Lauri-CoyoteFrostbite has some pretty good examples how the lightning Gods will snicker at your attempts to control it. You can search for some of her experiences.

 

[Lauri-CoyoteFrostbite]

.

".........any thoughts on coiling the coax?............ "

There may be science behind coiling a length of the antenna feed. The theory is the coil forms an inductive loop, in effect becoming an RF choke--of sorts. Since lightning is a high frequency pulse, this coiling of coax supposedly will block a low energy strike that was not sufficient to vapourize the whole she-bang.
Some of our guys swore by doing this-- and I don't disparage the practice. I have seen the results of what direct hits can do, especially to feedlines.

A memorable example was, at first, quite a mystery....... An electrical storm, a site goes off the air-- and when our guys arrived, I got this call ---

"Lauri, you got to see this ......!"
(I always loved calls that started like that)

"Did someone steal the antenna feedline ?"

Approximately 40 feet of large diameter Heliax was simply gone, -as was the vertical antenna it had been attached to. The equipment in a hut was untouched, though all the circuit breakers had been tripped. The first thought was that someone had stolen the line- maybe taken by aluminium/copper scrap collectors. But looking closely where the line had (formerly) lay there was a trail of gray dust leading from the tower to the hut.
Inside the hut the Heliax passed through a thick piece of copper plate/common ground-- then to a coax barrel/surge protector adapter -- and then to a coil of coax. The static (lightning "arrestor") gizmo was fused to this plate, but the coiled coax was untouched.
In a brief flash the Heliax was simply 'gone." But did the coil of coax arrest the further surge ?

Ever after I have always added a few loops to any coax lines as it enters a building.

Call it Black Magic--- but hey, what can it hurt ?


Lauri




______________________________________________________


(irregardless, my personal radios I disconnect, when possible, any antennas and power supplies when not in use)

.

 

[RFI-EMI-GUY]

There is an FM broadcaster manufacturer, Nautel if I recall, that mandates a couple huge ferrite donuts be installed on the jumper from the transmitter to the hardline. They are simply slipped on, not loops. If not installed, they will balk at warranty for lightning events.

I should add that the lightning protection I have constructed for my sprinkler controller includes ferrite donuts on the cable where it comes into the protector and the wires between the protector and the RainBird timer.

 

[W8HDU]

This gets a little deep into the woods on the subject, but this Motorola book (PDF) has good information. Note, it's 8.1 mb

The issue of lightning mitigation is usually a factor of not knowing the issues of lightning, or the willingness to do it cheaper, and not better. Here's a few things we do in high power broadcasting.

I mentioned the line bonding which is really important on towers. The lightning is looking for the best path of least resistance to ground. I've seen big towers, greater than 300', have bonding to the tower at the antenna, 6' above transition, and sometimes in the middle of the vertical run or even at multiple places in the run. Usually an Andrew lightning kit is used.

Ground rods are crucial, and long rods which can get into moist soil or the water table are preferred. At our TV station in Lima, we came off each leg of the tower out, away from the tower 12', and drove a 10' rod down to 23' so it was in the water table. The tower should be grounded with either strap, (Georgia Copper is where I got mine), or braided copper strands. Electrical ground wire is OK on power box installations, but it appears as a resistance to a lightning strike so it's slightly ineffective.

When power is on a tower, such as tower lights or power for amplifiers, etc, an Austin Transformer is used to bridge tower to building. Looks like two doughnuts interlinked with each other.

For hot towers, AM and high power HF, an isocoupler is used between station and tower to allow RF to continue on to the antenna while making that path appear high impedance to lightning. Usually we mount the isocoupler on a pole next to the tower, and on the tower side add a spark gap just to hedge our bets.

Coiling the coax in 6 turns of coax on a 9" form helps lightning sees this as a resistance, and will want to take the path of least resistance. I know it's hard to do with RG58, but a small piece of PVC sewer pipe will make the form you need. U.S. Plastics has some acrylic tube which I love using for coil forms. Their web site is hard to navigate, so keep looking. However, if you're ever on I75 by Lima, their outlet store sells tubes of it for as little as $4 per foot, which is cheaper than sewer PVC. Also, they sell discards of cutting board material which I've used for large coil forms and to wrap coax. (I think I have a picture of a form).

I've worked in broadcasting for 50 years, so I've had a lot of experience with the damage of lightning on equipment and facilities. Most of the fires and trashed equipment can be traced back to lightning. We have dozens lightning hits during this year, but no equipment or building damage ever occurred. It's worth the money to install good lightning protection to save your stuff, and not go on the cheap.

 

[W4EMS]

mmkenna and all thanks. Some good info in here with the truth that a direct hit rarely ends well outside of a very hardened system. One of our commercial installers showed me a photo of an AC line he had coiled and was laying on the floor which up to the coil was vaporized and beyond which the gear was not damaged but also noting other mitigation equipment was being used too.
I was just pondering the coax feedline which as noted is easy to do with smaller cable, near impossible to accomplish with hardline.
The multiple mitigation approaches noted above are the best way, none of which are 100%.

 

[W8HDU]

Hardline sometimes needs a wider radius depending on size. LDF4-50A can be formed into a 12" roll with careful hand-over-hand forming. LDF5-50A needs 15-18".

This is what I make for forms. The white is cutting board material. The metal brackets are old street signs (gotta love Municibid), and the hardware is stainless 5/8. I also use the same forms for winding #10 copper wire, or 1/4" copper water line to make RF coils. The ones in the picture I'm going to use with copper water line to make a "T" network for 160 meters.