Lightning arrestor and protection for tower

[TonyV225]

Ok heres the deal Tower was started today should be completed within the next 2 weeks I am looking for some safegaurd ideas for lightning protection I remember seeing gas charged arrestors years ago and recently seen the 3 groundrod 1 for each leg and attatched to them with ground strap. I know when your hit your hit and theres noway around it but I still want to take precautions. do unhook antennas but sometimes when away from home them unexspected storms come in Im up pretty high on a hill so I want to do a little extra to protect against that dreaded thing happening. Any ideas or suggestions????

 

[W5LZ]

TonyV225,
The main idea with lightning protection is to keep it out of the house, so to speak. That's done by opening any path into the house, and/or giving it an easier path to someplace else (dirt-ground, hopefully).
The simplest method is to disconnect antennas -AND- grounds from the radio(s) so that lightning can't get to them. The larger that 'gap' is, the better. That 'juice' from lightning can get into electrical devices from the ground side too.
Another part of that is to provide a path of 'least resistance' for that 'juice' so that it doesn't 'want' to follow the feed lines/ground lines into the house. That typically means good grounding on the tower/pole/whatever the antenna is on. Since there's a lot of voltage and current in that lightning 'juice', large ground conductors, or lots of them buried in soil with good conductivity usually means less resistance.
Some of the 'catches' to all that are the connections connecting all that grounding. They have to be good mechanically as well as electrically. Welding or brazing rather than soldering (even silver soldering). Bolting it all together, then welding the bolts is sort of 'over-kill', but not really a bad idea, sort of. Braided straps are not the best option! Unless, that braid is made from #14 wire and thick as a mattress. The number of ground conductors from the tower to dirt does matter, the more the better. and as long as possible/practical too. That "possible/practical" thingy plays a huge part in lightning protection.
Does it sound a little 'extreme'? Yeah, but you get the idea, right?
Commercial lightning protectors are a little over-rated, sort of. They do work! Most of them. Some just work 'better' than others. Any 'protector' that involves a 'gap' is a loosing proposition to start with. None of them are -absolute- protection.

This whole topic is a large and fairly complicated one for people who are not really familiar with it (that's most of us, by the way). I'd really recommend doing some research about it. Commercial radio stations usually have the best lightning protection schemes. Poking around one or two of those stations wouldn't be a bad idea (with permission and an engineer if you can get him off his 'walkman' ).
- 'Doc

 

[Captain Kilowatt]

TonyV225,

This whole topic is a large and fairly complicated one for people who are not really familiar with it (that's most of us, by the way). I'd really recommend doing some research about it. Commercial radio stations usually have the best lightning protection schemes. Poking around one or two of those stations wouldn't be a bad idea (with permission and an engineer if you can get him off his 'walkman' ).
- 'Doc

Lightning protection at a broadcast station is not taken lightly. First the tower,which IS the antenna in at an AM site, has 120 radials each 1/4 wavelength long. They first serve as a groundplane and second as a means of lightning protection. They are all bonded together at the base with either W-I-D-E strap or 3/4 -1 inch copper tubing. The tower is insulated from ground by sitting on a large ceramic insulator.At the base of the tower is a set of static balls. These balls are a couple inches in diameter and are make of plated iron so as not to rust. Some are brass. One ball is mounted on the tower and the other on the tower insulator mounting plate which is connected to ground with W-I-D-E copper strap. The space between the balls is adjusted so that they do not arc with normal TX power and modulation. When static builds up it will arc across the gap to ground. The feedline from the ATU (antenna tuning unit) is generally copper tubing and has a single turn in it to offer some inductance to the huge surge current of a strike.Inside the ATU building there is a static drain choke that consists of a couple hundred turns of 16-18 gauge enameled wire about 2-3 inches in diameter.This is connected across the feedline to ground. It has very high impedance to RF but acts as a dead short to DC.It's job is to bleed static from the tower before it builds high enough to arc. Often there is another set of static balls between the ATU and the transmitter. There is also a large mica transmitting capacitor in series with the RF that acts as a DC blocker which blocks the DC lightning but allows the RF to pass.There is nothing you can to to prevent a strike,only minimise the chanches of getting hit. AM sites are the hardest to protect because they operate so low in frequency that resonances can occur with the actual TX components (large coils and capacators) that react unfavorably to the frequencies generated during a lightning strike. FM sites are easier to deal with because they operate in the VHF region and these resonances do not occur.We usually just ground the crap out of everything there. TX cabinet,feedline shield,and tower itself are all grounded directly.

 

[TonyV225]

Ive actually been in one of those tower stations (buildings) thats wild almost insane I cant imagine long it takes to get that all setup. I ofen wonder when seeing as we drive how many times or how often those cell and radio towers get hit. Now wouldnt these guy wires depending on how there installed or hooked up act as a feed to ground aswell?

 

[Captain Kilowatt]

Guy wires as grounds is not a great idea as they are wrapped around a thimble with a bolt through the middle. There is only physical pressure and nothing electrically bonded.even if the guy wire is connected to the tower and has no insulators inline it still is not a great ground as it cannot be depended upon.Most of these towers have a huge ground wire connected at the anchor point which pretty much serves to protect the guy wire itself from being vapourised in a strike.These sites use multiple ground rods with HEAVY cable connecting them to the tower.All coax cable shields are bonded to a common ground either just before entering the building or just inside.All equipment racks are also bonded to a common ground inside the building.

 

[TonyV225]

That is just wild but I guess when your talking that kind of money for equipment you better have the money and time to ground it properly. I was asking about the guy wires only because I often thought about that being on a regular non comercial tower it seems that the guy wires would be the first or closest (HWY) pathe to ground anyways. I would never rely on that as a ground or know anyone else whos even brought this up but I can see how one could missconcept that. Am I thinking logically or am I way off?? Ok so now to resolve this can you give me some pointers on how you would do this yourself if it were you doing it?

 

[Captain Kilowatt]

All I can say is invest in good copper ground rods. I use 1/2 or 3/4 inch copper water pipe since it has a large surface area,remember it has an outside AND an inside and it will never rust like some of the cheap rods and it is better than the galvanized rods.I placed one ground rod at each tower leg and connected them together with #6 solid copper and then connected 2 inch wide copper braid from each rod to a tower leg. All copper-copper connections were welded using phosphor-bronze rods. NEVER use regular solder.A strike will vapourise the solder.My feedlines and rotor cables come down the INSIDE of the tower and have a one turn loop at the bottom before going underground for about 25 feet into the house.I really should do more work but I plan to completely replace the entire tower in the next year or two at the most so I will put all the effort into it then. BTW I also disconnect all feedlines from the equipment when not in use during thunderstorm season.You can also install static dissapation devices that look like a porcupine on the tower.You can make them yourself from stainless steel cable and fray out the ends. Use a couple pieces of cable and mount to a ring connector and bolt to the tower near the top and middle. This provides many little sharp points to help bleed off static before it builds up enough to cause a strike. The Wire Man sells them for about $35-40 each but it easy and much cheaper to make them yourself and they DO work.

Product Pictures 4 scroll down to # 8741

 

[W5LZ]

Are you ever around any 'oilfield' people? See if they know of a company doing pipe cleaning. No idea what kind'a pipe, but it must be between 6 and 10 inches in diameter. Happened to have a neighbor once who did that. Usually brought a trailer home loaded with all kinds of stuff, those pipe cleaning brushes 6 to 10 inches in diameter just some of it. Asked him what they did with the old ones. He promptly unloaded a bunch and said they threw them away, did I want them? What do you think I said??
- 'Doc

 

[Captain Kilowatt]

Just make sure they are not the newer plastic type. :laugh:

 

[TonyV225]

LOL oil field people in Wisconsin??? NOPE cheese makers and distributors (kidding) but that dont help. Anyways thanks for the help I knew there would be help out here for this. I know when lightning hits it hits as I said but my main concern is the other saftey issues that usually come thith those dreaded bolts of lighting Im going to look around and look at my options. I find it interesting what was said about some of the things we can buy being over rated and over priced which people dont think about at times they see a price tag and figure well that must be the way to go I probally would have thats why I asked here