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Amateur Radio Antennas For discussion of all amateur band designed antennas and related accoutrements. This includes base, handheld, mobile and repeater usage. For commercial antennas on the amateur bands please use Commercial Radio Antennas below.

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Old 11-15-2012, 12:22 PM
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Default Lightening Surge Protector (How they're made!)

Alright so, I've been looking at lightening protection a lot lately, because really who wants that into their shack when bleeding that off and sending it to ground is a better choice. It's important to know that nothing you put in your coax is going to protect anything if a bolt of lightening smashes into your tower or your 43 foot vertical. But that is not really what lightening surge protectors do anyway. It's important to understand that all they do is take the static build up on the coax and what is being picked up by your antenna from being delivered in a huge snap down to your rig(s). It's slightly more complex than that but that is essentially what it does. There are multiple designs, in fact the one I'm going to share has could be altered even. But in short, surge protectors merely shunt high voltage to ground, keeping it out of your rig. The main item responsible for this is a "Gas Discharge Tube". If you want to read all about them you can go over to DigiKey and do so. http://www.digikey.com/Web%20Export/...f?redirected=1

Before I continue... I'm not sure of the legalities with respect to designing your own home made lightening surge protector. I have no ideas what any insurance company would do or say if your house burns to the ground because you made your own lightening protection. If you make your own I'm not responsible, it's not my fault if your entire house burns to the ground and the insurance won't pay for it. Nor is anyone on this forum, or the owners of this forum. This is an educational thing, and hams have been building their own surge and lightening protection since the very start of ham radio, I just wanted to get the disclaimers out of the way.

Construction of your own home made system can cost as little as $15-20 with a metal case, in terms of items needed this is a relatively inexpensive build. I was only inspired to do it because I knew basically what is inside of these Polyphaser and Alpha Delta products (though NOT exactly, I've never reverse engineered either product). But the principals are basically the same as any other form of surge protection (except we're not going to use MOVs, never use a MOV in RF).

This is what your lightening surge protector looks like on the inside (more or less):


I guessed at the ceramic disc cap capacitance value, but for full legal limit you'd want a 3Kv or so cap in there. You can also add to this a resistor, say a 2-5 watts to ground (I'm not sure of value, I'm guessing you'd want it fairly high to not effect SWR, but I may be wrong) which would bleed static build up to ground constantly. The cap won't allow you to pass DC back to the input so you need to put your resistor (if used) and the GDT on the antenna side of the device. Also I want to point out that the GDT I used is (as far as I can tell) the same thing Alpha Delta uses in theirs and charges an arm and a leg for it costs $2.90 (or so) at http://www.alliedelec.com/ here's the direct link http://www.alliedelec.com/search/pro...x?SKU=70184211

Hope this helps..
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Last edited by acyddrop; 11-15-2012 at 12:26 PM..
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Old 11-15-2012, 1:26 PM
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Two big flies in that jar of ointment, the surge protector conducts at 1,000V which is more than enough to fry radio equipment and the capacitor passes high frequency voltage spikes (AC) as easily as RF. Static charge being DC an RF choke is better than a resistor having less than an ohm DCR while exhibiting infinite impedance to RF and will do a decent job of passing an EMP induced surge to ground being of relatively low frequency. You can eliminate the cap on your way to building a cheap, rudimentary protection device for HF equipment but >30MHz all bets are off, there you need well designed commercially available devices, hams swear by Alpha Delta.

The best protection however is proper grounding of towers, antennas, coax, etc. which has been argued here to death but the most important thing often overlooked. That is leaving lead-ins (twin lead, open wire ladder line, single wire, coax, etc.) disconnected at the entrance point unless in use. A lightning storm may be expected 24/7/365, I have seen lightning in snowstorms so THINK AHEAD and expect the unexpected.
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Old 11-15-2012, 2:41 PM
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Cool dictionary

i think you mean LIGHTNING !!!
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Old 11-15-2012, 2:44 PM
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Originally Posted by wtp View Post
i think you mean LIGHTNING !!!
Thank you Internet spelling Nazi

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Old 11-15-2012, 3:29 PM
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Wink Lightening

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i think you mean LIGHTNING !!!
A local TV weather guy has pointed out the word lightening is actually a gynecological term.
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Old 11-15-2012, 8:46 PM
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.....
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Old 11-16-2012, 10:04 AM
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Hopefully the trolls have left...

You can't really use less than 1,000v if you want to use full legal limit, so you're stuck there. The point I'd like to make that Alpha Delta uses the exact same device I linked so clearly it works (I guess?). The thing is though, the point of these devices isn't to protect you from lightening in the first place. They are more in line as a valve to stop huge spikes from hitting the rig, and more importantly to bleed off static (DC) to ground and not pass it along to your rig.

I'm a bit dodgy on my understanding of the use of chokes still, I understand what they do but have no idea what value you'd use. So I subbed in a resistor of several megs to just pass the charge directly to ground without adding much SWR, if you suggest a choke value or what have you then I absolutely agree that'd be better. The cap isn't a particularly expensive item and yes you could eliminate $3-5 from the build but for that tiny added amount of protection it kind of makes sense. These devices have such a limited amount of usefulness to begin with, so much so I'm not sure how AD can justify a 50 dollar price take. LOL.

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Originally Posted by kb2vxa View Post
Two big flies in that jar of ointment, the surge protector conducts at 1,000V which is more than enough to fry radio equipment and the capacitor passes high frequency voltage spikes (AC) as easily as RF. Static charge being DC an RF choke is better than a resistor having less than an ohm DCR while exhibiting infinite impedance to RF and will do a decent job of passing an EMP induced surge to ground being of relatively low frequency. You can eliminate the cap on your way to building a cheap, rudimentary protection device for HF equipment but >30MHz all bets are off, there you need well designed commercially available devices, hams swear by Alpha Delta.

The best protection however is proper grounding of towers, antennas, coax, etc. which has been argued here to death but the most important thing often overlooked. That is leaving lead-ins (twin lead, open wire ladder line, single wire, coax, etc.) disconnected at the entrance point unless in use. A lightning storm may be expected 24/7/365, I have seen lightning in snowstorms so THINK AHEAD and expect the unexpected.
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Old 11-16-2012, 4:35 PM
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"I'm a bit dodgy on my understanding of the use of chokes still, I understand what they do but have no idea what value you'd use."

That which has high impedance at the lowest frequency in use. That gets into some serious math and I don't remember the formula so 1mH would be a safe bet.
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Old 11-16-2012, 5:13 PM
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Reactance = 2 * Pi * F * L I think is the correct math

1uH doesn't have much reactance at all at 1.8MHz (bottom of the ham spectrum) if I did my math right anyway. I may be on the wrong thing altogether too, I've been up far too many hours now.

Ahh crap you said mh.. :/

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Originally Posted by kb2vxa View Post
"I'm a bit dodgy on my understanding of the use of chokes still, I understand what they do but have no idea what value you'd use."

That which has high impedance at the lowest frequency in use. That gets into some serious math and I don't remember the formula so 1mH would be a safe bet.
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Old 11-16-2012, 8:39 PM
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Lightning arrestors like Polyphaser and others do indeed protect from direct lighting hits to your antenna if the surrounding infrastructure and grounding is designed for it.I've seen many repeater sites survive many hits over the years with absolutly no equipment damage.

I recently helped replace a fiberglass StationMaster that got blitzed by a direct hit and the equipment is fine. Unfortunately most homes are not set up to support direct hits like a commercial radio site.
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Old 11-16-2012, 9:35 PM
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These surge devices (the ones we're discussing in this thread) are in NO WAY intended to take the brunt of the lightning striking the tower. I would assume that in MOST cases very little of the voltage discharge is conveyed into the coax. Maybe 30KV - 50KV at most (I'd guess), when compared to the millions of volts of the lightning this is insignificant. A GDT will deliver that to ground for a short period of time (a VERY short period of time). The tower would take the full brunt of the force and conduct it to ground, so yes you are right a good ground system and proper tower setup is important. But your statement that these surge systems "do indeed protect from direct lightning hits" is sort of misleading I think. Their primary purpose is to bleed off unwanted DC in your feed line and to shunt small (50KV or less) transient voltage spikes to ground. While I'm sure they make far more beefy devices for commercial towers, I'm quite sure they cost more than 50 bucks. I'm not saying they don't help, they do. But if the entirety of a strike was delivered down your coax, besides melting it, your GDT based Polyphaser or Alpha Delta is not going to help you much. So the protection they offer in lightning strikes is questionable at best.

As an aside to lightning stikes... I had lightning hit a tree in my backyard it was the loudest thing I've ever heard and absolutely terrifying. It knocked a big chunk of shingles off the roof and I'm noot sure how close it was to setting the roof on fire but the tree was a completely totaled. Oh and we lost a window too as I recall. The funny thing is the baby who was sleeping in the room right next to all this slept right through it, I have no idea how.

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Originally Posted by prcguy View Post
Lightning arrestors like Polyphaser and others do indeed protect from direct lighting hits to your antenna if the surrounding infrastructure and grounding is designed for it.I've seen many repeater sites survive many hits over the years with absolutly no equipment damage.

I recently helped replace a fiberglass StationMaster that got blitzed by a direct hit and the equipment is fine. Unfortunately most homes are not set up to support direct hits like a commercial radio site.
prcguy
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Old 11-16-2012, 10:56 PM
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I've been under a tree when it was hit by lightning and in life events it ranks up there with my birth.

The antenna direct strike survivors I'm familiar with all had Polyphaser lightning protectors. The tower ground does take the brunt of the strike and the feedlines are usually heavily bonded to the towers. Still no equipment damage inside the buildings even though the antennas did not survive in some cases.
prcguy



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Originally Posted by acyddrop View Post
These surge devices (the ones we're discussing in this thread) are in NO WAY intended to take the brunt of the lightning striking the tower. I would assume that in MOST cases very little of the voltage discharge is conveyed into the coax. Maybe 30KV - 50KV at most (I'd guess), when compared to the millions of volts of the lightning this is insignificant. A GDT will deliver that to ground for a short period of time (a VERY short period of time). The tower would take the full brunt of the force and conduct it to ground, so yes you are right a good ground system and proper tower setup is important. But your statement that these surge systems "do indeed protect from direct lightning hits" is sort of misleading I think. Their primary purpose is to bleed off unwanted DC in your feed line and to shunt small (50KV or less) transient voltage spikes to ground. While I'm sure they make far more beefy devices for commercial towers, I'm quite sure they cost more than 50 bucks. I'm not saying they don't help, they do. But if the entirety of a strike was delivered down your coax, besides melting it, your GDT based Polyphaser or Alpha Delta is not going to help you much. So the protection they offer in lightning strikes is questionable at best.

As an aside to lightning stikes... I had lightning hit a tree in my backyard it was the loudest thing I've ever heard and absolutely terrifying. It knocked a big chunk of shingles off the roof and I'm noot sure how close it was to setting the roof on fire but the tree was a completely totaled. Oh and we lost a window too as I recall. The funny thing is the baby who was sleeping in the room right next to all this slept right through it, I have no idea how.
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Old 11-17-2012, 4:12 PM
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Actually it's not the voltage so much as the current that does the damage. Current through a conductor causes heat causes damage, that's why we use the term "fried". When grounding remember Ohm's Law, a bolt carries from 10 to 50KA so kilovolts can develop across millohms. Improper grounding causes flashovers while a good ground system will dissipate the energy in the Earth it was seeking in the first place. Electricity takes the path of least resistance so when a tower takes a hit the tower carries most of the current and the equipment protection has little to deal with. Then when you divide tens of thousands of amperes the equipment protection still has plenty to contend with, get the picture?

Oh, a tree has a rather high resistance so it doesn't carry the current, only attracts the bolt, plasma carries it to ground. That's why the roof caught a flashover, another path to ground and more plasma and BTW at a temperature hotter than the sun it came very close to setting the roof afire and anything in its path to ground.

"The funny thing is the baby who was sleeping in the room right next to all this slept right through it, I have no idea how."
Think daddy, babies can sleep through anything and usually do. Why do you think after a good night's sleep people say "I slept like a baby"? Maybe because they don't scream for the 2:00am feeding? (;->)
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Old 11-18-2012, 6:59 AM
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Take it from someone who,in the last 4 yrs,has had my tower take 2 direct hits,one,unsuspecting.I lost a radio, modem,tv,wireless router,small stuff.The aroma of fried electronics.....The antenna had to be replaced(aluminum Astro-Plane)
The second time,I was out in my shack(garage) when it hit again,this time,everything was unplugged.I witnessed an arc come flying out of my coax,laying on the floor,split into two arcs,and found the nearest ground.That time,I lost 2 tv's,modem,router,stereo,and,a fiberglass piece of what used to be an Antron 99,on the tower top.There were fiberglass shards in every direction for about 100ft. I can honestly tell you,that, NOTHING survives a direct hit,NOTHING.I am just glad,that in fact,98% of it went straight to ground.Both times.
Like the previous post(KB2VXA) said,the best prevention,is disconnect,OUTSIDE of the structure.These experiences have made a believer out me,from the 'Fire in the Sky' !!
-Yeah,I had 'surge protectors',,,they got ate up also.
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Old 11-18-2012, 8:24 AM
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Not on topic, but lightning related..
A couple of months ago a lightning bolt hit so close to my house...
A fraction of a second before the strike, one of the lightning leaders searching for a ground came through our sunroof in the kitchen, literally passed through my fiancée, came out of her finger and continued out of our dining room picture window. My fiancée was absolutely fine, said it felt like sticking her finger in a 120 outlet that tensed up her muscles. I just happened to see the hole thing happen as I was looking towards the kitchen when it went through. Lightning is a strange thing, even with safeguards you can never tell what is going to happen. At least I now know than I am marrying a relation to Thor.

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Old 11-18-2012, 10:40 AM
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surge protectors are for voltage spikes in a power line like when a squirrel comes across a power line and then you get a spike. what is needed is a lightening arrestor like an mfj 270 then you may have a chance. but i am probably wrong lmao.

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Old 11-18-2012, 10:59 AM
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You went off the tracks when you said "MFJ"

But in all seriousness the MFJ thing is the same thing we've been talking about, it's just not made by Alpha Delta or Polyphaser or yourself.

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surge protectors are for voltage spikes in a power line like when a squirrel comes across a power line and then you get a spike. what is needed is a lightening arrestor like an mfj 270 then you may have a chance. but i am probably wrong lmao.

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Old 11-18-2012, 12:05 PM
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You went off the tracks when you said "MFJ"

But in all seriousness the MFJ thing is the same thing we've been talking about, it's just not made by Alpha Delta or Polyphaser or yourself.
10-4 GOOD BUDDY what ever you say lmfaorotf
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Old 11-18-2012, 12:17 PM
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You clearly haven't heard what MFJ stands for..

Mighty Fine Junk

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10-4 GOOD BUDDY what ever you say lmfaorotf
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Old 11-18-2012, 8:57 PM
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Not really, I have a TNC and tuner that work perfectly, you just have to know what you're buying.

A properly grounded tower with attention given to cable paths is a lightning rod protecting a circle the diameter equal to twice the height. Something is wrong considering the damage, checking into how the pros (commercial towers) do it surely would help doing it right.
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