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Conducting the Autopsy on a Dead Antenna

from Don Keith, N4KC on February 8, 2011
View comments about this article!

Conducting the Autopsy on a Dead Antenna
By Don Keith, N4KC
www.n4kc.com
www.donkeith.com

Maybe I have seen too much CSI on TV. But as I examined my recently expired homebrew hexagonal wire beam, I felt for all the world as if I was conducting an autopsy. An autopsy on an old friend who had stood by me faithfully for better than two years. But I also realized that such a post mortem can be helpful, to me (and hopefully to you) in future projects of a similar nature.

Let me back up a few steps. Several years ago, I began research on various possibilities for an antenna that would offer me some gain, some zapping of signals off the back side, and some side rejection, yet would otherwise fit a long list of other requirements I had imposed on myself. You know, the usual stuff like size, weight, cost, availability of components, and complexity of construction.

There were several possibilities, but I settled on the hexagonal wire beam, that odd-looking critter that most resembles an upside-down umbrella, but without the fabric on a real umbrella that keeps the rain off our bald spots. One reason for its choice was because truly wonderful notes and directions for its construction existed on the Internet, courtesy of Leo Shoemaker K4KIO and Steve Hunt G3TXQ. And I kept talking to guys on the air with big signals who sang their praises, usually at several dB over S-9.

So I gathered materials in my usual plodding way and built it, veering off in a few ill-advised (in retrospect) directions on my own. I was (and still am) so proud of my little upside-down umbrella that I wrote an article about it on eHam.net. It really did perform beyond my expectations, and especially for what amounts to a two-element beam with its elements folded into shapes a contortionist would avoid.

At least it performed well until a few weeks before Thanksgiving. That is when I noticed the SWR running higher than normal. I had long since stopped looking up at the beam every time I was outside and had started just assuming everything would be fine. But a quick glance upward the next time I was outside told me that the 20-meter wire element had come loose and was draped all over the other elements. And the 17-meter element hung down below the spreaders and base plate on one side. Somehow, the top two elements had let go their grip.

Aarrgh! Well, that was not exactly what I said, but you get the idea. The neighbor kids have sensitive ears.

So, I asked myself, do you pull it down and fix it or do you spring for a commercially made model that you can trust up there? I wrestled with that quandary for several weeks, continuing to use the antenna at 100 watts and, believe it or not, actually working a couple of new ones. 

See, I confess I have been concerned about a couple of things in my construction. One was that I had put more tension on the 20-meter wires than Leo’s instructions recommended, mainly because it looked perfectly fine to me the way I wanted to do it. And I also worried about where the driven elements tied into the bolts at the beam’s center post. I had used short coax jumpers made from stiff RG-8U between each set of elements. The beam uses one feedline for all bands and the jumpers to connect from the top down the length of the center post between sets of bolts that served as terminals for each set of driven-element wires. I had worried that those would either work their way loose or start taking on water, regardless the amount of goop I had used to protect them.

There was one determining factor in my ultimate decision about repairing or starting over: I no longer climb towers, and I do not wish to keep someone who does on retainer. Whatever went back up there would have to last. 

See, the truth is, I know the idiot who built my hexbeam. I did not totally trust his fix any more than I did his original construction job. I bought a commercially made beam after doing some more research. Lots of research, because I am a miserly so-and-so. 

There are several very, very good suppliers of these beams, but I chose the one sold by K4KIO for several reasons of my own. I have not regretted the purchase. K4KIO, DX Engineering, and Mike Traffie all offer wonderful products and all seem to have stellar customer service. I chose the one I did primarily because I liked the way the elements attached to the center post, which is sealed, and the fact that the antenna is not a kit and appeared to be very easy to put together, even for a guy with minor nerve damage from a previous immune-system disorder and who lacks most normal mechanical skills. 

In short, this version offered no short, stressed, thirsty coax jumpers. Good ropes out to all the spreaders to help hold the shape. And only a couple of hours of work to put it together. Even the price was not outrageous when you consider the fact that it is a six-band beam—I opted for the six-meter element, too, which would never have worked in my previous homebrew configuration.

When I got the old beam down, I decided to do a careful autopsy, not with scalpel and bone saw but with nut driver and diagonal cutters. If you do likewise, I suggest you do all you can to keep the antenna intact, just as it was, broke stuff and all. Avoid the temptation to tell your tower guy to just drop the dang thing. Try not to do any more damage on the way down and over to the corner of the yard for its autopsy…er…inspection.

When you get the chance, give the thing a thorough going-over. What else broke that you did not notice or that did not show up on the SWR meter? What gives the appearance of being on the verge of going bad before the other malady happened first? What can you do in the future to avoid this? On the other hand, what has held up well?

Here is what I found in my case:

My so-called stainless steel hardware from a big-box store rusted terribly. The bolts in the center post that held the ends of the wire elements were the worst, though they had not yet failed. It would have been only a matter of time, though.

On the other hand, the stainless steel U-bolts and hardware that I bought along with a commercially made aluminum base plate (from W4RDM) looked as good as they did the day the thing went up. Bright and shiny.

The fiberglass spreaders—also purchased commercially, from Maxgain Systems—looked fine. I did spray-paint them prior to construction to protect from those pesky UV rays.

Amazingly, those coax jumpers I most worried about held up just fine. I pulled the insulation back on a couple of them to see if they had taken on water and I saw no signs of it.

The antenna wire—a non-insulated flex-weave with stainless steel strands woven in—showed some signs of rusting but except for a few strands that had sprung loose, still seemed to be solid, even on the two elements that were drooping. The wires had not broken.

Ah, the real culprit. I used tie-wraps through hose clamps to hold the wires in place on the spreaders. At high-stress points, I backed those up with small bits of rope. Well, either the antenna wires sawed through several of the tie-wraps—maybe because of the wind moving the spreaders a bit—or the “UV-proof” tie-wraps weren’t. Several of those not also supported by short lengths of rope had broken and that was what allowed the elements to break loose. If they had held, I would not be writing this article. At least until the rusty “stainless steel” bolts gave way.

I did discover a double-whammy shaky connection in my coax connector that attached my feedline to the pig-tail I had going up to the antenna feedpoint. Whew! Glad I did! Turns out both the PL-259 and a barrel connector there BOTH had problems and were intermittent. That gave me and my tower climber a bit of heartburn for a few minutes until we isolated the problem. Neither of us wanted to take the antenna back down and check connections on it again. (And yes, we had done that—thoroughly—before we put it up there! The problems only showed up when we did the weather-proof wrap at the junction point.) 

Take advantage of having everything apart to thoroughly inspect feedline, connections, rotor and anything else that stays out there in the weather 24/7 while you are inside in your toasty, warm shack. Sometimes we concentrate on fixing whatever the glitch is and overlook something else that could go goofy on us.

So, if I decide to build a wire beam in the future, I will choose better quality hardware and use some kind of backup to the tie-wraps. I will also be more careful about putting undue stress on the wire elements and their attachment to the center post. I do still have a perfectly good base plate and spreaders and am contemplating doing a single-band, portable version, just for the heck of it. 

By the way, I do not want this article to reflect negatively on the hexbeam, bought or homebrewed. It is a very good antenna option if you want something light, durable, and surprisingly effective.

You know, I still have a suspicion that a very large hawk that was frequenting our neighborhood—hopefully feasting on coax-insulation-eating squirrels, but that is another story—may have had something to do with the sudden failure. We did not really have any serious wind or ice, but that phoenix-like critter might have hurried along the inevitable failure of my pride-and-joy beam.

Do hawks forfeit any protected status if they get in the way of my quest for DX and long-winded ragchews?

We’ll see what the guys at CSI have to say about that one!

Member Comments:
This article has expired. No more comments may be added.
 
Conducting the Autopsy on a Dead Antenna  
by K3AN on February 8, 2011 Mail this to a friend!
I, too, wonder about how UV-proof a black "UV-proof" tie wrap really is. I used some as end insulators for an insulated wire delta loop. There was only a few pounds of tension but the tie-wraps lasted less than a year. At our tennis club, they use tie wraps to hold wind screen fabric against the chain link fence surrounding the courts. There's at least one broken one lying on the ground many times when I am there and often a section of screening will flop down until new tie wraps are installed.
 
Conducting the Autopsy on a Dead Antenna  
by NY0K on February 8, 2011 Mail this to a friend!
Well-written and enjoyable to read.

I've also had issues with so-called stainless steel bolts. I'm careful to buy them from retailers who carry the "good stuff".
 
RE: Conducting the Autopsy on a Dead Antenna  
by K6AER on February 8, 2011 Mail this to a friend!
I live in Colorado and at 7000 feet I have found there is no such thing as UV proof plastic. If we use tie wraps I always wrap the ties with black tape. Its only function is to keep the UV off of the structural capabilities of the tie wrap. The UV index here in the summer is 12 where the average in the US is about 5.

As far as antenna hardware goes, if possible, never use stainless. Galvanized bolts and hardware are best and is what is preferred for used on commercial antennas. Now I understand small antenna manufactures have a harder time finding proper galvanized hardware and the narrative I ham radio is stainless is the way to go. But as mentioned stainless will rust with time and even worse the hardware can gal when the nuts are removed from the bolts.

It takes time to understand what is strong enough to withstand the riggers of weather without making the antenna to heavy. Antenna structural design is an art form. Static and well as dynamic forces have to be taken into account. How the materials will age and the stress and load of snow and ice will change the balance of a large array. Other issues such as antenna performance with weather and critical areas that can be effected by surge and lightning strikes.

On the marketing side you can build a boom proof antenna but if it is too expensive the best antenna in the world may be priced beyond what the market will bear. It is said the quickest way to make a small fortune in ham radio is to start with a large fortune.
 
RE: Conducting the Autopsy on a Dead Antenna  
by N4KC on February 8, 2011 Mail this to a friend!
Mike, agreed on all counts. The key is "properly" galvanized hardware. It's hard to tell! That's why I have typically relied on stainless steel. But, as noted, that can be a crap shoot, too.

It really is difficult for us to imagine what our antennas are going through out there. And those manufacturers who have products that work and work well for years and years without maintenance are to be commended.

We homebrewers just have to do what we can do. And keep handy a list of people who are willing to climb towers.

Don N4KC
www.n4kc.com
www.donkeith.com
www.facebook.com/donkeith
http://n4kc.blogspot.com
 
RE: Conducting the Autopsy on a Dead Antenna  
by NO9E on February 8, 2011 Mail this to a friend!
All tie wraps in my antennas broke. All screws from Lowe's (except brass) corroded. Part of a package in the commercial antenna is choice of components that will last a long time.

Then there is a question of product support over a long time. One screw in my Cubex quad fell off and all the substitutes are rusting in a few months. Cubex is nonresponsive; probably dead. I bought a number of stainless screws, and none of them fits.

Ignacy, NO9E


 
Conducting the Autopsy on a Dead Antenna  
by WW4CC on February 8, 2011 Mail this to a friend!
Nice job, Don. Ducky on NCIS would be proud! You're eye for detail rivals even his and your expository telling of the tale would make him proud.

The moral of the story might just be:

"We are HAMS. We experiment (and , yes, sometimes make it up) as we go. We learn from and share our victories and our mistakes. Finally, we NEVER take ourselves too seriously; but we do take our hobby VERY seriously. Kudos to you for sharing this. In reading it, I have learned, and I, for one appreciate the opportunity once more, to do so! See you on the nets!

73,
Carl
KC4TCG

 
Conducting the Autopsy on a Dead Antenna  
by KI8JD on February 8, 2011 Mail this to a friend!
I have worked with various fasteners for over 35 years as used in various types of machinery.
We purchase most of our bolts, screws, ty-wraps, etc. from a company named Kimball-Midwest. They have a very good stock of almost any kind of fastener you might need. www.kimballmidwest.com
I'm sure there are other companies that are just as good.
They offer a few different alloys of stainless bolts. One alloy has more iron, and is slightly magnetic. We don't use that alloy, and ours does not rust, even when exposed to Michigan's salty roads, and other corrosive materials. We do use never-seize in corrosive environments to protect both the bolt and the dissimilar metal(s) through which it passes.
The stainless fasteners we use are shipped dry. If you try to assemble something with DRY stainless bolts and nuts, the nut will seize to the bolt before they get very tight. I have learned this the hard way. I always use never-seize. If you use regular steel nuts on the stainless bolts, you don't get the immediate seizing problem, but the nut will rust sooner or later.
The black ty-wraps are UV resistant, not UV proof. The white ones aren't even worth buying, unless you like the color. With the good quality USA made ones, the white and black are usually the same price.
73 Jim ki8jd
 
Conducting the Autopsy on a Dead Antenna  
by WA2JJH on February 8, 2011 Mail this to a friend!
One of the best articals I have seen lately. You got talent. I hope to see more FB OM!
I am a Bio-medical engineer. I have done many M-n-N's (Morbidity and mortality) on many animals. Yes we did induce the neoplasti', chemicals, and even implanted RF devices in living rats. Google the ROBORAT PROJECT at Downstate, if you want to see what
WILL cure people of many Ills in the future.

Nough said,about some of the stuff, I have been the RF implant dude/engineer.

Back to Dead antennie. Forget the Calculas. All hams of any experience level can use their eyes and nose. Fried Radio's, Tuners, and most important and passed by is the SKYHOOK(Antenna)

IMHO, the best to autopsy are antenna's(i) that seemed to die by no obviouse reason. Many do not have the spare bux to do destructive testing.

The burn patterns on traps and inductors can tell the story.
Using an all in one ant analyser gives more possible proof. Why do antenna's short, open or fry.

We all know a quasi direct lightening hits will do the most destruction. A lighting hit over 100 meters away fried a Hams antenna. He sent me the photo of an entire TS-850 front end that was a work of abstract art in burns. I sold him a spare board. Low RX sensitivity was with the board swap.

He then found the antenna and ATU were F.U.B.A.R.E.D. Every Trap had some degree of destruction.

If you use a cheapo 10M 5/8 wave vertical, remove the gamma match. Add your own non freq dependant HV/EMP/static coax fuse.

Best antenna mystery I fixed was an oxidised antenna
connection. The oxidation created a diode like effect.
In other words, I had an unwanted MIXER at the coax interface. Took me weeks to wonder why I had new spurs, birdys, IMOD, and not too mention low selectivity coupled with high sensitivity on freqs I DID NOT WANT!!! TNX AGN FER a needed artical. 73 DE MIKE
 
Conducting the Autopsy on a Dead Antenna  
by KG4FET on February 9, 2011 Mail this to a friend!
I didn't read all of the replies, but a quick test for "real" Stainless is that it WILL NOT stick to a magnet. Stainless hardware is better purchased at your local marine store vs the "big box" stores, you will pay a little more BUT it is more likely to be Stainless.
73
de KG4FET Sandor
 
Conducting the Autopsy on a Dead Antenna  
by KG4FET on February 9, 2011 Mail this to a friend!
I didn't read all of the replies, but a quick test for "real" Stainless is that it WILL NOT stick to a magnet. Stainless hardware is better purchased at your local marine store vs the "big box" stores, you will pay a little more BUT it is more likely to be Stainless.
73
de KG4FET Sandor
 
Conducting the Autopsy on a Dead Antenna  
by N4KD on February 9, 2011 Mail this to a friend!
I don't agree with the comments on cable ties. We use cable ties by the thousands and they don't fail, at least not in the 15 years I've been working with them. Just use good, UV stabilized, nylon ties from a reputable source. Here's one example, http://www.newark.com/jsp/search/productdetail.jsp?SKU=46N2677. One note, though, we do see these ties become brittle when they are in constant contact with oil, whether or not they're exposed to UV.

I concur with the comments regarding galvanized hardware. That's the best you can do for outside applications.
 
Conducting the Autopsy on a Dead Antenna  
by N4KD on February 9, 2011 Mail this to a friend!
I don't agree with the comments on cable ties. We use cable ties by the thousands and they don't fail, at least not in the 15 years I've been working with them. Just use good, UV stabilized, nylon ties from a reputable source. Here's one example, http://www.newark.com/jsp/search/productdetail.jsp?SKU=46N2677. One note, though, we do see these ties become brittle when they are in constant contact with oil, whether or not they're exposed to UV.

I concur with the comments regarding galvanized hardware. That's the best you can do for outside applications.
 
Conducting the Autopsy on a Dead Antenna  
by N4EWS on February 9, 2011 Mail this to a friend!
Hi All,

As far as the stainless steel parts go...
I always buy from a company called,"Fastenal"! And yes they have a website but they have stores in most towns or cities with heavy industries in the area. As for prices, they have all of the all-in-one, stop-n-shop hardware places beat by a long----shot !

TNX & 73
 
RE: Conducting the Autopsy on a Dead Antenna  
by W8JI on February 10, 2011 Mail this to a friend!
Stainless will not rust. The problem is people buy things that are not what they are represented to be, and then they make a silly rule up like "stainless will rust and galvanized will not". The only thing that can cause stainless to rust is if the steel contaminated with iron, or it wasn't stainless to start with.

On the other hand, it is extremely difficult to find galvanized hardware that does not rust. It must have a thick dipped coating or it will eventually rust.

I use stainless in all of my antennas and I've never yet had any rust, but I have some Rohn tower bolts and other galvanized hardware that look terrible from rust.
 
RE: Conducting the Autopsy on a Dead Antenna  
by K0BG on February 10, 2011 Mail this to a friend!
This site isn't antenna related, but it sure explains the issues behind stainless:

http://www.fantes.com/stainless-steel.html

Alan, KŘBG
www.k0bg.com
 
RE: Conducting the Autopsy on a Dead Antenna  
by KE3WD on February 10, 2011 Mail this to a friend!
I was told by our resident metallurgist at the time that is is the Carbon content of certain Stainless Steels that causes the rust.

Apparently the good Stainless has more nickel in it, lower grades have nickel but carbon as well.

He also told me that ALL of it will rust eventually, its just that the better grades will take a much longer time to do so.


73
 
RE: Conducting the Autopsy on a Dead Antenna  
by W8JI on February 10, 2011 Mail this to a friend!
Carbon has nothing to do with rust. The chromium is builds the protective layer on stainless.

http://www.ssina.com/faq/index.html

http://chemistry.about.com/cs/metalsandalloys/a/aa071201a.htm

Some of my stainless bolts, screws, and plates are 40 years old, been outside most or all of the time, and still look like new. The same is true for my tower bolts and clamps.

73 Tom
 
RE: Conducting the Autopsy on a Dead Antenna  
by WA2JJH on February 10, 2011 Mail this to a friend!
FB TOM. TNX FER "Ultra Primo" info. I want to pass a screwball idea.

Sun anti-tan lotion has an SPF of 50 max! P.A.B.A, the active UV block agent in OTC sun burn lotion can be made psuedo-water resistant.

Of course, one the beach, I showed my chronies PVC black electrical tape. Tongue in check, I told them..................Electical tape has an SPF of 1000% hi-hi.

Serious question.....Is there any type of high viscosity spay on co-polymer antennie spray that could last a few months.. In english, UV spray in the "Skunk Work scene"?

I am sure fakes and Mil DARPA might be working.
If it is a Northrop aviation product, I understand if folk cannot or will not share. Heck, might make for a decent provisional patent pending deal.Perthaps not. Sounds chemical problomatic deluxe.hi-hi

Darn it,,,,,,did I give MFJ enough credit, if they all of a sudden make an ultra crapiola-cheapskate facimile.
J
73 DE JJH

 
Conducting the Autopsy on a Dead Antenna  
by NX7TT on February 10, 2011 Mail this to a friend!
Very well written and enjoyed it very much...
Got to love them Hexes..I do mine
 
RE: Conducting the Autopsy on a Dead Antenna  
by K9MHZ on February 10, 2011 Mail this to a friend!
From KE3WD: >>>>I was told by our resident metallurgist at the time that is is the Carbon content of certain Stainless Steels that causes the rust.
Apparently the good Stainless has more nickel in it, lower grades have nickel but carbon as well.
He also told me that ALL of it will rust eventually, its just that the better grades will take a much longer time to do so.<<<<


Steel is an alloy of iron and other elements, mostly carbon, to give it strength. The alloying elements are heated so to go into solution and then harden to exist at the grain boundaries of the iron structures. Depending on heating, concentrations of alloying elements relative to the quantity of iron, and the types of alloying elements themselves, you can engineer a wide variety of characteristics into the resulting steel.

Stainless steel uses elements like chromium and nickel in addition to carbon, to provide corrosion resistance. The carbon itself does not corrode the steel....my guess is that your friend was making a comparison between straight carbon steel and stainless steel, in how much carbon is used in each case. For stainless, with the added alloying elements, you'd see a lessening of carbon used, to make way for the other elements added....in this case, those that provide more corrosion resistance. You can alloy only so much before your steel's strength will suffer.

BTW, there are lots and lots of other alloying elements used in differing types of steel products. Still, carbon rules, and has for hundreds of years.

Brad, K9MHZ
 
Conducting the Autopsy on a Dead Antenna  
by KE4NU on February 11, 2011 Mail this to a friend!
Good article Don, and yes I had the same problem with my homemade hexbeam along with an osprey using it as a catapult. I rented a manlift and went up there and replace all the cable ties and used name brand ones this time around. I read about a week after that I should have wrapped the ties with black electrical tape. Oh well! The hexbeam is working better than ever now and I replaced the homemade choke coil with a ferrite bead choke. Probably in a couple of years I'll replace the cable ties again. Sorry you gave up on yours! take care my friend..KE4NU in Victor, MT
 
RE: Conducting the Autopsy on a Dead Antenna  
by N4KC on February 12, 2011 Mail this to a friend!
Aw, Alan, I didn't give up on it. It's really in better shape than I thought. If I replace the bolts in the center post, I think I can easily string up a couple of bands for portable use. One other lesson I learned: I glued the fiberglass spreaders together, so they're a bit long now to carry around. I have a pickup truck, so for Field Day or a special event locally, I can get it there, I think. I'm thinking through the best way to package the elements and rope for quick assembly on-site. I may just use the nice plastic bags the K4KIO unit came in...already marked!

73, and stay warm up there in the Bitterroots!

Don N4KC
www.n4kc.com
www.donkeith.com
http://n4kc.blogspot.com
 
RE: Conducting the Autopsy on a Dead Antenna  
by WA2JJH on February 14, 2011 Mail this to a friend!
Carbon is one of the most important elements in Organic, INorganic, and industrial chemistry.
It is a Metaloid not a semi-conductor, metal, HCLBRIF-SPSE. honclbrif spse---what?

Practice that, if you please. What is in it for anyone? . You have every single non-metal.

Hydrogen, chlorine, bromine, iodine, flourine.
thats the hclbrif(honclbrif) SPSE is Sulfer,phosphorous, Selenium.

Carbons valance of 4 allows it to make Organic or Inorganic molecules. The SP ring hybridisation makes it the back bone of many materials. Linus Paulings big discovery. Not vitamin C can help with colds and flu's.
CARBONE is very abundant everywear. The new O.L.E.Ds,
Ogranic LEDs are FAR CHEAPER to make than Gallium Arsenide LEDs. Look for O.L.E.Ds for your next project.

My last buck 380 on tnis post. Buck 380 is 2 cents with inflation+Carbon credits wasted by Cessna's flown by corperate big wigs.
 
RE: Conducting the Autopsy on a Dead Antenna  
by AF6AU on February 14, 2011 Mail this to a friend!
I have Owls that like to perch on top of my 35 foot mast, so I don't need to buy the cheezy plastic Owls that HRO sells! Some of these Owls are big, (comparing to the trusses in the tower), must be 18 inches tall, tail to top of head. When they push off to fly the top mast bends/flexes and the guys move. You would think that Owls in Southern California would not be so big, but with the proliferation of nocturnal rodents, they are well fed.

However, a big one missed the top perch, and tried to sit on the dipole wires, near the dipole center insulator. I heard it "Hoot" calling to it's buddies, then I heard the antenna hit the roof. The 12 gauge insulated wire held up fine, but the dacron rope loop broke instead, failing under the 'fat' bird's weight and the pull of coax and wire. Down came the dipole. I wonder how heavy that owl was. I also think that various birds, pick at any fiberous objects, just as you noted, and with weather, they fail.

It takes only about 1/2 hour to fix the issue, and I actually like the Owls around keeping night vermin at minimum. This time I used a wire loop.

JML
AF6AU

 
Conducting the Autopsy on a Dead Antenna  
by AF6IT on February 16, 2011 Mail this to a friend!
There are MANY flavors of stainless steel. 304 for example can and will rust a little normally and is slightly magnetic. Will rust a lot when used with brine. Yet is is genuine stainless, though not necessarily the best formula for every purpose. 316 is much more suitable for corrosion sensitive applications, yet even it isn't best for every application. Never been an issue anywhere I've used it, though. But these were in specialized pipe & fittings not fasteners. Point is do your homework if it is critical. Now here is something which will make many pause & scratch your heads. Stainless may not itself rust, but being more noble can and does actually accelerate other metals rust or corrosion! Dissimilar metals, when even a weak electrolyte is present, make what, class? A battery! Current flows, electrons transfer, and corrosion happens. (Google galvanic corrosion) For our purposes it probably won't be a major factor, although if you live in a coastal area your "fix" might actually be the worst thing to do when dissimilar metals are involved. Best example of an issue is using stainless bolts in an outboard motor lower unit. Especially in salt water. Ask yourself if you'd rather have a less rust on your bolts and more corrosion on the housing (or aluminum, copper, or brass parts of an antenna assembly)- or can you tolerate a little rust on fasteners for the sake of preserving the rest of the assembly? Marine product manufacturers use carbon steel fasteners for a reason on many products- unless it is all from the same material. Since most of us do not throw our antennas into the sea we may never see this become a problem particularly in more arid climates. But in coastal areas, this might be a case which is counter-intuitive. On the other hand, if you can find a magical way to keep a junction dry what difference will it make what materials are used?

Stu AF6IT
 
Conducting the Autopsy on a Dead Antenna  
by VE7ZN on February 17, 2011 Mail this to a friend!
Great article and from a fellow hex-nut, I feel your pain. I too built mine from Leo's notes and Steve's design. It's a terrific antenna for what it cost to build and, the best part: folks think it is some kind of weird TV Sat antenna or a clotheshanger...

Fortunately, UV damage up here at 49N and at sea level is minimal but hardware is an issue. I used marine-grade stainless and it's been excellent. Checked it about a week ago and after almost 3 years, it's as bright as new.

As we sailors say: Stainless only means it "stains less".

Best 73,
Robert
VE7ZN
 
Conducting the Autopsy on a Dead Antenna  
by AB3MO on February 20, 2011 Mail this to a friend!
Stainless steel hardware from China may be an oxymoron. Marine bronze hardware from China, as one of my colleagues discovered, is brass with added lead (looks like bronze) -- does not have the strength or corrosion resistance of REAL bronze. Hardware is only as good as the quality control of the marketer standing behind the product. You night try a marine supply store (West Marine or Defender Industries come to mind).
-
AB3MO is a retired analytical chemist (PhD) and long time sailor returning to Ham Radio after a 50 year absence.
 
Conducting the Autopsy on a Dead Antenna  
by WA9JOQ on February 20, 2011 Mail this to a friend!
Very good article, well written...K4KIO website also informative - Thanks!
 
RE: Conducting the Autopsy on a Dead Antenna  
by WA2JJH on February 22, 2011 Mail this to a friend!
"Rust never sleeps" Add powdered Aluminum. Do not try this at home.

EXOTHERMIC-enought to weld Rail road track sections.
 
RE: Conducting the Autopsy on a Dead Antenna  
by KE5ZB on February 22, 2011 Mail this to a friend!
Unfortunately, not all galvanized parts really are - before imports drove a lot of US-made stuff off the market, galvanized used to mean a zinc layer thoroughly applied by electrochemical or hot-dip processes, and it offered long-term protection. Now all I can find in stores comes from China and the "galvanization" has the appearance of being only a rough coating of powdered metal that was loosely sprayed on. Some of it came off when handled, and the items I used on an antenna started rusting in just a day or 2, very heavily on bolt threads where a nut had passed over. Whatever happened to quality control?
 
RE: Conducting the Autopsy on a Dead Antenna  
by AA4HA on February 23, 2011 Mail this to a friend!
Excellent autopsy report, very well written.

I have had the misfortune of a crew putting up a 9 dB omni on top of a 375' tower and not using the anti-seize compound and getting a gall going between the nut and the thread on the U (really V) clamp. They had to lower the antenna all the way back down to the ground so the ground crew could try to un-stick the nut. After a hour's wasted time we had to cut off the clamp with a hacksaw.

I think the problem with stainless galls is caused by using the same grade and hardness of stainless steel for the bolts and the nuts. Since these threads may not be perfect it just takes one tiny little spot to start a gall on a thread that rolls up into something that will lock the nut as tight as if you welded it there.

Using 316 it has always held up very well. Even in places like on top of a smokestack where there are corrosive flue gases. (+25 years stupervising antenna installation crews)

Those plastic tie-wraps are at the best, UV resistant. For permanent installations you may want to look at antenna feed-line hangar kits (stainless steel parts with a bolt and nut to grasp the feed-line). There are even some stainless steel banding kits for holding feed-line to towers. Nearly every place that has used black zip-ties I have been able to yank on the coax and tear off 10-20 of those things in a few seconds from the ground.

The right kind of hangars only cost $2.40 ea (USD). ( https://www.tessco.com/products/displayProductInfo.do?sku=499150&eventPage=2 )
You would never need to replace them.

The owls are funny. At one hotel I stayed at they had a plastic owl on the roof of the building right next to mine. The owl was pointed right at my window (about 30 feet away). Unnerved, finally at 2 am I had to close the blinds because I thought the plastic owl was staring at me (yes, I know there are medicines to treat that sort of condition <lol>).
 
Conducting the Autopsy on a Dead Antenna  
by AA8GK on March 5, 2011 Mail this to a friend!
You write very well! Sadly, not enough people do. Great article. Thanks for sharing!

72,
Pete
 
RE: Conducting the Autopsy on a Dead Antenna  
by N4KC on March 5, 2011 Mail this to a friend!
Pete, thank you. And thanks to all the others who commented. I've learned more about stainless steel than I ever thought I would.

I hope everyone else appreciates what a resource eHam and its readers are.

73,

Don Keith N4KC
www.n4kc.com
www.donkeith.com
 
Conducting the Autopsy on a Dead Antenna  
by W8VKD on March 6, 2011 Mail this to a friend!
A short note on stainless steels: Type 303 Stainless is a non magnetic grade whereas the Type 416 stainless is a magnetic variety. Any stainless steel can rust if not properly treated after machining or forming. The most common post-process for stainless steels is called passivation. This is nothing more than surface treating the prodict with a nitric acid dip and a low temperature bake after passivation. The nitric acid will prevent the iron inclusions from forming rust on the surface and keeps the product from pitting. I don't know whether or not commercial grade stainless fasteners are done this way but I can almost guarantee that ANY stainless fastener sold for marine or government application would require this post-processing.
 
Conducting the Autopsy on a Dead Antenna  
by K5CQB on March 13, 2011 Mail this to a friend!
I use to zip ties at the top of my tower. I always tie a few of them at the base so I can monitor their exposure. Once the ones at the base start looking bad then I climb up and replace the ones up top.
 
Conducting the Autopsy on a Dead Antenna  
by W4RDM on March 13, 2011 Mail this to a friend!
Don,
The stainless u-bolts that I supplied on your baseplate kit were type 304 and the flange bolts were type 316.

Great article.

73,

Ron W4RDM
www.hexkit.com
 
RE: Conducting the Autopsy on a Dead Antenna  
by KC4SJC on March 16, 2011 Mail this to a friend!
I've been in the COMM business for over 35 years (Military and Civilian). I'm a member of the DoD Corrosion control exchange, and have served on Corrosion Prevention Advisory boards. I've installed, worked on, repaired and replaced antennas (and other systems) from the Arctic, to the middle of Oceans; from deserts to high mountains. From Jungles to suburbia. Corrosion is one of my pet peeves. Here are some of my observations:

Stainless steel and aluminum don't go together well (check any nobility of metals table--the further apart to metals are the worse the galvanic corrosion). The aluminum suffers the most but any 300 series SS will eventually rust passivated or not (in S. Florida (Homestead AFB) I've seen it start to rust pit in as little as 6 weeks AND it was MIL-SPEC!). The atmoshpheric and climatic conditions either speed up or slow down this process, but it will eventually occur. Hot dipped galvanized hdwe is superior in that regard and will still eventually corrode but you can slow the process by application of CPC (Corrosion Preventive Compounds) or touch ups with a high Zinc solids organic paint (ZRC is a good product). Don't spray Zinc on any radiating parts of the antenna! My favorite CPC is a product called NO-OX-ID from Sanchem...I use it liberally on AL/CU, AL/SS, and AL/FE bonds. Basically I use it on any metal to metal bond! It's RF transparent well into UHF so don't worry about coating antenna clamps and such. This stuff won't wash off and you can't get it off with "hand grenades and kerosene". I've seen applications using it over 50 years old where there was little to no corrosion. Wear old clothes if you use it because it won't wash out either. BTW: The stuff is safe to use in potable water tanks so its 'ecologically sound'!!!

As for ty-wraps, black is the only color to use outdoors period. However, I've encounterd none that last for more than a few years. Even high quality tie wraps can fail in extreme cold (embrittlement) and break at the first puff of wind. They fare very well in moderate climates but will still fail. Desert extremes (hi or low desert) vary with the composition of the ty-wrap. As AA4HA stated steel banding kits work well. I use self-vulcanizing rubber tape and a product called 'Wrap-Loc' over that for suspending coaxial and control cables on messenger spans.I've seen HF installations from the 1950s that were still together using this method despite their austere locations. Don't forget your 'drip loops' where the cables enter the shelter or facility.

The average life span of most well built commercial and MIL-SPEC antennas (counting those made with fiberglass) is 5-9 years under average conditions +/- care in assembly and installation. Fiberglass radomes and components (depending upon the thickness of the gelcoat or other coating) on antennas age faster putting those at the middle to bottom end of the scale. However, cable and especially connector failure at the antenna end account for over 85 percent of 'antenna' failures I've seen or heard of. Cable failures primarily due to high loss--contamination/water ingress; connector failures mainly due to improper assembly (inclusive of securing the coax from any movement or slippage on the antenna support arm/pole) followed by failure of the weather proofing. Additionally, crimp on connectors fail much faster than clamp/solder types. My absolute favorite weather proofing for connectors is heat shrink with hot melt glue interior covered with coax seal. The hot melt glue really seals up voids and with the heatshrink tends to hold the connector and coax together while the moldable coax seal provides a very long lived first line of defense. Here's a tip on using coax seal: Its very sticky, but after you get it wrapped up tight, spray your hands with a little soapy water and you can mold that stuff to where there are no seams...basically it turns into one solid boot!

There's tons more...enough to write a book, but that's the high spots.
 
RE: Conducting the Autopsy on a Dead Antenna  
by N4KC on March 16, 2011 Mail this to a friend!
Now that is some great info, Dave. I guess the bottom line is, do the best you can, but Nature wins eventually. I've seen broadcast stations go to all sorts of extremes to protect installations but they still have to do regular and involved maintenance to try to stay ahead of weather.

Just another reason to inspect anything outside on a regular basis. Or wait until it fails and then try to find it...in the rain, in the dark, with lightning flashing!

73,

Don N4KC
www.n4kc.com
www.donkeith.com


 
RE: Conducting the Autopsy on a Dead Antenna  
by KC4SJC on March 18, 2011 Mail this to a friend!
Roger that! After you get a feel for your equipment's 'personality', and it's environment you can decide the proper intervals for PMs (Preventive Maintenance). Most technicians realize this intuitively. There are things you can avoid, and things you can temporarily mitigate, but you hit the nail on the head. Only ONE guarantee...sooner or later it's going to fail...and it'll be "O'dark thirty and 30 below" when it does, HI.

73 de KC4SJC, ex AFA7DC, ex DA2DC.
 
RE: Conducting the Autopsy on a Dead Antenna  
by KC4SJC on March 18, 2011 Mail this to a friend!
One last thing I forgot to comment on:

Stainelss steel is expensive to manuafacture. The BEST SS is Austenitic with a higher Nickel-Molybdenum content. Unfortunately this type is super expensive, and as someone else mentioned earlier would seriously 'up' the cost of already expensive antennas. Beware: Even if the SS you use doesn't corrode, if it's attached to aluminum the aluminum will oxidize very rapidly at the connection. Aluminum is a more active metal (anode) than stainless steel (cathode) and the anode will corrode faster in the presence of an electrolyte (e.g. rain water + pollution esp. Sulfer dioxide).

If antennas lasted forever neither antenna manufacturers or us Hams would stay busy!
 
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