Aluminum oxidization &
protection of Yagi elements

The following discussion about the Aluminum oxidization & protection of Yagi elements took place in the Moon-Net reflector. I found the subject so interesting that I decided to put together all the messages in this page. (Click here for related books)

On 29-March-1999 VE7BQH wrote:
Does anyone have any specific idea of how much degredation (if any) is caused by oxidization of aluminum 6061-T6 elements on 2 meters??

I live in a sea coast city which means after about one year the elements have turned "gray" with oxidization. Once oxidized, it stays about the same over the years.

I have never been able to quantify the degredation. In years past, I have completely cleaned the array but could never quantify if this improved performance or not. My conclusion at the time was if I could not tell, then it must be to small to measure.

Any input would be appreciated.

On 30-March-1999 I3DLI wrote:
Intriguing question.
Despite any attempt in focushing about RF skin-losses (I^2R) by many autors, I believe there are no matter at 144 MHz with Al antenna mount elements. In fact the losses for reduced skin conductivity of oxidized aluminium (i.e. higher resistence) are surely negligible. Try this: let resonate a little 1/4 lambda grond-plane (made by oxidized metal) were you put an 8877 power into.
Keep key-down your PA as much time  as you can, then shut-off the PA and quikly lets control the antenna rod temperature at the higher RF courrent point.
Since the 1 dB loss means about 200 Watt not trasduced into RF field, that power   must be dissipated in heating the GP rod. If the GP rod is made small enough in diameter, then the surface submitted to the RF is far small to dissipate 200 watt without rise in temperature!. Fingers may suffice as test instrument...
Seriously:
as you know, the series-resistence due to skin ohmic losses do have importance IF it is a large enough part of the whole antenna impedence (real part of complex impedence compared to loss resistence).

On 30-March-1999 WA6PY wrote:
Resistive losses will be only at high current parts of the yagi element,  in the middle. I used clear coat for my yagi in San Diego. It looks better. I did not see any degradation in performance comparing newly polished , corrodated and painted with thin layer of clear coat, although single yagi system is very sensitive.
DJ9BV did not observe any significant degradation of his 4 yagi system on 432 although in Hamburg everything is badly corroded.
Also when the mesh of my dish started to be rusted I coudn't see degradation of the performance even on 13 cm.  My 10 ft dish for 10 GHz in San Diego was also very much oxidated. I could not see any improvements in moon noise and my echoes
when I polished the surface.

I certanly look and feels better, but in my experience those losses are small.

On 30-March-1999 9H1PA wrote:
I am curious on more or less the same aspect of Oxidized Alum , but in my case it is anodized Aluminium rod that I have for elements . What would the skin effect have on anodized elements . I know that Shark uses them for there elements on VHF yagi's . The performance of the yagi's seems OK .
   Manybe one on knows the answer .

On 31-March-1999 K3PGP wrote:
I can't offer much in the way of scientific numbers as to degradation but I can tell you that I have noticed a decrease in antenna performance when things become oxidized.  However, in my case it always seemed to be caused by poor electrical connections in the feeder system or any joints in high current areas.   Once these problems were fixed the array seemed to work
again even though the boom and elements looked ugly.

Approx. 25 years ago I started coating most of my antennas with Krylon spray.  Some of these antenna have been in the air all that time and look the same as when I put them up!!!  I never had any problems with these antennas yet others that were NOT coated required frequent maintenance to keep them going.

I know it's a pain to coat something like a 96 element array but I did this and was happy I did.  The array ran for 18 years and required no maintenance whatsoever.  What finally destroyed it was when part of the neighbors aluminum shed blew apart in a 75 MPH wind storm and a six foot square piece of aluminum siding managed to impale itself on one end of the array turning it into a gigantic windmill which stripped the gears in the rotators and completely wiped out the array. There was nothing left to rebuild.  All that was left was the tower!

Krylon spray comes in clear as well as colors.  In the past I have always used the clear but it is easier to see where one has sprayed if anything other than clear is used.   I now coat the entire boom and all the elements as well as all connections.   After seeing how it has held up on antennas that have been flying in the breeze for 25+ years I'm convinced it's worth the extra effort.

On 31-March-1999 GM4JJJ wrote:
I am interested to know if spraying antenna elements with something like Krylon has any detrimental effect on performance of modern highly optimised yagis?

I seem to suffer from quite rapid corrosion at my QTH, not from salt but rather from other pollution (acid rain?).

One of my 432 MHz antennas is very pitted after 5 years. The elements appear to go brittle where the stainless keepers contact the aluminium.

I used to spray elements with clear plastic coatings designed for HT ignition leads, but stopped that because of fears of upsetting performance.

Anyone got any ideas whether coating elements is a problem?

On 31-March-1999 K3PGP wrote:
I've used Krylon on antennas, feedhorns, INSIDE waveguides and transmitter cavities (up through 10 Ghz) with no difference in performance and no detuning effects.  I've even sprayed 10 Ghz free running oscillators with very minimal effects.

I've also sprayed the PCB boards that some of my low noise preamps are built on (after construction is complete), antenna relays (keep if off the contacts!), coax fittings (outside only and AFTER they are tightened)  and just about anything else that I want to keep from oxidizing.

From what I've seen Krylon appears to have excellent RF properties.  I've used it in places where some materials would get warm or hot and maybe even catch fire like at a voltage maximum point inside high power transmitter cavities (biggest was a 100 kw FM broadcast rig).  I've never seen the tuning change after spraying any of these Tx cavities.  Part of this may be due to the extremely thin layer which is deposited if applied properly.  It even stopped an arcing problem in one case.  (I didn't have a piece of teflon with me at the time.)  One thin coat always seems to hold up better than one extra heavy coat plus it goes further.  If you put it on too heavy there is more of a tendency for it to chip off when an impact occurs.

I've also used it on HV power supplies (2 to 30 kv) that previously had problems with damnpess.  I dry everything out by heating it then letting it cool till it's warm to the touch then spraying it.  Seems to fix the problem every time and it keeps everything looking new.

Most of my experience is with Krylon Acrylic Crystal Clear.  So far I can say the same for the colors that I've tried but I have no way of knowing if perhaps some color pigments might present a problem in some areas.  The only reason I experimented with some of the colors is it is easier to see any spots that are missed.  This makes it easier when hanging on a tower where
you might not have the best angle to see what you are doing.  For inside cavities I think I'd stick with the crystal clear product.

What I find so amazing is how it holds up on stuff that has been outside in the air for 25+ years.  The tower has needed repainted several times yet the antennas look like new.  Maybe I need to Krylon the tower!!!  I've noticed in a couple of places where I managed to bang something into one of the antennas and scratched the coating that the metal started to oxidize and really looks ugly compared to the rest of the antenna which looks like brand new aluminum.

In general I have noticed that antennas that are NOT coated don't hold up as well as they did many years ago.  I think our atmosphere is slowly becoming more corrosive.   Acid rain is probably part of the problem.  Many years ago uncoated copper parts on my antennas used to turn black.  Now they turn green.  Aluminum parts used to turn dull gray with a frosted appearance now they turn white and have a loose white powder on them.  If left untreated the aluminum turns brittle and eventually cracks.  I've even seen bronze bolts eaten away so now I coat all hardware as well.

Both my 144 MHz 96 element array and my 432 MHz 48 element array were given this treatment and ran for 18 years without requiring any maintenance, that is till the windstorm wiped them out.  Then there was nothing left to repair!

I just went and grabbed a can of Krylon to read the techinical info and found out it is no longer listed on the can.  I remember seeing things like dielectric constant etc. listed on the can.

I found out they have a web site http://www.krylon.com/ but there was no useful technical data there either.  However, I did see a UV-Resistant Clear Coating which I have NO experience with.  From what I could gather this blocks UV radiation from reaching whatever it is sprayed on.  From my own experience Krylon Acrylic Crystal Clear the paint itself seems unaffected by UV.  My guess is the UV passes right through to the object that is coated which probably doesn't mean anything for what most of us have in mind but the UV stuff might prove useful for coating plastic parts or any other item that might be susceptible to UV damage.

On the subject of UV deterioration, I used a 50 pair telephone cable for the control wiring out to my old 24 foot dish.  I left the ends of the wires uncoated and exposed to sunlight.  Funny thing happened.  All the insulation on the red wires became extremely brittle, turned white and fell off leaving only the bare copper wire.  The other colors were unaffected.  Thinking about this I came to the conclusion that the red paint reflects only red meaning it is absorbing UV.  I'm not sure why only red was affected though. If the above were true then the black wires should have suffered the same problem.  Something to think about as color has a LOT to do with how some parts hold up under direct sunlight.

Maybe someone else can ad to this or knows something that I'm missing but it works for me and has withstood the test of time.  If you try this remember to coat things after they are assembled, tightened etc.  If you have to turn something after you are done, recoat it.  This will cover any fine cracks in the coating that were caused by the movement.

On 31-March-1999 WA6PY wrote:
What's about losses of the Krylon or simmilar paint. For instance black one can contain coal which can be lossy. Clear seems to be more safe?
Any comments?

On 31-March-1999 VA3RR wrote:
I used Krylon "satin" finish on some yagis that I just constructed, as I found it easier to determine where the coating was applied, as well as cutting down on reflected sunlight (I polished all the AL tubing and rod with a non-metallic scotchbrite pad, so the metal was quite bright).

I took a measurement of the SWR bandwidth before and after, and the coating had zero effect.  I cannot comment on it's effects vis-a-vis efficiency.

Also, the satin finish looks very good even when applied with a brush.  It would certainly be more economical if you wanted to paint a large array, as opposed to the wasted overspray from a spray bomb.

Incidentally, I did see a Krylon product called "Krylon Antenna" but it was only available in a spray can.

On 31-March-1999 K3PGP wrote:
I take it you were able to find Krylon in a can rather than the spray?   Do they sell clear this way also?

What I've been doing for small touch up jobs where I don't want the spray going everywhere is to spray some in the plastic lid that comes with the can then dip a small paint brush in.  The stuff dries VERY quickly though so I have to spray a little bit out at a time.  Maybe the stuff in the spray can has a different formula to make it dry quicker that what comes in the can?

Another trick is to stack as much of the aluminum as close together as possible so it intercepts as much of the spray as possible.  Like you, I find the spray quite wasteful usually managing to get more on myself than on the antenna.  One should ALWAYS determine which way the wind is blowing before hitting the spray button!

On 31-March-1999 W3IWI wrote:
Another very good material is Polyurethane Spar Varnish, as used to protect wood and metal on boats.

On 1-April-1999 K0XP wrote:
John, do you "prep" the aluminum antenna elements in any way? For example, wipe them down with some solvent, or soapy water, etc.? Have you sprayed parts that were not cleaned, and how did the Krylon take to that?

How about Flecto Varaphane; I've heard of guys using that for the same purpose and since it comes in cans, it's easier to apply to some parts.

How about coaxial connectors and adapters outside: do you tape them, then Krylon the taped assembly? What about Heliax connectors that have a remnant of the silicone grease used on the O-rings: do you wipe those off first? If you tape your connectors, what kind of tape, and what's your experience with other kinds? Personally, I've been successful using nearly any black electrician's tape over connectors/adaptors (I've run into a few real cheapy rolls at swapmeets that don't stick even indoors, however); I double wrap with half-overlaps then wind seperate wraps at each end over the ends of the bottom wrappings to prevent unwinding in the wind. Each added wrap is wound opposite the lower layer. Usually, I can even reuse the same unwrapped tape after two or three years except for the short pieces on the ends which I always replace. Have never had water-ingress through a good taped wrap that I know of.

ANTENNAS IN THE AIR FOR 18+ YEARS WITH NO CHANGES???!! As Lew McCoy or whomever used to say, they clearly were NOT large enough!!

And what about these stories I keep hearing about Molex connectors used for control and rotor wires rusting away?? I've had one rotor with a Molex connector (plated steel pins, according to my magnet!) which I packed with silicone grease. Have had no problem with it over four years that I know of. The auto manufacturers do the same with harness connectors (which are the same general construction as Molex) in the engine compartment although those connections, it's true, aren't exposed to nearly as much water.

Your tips and hints here would be another fine addition to your web page!

As for the red-insulated phone cable, the insulation must have been something entirely different from the other wires for some reason; or perhaps a different batch of insulation material that was improperly mixed, etc.

On 1-April-1999 Terry Dobler wrote:
   My experience with tape is that it does an excellent job of holding in the water.   I use strip caulk which you can get at any good auto parts store. I wrap it around the connector and then squeeze it into place so that there are no gaps.   You could just leave it there, but I like to put a layer of heat shrink tubing over the caulk to protect it from the weather. I use tape over the caulk in hard to get to spots.   Again, the tape is only there to protect the caulk, the caulk is what keeps the water out. I recently opened up some air dielectric copper and brass matching stubs that were sealed several years ago and the insides were still shinny and new looking.   The outside which had been exposed to the weather was black.

On 1-April-1999 K3PGP wrote:
What exactly do you mean "Goes away"?  I have never heard this report before but I see we now have at least two reports on MOON-NET of it not lasting long.  As this differs significantly from my own observations and other reports that I've received up till now I'd like to hear more specifics of the failure mode.  I have a few samples of aluminum tubing here that have been up in the air for over 25 years and I can still scrap the Krylon off with a knife.

I'm beginning to wonder if some types of Krylon are less suitable than others or perhaps it wasn't applied properly as many other people living along the coast in hot areas haven't had this problem and they're talking about years of use not months.  It would be nice to find out why there is such a difference.  Maybe Krylon is making some inferior products these days and it would be nice to know which ones they are so they can be avoided.

On 1-April-1999 WB5APD wrote:
Normally aluminum has to be primed with zinc chromate primer for paint to adhere to the aluminum. That is what is used on aircraft before painting.

On 1-April-1999 VE1ALQ  wrote:
I have been using Krylon around here for perhaps 15 years and it is available at our local Home Hardware Store.

Krylon Clear Coat does NOT stand up under direct sunlight and UV radiation.

Krylon "Silver Coat" does appear to withstand direct sun UV radiation.  But then I have also used Tremclad "Aluminium" spray coat for the same applications outside with the same success in direct sun.

I have 1296, 432 & 144 Yagies that have been installed here since we arrived 20 years ago......near the Bay of Fundy, and they look just as clean now as they did then....under the coating. I believe during this 20 years I have re-coated the Yagies perhaps 3 times.

In short, if you want protection to last for a reasonable length of time do  NOT use a "clear coat" material.  Use a coating that offers UV protection or it simply cracks under UV radiation and WASHES away under rain.

On 1-April-1999 K3PGP  wrote:
I am really glad I mentioned Krylon on MOON-NET.

It is obvious the common Krylon "Clear Acrylic Coating" that is commonly available today is NOT what I used many years ago.  I visited http://www.krylon.com and I am even more confused now.

After considerable searching I found the following link off the main web site: http://www.sprayon.com/prod_main.htm

There I found something called "Clear Insulating Varnish".   It has a dielectric strength rating of up to 2,100 VPM.  I remember seeing this on the old Krylon spray cans that I used to coat my antenna, cavities, etc. but what I used was NOT called "Clear Insulating Varnish".   They have so many products today it's extremely confusing to say the least and I don't know if the above is the current name for what I used or not.

This product is listed for use on Motor windings, transformers, commutator ends, sealing electrical and electronic components, field coils, armatures, stator windings, rings and frames, bus bars and switchboard parts. Ideal for general coating, impregnating and insulation for electrical and electronic products, particularly small field and magnet coils, and inside walls of control boxes.

It says nothing about outdoor use on aluminum and may have a UV problem. Also keep in mind that we are being bombarded with more UV today that we have in the past and it varies with different locations so my past experience may not mean as much as I thought it did.

Because of all the confusion I have contacted Krylon to see if I can determine exactly which product is recommended for use on outdoor aluminum antenna parts.

I want to thank everyone that responded so far.  As many of you know I am doing some major antenna work this year and I think everyone here has just saved me from wasting a lot of time and money.

Also found a Moisture- and Fungus-Proof Varnish http://www.sprayon.com/prod_main.htm

Uses: Communications equipment, tools, electric parts and components, wires, stencil protection, insulation.

Leaves a smooth, transparent coating that won't crack, splinter  or remain tacky.
===> Ideal for protecting communications, electronic and electrical equipment,   especially tools and materials being transported by ship Meets performance requirements of MIL-V-173C Does not contain chlorinated solvents or Class I and II compounds. Equipped with DanVern Fanspray valve

On 1-April-1999 W3IWI  wrote:
My personal recommendation, available widely, is boating Spar   Varnish. I personally prefer the polyurethane spar varnish. You get it in a can, and apply it with a brush. It seems to stick to aluminum without needing any special primer coat. It is pretty thick and also has worked well waterproofing connectors (I apply it over the to of Scothh #88 tape), and for rustproofing non-stainless nuts, U-bolts, etc.

On 1-April-1999 GM4JJJ  wrote:
Getting away a little ffrom the oxidization thread but here are some observations on general waterprooofing issues:

I use 'self amalgamating' rubber tape and then cover with PVC tape (to stop UV damage to the rubber tape). If done properly, this is very effective and when removed (with difficulty) everything looks brand new. You can't just unwind it, it has to be cut off with snips or careful use of a knife.

There are different grades of self amal tape, from very thin to some nice thick rubbery stuff that stays soft. You need to stretch the tape as you apply it and it then makes a solid rubber covering over your connector.

Some folks use 'Denso' tape (spelling?) which is a cloth soaked in horrible gungy masticky stuff. It works nicely but what a mess.

The three most useful products that I have found for protecting outside connections are:

1: Self amalgamating rubber tape for wrapping over Coax connectors

2. Hot Melt Glue - For covering exposed terminals and sealing up connectors and scews.

3. Waxoyl (WaxProtect in the USA) - For all exposed metal parts. Use it over steel unplated bolts and they won't rust. This product is sold for treating autos so they won't rust with salt on the roads.

On 2-April-1999 G3SEK  wrote:
Same three here, and also

1b: Coax Seal in *small* quantities to fill spaces where self- amalgamating tape won't go - for example the hole where the male
connector from the power divider goes into the preamp box. Coax Seal bonds to plastic boxes, and self-amalgamating tape bonds to Coax Seal.

2b: screw-sealing cable glands, to carry coax cable through the walls of boxes. It's very difficult to waterproof a bulkhead connector - it's better to take a 'tail' of cable through a sealing gland, and then use an in-line jack which is a much easier shape to wrap with tape.

On 2-April-1999 ZS6AXT  wrote:
In your experiments with the element surface protection do not forget that you may greatly detune such antenna by introducing some velocity factor with a layer of insulating material on the elements !! So - be aware.

On 2-April-1999 N4PZ  wrote:
Regarding coax seal,  the same exact product is available in hardware stores in the USA.  It is sold as a repair item for gutters on your house.   It comes in 2 inch wide by 10 feet rolls for 3 to 4 dollars.  You may have to hunt for it, but is so much cheaper than coax-seal that it is worth the effort

On 2-April-1999 GM4JJJ  wrote:
Ivo ZS6AXT wrote:
>
> In your experiments with the element surface protection do not forget that
> you may greatly detune such antenna by introducing some velocity factor
> with a layer of insulating material on the elements !! So - be aware.

I asked the Moon-Net if this was a concern the other day and no-one has mentioned it until now.

A number of 144 MHz EME stations have reported using all sorts of stuff ranging from spray paints and varnishes to wax products for undersealing autos. No-one has admitted that there might be a problem with performance. Wonder what the antenna manufacturers say? - Or do they want the antennas to oxidise and fall apart so we buy new shiny ones from them every 5 years? :-)


Finally - Today I sprayed my new 144 MHz array with Clear Laquer (acrylic). Hope it isn't affected... Guess I can always remove the laquer...

On 3-April-1999 K0XP  wrote:
>In your experiments with the element surface protection do not forget that
>you may greatly detune such antenna by introducing some velocity factor
>with a layer of insulating material on the elements !! So - be aware.

To the doubters: this is completely true, although I've only noticed the detuning effect on 80 and 40 meter wire antennas. For example, the resonant length of a dipole cut from uninsulated copper bus wire will be somewhat longer than one cut from insulated house wire. When I first noticed this, I thought the insulated house wire was stretching, so I took it down and measured it again. Nope: it had only stretched an inch since it was originally cut several days before. I've generally found I have to shorten insulated copper house wire dipoles around 2 to 3% to get them to resonate. In comparison, I've rarely found the resonant frequency to shift more than a few kilohertz when cutting such dipoles from, say, AWG 10 wire compared to AWG 14.

But it's hard to imagine the same amount of detuning on a V/UHF array. A shift from 432.0 MHz to, say, 425 MHz is a length increase of only about 1.6%. It would seem more likely that varying construction techniques, such as slight differences in boom-to-element clamps, etc., would have just as large, if not large, effect.

However, I believe I've seen someone once use teflon sleeves slid over yagi elements to shift the resonant frequency slightly. Thus, a Swiss quad that I built years ago using insulated house wire stood no chance of resonating where I originally cut it compared to a later model I built using uninsulated copperweld wire of the same gauge.

On 3-April-1999 W2DRZ  wrote:
The difference of using insulated wire which changes the velocity factor over open wire is in the tech book's published by many:
 ARRL, RSGB, ect..

There is a great need of the guys to go back to basics and learn to read !!!!!!!
As a large amount of questions on the reflector are answered in the tech books...... May be just need to quit looking for easy answers and do some book reedin!!!!!!!!!!

On 3-April-1999 K3PGP  wrote:
I've never seen any detuning effects when using Krylon Clear Acrylic spray and I've sprayed antennas and cavities from 144 to 10 Ghz.  As an acid test I sprayed a 10 Ghz free running osc. and noted very minimal effects.  See my previous posts for more info.

I think the thickness of the insulator one is applying to the elements has some bearing on the amount of detuning.  The typical acrylic spray on coating is rather thin and if there is any detuning or any other effect it is beyond my means for detecting it.  As far as I'm concerned detuning when using such thin coats is simply a non issue.

However, what is causing me some concern are a couple of recent reports of Krylon "not lasting very long".  (I'm still interested in exaxtly what this means?   Did it crack, fall off, wash away or what?)  What I sprayed with Krylon Crystal Clear 25+ years ago still looks like the day I put it up. I'm only hoping what I am doing now works half as well but I'm starting to think that we aren't all using the same Krylon coating as there appears to be many many different varieties of the same product and widely different reports as to how well it held up.

On 3-April-1999 GM4JJJ  wrote:
> The difference of using insulated wire which changes the velocity factor
> over open wire is in the tech book's published by many:
>  ARRL, RSGB, ect..
>
> There is a great need of the guys to go back to basics
> and learn to read !!!!!!!
> As a large amount of questions on the reflector are answered in the tech
> books...... May be just need to quit looking for easy answers and do
> some book reedin!!!!!!!!!!
> --

The discussion was not originally whether insulated wire would affect HF antennas, it was whether a light covering of some insulating spray on a VHF yagi element would detune the yagi significantly. I haven't seen the ARRL cover that one.

True there are some answers in the books, but there are a lot things of a PRACTICAL nature that are not in the books. This is where asking someone who has actually done it is a big help. There are also plenty of mistakes in the books, so like with all things it pays to get a few opinions and make a judgement for yourself.

On 3-April-1999 W2DRZ  wrote:
As have put foot in place of brain in previous post, will try to redeem self with a bit of information I have found.

As have discarded all the old type KRYLON , can only find 1 recent type a few years old and some later cans of KRYLON.
1.
KRYLON part # 1302 for RADIO, TV. ALL ELECTRONIC USES. This is on the can.
MFG. of this KRYLON is: Division of Borden Inc., Chemical Products
Group, Columbus OH  43215
Only chemical listed is : Toluene.

2.
 Latest purchased KRYLON is # 1301. MFG. is Division of Sherwin-Williams
Company, Solon, OH 44139
Chemical listed on can is : ketones, xylene, toluene, alcohols, aromatic naphtha.

As the older KRYLON may have been of the real good chemicals that cannot be used in consumer products today !!!!

As it maybe, able to obtain industrial grade KRYLON then it may have the old stamina of bygone years ( good for 20 + years in the sun ) ????

General speaking the industrial grade stuff contains the old ( good ) chemicals. Usually restricted to Industrial plant use and / or purchase if can find ???

On 3-April-1999 K7RR  wrote:
It would seem that the only ingredient of importance is ACRYLIC or perspex in Europe.  No mention of it?  Only that is UV resistant. 

On 3-April-1999 9H1PA  wrote:
I didn't think that aluminium could be that interesting My system has anodized elements and echoes seem to be OK when elevated ( no Ground Gain ) 4 x 10el and 700watts . Regarding degredation on Anodizing these elements were on my 2 x 4wl for 2years and are still new. Types of anodizing varies
We find over here Alum. Welding rod 4mm , and after 2 years they really start to corrode with the salt water being very close , so some type of protection is needed what ever or elements will not last long. Who knows if there is more gain in these antennas without the anodizing .

On 3-April-1999 W0VD  wrote:
I have been watching this discussion and just wanted to add my 2 cents.
I have been painting my antennas black for years and never noticed any change in the swr or performance of my antennas.
I have always used a black epoxy spray that you get at walmart. The reason for black is a optical illusion the human eye just doesnt lock on to a black object like it does a shiny object. So my neighbors don't see my antennas in the trees. They just look like tree limbs.
When I put up my M2 18el 2 years ago I checked the swr before painting and noticed no difference after painting.
For the ones that is worried about the detuning effects why don't you just paint the boom? Leave the elements unpainted that way the boom is protected.
The elements on 2 meter antennas are just 3/16" rod easily purchased at welding supply stores so easily replaced.
This spring I am getting ready to paint my antennas will probably paint the whole antenna with the black epoxy as soon as it gets warm enough. I noticed that the paint holds to the metal better if it is allowed to weather for a while. The antennas I am going to paint has been up for over 6 months now so should hold fairly well.
The epoxy paint holds up well I have antennas here that I painted 15 years ago and the paint is still there. On the antennas I painted before putting up, some of the paint flaked off I guess probably some oil was on the metal. That is the reason I let the antenna weather a bit before painting now it holds better and I think it has a rougher surface for the paint to hold to. In my opinion the very thin coat of paint DOES detune the antenna but so little you never know it. If you would spray very heavy coat on the antenna like there is on house wiring then you sure would notice the detuning but for coats just a few thousands thick then just not enough there to notice the difference if the antenna is resonate at 144.100 or 144.090.
Well that is my 2 cents worth and worth every penny.

On 3-April-1999 K3PGP  wrote:
Very interesting stuff posted here!!!  Thanks to all so far both pro and con.

The cans I have read "Crystal Clear Acrylic Coating".  Unfortunately that is ALL.  No other items are listed anyplace on any of the cans.  Guess it's a secret formula !!!

In the fine print it reads, "Should the product be used in the workplace, you may get material Safety Data Sheets (MSDS) [thought it said MSDOS there for a second!] by writing to:

Krylon Division of The Sherwin-Williams Company, Solon, Oh. 44139

So does this mean it will stand up under UV?  Where did you get the UV data on Acrylic / Perspex?  This may be common knowledge but I'm realing trying to nail this thing down as I've had such good luck with Krylon in the past but now I'm confused by all the products out there that carry the Krylon name.  I'm sure others are in the same boat and would really like to know which products are suitable and which aren't!

The Krylon I used in the past really stuck to the aluminum.  After 25+ years in the air it takes a knife to scrape it off.  I'm really amazed by this...

On 3-April-1999 GM4JJJ  wrote:
The spray I ended up using is an acrylic formula designed as the final top coat on motor car paints. (A clear Laquer). I guessed that if it is designed to last on a motor car outside in all weathers, it should do OK on my antennas!

For UK residents: I used Halfords Clear Laquer.

On 3-April-1999 AL7EB  wrote:
Hi everyone, and especially David Anderson,
Since I too am finishing up an array of four M2-xpol-20's, the discussion on oxidation protection has been pertinent.  Dan W0VD, addressed a subject I had a question on, and I especially liked his solution to preparation of the aluminum before "painting".  Just put it up and use it for six months. Hey, I can do that!   Considering it is still below freezing at night, here, and snow is still two foot deep, and I never liked spray painting indoors. better to wait till June when it is nice out.

Dave congrads on finishing your array.  Hope to get all mechanical assembly done this weekend and test next weekend.  I rewired the two antennas that are up, but the homemade RG-11 phasing lines not right (never could get the vel. factor from the store), high swr.  I'll just finish now getting other two ant. up, run the rest of the LMR-400 lines (decided to make them 5/2 wavelength long), and use the M2 4-way dividers.   Got slowed a little by three days of snowfall (in spring?!?).

On 6-April-1999 K3PGP  wrote:
Here is the response I got from Krylon.

Based on what I have learned so far the product called "Crystal Clear Acrylic Coating" #1301 should do the same job as what I used 25 years ago.

I've had the same results spraying it on nice shiny aluminum as I've had on aluminum that has already been weathered.  Just make sure there is no dirt, grease, wax, moisture, rust, or other loose particles on the surface before you spray.  Although the best temperature for application is listed as 70 degrees F, I've used it in the winter for emergency repairs with about the same results.  If you spray it on when the humidity is high the acrylic film will have a cloudy appearance but still seems to hold up about the same.

>Dear John,
>
>The product you were using 25 years ago and the Krlon Acrylic Clears today do not differ very much at all.  Although the solvents have changed slightly, the resin system is virtually the same.  After contacting the lab I found that when the product has dried, the paint film is the same.
>
>Thank you for your inquiry,
>
>Consumer Affairs

On 6-April-1999 G3LTF  wrote:
Sorry if I missed it but has anyone any experimental evidence of degradation on 432 yagis? like a degradation in cold sky to gnd or sun noise normalised to sun flux... should show up more at those frequencies. I do remember painting my yagis with polyurethane marine varnish in the 60's... but with tropo operation and 3 dB transistor front ends you never would see the difference!!

On 6-April-1999 K3PGP  wrote:
Many years ago I was using a homebrew 96 element array on 144 and 432 EME, before I switched to the 24 foot dish on 432.  I never saw any difference in sun noise or performance before or after spraying with Krylon Acrylic.  Same with the dual dipole feed 432 MHz feed in the dish.

However, the yagi antennas that were NOT coated required frequent maintenance to maintain performance.  All of these problems were traced to electrical problems in places where two different metals were in contact, like copper to aluminum, etc.  Although the elements looked ugly as long as the electrical connnections were good it seemed to work just as well as the coated antenna.  However, my uncoated antenna elements eventually became brittle and finally started to break when loaded with ice, high winds etc. The coated antenna never had this problem.

So I guess the original question remains unanswered as to whether there is a detectable difference between ugly looking weathered elements and nice looking new ones.  As far as I can determine there is no detectable difference in element tuning or performance when using THIN coats of acrylic.  I'm sure if the coating were thick enough the element would detune but I don't think one could spray or paint it on that thick.

I think Dave, GM4JJJ just coated his array so you might want to ask him for more recent observations.

Thanks to Cliff, K7RR I was pointed in the right direction.  Here is what I found out about acrylic.

Acrylic will pass light from 400 nm to well down into the infrared range. HOWEVER, it has an EXTREME cutoff at wavelengths just above 400 nm and passes almost 0% light at wavelengths shorter than approx. 380 nm.

I also noticed in the Edmund Scientific Catalog that lens made out of acrylic are useable from 400 nm down into the IR region.  However, once again they have an extreme cutoff and become almost opague to light with wavelength shorter than 350 to 380 nm.

So it seems that most any coating that contains acrylic should block UV.

I did notice when replacing some old outdoor wiring that the insulation on the red wires exposed to the sun turned white and fell off.  Those same same red wires were coated with Krylon in other places and look just like new.

On 6-April-1999 N7STU  wrote:
With all of this talk of protection and performance I wonder if anybody noticed any reduction in precipitation static after coating the elements? I know several HF contesters that have backup lowband dipoles made of insulated wire for receiving when their yagi's have high levels of precipitation static.

On 7-April-1999 K3PGP  wrote:
I have terrible problems with this especially during snow storms.   Coating the antenna with Krylon did absolutely NOTHING here to eliminate this problem !!!  However, sometimes I thought the precip static I was hearing was actually coming from other antennas near by and not the one I was connected to.

On 7-April-1999 K7RR  wrote:
Many thanks for the credit line John.  Nice of you to do so.   Yes, Acrylic is very good stuff to block UV! 

What you got from Krylon is pure bull puckey!!!  The solvent might have changed but the abilty to protect from UV and stick to surfaces is far different.  The old stuff was good!  The new is garbage! 

On 7-April-1999 PE1KXH  wrote:
We, in the southern part of holland near Thorn Citty, call the Krylon stuff what is now heavily discussed " veurdeurlak"

On 7-April-1999 I3DLI  wrote:
I believe static rain does promote wideband energy release when it impacts over more or less conductive surfaces of different electrical charge.

Thus, static noise can be produced not only by impacting our antennas, but also when impacting against the boundary metallics and even between acid-rain drops themselves (hiss noise?).

Since we are able to detect EME signals, we can detect any other useful or disturbing RF source. as  that one caused by the
phenomenon just depicted.

Coating elements may probably reduce it to some extents, not eliminate it.

Moreover another static disturbing source is the electrostatic energy cumulating by some antenna systems, when in static environmental area, having no provision for DC grounding at feedpoint or elsewere (for example: open baluns+DC-open radiators+LNA input capacitor-coupled+ insulated elements).

Addendum

On 15-September-2001 VE7BQH  wrote:
About two years ago there was quite a discussion on MOON-NET about what kind of coatings would work on aluminum elements to stop them oxidizing in various climates.

At that time various coatings were suggested like KRYLON or equivalent products. All had been tried at VE7BQH in the past, none with any kind of positive results. I live about 6KM from the sea and while I do not get what I would call excessive salting, elements turn gray fairly quickly.

At the time of the discussion, Paul, WA6PY suggested that a true automative clear coat might work well as it was meant to be used in harsh enviroments.

The idea seemed sound so I decided to trial it. I was able to obtain Automotive Clear Coat in standard spray cans easily from Canadian Tire a Canada wide outlets. Four 2 meter halfwave elements were coated.
 
I cleaned the test elements thorougly with steel wool and then wiped them down several times with laquer thinner. I was careful not to touch the aluminum with my bare hands. I then applied two thin coats. The Clear Coat dries very fast.

After two years, the elements are as clear as the day I put them up.

I am just passing on the results for those who might be interested.    

On 7-June-2010 DG7YBN wrote:
When exposed to atmosphere Aluminum (and like wise Stainless Steel, Lead and more metals) cover with oxide, the scientific term is Spontaneous Passivation. On a very even and clean surface the average thickness of the evolving layer may be some microns. Once fully covered the reaction of oxidation stops and we have a very stable passive layer coating our Yagi element. However long term exposure, heat, sea salt environment or generally and enrichment of the exposed to environment with ions that are the base for electrolytes will act as a reaction driver and force the build up of thicker layers. Myself I am using aluminium rods from EN AW6061 that come with an eloxal layer of 8…10 microns. They haven’t changed their beamless brightness in 4 years. They seem to stay like that for quite a while since the Passivation Layer is applied in a controlled technical process and thus very even and smooth.

Cleaning the aluminium with a corrosive material (as the mentioned steel wool) will potentially contaminate the Passive Layer with Corrosion Bridges; if small particles of iron are worked into the aluminium surface they might stick out of the thin natural passive layer and act as a gateway for further corrosion i.e. oxidation. A better way of cleaning should be through the use of sanding paper or non iron brushes or etching. Etching aluminium surfaces as for welding or gluing is done with Caustic Soda (watery NaOH solution). One may find an easy access to such in a drug store (most Drain Pipe Cleaners). The etched part must be rinsed with plenty of water after the etching is completed. And of course safety is first: protective wear as safety glasses and rubber gloves are the minimum as well as care for children and animals.

On the issue of potential losses or performance of antenna systems Leif Asbrink did a fundamental investigation: For non coated 5 mm elements he measured a Q of 5480 whilst an oxide layer of 15 microns dropped the Q to 5315 and a coating with polyester paint of 100 microns resulted in a Q of 3846 on 413 MHz (http://www.sm5bsz.com/antennas/sa/losses413.htm).

A so far unmentioned issue is that of insulator material degradation. Most plastics soak water and thus watery solutions of any electrolyte too by an amount of 1…3% roughly for PA, 1% for PMMA (Acryl) but almost non for PTFE. The water will sweep in electrolytes with time passing and so electrolyte dipoles may arrange on and just below the surface of our insulators. They may be ‘overhauled’ by rinsing in deioned water and isopropyl alcohol.


 


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