| Author |
Message |
    
Admin
| | Posted on Saturday, February 15, 2003 - 12:16 pm: | 
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On the Copper Electronics forums, we have heard over and over from people who believe in a 'settling time' for all aluminum antennas. Many people have posted that an aluminum antenna needs some time, which has been described from several weeks to several months, to work its best and give the lowest SWR. We have also read that the tuning sometimes changes during this 'settling time', but after this time the tuning changes no more. How can this be? Does aluminum change that much with exposure to RF? Are these people nuts?
This phenomenon can be answered very easily. First, we have to look at the characteristics of the aluminum material itself. Aluminum is a very, very soft metal, which unless mixed with some other metal, is useless for antenna elements because it is too soft and bendable. When aluminum is mixed with small amounts of stiffer metals, it becomes an alloy; aircraft aluminum is one common aluminum alloy. The downside to these aluminum alloys is that they corrode over time. Some alloys, like the inexpensive ones used for aluminum antenna elements, can develop surface corrosion in a very short time. This corrosion itself is called 'aluminum oxide' and is the direct result of exposure of aluminum to an oxygen atmosphere. You can't 'see' aluminum oxide unless it becomes much worse, then it is commonly called simply 'corrosion'.
You can use the aluminum oxide and its unique properties to your advantage. For instance, when you see aluminum that is coated with a colored finish, it is called anodized. Anodizing is a process that dyes the aluminum oxide with color. This is normally done by boiling the aluminum oxide covered aluminum in a chemical or dye to produce the correct color. Additionally, anodizing also helps to seal the aluminum oxide, which slows the oxidizing process.
The downside to aluminum oxide is its electrical insulating properties. If enough aluminum oxide accumulates on the aluminum surface, it builds a substantial electrical resistance. When you order an aluminum antenna, from the time the aluminum is made to the time it finally finds its way to you in the form of an antenna element, it has developed a microscopic, yet substantial thickness of aluminum oxide on its surface. Since aluminum oxide itself is an insulator, when you mate the various surfaces of the aluminum tubing and parts together, unless the aluminum oxide is removed, there is a small amount of RF resistance between them. Over time, wind and temperature expansion and contraction will force the mating surfaces to grind against each other and work through the small surface oxidation until they make better and better electrical contact. This is how we can explain the 'settling time' of an aluminum antenna.
Of course, this whole 'settling time' can be avoided by removing the aluminum oxide from all surfaces of the aluminum which will contact other aluminum. Completely sanding all the outer and inner ends of the tubing, surfaces of brackets, and hardware prior to assembly will eliminate any settling time you may have experienced with aluminum antennas in the past. Also, if you use some sort of sealant (like clear spray paint) after assembly, you will extend the life of your antenna hardware and have a longer lasting antenna that does not experience SWR fluctuations with moisture. Last but not least, use of Penetrox on all hardware will prevent the dissimilar metals from corroding against each other. If you cannot find Penetrox, grease can be substituted with a small decrease in effectiveness.
Overall, aluminum antennas will typically outperform similar design fiberglass antennas like the ones we commonly find available today. With proper preparation in construction and installation, aluminum antennas will outlast their fiberglass counterparts too.
Tech 833 |
Mikefromms
| | Posted on Saturday, July 05, 2003 - 7:28 pm: |
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Very informative reply. I'm seeing improvements in my Astro plane as it just stays on the roof. I'm still going to raise it a few feet and change that coax.
mikefromms |
Znut
| | Posted on Sunday, July 06, 2003 - 3:47 pm: |
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I scotch-brited everything when I made my quad. I didn't seal it though and the price will be that I will have to undo the clamps and re-scrub all the mating surfaces again, inevitably. |
Mikefromms
| | Posted on Tuesday, July 08, 2003 - 12:46 pm: |
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Maybe we should all just get fiberglass?
mikefromms |
Znut
| | Posted on Tuesday, July 08, 2003 - 7:04 pm: |
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You gotta love those aluminum ears. I've had an A-99 for almost 5 years. I had a V-5/8 for 6 months before that. The V-5/8 was a little narrow banded and required much "tweaking" before I got it right but would wear me out on winter Sunday afternoons on SSB. That big aluminum antenna was AWESOME. Not like a beam but I didn't have to turn it. Great antenna. |
Legend
Junior Member
Username: Legend
Post Number: 12
Registered: 12-2002
| | Posted on Wednesday, March 10, 2004 - 7:09 am: |
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Any particular type or brand of "clear spray paint"? No effect on SWR? If not, where can I get some?
Thanks. |
Tech808
Moderator
Username: Tech808
Post Number: 1753
Registered: 8-2002
| | Posted on Wednesday, March 10, 2004 - 9:35 am: |
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Legand.
Get Clear Enamel or Laquer Spray Paint any brand will work.
Will not effect SWR.
You can buy it at Walmart,K-mart any Auto Store or Hardware, or places like Home Depot, Meneard's or Lowes.
Lon
Tech808 |
Bulldog369
Member
Username: Bulldog369
Post Number: 60
Registered: 2-2004
| | Posted on Wednesday, March 10, 2004 - 10:01 am: |
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so what i gather from all this information is when you get an aluminum antenna you should
1.sand the bottom nd the inside of the tubbing where you put them together
2. spray the antenna with a clear finish..
i am going to buying the alpha v.. so if this is right i should sand before putting it together, an spray it after its together...??? |
Tech833
Moderator
Username: Tech833
Post Number: 583
Registered: 8-2002
| | Posted on Wednesday, March 10, 2004 - 9:50 pm: |
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Spray after it is all together. If you feel the need to spray at all. |
Keithinatlanta
Intermediate Member
Username: Keithinatlanta
Post Number: 195
Registered: 3-2003
| | Posted on Sunday, March 14, 2004 - 8:21 am: |
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Ok, guys, living in Atlanta, we get a lot of humidity in the spring and even MORE in the summer. I am going to get this super scanner up sometime this spring. I had never heard of spraying an antenna before reading this. Would it be in my best interest to do so? Thanks.
Keith in Atlanta |
Tech833
Moderator
Username: Tech833
Post Number: 594
Registered: 8-2002
| | Posted on Tuesday, March 16, 2004 - 1:57 pm: |
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Not really. I was only providing an answer to a question.
A coating of protectant oil would be better. |
Legend
Junior Member
Username: Legend
Post Number: 45
Registered: 12-2002
| | Posted on Saturday, April 24, 2004 - 2:32 am: |
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"protectant oil"
I've never used it before. Any particular brand names so that I can know I'm buying the right type of oil? Does it spray on?
Thanks... |
Legend
Junior Member
Username: Legend
Post Number: 46
Registered: 12-2002
| | Posted on Saturday, April 24, 2004 - 2:36 am: |
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Ohhh... I forgot to ask. I just received an I-10K from Jay in the Mohave. Should we sand a brand new antenna before construction? Thanks again! |
Tech833
Moderator
Username: Tech833
Post Number: 652
Registered: 8-2002
| | Posted on Saturday, April 24, 2004 - 12:59 pm: |
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Legend,
Any non reactive petrolium oil or oil based varnish will do.
Yes, you sand a new antenna. Read the article for the reasoning. |
Keithinatlanta
Advanced Member
Username: Keithinatlanta
Post Number: 534
Registered: 3-2003
| | Posted on Wednesday, March 23, 2005 - 10:10 pm: |
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Tech 833, what if I put up this super scanner and do nothing to it. What happens then?
Thanks.
Keith
CEF 150 |
Tech808
Moderator
Username: Tech808
Post Number: 5328
Registered: 8-2002
| | Posted on Wednesday, March 23, 2005 - 11:11 pm: |
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Keithinatlanta,
Go back to the top and read the article by tech833.
He covers what will happen without coating it.
In short (The downside to these aluminum alloys is that they corrode over time. Some alloys, like the inexpensive ones used for aluminum antenna elements, can develop surface corrosion in a very short time. This corrosion itself is called 'aluminum oxide' and is the direct result of exposure of aluminum to an oxygen atmosphere. You can't 'see' aluminum oxide unless it becomes much worse, then it is commonly called simply 'corrosion'.) from Tech833's article above.
Hope this helps,
Lon
Tech808
CEF808
N9OSN
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Kid_vicious
Intermediate Member
Username: Kid_vicious
Post Number: 310
Registered: 9-2004
| | Posted on Thursday, March 24, 2005 - 12:38 am: |
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im putting my top one up in the next week or so. i spray painted it flat black, and used a clear coat on it. i wire wheeled all the mating surfaces, and i use automotive type dielectric grease for the threaded connections. does anyone see any downsides to using this instead of penetrox?
matt |
Keithinatlanta
Advanced Member
Username: Keithinatlanta
Post Number: 537
Registered: 3-2003
| | Posted on Thursday, March 24, 2005 - 7:36 am: |
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Kid vicious, where did you get the dielectric grease? Can I get that at Pep Boys or Auto Zone, places like that? What is it in? A little squeeze tube maybe? Obviously, it would not take a lot!
Thanks.
Lon, thanks for your help there. Guess I was just too tired and read right over it!
Keith |
