Anodized Alumium for Antenna Elements

Hi folks, I'm in the process of building myself a screwdriver antenna for my truck. Being the vain sort, I'd like it to end up being black
as that matches nicely with the other bitties sticking out of the vehicle.
Q.- Does anodyzing negatively impact aluminum's ability to efficiently radiate? I seem to recall reading somewheres that anodyzing leaves a non-conductive surface, but on the other hand aluminum oxide ain't supposed to be that great a conductor either & that whats on the surface of any piece of aluminum thats seen air for more than a few minutes.
Enquiring Minds want To Know-
Howard.
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The radiating surface don't care. Just make sure all mechanical contacts which need to conduct penetrate the anodizing. Like where the coax connects, or where the coil is connected.
-- Crazy George The attglobal.net address is a SPAM trap. Please change that part to: att<dot>biz properly formatted.

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Hello Sir George and Howard:
Anodizing the aluminum is kind of over kill as I have measured new antennas and old antennas with 30 plus years of exposure to the elements. No difference measured.
What did throw me a curve was buying Anodized Surplus Aluminum Tubing in Burbank Ca, and making a vertical for the VHF Low Band. Ok no problem getting it together and should have tuned in a few minutes.
But no it was responding to a much higher frequency than the 31 Mc I wanted it to tune to. After checking and double checking everything and replacing the coax and antenna analyzer it still measured a way high frequency SWR null.
Now faced with the strong reality that this thing was gonna kick my a$$, after a hole day of going nutzoid. I got my old Simspon 260 VOM and measured continuity from all the elements. I found that one of the vertical elements had been anodized on the inside causing a no connection condition.
Cutting off a metal wire brush and putting the shank in Mr. 1/2 inch chuck, drill motor, and the 100 foot cord (I have given up on battery operated drill motors) the inside of the tubing was now nice and shinny bright aluminum.
The antenna tuned up as designed. So keep your eyes open when using anodized aluminum tubing. And I think this is why some antenna manufactures do not anodize their aluminum tubing. Plus the added manufacturing costs.
Jay in the Mojave
Crazy George wrote:

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On Sat, 09 Apr 2005 15:38:23 -0700, Jay in the Mojave

That might be ture in the Mojave but come up here on the norhern California coast - on the ocean - and you 30+ aluminum antenna will be noting more that a memory.
Danny, K6MHE
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Hello Dan:
So what do you use for being near the ocean?
Do you have to anodize all the aluminum tubing to keep the antennas up?
Jay in the Mojave
Dan Richardson wrote:

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Jay,
We just replace them more frequently than dry desert dwellers. After about five years (sometime sooner) they are about shot.
My two-meter omni is incased in a fiberglass radome and my wire antennas are made with insulated wire with ends sealed.
Danny, K6MHE
On Sun, 10 Apr 2005 02:08:57 -0700, Jay in the Mojave

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Dan Richardson wrote:

How close to the ocean are you? It sounds like you are right in the spray!
    - Mike KB3EIA -
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On Sun, 10 Apr 2005 23:58:12 -0400, Mike Coslo

About a half mile. I live in the northern California "Mendocino" coast. We have a lot of rain too and that combination is a killer for aluminum exposed to the elements.
Danny
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The (inappropriately named) Pacific coast where Danny lives has fair-sized waves almost constantly, particularly in the winter. When they break along the shore, a very fine mist of salt water droplets is created, and those drift for a long distance. In the winter, the prevailing wind direction is from the west, so the salt water mist is blown farther yet. The result is that the air itself contains a suspension of salt water. Aluminum corrodes fairly quickly, and good sized bare copper wire turns into a blue powder in a year or less. Where I live, in the Willamette valley of Oregon which is about 70 miles inland, it rains pretty constantly from about October through June -- not an extraordinary amount, but everything outside stays wet for the whole winter because of the lack of direct sunshine and the frequent rain. But aluminum lasts forever and so does copper, which only gets a thin, dark oxide coating. It's the salt water suspension that's the killer on the coast.
Roy Lewallen, W7EL
Dan Richardson wrote:

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wrote:

Yea, but those launch angles to the west. <G>
Danny, K6MHE
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Once long ago I was driving down highway 101 in my VW squareback, operating mobile CW late at night on 40 meters. Rig was homebrew, about 8-9 watts output (10 watts input). Antenna was a CB mobile whip on a bumper mount, base loaded with a coil wound on a powdered iron toroid core, Q about 200 - 250. Worked JA, solid copy. Yea, that salt water does wonders for a vertical.
Roy Lewallen, W7EL
Dan Richardson wrote:

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wrote:

Has anyone done any testing (RF resistance) on squirting some NOALOX compound (or other anti-corrosion sealants) between the aluminum elements and scrubbing them clean to remove the oxide film before bolting them together? Should help a lot, especially along the coast.
Works great on AL power wire at 60Hz...
--<< Bruce >>--
(KBPY-8540 - wait, they discontinued those calls. Oh well...) ;-)
--
Bruce L. Bergman, Woodland Hills (Los Angeles) CA - Desktop
Electrician for Westend Electric - CA726700
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The problem with aluminum at the coast isn't an oxide that has to be removed. It's just the opposite -- the problem is that salt water removes the oxide that needs to be kept intact. Aluminum is a very active metal, which oxidizes almost immediately on exposure to air. The oxide is a hard, non-porous ceramic which, after forming a very thin layer, prevents any further contact of the aluminum with air. The problem is that aluminum oxide is slightly soluble in salt water and other acids. So the oxide coating is removed by the salt water, exposing more aluminum to salt water and air, allowing it to corrode. It does help to coat metals with grease, but only because it prevents the salt water from contacting the metal or, in the case of aluminum, the oxide coating. But the last thing you want to do is intentionally remove the oxide coating.
Roy Lewallen, W7EL
Bruce L. Bergman wrote:

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Jay in the Mojave wrote:

> than the 31 Mc ... ^^ Showing our age, are we Jay? :-)
--
73, Cecil http://www.qsl.net/w5dxp

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Hello Cecil:
Ok well thats two of us then, .... hehhehe
Jay in the Mojave
Cecil Moore wrote:

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Cecil Moore wrote:

You know I didn't even notice that when I read it. :-) ...lew... ( ex W3SLX circa. 1950 )
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Jay in the Mojave wrote:

Interesting, as I have measured antennas with only 2 years exposure that had .5 dB measured difference. A 432 MHz antenna scrubbed with a ScotchBrite showed a .6 dB gain increase.
So B as in B, S as in S, as we say here in Minnesota.
tom K0TAR
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wrote:

Hi Tom,
You could measure to the accuracy of better than 0.2dB between two separate tests? And at UHF too? Care to share how?
73's Richard Clark, KB7QHC
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Richard Clark wrote:

Well, you'd have to ask Mark Thorsen, WB0TEM, what equipment was used, but the range is checked several times against the reference antenna during each band we run, and is generally within .1 dB between checks. Except that one day in KS. Boy was it hot.
I wouldn't bet absolute values are on the mark, but an antenna measured against itself was reproducable. So I do believe the antenna improved due to having the oxide scrubbed off.
tom K0TAR
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wrote:

Hi Tom,
But the point of accuracy, even reproducible accuracy, requires a very absolute source to compare against. Sometimes that absolute is quite simple to achieve, but now you have upped the ante to 0.1dB. This implies a measurement accuracy of at least three times better; which, in turn, means you have access to a standard that can discern 0.8%.
To say you test the antenna "against itself" does not really say much when it comes to power and gain. That is no benchmark. The presumption here is that you have an external source of power that is constant. This then raises the same question. Over a span of time, what guarantees this degree of accuracy? By what method is it confirmed? That source's "absolute" power level needn't be an issue, but there is no way to escape casting that "absolute" requirement into another standard to confirm the fact of its stability.
73's Richard Clark, KB7QHC
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