On Sat, 09 Apr 2005 21:12:47 -0500, Tom Ring
wrote:
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.

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

Richard Clark wrote:

On Sat, 09 Apr 2005 21:12:47 -0500, Tom Ring
wrote:

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.


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

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

Based on some of the other responses you received it may not be worth
it but there is another type of coating for aluminum called alodyne
which protects the same way as anodizing but is electrically
conductive.

jtm

Jim Miller wrote:
there is another type of coating for aluminum called alodyne
which protects the same way as anodizing but is electrically
conductive.


Alodine (R) coatings are not conductive. You can specify a "type 3"
coating that is thin enough that fasteners will usually punch through
the coating layer.

See MIL-C-5541 chromate conversion coatings.

Kevin Gallimore

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Another corrosion-inhibiting coating for aluminum is iridite. There are
conductive and non-conductive versions, something I learned the hard way
long ago.

Roy Lewallen, W7EL

axolotl wrote:
Jim Miller wrote:
there is another type of coating for aluminum called alodyne

which protects the same way as anodizing but is electrically
conductive.



Alodine (R) coatings are not conductive. You can specify a "type 3"
coating that is thin enough that fasteners will usually punch through
the coating layer.

See MIL-C-5541 chromate conversion coatings.

Kevin Gallimore

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On Sun, 10 Apr 2005 14:30:04 -0700, Roy Lewallen
wrote:

Another corrosion-inhibiting coating for aluminum is iridite. There are
conductive and non-conductive versions, something I learned the hard way
long ago.

Tell me about it [g].

I was the engineer responsible for transferring the design of the then
new Phoenix Missile IMPATT diode transmitter from the development lab
to the production floor.

The transmitter had three stages: a single diode driven by a
phase-locked Gunn oscillator fed a three diode cavity that drove a 16
diode cavity.

The development hardware used aluminum cavities that were comprised of
two pieces, with third copper piece that mounted the sixteen diodes.
So there was one aluminum-to-aluminum and one aluminum-to-copper
interface in each sandwich. Since this was a product for the U.S.
military, "passivation" was required for all aluminum parts.

I won't go into the considerable amount of detective work that it took
to decide that despite being "conductive" Alodine and its ilk are not
suitable coatings for rf components.

Gold is your friend, if of course, it's thicker than a few skin
depths, which is another long story. [g]


Roy Lewallen, W7EL

axolotl wrote:
Jim Miller wrote:
there is another type of coating for aluminum called alodyne

which protects the same way as anodizing but is electrically
conductive.



Alodine (R) coatings are not conductive. You can specify a "type 3"
coating that is thin enough that fasteners will usually punch through
the coating layer.

See MIL-C-5541 chromate conversion coatings.

Kevin Gallimore

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Amen! If gold did not exist, it would need to be invented just for EE
purposes. 73 Mac N8TT

--
J. Mc Laughlin; Michigan U.S.A.
Home:
"Wes Stewart" wrote in message
...
snip


I won't go into the considerable amount of detective work that it took
to decide that despite being "conductive" Alodine and its ilk are not
suitable coatings for rf components.

Gold is your friend, if of course, it's thicker than a few skin
depths, which is another long story. [g]

Since you're wanting to make it black to match other accouterments on
your vehicle, consider that most, if not all, black-dyed anodization
will fade in the sunlight, and it doesn't take all that long. In
addition, depending on the aluminum alloy, the "black" may not be all
that black to begin with. Why not instead give the antenna a coat of
automotive enamel or lacquer? You can either mask off areas that need
to have electrical contact, or scrape them after painting. Perhaps you
can paint after the antenna is assembled. That way, you can get a
color that really matches other items.

Cheers,
Tom

Thanks Tom (& everybody else). The problem is that I'm planing on
having an 8' two section whip on the top that will power extend &
retract through the loading coil into the bottom mast.

Why?

Call it a combination of lazyness & a prepondarence towards low
ceilings in parking garages. Also (bonus), with the coil retracted
I'll be able to vary the height of the whip for the upper bands.

So what I was really looking (hoping) for is a black coating that
maintains electrical contact between the inner & outer whip sections
as one slides in & out of the other.

Don't look like I'm gonna get it .

Maybe it would be easier just to build a test range insted .

H.

On 11 Apr 2005 12:01:05 -0700, "K7ITM" wrote:

Since you're wanting to make it black to match other accouterments on
your vehicle, consider that most, if not all, black-dyed anodization
will fade in the sunlight, and it doesn't take all that long. In
addition, depending on the aluminum alloy, the "black" may not be all
that black to begin with. Why not instead give the antenna a coat of
automotive enamel or lacquer? You can either mask off areas that need
to have electrical contact, or scrape them after painting. Perhaps you
can paint after the antenna is assembled. That way, you can get a
color that really matches other items.

Cheers,
Tom