Suppose my square loop antenna oxidizes. Does that affect its
characteristics?

Thanks,
John KD5YI

In article , John S wrote:

Suppose my square loop antenna oxidizes. Does that affect its
characteristics?

Yes. Its color changes :-)

Beyond that - as far as RF characteristics go - the answer is probably
"Yes, but probably not enough that you would be able to detect the
difference in practice."

What I believe would happen:

(1) As the surface oxidizes, its resistance rises. This will cause
some amount of additional signal loss, as current flows through the
resistive layer.

The actual amount of added loss will depend on the depth of the
oxidized layer, its actual resistance per square compared to
that of the underlying copper, and on the frequency (which
influences the *skin depth" of the material).

Interestingly, the greatest amount of added loss does *not*
occur when the oxide layer's resistance is at a maximum (near-
infinite), since little or no current will flow through the
oxide... it becomes "invisible", and the current will flow
through the metallic copper under the oxide. The losses are
highest when the oxide layer is (1) of moderate resistance, and
(2) fairly thick, compared to the skin depth. At this point,
most of the current will be flowing through the oxide, and
excluded from the metallic copper by the skin effect.

I don't know the actual numbers involved here (i.e. point of
greatest loss, for any given frequency). In practice I don't
think you'll come anywhere near these conditions for a copper-wire
antenna at UHF frequencies.

(2) Copper oxide is not electrically linear - it behaves somewhat
like a semiconductor (you can actually make a diode out of it).
This nonlinearity may result in the generation of some second-
and higher-order harmonics, and possibly some intermodulation
products, if a significant amount of current is flowing through
the oxide layer.

I doubt that this will be detectable.

(3) If you manage to get oxidation into your actual metal-to-metal
contacts (and not just on the surface of the metal) the problem
in (2) becomes a lot worse, since you can have *all* of your
signal power flowing through what amounts to a diode. Harmonics
and IM products can become much more of a problem.

In practice, I'd say that if you make sure that (3) is not a
problem... that is, all of your actual metal-to-metal contacts are
soldered or welded (or gooped with a conductive anti-oxidant paste
prior to assembly) you'll be OK, electrically. Surface oxidation
on the loop is unlikely to be a problem.

You could always scrub down the loop with Brasso, wash it
carefully and dry it, and then spray it with an industrial-
strength outdoor-rated UV-proof clearcoat. That would leave it
shiny and bright for quite a long time.

--
Dave Platt AE6EO
Friends of Jade Warrior home page: http://www.radagast.org/jade-warrior
I do _not_ wish to receive unsolicited commercial email, and I will
boycott any company which has the gall to send me such ads!

On 11/4/2011 1:17 PM, Dave Platt wrote:
In , John wrote:

Suppose my square loop antenna oxidizes. Does that affect its
characteristics?

Yes. Its color changes :-)

Beyond that - as far as RF characteristics go - the answer is probably
"Yes, but probably not enough that you would be able to detect the
difference in practice."

What I believe would happen:

(1) As the surface oxidizes, its resistance rises. This will cause
some amount of additional signal loss, as current flows through the
resistive layer.

The actual amount of added loss will depend on the depth of the
oxidized layer, its actual resistance per square compared to
that of the underlying copper, and on the frequency (which
influences the *skin depth" of the material).

Interestingly, the greatest amount of added loss does *not*
occur when the oxide layer's resistance is at a maximum (near-
infinite), since little or no current will flow through the
oxide... it becomes "invisible", and the current will flow
through the metallic copper under the oxide. The losses are
highest when the oxide layer is (1) of moderate resistance, and
(2) fairly thick, compared to the skin depth. At this point,
most of the current will be flowing through the oxide, and
excluded from the metallic copper by the skin effect.

I don't know the actual numbers involved here (i.e. point of
greatest loss, for any given frequency). In practice I don't
think you'll come anywhere near these conditions for a copper-wire
antenna at UHF frequencies.

(2) Copper oxide is not electrically linear - it behaves somewhat
like a semiconductor (you can actually make a diode out of it).
This nonlinearity may result in the generation of some second-
and higher-order harmonics, and possibly some intermodulation
products, if a significant amount of current is flowing through
the oxide layer.

I doubt that this will be detectable.

(3) If you manage to get oxidation into your actual metal-to-metal
contacts (and not just on the surface of the metal) the problem
in (2) becomes a lot worse, since you can have *all* of your
signal power flowing through what amounts to a diode. Harmonics
and IM products can become much more of a problem.

In practice, I'd say that if you make sure that (3) is not a
problem... that is, all of your actual metal-to-metal contacts are
soldered or welded (or gooped with a conductive anti-oxidant paste
prior to assembly) you'll be OK, electrically. Surface oxidation
on the loop is unlikely to be a problem.

You could always scrub down the loop with Brasso, wash it
carefully and dry it, and then spray it with an industrial-
strength outdoor-rated UV-proof clearcoat. That would leave it
shiny and bright for quite a long time.



My prior 'Net search revealed opinions from at least two camps, so I
thought I'd ask here.

Color, I'll check with my decorator :-)

Item (3), connections will be soldered.

I will be using #14 gauge wire as used in house wiring. I could leave
the insulation on the wire, but moisture has a habit of wicking into the
tiniest exposed crevice, as you are aware, and I'd rather not have to
perform heroic efforts to prevent oxidation. By removing the insulation,
I can at least observe the severity of oxidation and guess at whether it
correlates to any observed communication problems.

Thanks for the complete and thoughtful answer, Dave. You have persuaded
me to proceed without worry.

73,
John KD5YI

On 11/4/2011 12:11 PM, John S wrote:
On 11/4/2011 1:17 PM, Dave Platt wrote:
In , John
wrote:

Suppose my square loop antenna oxidizes. Does that affect its
characteristics?

Yes. Its color changes :-)

Beyond that - as far as RF characteristics go - the answer is probably
"Yes, but probably not enough that you would be able to detect the
difference in practice."

What I believe would happen:

(1) As the surface oxidizes, its resistance rises. This will cause
some amount of additional signal loss, as current flows through the
resistive layer.

The actual amount of added loss will depend on the depth of the
oxidized layer, its actual resistance per square compared to
that of the underlying copper, and on the frequency (which
influences the *skin depth" of the material).

Interestingly, the greatest amount of added loss does *not*
occur when the oxide layer's resistance is at a maximum (near-
infinite), since little or no current will flow through the
oxide... it becomes "invisible", and the current will flow
through the metallic copper under the oxide. The losses are
highest when the oxide layer is (1) of moderate resistance, and
(2) fairly thick, compared to the skin depth. At this point,
most of the current will be flowing through the oxide, and
excluded from the metallic copper by the skin effect.

I don't know the actual numbers involved here (i.e. point of
greatest loss, for any given frequency). In practice I don't
think you'll come anywhere near these conditions for a copper-wire
antenna at UHF frequencies.

(2) Copper oxide is not electrically linear - it behaves somewhat
like a semiconductor (you can actually make a diode out of it).
This nonlinearity may result in the generation of some second-
and higher-order harmonics, and possibly some intermodulation
products, if a significant amount of current is flowing through
the oxide layer.

I doubt that this will be detectable.

(3) If you manage to get oxidation into your actual metal-to-metal
contacts (and not just on the surface of the metal) the problem
in (2) becomes a lot worse, since you can have *all* of your
signal power flowing through what amounts to a diode. Harmonics
and IM products can become much more of a problem.

In practice, I'd say that if you make sure that (3) is not a
problem... that is, all of your actual metal-to-metal contacts are
soldered or welded (or gooped with a conductive anti-oxidant paste
prior to assembly) you'll be OK, electrically. Surface oxidation
on the loop is unlikely to be a problem.

You could always scrub down the loop with Brasso, wash it
carefully and dry it, and then spray it with an industrial-
strength outdoor-rated UV-proof clearcoat. That would leave it
shiny and bright for quite a long time.



My prior 'Net search revealed opinions from at least two camps, so I
thought I'd ask here.

Color, I'll check with my decorator :-)

Item (3), connections will be soldered.

I will be using #14 gauge wire as used in house wiring. I could leave
the insulation on the wire, but moisture has a habit of wicking into the
tiniest exposed crevice, as you are aware, and I'd rather not have to
perform heroic efforts to prevent oxidation. By removing the insulation,
I can at least observe the severity of oxidation and guess at whether it
correlates to any observed communication problems.

Thanks for the complete and thoughtful answer, Dave. You have persuaded
me to proceed without worry.

73,
John KD5YI
Loops are good! I have a full wave 160 meter loop, horizontal, at 35ft.
The copper begins to turn color within a month or so.

I see your address is Plano, TX. If you are down wind from any chemical
companies or oil refineries or houses that use oil heat, or even natural
gas users, the antenna and soldered connections will not just oxidize,
but will have other chemical reactions to the sulfur and other acids in
the air.

When I lived in Portland, Oregon, years ago, we and all the neighbors
had oil heat. She sulfur from burning oil caused lots of corrosion on
copper and soldered connections. Hope you have better results. As noted,
clear plastic spray will help a lot on the soldered parts.

Paul, KD7HB

On 11/4/2011 9:25 PM, Paul Drahn wrote:
On 11/4/2011 12:11 PM, John S wrote:
On 11/4/2011 1:17 PM, Dave Platt wrote:
In , John
wrote:

Suppose my square loop antenna oxidizes. Does that affect its
characteristics?

Yes. Its color changes :-)

Beyond that - as far as RF characteristics go - the answer is probably
"Yes, but probably not enough that you would be able to detect the
difference in practice."

What I believe would happen:

(1) As the surface oxidizes, its resistance rises. This will cause
some amount of additional signal loss, as current flows through the
resistive layer.

The actual amount of added loss will depend on the depth of the
oxidized layer, its actual resistance per square compared to
that of the underlying copper, and on the frequency (which
influences the *skin depth" of the material).

Interestingly, the greatest amount of added loss does *not*
occur when the oxide layer's resistance is at a maximum (near-
infinite), since little or no current will flow through the
oxide... it becomes "invisible", and the current will flow
through the metallic copper under the oxide. The losses are
highest when the oxide layer is (1) of moderate resistance, and
(2) fairly thick, compared to the skin depth. At this point,
most of the current will be flowing through the oxide, and
excluded from the metallic copper by the skin effect.

I don't know the actual numbers involved here (i.e. point of
greatest loss, for any given frequency). In practice I don't
think you'll come anywhere near these conditions for a copper-wire
antenna at UHF frequencies.

(2) Copper oxide is not electrically linear - it behaves somewhat
like a semiconductor (you can actually make a diode out of it).
This nonlinearity may result in the generation of some second-
and higher-order harmonics, and possibly some intermodulation
products, if a significant amount of current is flowing through
the oxide layer.

I doubt that this will be detectable.

(3) If you manage to get oxidation into your actual metal-to-metal
contacts (and not just on the surface of the metal) the problem
in (2) becomes a lot worse, since you can have *all* of your
signal power flowing through what amounts to a diode. Harmonics
and IM products can become much more of a problem.

In practice, I'd say that if you make sure that (3) is not a
problem... that is, all of your actual metal-to-metal contacts are
soldered or welded (or gooped with a conductive anti-oxidant paste
prior to assembly) you'll be OK, electrically. Surface oxidation
on the loop is unlikely to be a problem.

You could always scrub down the loop with Brasso, wash it
carefully and dry it, and then spray it with an industrial-
strength outdoor-rated UV-proof clearcoat. That would leave it
shiny and bright for quite a long time.



My prior 'Net search revealed opinions from at least two camps, so I
thought I'd ask here.

Color, I'll check with my decorator :-)

Item (3), connections will be soldered.

I will be using #14 gauge wire as used in house wiring. I could leave
the insulation on the wire, but moisture has a habit of wicking into the
tiniest exposed crevice, as you are aware, and I'd rather not have to
perform heroic efforts to prevent oxidation. By removing the insulation,
I can at least observe the severity of oxidation and guess at whether it
correlates to any observed communication problems.

Thanks for the complete and thoughtful answer, Dave. You have persuaded
me to proceed without worry.

73,
John KD5YI
Loops are good! I have a full wave 160 meter loop, horizontal, at 35ft.
The copper begins to turn color within a month or so.

I see your address is Plano, TX. If you are down wind from any chemical
companies or oil refineries or houses that use oil heat, or even natural
gas users, the antenna and soldered connections will not just oxidize,
but will have other chemical reactions to the sulfur and other acids in
the air.

Plano is north of Dallas. The prevailing winds are from the south. That
says it all.

When I lived in Portland, Oregon, years ago, we and all the neighbors
had oil heat. She sulfur from burning oil caused lots of corrosion on
copper and soldered connections. Hope you have better results. As noted,
clear plastic spray will help a lot on the soldered parts.

Paul, KD7HB


The antenna looks like a diamond and is only about 1 foot in its
greatest dimension. It will be mounted no more than 6 feet above ground.
If I give it some thought, I can probably design the whole project such
that the antenna can be replaced without too much trouble.

Thanks for your input, Paul.

73,
John KD5YI