One place where I can clearly see the difference between copper and aluminum
is comparing my (copper) Nott screwdriver with my (aluminum) Tarheel
screwdriver or my (aluminum) Hi-Q mobile antenna on 20 meters.
Mounted on my Durango, at resonance the Nott's impedance is 9 ohms, while
the Tarheel is 20 ohms and the (smaller tube) Hi-Q is 30 ohms; Measured with
the same whip in all cases.
This is a case of a short antenna.
The difference is significant and easily measured.
73
H.
NQ5H

"Tom Bruhns" wrote in message
m...
Hmmm...My book says aluminum's resistivity is about 2.6 microohm-cm,
and copper's is 1.7, only a 1.5:1 ratio--though it may not be quite
that good for commonly used aluminum alloys. OTOH, copper also
suffers from being alloyed. But in any event, it's good to keep in
mind that the RF resistance ratio for non-magnetic materials goes as
the square root of the bulk resistivity ratio, because higher
resistivity materials have larger skin depth. So a 2:1 ratio at DC
ends up being only 1.41:1 at RF, and 1.5:1 at DC is only a bit over
1.2:1 at RF.

Since both copper and aluminum have good conductivity, it's just not
worth sweating in practically all cases, unless the antenna is very
short (and thus has very low feedpoint radiation resistance).

Actually, what I thought Gary might be getting at is the protection
from corrosion that gold might offer, as compared with bare copper.
I'd say that it IS worth worrying about protecting your antenna from
corrosion. Maybe you just have to think about it long enough to
understand that you are lucky to live in a place where corrosion isn't
a problem, or maybe you live next to the ocean where salt spray will
get the best of almost anything metallic. But like Roy says, gold
over nickel is probably a bad idea. Unplated stainless steel antenna
wire is probably a bad idea. Painted copper pipe, or anodized
aluminum tubing, will probably work well for a long time.

Cheers,
Tom


"H. Adam Stevens, NQ5H" wrote in message
...
Hi Roy;
It's worse than that: Copper will diffuse throught the gold and pile up
on
the surface.
I showed that with an Auger microprobe at Motorola decades ago.
So to go to a gold surface, nickel is mandatory, then a thick gold
coating;
Too expensive!
It's not like the switch from aluminum to copper, which is a 2x
resistivity
improvement.
You just can't beat plain old copper.
73
H.
NQ5H

That's much, much more difference than can be explained by the different
conductivities of the metals. Either some very resistive alloys are
involved, or there are differences between the antennas other than the
type of metal.

Roy Lewallen, W7EL

H. Adam Stevens, NQ5H wrote:
One place where I can clearly see the difference between copper and aluminum
is comparing my (copper) Nott screwdriver with my (aluminum) Tarheel
screwdriver or my (aluminum) Hi-Q mobile antenna on 20 meters.
Mounted on my Durango, at resonance the Nott's impedance is 9 ohms, while
the Tarheel is 20 ohms and the (smaller tube) Hi-Q is 30 ohms; Measured with
the same whip in all cases.
This is a case of a short antenna.
The difference is significant and easily measured.
73
H.
NQ5H

"Tom Bruhns" wrote in message
m...
Hmmm...My book says aluminum's resistivity is about 2.6 microohm-cm,
and copper's is 1.7, only a 1.5:1 ratio--though it may not be quite
that good for commonly used aluminum alloys. OTOH, copper also
suffers from being alloyed. But in any event, it's good to keep in
mind that the RF resistance ratio for non-magnetic materials goes as
the square root of the bulk resistivity ratio, because higher
resistivity materials have larger skin depth. So a 2:1 ratio at DC
ends up being only 1.41:1 at RF, and 1.5:1 at DC is only a bit over
1.2:1 at RF.

Since both copper and aluminum have good conductivity, it's just not
worth sweating in practically all cases, unless the antenna is very
short (and thus has very low feedpoint radiation resistance).

Actually, what I thought Gary might be getting at is the protection
from corrosion that gold might offer, as compared with bare copper.
I'd say that it IS worth worrying about protecting your antenna from
corrosion. Maybe you just have to think about it long enough to
understand that you are lucky to live in a place where corrosion isn't
a problem, or maybe you live next to the ocean where salt spray will
get the best of almost anything metallic. But like Roy says, gold
over nickel is probably a bad idea. Unplated stainless steel antenna
wire is probably a bad idea. Painted copper pipe, or anodized
aluminum tubing, will probably work well for a long time.

Cheers,
Tom

On the other hand, aluminum is lighter. Might be worthwhile to compare the
resistance of an Al and Cu conductors (solid and tube) of the same length
and the same weight. I am pretty sure AL wins at 60 Hz.

Tam/WB2TT


"H. Adam Stevens, NQ5H" wrote in message
...
Hi Roy;
It's worse than that: Copper will diffuse throught the gold and pile up
on
the surface.
I showed that with an Auger microprobe at Motorola decades ago.
So to go to a gold surface, nickel is mandatory, then a thick gold
coating;
Too expensive!
It's not like the switch from aluminum to copper, which is a 2x
resistivity
improvement.
You just can't beat plain old copper.
73
H.
NQ5H

But then, maybe SILVER (AG) ! Silver is one heck of a conductor, and what,
pray , when it Oxidizes (AG - O) ? Turns out that the conductivity of
Silver Oxide is almost as great as SILVER! (but, as for the effeciency, ,
unless severe resistance (perhaps in a hi "Q" loading coil for a mobile)
Doubt would make much difference that could be detected! Jim NN7K

--
No trees were killed in the sending of this message. However, a large number
of electrons were terribly inconvenienced !


"H. Adam Stevens, NQ5H" wrote in message
...
Hi Roy;
It's worse than that: Copper will diffuse throught the gold and pile up on
the surface.
I showed that with an Auger microprobe at Motorola decades ago.
So to go to a gold surface, nickel is mandatory, then a thick gold
coating;
Too expensive!
It's not like the switch from aluminum to copper, which is a 2x
resistivity
improvement.
You just can't beat plain old copper.
73
H.
NQ5H

"Roy Lewallen" wrote in message
...
I've seen real-life cases with high-Q microstrip structures where gold
plating actually caused a significant lowering of efficiency. As you
point out, nickel is used as a barrier metal to prevent alloying of the
gold with the underlying copper. If the gold isn't at least several skin
depths thick, significant current flows in the nickel. Nickel is a
particularly poor RF conductor, very much worse than copper, because the
skin depth in nickel is decreased dramatically by its ferromagnetic
permeability. So, if you're able to calculate skin depth, and know what
you're doing, and are willing to use quite a bit of gold (particularly
necessary at HF and below) you can achieve efficiency with gold plating
that's pretty much indistinguishable from that of copper. If you don't
know what you're doing, it is possible to substantially degrade the
efficiency by gold plating. I'm sure somebody could be conned into
buying one, though.

Roy Lewallen, W7EL

Gary V. Deutschmann, Sr. wrote:

Hi Gang

Since the radiation of an antenna is done primarily on the surface of
the elements (or wire) would gold plating the elements increase the
efficiency of the antenna in any way?

Gold sounds expensive, but if thin enough, one ounce of gold could
plate an entire football field. Brass corrods, nickel is usually used
as the first plating before another metal like gold is plated over
that. If the cost for gold over the cost of brass is only about 1
buck per foot of element length, making cost not relavent to the
question. Would a gold plated antenna work better than aluminum or
nickel plated?

TTUL
Gary

Ah, finally, someone who knows what the conductivity of silver oxide is.
Although I believe silver sulfide is much more common than oxide, I've
been able to find the conductivity of the sulfide but not the oxides.
Just what are the conductivities of the silver oxides (AgO and Ag2O)?
Which are we most likely to find on the outsides of wires? Are they
really more common than the sulfide?

Roy Lewallen, W7EL

Jim wrote:
But then, maybe SILVER (AG) ! Silver is one heck of a conductor, and what,
pray , when it Oxidizes (AG - O) ? Turns out that the conductivity of
Silver Oxide is almost as great as SILVER! (but, as for the effeciency, ,
unless severe resistance (perhaps in a hi "Q" loading coil for a mobile)
Doubt would make much difference that could be detected! Jim NN7K

Roy Lewallen wrote:

Ah, finally, someone who knows what the conductivity of silver oxide is.
Although I believe silver sulfide is much more common than oxide, I've
been able to find the conductivity of the sulfide but not the oxides.
Just what are the conductivities of the silver oxides (AgO and Ag2O)?
Which are we most likely to find on the outsides of wires? Are they
really more common than the sulfide?

Roy Lewallen, W7EL


An interesting and eventually amusing link on silover sulfide


http://www.eecs.cwru.edu/misc/AMANDA...er_revised.doc

another:

http://www.brushwellman.com/alloy/tech_lit/sep02.pdf


and this:

http://nepp.nasa.gov/whisker/reference/tech_papers/chudnovsky2002-paper-silver-corrosion-whiskers.pdf

It is interesting that the NASA paper refers to silver sulfide as
non-conductive, while the first paper gives a short and tantilizing
tidbit about forcing it into conductivity.

Hope you find the links interesting!

- Mike KB3EIA -

Nickel can also be the source of IM.

Anyway, isn't Gold's conductivity really low?

--
Steve N, K,9;d, c. i My email has no u's.

"Roy Lewallen" wrote in message
...
I've seen real-life cases with high-Q microstrip structures where gold
plating actually caused a significant lowering of efficiency. As you
point out, nickel is used as a barrier metal to prevent alloying of the
gold with the underlying copper. If the gold isn't at least several skin
depths thick, significant current flows in the nickel. Nickel is a
particularly poor RF conductor, very much worse than copper, because the
skin depth in nickel is decreased dramatically by its ferromagnetic
permeability. So, if you're able to calculate skin depth, and know what
you're doing, and are willing to use quite a bit of gold (particularly
necessary at HF and below) you can achieve efficiency with gold plating
that's pretty much indistinguishable from that of copper. If you don't
know what you're doing, it is possible to substantially degrade the
efficiency by gold plating. I'm sure somebody could be conned into
buying one, though.

Roy Lewallen, W7EL

Gary V. Deutschmann, Sr. wrote:

Hi Gang

Since the radiation of an antenna is done primarily on the surface of
the elements (or wire) would gold plating the elements increase the
efficiency of the antenna in any way?

Gold sounds expensive, but if thin enough, one ounce of gold could
plate an entire football field. Brass corrods, nickel is usually used
as the first plating before another metal like gold is plated over
that. If the cost for gold over the cost of brass is only about 1
buck per foot of element length, making cost not relavent to the
question. Would a gold plated antenna work better than aluminum or
nickel plated?

TTUL
Gary

Steve Nosko wrote:

Nickel can also be the source of IM.

Anyway, isn't Gold's conductivity really low?


Relative Conductivities:

Copper 1.00
Aluminum 0.61
Gold 0.706
Nickel 0.198

Now what is IM??

Deacon Dave, W1MCE

Gang:

Way back in the 60s, I think, there was a very thorough research article in
JIEE (Aust.) about RF skin conductivity of various practical metals. Oxygen
Free High Conductivity (OFHC) Copper won hands down. Until you heat it,
bend it, or look at it cross-eyed, that is. Silver plate is next best, but
only if it is hard Silver, not cosmetic Silver which is what you get at your
local plating shop. Hard Silver plate is difficult to come by, and uses
chemicals which I'm guessing have since been banned by EPA. In my day
(1960), hard Silver plate with a Rhodium flash was the most practical high
RF conductivity process available. Nowadays, who knows?

--
Crazy George
Remove N O and S P A M imbedded in return address

Thanks for all the excellent commentary guys!

My reason for the question was not really looking for a major
improvement in the operation of the antenna, but more longetivity.

I'm getting close to retirement and have moved to a new state.
Whatever I put up, I want it to stay up and keep looking nice for
about 20 years or longer.

I lived in my last home for over 20 years, my backyard was almost
solid copper from all the radials I had run over the years, plus when
I first moved there, I did the entire backyard in 2x4 welded wire
fabric, a layer of straw and some grass seed, then another layer of
2x4 welded wire fabric running the other way, then eventually sod over
that. The last antenna I put up, a Butternut I used 3,500 feet of
wire to make the radials and tied them to the welded wire fabric.

I have set up an area at the top of a hill, am in the process of
grading this area to flat, and hopefully within a couple of months
have everything up except the antennas.

I have cheap access to a plating company who will plate everything to
keep it from corroding. When I checked into the price of gold
plating, it was only a couple of bucks more than stainless silver or
stainless brass and I was just thinking perhaps the gold would last
longer and perhaps even work better.

I have 1,225 sq. ft. of small link aluminum chain link fencing that is
going to be buried as the start of my ground system in this graded
area.

I am also having a 62 foot fiberglass utility pole (50 feet after
installation) installed at the corner of the house, this will hold my
VHF/UHF antenna's and the my HF Inverted Vees, plus be the center of
two dipoles, etc. Up near the antenna farm there will be another 30
foot fiberglass utility pole (after installation), which will be
horizontal with the 50 foot pole at the house.

I'm just trying to get everything planned out on paper before I do
anything as it's easier to erase a pencil line than redo an antenna
farm after the fact.

In effect, I'm going to duplicate as closely as possible what I had in
St. Loo and hopefully add a few more, since I now have the space.

TTUL
Gary