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

On Fri, 16 Apr 2004 20:40:53 -0400, "JLB"
wrote:


"S" wrote in message
. net...
silver is a better conductor than gold, but will tarnish very easily,
might
now be a good idea for what you are intending

I thought that silver oxide was a decent conductor, which is why it is
sometimes used as a plateing material.

Hi All,

It hardly matters unless you are speaking of switch contacts.
Insulated wire's insulation is absolutely unconductive, and yet in the
context of antennas it doesn't impact the wire's capacity to carry
current.

Oxidation products only become a problem at interfaces where they
either resist current between the joined conductors, or create a
semiconducting barrier.

The technician is taught to clean surfaces of tarnish to bring bright
metal into contact. Then crimp them (or twist the wire - same thing)
for a gas tight seal. Then solder them to weather proof the seal
(solder is never meant to be a mechanical join or the conductive
path). Common practice allows for solder to provide more
functionality than what I describe - this does not elevate the method.
Barring the final solder, switch contact faces must meet the same
conditions of bright metal and gas tight seals. This is often
achieved by pressure (some mistake the so-called "wiping" action as
meaning to scrub the oxide away - a useful metaphor but only that;
otherwise switches would self demolish in very few operations) and a
sustaining current (wet vs. dry contacts).

73's
Richard Clark, KB7QHC

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

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

Roy
The measurements are reproducible. That's for sure.
And you can bet the aluminum in the Tarheel and Hi-Q are alloys.
Using the Nott (just copper, no plating) I get a 9 ohm load at resonance on
20, 10 ohms on 40 and 80.
With a simple toroidal autoformer the mobile rig sees 50 ohms resistive at
resonance on all three bands.
73, NQ5H
H.

"Roy Lewallen" wrote in message
...
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

Roy
I looked up the numbers.
The Nott is 2" diameter bare copper 3' long.
The Tarheel is 2" diameter painted aluminum 4' long.
The Hi-Q is 1" diameter powder-coated aluminum 3' long.
I used the same whip for all measurements.
If we take the conductivity of copper to be 100, aluminum is then 60 and
aluminum alloys are as low as 30.
That's a factor of two between the Nott and Tarheel and the reduced surface
area of the Hi-Q explains the additional resistance there. Considering the
difference in surface area and resistivity among the antennas, the measured
impedances seem quite reasonable to me.
73
H.
NQ5H


"Roy Lewallen" wrote in message
...
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

H. Adam Stevens wrote:
With a simple toroidal autoformer the mobile rig sees 50 ohms resistive at
resonance on all three bands.

Got any idea what the efficiency of your autoformer is?
I'm assuming a single coil for a primary, tapped down for
the load. Would a 4:1 transmission line transformer be more
efficient over all the bands?
--
73, Cecil, W5DXP



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It's measurably better than a tuner in terms of near-field strength;
14 turns of #12 insulated copper wire on a ferrite toroid ripped from an R7.
How much coax is needed for that transmission line transformer?
Mobiles are so inefficient, I'm always looking for that last 0.1 db.
73
H.
NQ5H

"Cecil Moore" wrote in message
...
H. Adam Stevens wrote:
With a simple toroidal autoformer the mobile rig sees 50 ohms resistive
at
resonance on all three bands.

Got any idea what the efficiency of your autoformer is?
I'm assuming a single coil for a primary, tapped down for
the load. Would a 4:1 transmission line transformer be more
efficient over all the bands?
--
73, Cecil, W5DXP



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