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

By the way, I found a very nice and complete listing of conductivities
of aluminum alloys at
http://www.ndt-ed.org/GeneralResourc...ctivity_Al.pdf
just after I posted last night. Others may find this useful. Even
the worst of them is not as much as three times the DC resistivity of
the best. So at RF, the worst aluminum alloy will have about twice
the loss of the same diameter copper conductor.

Cheers,
Tom

There are several variables here other than the conductivity of the
primary metal. Again, what you're seeing is not "the difference between
copper and aluminum" as initially stated, but a number of other factors
-- diameter, length, coating, and alloy --, combined.

If the DC conductivity of two materials differs by a factor of two,
their RF conductivity differs only by a factor of the square root of
two, or about 1.4. This is because the skin depth is greater in the less
conductive material, which partially offsets the conductivity
difference. The relatively small difference in DC conductivity between
pure copper and aluminum is further reduced by this effect, so you'll
very seldom be able to see any difference.

Roy Lewallen, W7EL

H. Adam Stevens, NQ5H wrote:
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
. . .

"H. Adam Stevens, NQ5H" wrote in message ...

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.

A 2" diameter bare copper rod or cylinder at 14MHz, 3' long, should
have an RF resistance about 6 milliohms. The worst aluminum alloy
you're likely to see should be about 12 milliohms; 24 for the 1"
diameter. What am I missing here? How does that translate to a
change from 9 ohms to 20 ohms to 30 ohms at the feedpoint? If the
cause is resistance heating of the copper or aluminum tube, what's
doing the impedance transformation, and how is it so efficient? That
much loss should result in measurable temperature rise in the tube (or
wherever the loss is), at 100-W power levels.

Or perhaps my image of what you're measuring is all out of whack.
Same loading coil in each case? I'd kind of expect the loading coil
to be the main loss mechanism, if all the connections are tight.

Puzzled and seeking enlightenment,
Tom

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

What about silver plated RF connectors?

As far as that goes, there are also plenty of gold plated connectors out
there.

Jim
N8EE

"Richard Clark" wrote in message
news
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

On 17 Apr 2004 21:30:46 EDT, am (Gary V.
Deutschmann, Sr.) wrote:

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.

Hi Gary,

Ships at sea, for millennia, have used bronze for durability. Talk
about an aggressive environment. One of my buddy's told about his
experience at the Naval Research Lab where a scientist offered a cube
of solid stainless steel for testing. They dumped it into sea water
and dissolved it.

73's
Richard Clark, KB7QHC

On Sat, 17 Apr 2004 21:45:46 -0400, "JLB"
wrote:
What about silver plated RF connectors?

As far as that goes, there are also plenty of gold plated connectors out
there.

Hi Jim,

What about them indeed? If they don't meet the requirements of bright
untarnished metal, then they need pressure mating (all the good ones I
know specify this - but deeply embedded within their core
manufacturing specs) e.g. Amp RF connectors:
"Insufficient contact force will give rise to metal to oxide
junctions. The classic rectifiers were metal oxide by
composition.

"The applied mounting force is concentrated in the surface area of
the protrusion which, on engagement with the panel, punctures the
existing oxide layer to give a metal-to-metal, gas-tight
junction."

The gold plating, presumably, precludes giving rise to oxidation
products; however, pressure then becomes an issue of mating surface
area (Ohms). Every precision contact used for Resistance and Voltage
standards (in the old days) were tapered brass plugs that could be
wedged into the jack with a twist (pressure). They knew about gold
then too, but brass served admirably.

73's
Richard Clark, KB7QHC

Well Tom, I'm just looking to explain the data: I'm puzzled as well.
Same truck, Durango with a ball mount right rear.
Same MFJ analyzer. Same very short coax from inside the truck.
Everything grounded with 2" copper strap.
Same 14.300 MHz; Same whip. The measurements repeat reliably.
Three motor-tuned antennas, Nott, Tarheel, Hi-Q.
Three different impedances at resonance (ie purely resistive load.)
9, 20 and 30 ohms. Now I can see the radiation resistance being slightly
higher with the Tarheel, it's a foot longer, but that hardly explains a
factor of two. So it must be the loss resistance. Part of the difference is
the base tube, and the copper/aluminum/diameter issue obeys the appropriate
scaling laws. (BTW I think the Hi-Q is 1.5" diameter, but I'm not sure and I
am not at the ranch where the antenna is stored.)
When I adjust the tap on the transformer to give a 50 ohm load to the MFJ
for each antenna, the Nott gives the greatest near-field signal strength.
Perhaps a further investigation of the remaining sources of resistance is in
order. The Hi-Q should have the least leakage, it's a beautiful piece of
work. The Tarheel appears to be built of better materials than the Nott.
(Lexan vs PVC for example.) Go down to 80 meters and they're all 10 ohms;
coil losses clearly dominate there where radiation resistance is tiny.

I think a complete solution to Maxwell's Equations would be helpful, but I'm
busy at the moment.

For all I know the paint or powder coating on the aluminum antennas is the
real culprit.
The Nott's just bare copper.
What is the radiation resistance of an 8 foot whip antenna resonant in a
16.5 foot world?
Just a bit less than 10 ohms, right?
Maybe the comparison should be to BARE aluminum.
Just my morning thought on a puzzle I've been looking at for several months.

73 es tnx fer qso
de nq5h
k


"Tom Bruhns" wrote in message
m...
"H. Adam Stevens, NQ5H" wrote in message
...

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.

A 2" diameter bare copper rod or cylinder at 14MHz, 3' long, should
have an RF resistance about 6 milliohms. The worst aluminum alloy
you're likely to see should be about 12 milliohms; 24 for the 1"
diameter. What am I missing here? How does that translate to a
change from 9 ohms to 20 ohms to 30 ohms at the feedpoint? If the
cause is resistance heating of the copper or aluminum tube, what's
doing the impedance transformation, and how is it so efficient? That
much loss should result in measurable temperature rise in the tube (or
wherever the loss is), at 100-W power levels.

Or perhaps my image of what you're measuring is all out of whack.
Same loading coil in each case? I'd kind of expect the loading coil
to be the main loss mechanism, if all the connections are tight.

Puzzled and seeking enlightenment,
Tom

Thanks Richard

You may have solved my problem!

I will definitely check into using bronze.

Thanks
Gary

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.

which will most likely disintegrate in the ground into white powder.

Yuri, K3BU