Jon Kåre Hellan wrote:
Roy Lewallen writes:

bob wrote:
I dont have NEC4 is it too much to ask you to run the
model. Radials over sea water versus a direct connection?
Sure. How many, how high, and how long? The foot-long wire produces
efficiency of virtually unmeasurably close to 100%. So radials can't
be significantly better. What sort of efficiency are you expecting
from the radials?

How does a copper wire behave when submerged in salt water? Won't it corrode
rapidly, so that you don't get a metal to salt water connection, but
a capacitive coupling across copper oxide?

Not a rhetorical question, btw. I really don't know the answer.

73
LA4RT Jon

The copper alloys widely used in wires are quite resistant to corrosion.
Even when immersed in pure seawater, their corrosion rate there is on
the order of 0.025 mm/year. Unfortunately polluted waters can increase
that rate.

The metal to water interface may indeed be affected by the corrosion
layer. This problem is frequently seen by electricians when installing
grounding rods in the earth. However, I imagine the capacitance in this
case would provide sufficient coupling at RF so that it would not be a
problem. Biofouling might be of greater concern if corrosion does not
occur fast enough.

73,
Chuck
NT3G

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chuck wrote:



The copper alloys widely used in wires are quite resistant to corrosion.
Even when immersed in pure seawater, their corrosion rate there is on
the order of 0.025 mm/year. Unfortunately polluted waters can increase
that rate.


What then, would be polluted water? Salt water seems polluted enough.

tom
K0TAR

Tom Ring wrote:
chuck wrote:



The copper alloys widely used in wires are quite resistant to
corrosion. Even when immersed in pure seawater, their corrosion rate
there is on the order of 0.025 mm/year. Unfortunately polluted waters
can increase that rate.


What then, would be polluted water? Salt water seems polluted enough.

tom
K0TAR




Copper piping and water jackets are often badly corroded when decaying
plant and animal mater and sediment are dormant in the pipe. This is
likely to be more troublesome in marinas and harbors than in the open
ocean (Sargasso Sea excepted, maybe).

"Particularly detrimental are sulfate-reducing bacteria in bottom mud
and sediment and on the natural sulfates in seawater." from "The
Boatowner's Guide to Corrosion" by Everett Collier.

73,
Chuck
NT3G

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You are all making a song and dance about it.

Whatever the ground electrode system happens to be, the impedance to
Earth cannot possibly be less than the series impedance of the
connecting lead. Which can be quite high at HF.

In my opinion, the most effective ground will always be a short,
thick, direct connection from the radio equipment to the internal hull
of a metal boat.

If you like, you can connect whatever else you have in mind in
parallel with it, probably at the other end of a long lead, and it
won't make the slightest improvement in performance.

Just use your loafs. And Happy sailing!
----
Reg, G4FGQ.

Reg Edwards wrote:

You are all making a song and dance about it.


And it seems I don't know the words.

Whatever the ground electrode system happens to be, the impedance to
Earth cannot possibly be less than the series impedance of the
connecting lead. Which can be quite high at HF.


Yes, but who's to say where the
connecting lead begins. Simply imagine
the antenna extending all the way to the
ground electrode system and the tuner
inserted, say four feet above it. The
tuner may need some RF choking, of
course, but ground lead impedance is now
near zero ohms.

In my opinion, the most effective ground will always be a short,
thick, direct connection from the radio equipment to the internal hull
of a metal boat.

Not so practical a solution from inside
an FRG hull.


If you like, you can connect whatever else you have in mind in
parallel with it, probably at the other end of a long lead, and it
won't make the slightest improvement in performance.


Certainly true for a metal hull in
sal****er.

Just use your loafs. And Happy sailing!
----
Reg, G4FGQ.


73,

Chuck

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In article ,
"Reg Edwards" wrote:

You are all making a song and dance about it.

Whatever the ground electrode system happens to be, the impedance to
Earth cannot possibly be less than the series impedance of the
connecting lead. Which can be quite high at HF.

In my opinion, the most effective ground will always be a short,
thick, direct connection from the radio equipment to the internal hull
of a metal boat.

If you like, you can connect whatever else you have in mind in
parallel with it, probably at the other end of a long lead, and it
won't make the slightest improvement in performance.

Just use your loafs. And Happy sailing!
----
Reg, G4FGQ.

True, except most of the folks discussing Rf Grounds here aren't
working with metal hulled vessels. They are dealing with wood or
plastic (Fiberglass) hulls, where an effective RF Ground is
significantly harder to build.

What then, would be polluted water?

====================================

Well, for starters, you could urinate in it.

For use in salt water, a number of Cu alloys have "excellent" corrosion
resistance. Among those that are available are the Admiralty Brasses
(C44300 with As or C44500 with P). They have about 25% conductivity wrt to
soft Cu. (Brass is mostly Cu and Zn.)

Phosphor Bronze (C52100) is also a candidate with 13% conductivity.
This is particularly good for antenna wire use.

Pure Cu is expressed as having "good" resistance.

Find a thin plate of Admiralty brass and bond Cu or phosphor bronze wire
to the plate. Put the assembly into the water as "ground" and you are done.

73, Mac N8TT
--
J. Mc Laughlin; Michigan U.S.A.
Home:

chuck wrote:

The copper alloys widely used in wires are quite resistant to corrosion.

[...]

73,
Chuck
NT3G

I don't know about corrosion resistance, but the copper wire used in
electrical conductors is very high purity. This is needed since any
contaminants reduce the conductivity. Here are a few quick references:

Copper is made with different purities depending on the application.
The highest grade copper is electrical grade. It is 99.99% pure and
is used for electrical cables because it has the best electrical
conductivity. Electrical grade scrap must never be mixed with any of
the lower purity grades such as plumbing tube scrap. This contains
too much phosphorus which drastically reduces the electrical
conductivity.

The lower grades of scrap can be used to make copper alloys or
chemicals. The copper sulphate you use in your school laboratory has
probably been made with scrap copper.

http://www.schoolscience.co.uk/conte...opch32pg3.html

Copper Facts

Electrical

Copper is the standard benchmark for electrical conductivity. It
conducts electrical current better than any other metal except
silver.

Copper is routinely refined to 99.98% purity (even more pure than
Ivory Soap) before it is acceptable for many electrical
applications.

Number 12 (AWG) copper wire is the most common size used for branch
circuit wiring in buildings. The amount of copper products consumed
in the U.S.A. this past year would make a size 12 wire that could
encircle the Earth 2,630 times or make 140 round trips to the Moon.

http://www.copper.org/education/c-fa...lectrical.html

Regards,

Mike Monett