bob wrote:
Roy Lewallen wrote:
I put this aside until I could do a little modeling. A lot of postings
have been made in the interim, but I don't see too much in the way of
answers. I'll try to answer some of your questions.

I think we all would be interested in how a small piece of metal buried
in sea water can provide an efficient ground versus one or 2 elevated
radials. I also dont see how its efficient concentrating all your
current in such a small area. Since the salinity of salt water is not
constant using one or 2 radials on yacht would be more efficient.

Imagine for a moment that instead of salt water that the ocean was
covered by a thick metal plate. How would you effectively use that as a
ground? Salt water isn't as good a conductor as metal, but it acts more
like that than dirt.

I don't know how much the salinity or conductivity of sea water varies,
but suspect that even at its worst it's quite a good conductor.

How can salt water which would have some resistance even though
its
conductivity is high compared to earth behave better than copper wire
when returning antenna currents to the feedpoint.

Cross sectional area. Replacing all the sea water with copper would
improve it, but scattering a bunch of copper radials out and replacing
only tiny parts of it wouldn't make much difference. And the loss is so
low to begin with that even replacing it with copper wouldn't make any
difference.

The small amount of
current flowing in a 100 watt signal i would not want to waste sending
it into salt water.

It won't go in very far. It'll stay very close to the top. And the waste
is negligble.

Salt makes good resistors, why would you introduce
a loss into the equation which radials seem to eliminate even though we
dont have ground loss over sea water? We also have the issue of the
skin depth of sea water to consider.

Solid salt is actually a decent dielectric, I believe. Again, the trick
is cross sectional area. The current is spread over a large area of
water, so the overall loss is negligible.

The analysis I did took skin effect into consideration. The skin depth
is even less in metal, yet metal has low RF loss.


Yes. A foot-long wire "ground rod" below the antenna provides a nearly
lossless ground connection at HF.

This is not how most yachts connect their ground connections. They
connect to the sea cocks well below the top of the water anywhere for
3ft to 5 ft down. Some even use slim flat ground shoes again well below
the water line. Its impractical for a any sail vessel to maintain a
connection to sea water close to the surface because loading and the
yacht heeling when sailing.

I'm sorry to hear that, because any connection below a few inches is
ineffective at HF.


How can a piece of copper metal about 1 ft square equal several
radials laying on the boats deck?

Radial wires are used for land based systems because of the poor
conductivity of soil. Radial wires reduce the resistance of the path
current takes going to and from the antenna base. Salt water is a good
conductor and doesn't need -- and won't benefit from -- radial wires.

Indeed radials do perform this way. I would still want to use radials
wires even 1 or radials wires even on a yacht since the length of the
radials will have a greater capacity to sea water ground.
It also would
be more efficient in providing a current return.

More efficient than a deep plate, for sure. Not any more efficient than
a foot long uninsulated wire extending downward from the surface. But by
all means use whatever makes you feel well grounded.


Why do i have to use copper foil when most other people suggest
using ordinary copper wire?

You don't. And won't copper corrode rapidly in salt water?

Over seawater what would be the best number of radials to use
considering that maximum length i can run is 40 ft. I am planning to
use a backstay antenna with a SGC 230 Tuner.

None. A simple wire down into the water is adequate. Or use a small
plate very near the surface if you prefer.

Again yachts bury their ground connection well below the skin depth.
Some even run the ground wire from the tuner down to the keel which is
well submersed in salt water.

If the wire is uninsulated, the first few inches of the wire will
provide the ground connection. If it's insulated, they'll have no HF
ground connection at all except what's provided by capacitive coupling
through the first few inches of insulation.

All they are using is one short piece of
foil that is behaving like a small radial. We will see what the models say.

By all means, do some modeling. The only program I know of which will
allow modeling submerged conductors is NEC-4 and derivatives.

2 elevated radials over seawater versus a 1 ft square piece of metal
buried below the skin depth. My money would be on the radials.

Certainly elevated radials would be better than metal more than a skin
depth or two deep. Better yet is a wire extending from the surface to a
few skin depths. Why isn't that possible?

Incidentally, I'm not proposing replacing the standard grounding system,
which I'm sure is important for other uses including, probably,
lightning protection. It will just need to be supplemented if you want
an effective HF ground.

Roy Lewallen, W7EL

Roy Lewallen wrote:
bob wrote:
Roy Lewallen wrote:
I put this aside until I could do a little modeling. A lot of
postings have been made in the interim, but I don't see too much in
the way of answers. I'll try to answer some of your questions.

I think we all would be interested in how a small piece of metal
buried in sea water can provide an efficient ground versus one or 2
elevated radials. I also dont see how its efficient concentrating
all your current in such a small area. Since the salinity of salt
water is not constant using one or 2 radials on yacht would be more
efficient.

Imagine for a moment that instead of salt water that the ocean was
covered by a thick metal plate. How would you effectively use that as a
ground? Salt water isn't as good a conductor as metal, but it acts more
like that than dirt.

I don't know how much the salinity or conductivity of sea water varies,
but suspect that even at its worst it's quite a good conductor.

How can salt water which would have some resistance even though its
conductivity is high compared to earth behave better than copper wire
when returning antenna currents to the feedpoint.

Cross sectional area. Replacing all the sea water with copper would
improve it, but scattering a bunch of copper radials out and replacing
only tiny parts of it wouldn't make much difference. And the loss is so
low to begin with that even replacing it with copper wouldn't make any
difference.

The small amount of current flowing in a 100 watt signal i would not
want to waste sending it into salt water.

It won't go in very far. It'll stay very close to the top. And the waste
is negligble.

Salt makes good resistors, why would you introduce a loss into the
equation which radials seem to eliminate even though we dont have
ground loss over sea water? We also have the issue of the skin depth
of sea water to consider.

Solid salt is actually a decent dielectric, I believe. Again, the trick
is cross sectional area. The current is spread over a large area of
water, so the overall loss is negligible.

The analysis I did took skin effect into consideration. The skin depth
is even less in metal, yet metal has low RF loss.


Yes. A foot-long wire "ground rod" below the antenna provides a nearly
lossless ground connection at HF.

This is not how most yachts connect their ground connections. They
connect to the sea cocks well below the top of the water anywhere for
3ft to 5 ft down. Some even use slim flat ground shoes again well
below the water line. Its impractical for a any sail vessel to
maintain a connection to sea water close to the surface because
loading and the yacht heeling when sailing.

I'm sorry to hear that, because any connection below a few inches is
ineffective at HF.


How can a piece of copper metal about 1 ft square equal several
radials laying on the boats deck?

Radial wires are used for land based systems because of the poor
conductivity of soil. Radial wires reduce the resistance of the path
current takes going to and from the antenna base. Salt water is a
good conductor and doesn't need -- and won't benefit from -- radial
wires.

Indeed radials do perform this way. I would still want to use
radials wires even 1 or radials wires even on a yacht since the
length of the radials will have a greater capacity to sea water ground.
It also would be more efficient in providing a current return.

More efficient than a deep plate, for sure. Not any more efficient than
a foot long uninsulated wire extending downward from the surface. But by
all means use whatever makes you feel well grounded.


Why do i have to use copper foil when most other people suggest
using ordinary copper wire?

You don't. And won't copper corrode rapidly in salt water?

Over seawater what would be the best number of radials to use
considering that maximum length i can run is 40 ft. I am planning to
use a backstay antenna with a SGC 230 Tuner.

None. A simple wire down into the water is adequate. Or use a small
plate very near the surface if you prefer.

Again yachts bury their ground connection well below the skin depth.
Some even run the ground wire from the tuner down to the keel which
is well submersed in salt water.

If the wire is uninsulated, the first few inches of the wire will
provide the ground connection. If it's insulated, they'll have no HF
ground connection at all except what's provided by capacitive coupling
through the first few inches of insulation.

All they are using is one short piece of foil that is behaving like a
small radial. We will see what the models say.

By all means, do some modeling. The only program I know of which will
allow modeling submerged conductors is NEC-4 and derivatives.

I dont have NEC4 is it too much to ask you to run the model. Radials
over sea water versus a direct connection?



2 elevated radials over seawater versus a 1 ft square piece of
metal buried below the skin depth. My money would be on the radials.

Certainly elevated radials would be better than metal more than a skin
depth or two deep. Better yet is a wire extending from the surface to a
few skin depths. Why isn't that possible?

Theres no easy way of making sure that the wires will submerge
precisely or close to the ideal skin depth. The loading and heeling of
the yacht would affect this depending on the sailing position wind
speed and other factors. The motion of the waves and swell conditions
will also be another variable. It would work great when you anchored.


Incidentally, I'm not proposing replacing the standard grounding system,
which I'm sure is important for other uses including, probably,
lightning protection. It will just need to be supplemented if you want
an effective HF ground.

Roy Lewallen, W7EL

Well if you read the many sailing web pages and the Icom marine
guides they all advocate installing your RF ground system well below
the skin depth of salt water. They also advocate bonding all your on
board metals to submerged objects like the keel and copper ground
shoes, which is clearly wrong.

A yacht with elevated radials installed below the deck would radiate a
better signal in my view. However what constitutes an effective radial
system over seawater for frequencies between 1 and 30 mhz using a
random wire backstay antenna versus a direct connection to sea water i
cant answer without the modeling software.

Bob

On Sun, 28 May 2006 04:59:49 +1000, bob wrote:

Well if you read the many sailing web pages and the Icom marine
guides they all advocate installing your RF ground system well below
the skin depth of salt water. They also advocate bonding all your on
board metals to submerged objects like the keel and copper ground
shoes, which is clearly wrong.

Hi Bob,

As I offered some time ago, how deep is fairly immaterial and your
dismissal of "many sailing web pages, Icom" and so on to then come to
the conclusion that they are "clearly wrong" is not quite so clear
why.

There are only two paths to that ground system well below the skin
depth of salt water:
(1) Through the water;
(2) Through a lot of air within the boat.

For (1), that already takes care of itself, but is a very odd method
to getting to that dynaplate. Besides, a wire tacked to the outside
of the hull, or worse simple thrashing in the surf, has got to add to
drag. Following this wet path automatically snubs how much current
will make it to the plate anyway. As Reggie offers, after 40 inches
at 7MHz it is immaterial and that wet path to the plate makes the
plate simply a tie-point. In short, you have to penetrate that skin
depth to get beneath it. Penetrating it solves the "problem" of going
too deep.

For (2), what do you stand to lose with a deeper connection that is
approached through the interior of the boat? This is a matter of
matching characteristics, which lead to issues of loss. You have the
same connection loss anyway you look at it.

So, what value is there in these page's recommendations? It insures a
connection.

Of course, I could be wrong. I've only had experience in electronics
on Big Gray Boats in salt water, or in Big Gray Submarines beneath
salt water. Ground was everywhere and death as far away as a power
lead (several dozen nuclear warheads were only slightly further away).

73's
Richard Clark, KB7QHC

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?

[I wrote:]
Certainly elevated radials would be better than metal more than a skin
depth or two deep. Better yet is a wire extending from the surface to
a few skin depths. Why isn't that possible?

Theres no easy way of making sure that the wires will submerge
precisely or close to the ideal skin depth. The loading and heeling of
the yacht would affect this depending on the sailing position wind
speed and other factors. The motion of the waves and swell conditions
will also be another variable. It would work great when you anchored.

Why can't you extend a wire or strip all around your boat, or make it
several feet long? There's no penalty for having it extend beyond
several skin depths. Fishermen somehow manage to keep their lines and
nets in the water -- surely you can work out a way to keep a wire in the
water.

Well if you read the many sailing web pages and the Icom marine
guides they all advocate installing your RF ground system well below
the skin depth of salt water. They also advocate bonding all your on
board metals to submerged objects like the keel and copper ground
shoes, which is clearly wrong.

Yes. There's a vast amount of incorrect information on the web. Have you
ever browsed around audiophile pages dealing with speaker wire? I'm sure
there are innumerable astrology pages, too.

A yacht with elevated radials installed below the deck would radiate a
better signal in my view. However what constitutes an effective radial
system over seawater for frequencies between 1 and 30 mhz using a
random wire backstay antenna versus a direct connection to sea water i
cant answer without the modeling software.

All I can do is present the results that physical laws dictate. It's not
uncommon for that to be inadequate to change a person's beliefs.

Roy Lewallen, W7EL

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

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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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