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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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.
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