chuck writes:

Jon KÃ¥re Hellan wrote:
We don't seem to have widely used, descriptive names for these
configurations. Cecil is correct, and perhaps the OCF referred to
should be called an OCF "L". The vertical radiator with a single,
elevated, horizontal, resonant "radial" perhaps should be called an
"L" dipole.

On inspection, either antenna, on a boat with a tuner at the
feedpoint, could be mistaken for the other. You could tell the
difference only by observing how the antenna is operated. If the
antenna is operated only on those frequencies for which the horizontal
element is an odd multiple of a 1/4 wavelength, we would call the
antenna an "L" dipole (or whatever).

If that same antenna were operated not only on those frequencies, but
on all others (HF spectrum) as well, we would call it an OCF "L".

But if, on inspection, the antenna has multiple resonant radials, that
would unambiguously differentiate it from the OCF.

Whenever the two antennas are physically identical, they will
obviously operate identically.

Make sense, Jon? Sorry for the confusion.


Sure. Thanks.

chuck wrote:
Richard Clark wrote:
On Tue, 30 May 2006 09:21:56 -0400, chuck wrote:

If anyone spots any errors of fact or significant omissions, I'd
welcome appropriate "recalibration". Thanks in advance.

1) Grounding plates

Will not work if submerged as much as four feet

Hi Chuck,



Hello Richard,

Perhaps the context for the summary was unclear. My objective was simply
to identify several existing recommendations for obtaining RF grounds on
plastic and wood vessels over sal****er. Regrettably, I lack knowledge
of any published theoretical or empirical comparison of these proposals
that provides an objective, quantifiable measure of performance.

Don't know how you got this miss-impression.


That it will not work if submerged as much as four feet? From Roy's
report on his NEC-4 modeling. It is presumably based on the known skin
depth of RF at 14 MHz.

2) Wire in water

A one-foot length of wire immersed near water surface is sufficient for
near-perfect results based on W7EL's NEC-4 model results. Assumed
performance is similar to grounding plate.

This conclusion is conflict with the first, making it a mystery how
you came to either in summary. The focus on "water surface" is as
though you are trying to force it work like a pool of mercury. Water
is NOT a ground plane in the sense of conductivity. Water is a
terrible conductor. It is only its huge mismatch with air that gives
it such superb propagation, not match, characteristics. Distinguish
between the two.


Well, some of what you are saying is pretty much what I had thought. If
you read my posts on the other thread, you'll see where I was heading.

We agree that seawater's conductivity is lower than copper's but greater
than earth's. We agree that a single ground rod driven into the earth
will perform poorly as the only return path for a vertical antenna over
land, but at least in some cases will perform better than if it were not
there. Will a wire dipped into the sea perform better than the ground
rod driven into the earth? I doubt there is much disagreement on that,
even though water might be characterized in relative terms as a
"terrible conductor". The only relevant question, then, is "how much
better?" and so far, the only numerical answer that I am aware of has
come from NEC modeling.

The characterization I reported of a wire dipped into the sea is based
on Roy's modeling, assuming I have not misunderstood of course. Others
have made the same point, but now we have model results to support it.

BTW, I have just discovered a response from Roy to one of my posts on
the other thread that is available on Google, but has never shown up on
either of the two newsgroup subscriptions I have. Roy addressed some of
my concerns in that post so if you have not seen it you might do a
search for it on Google.


3) Radials

Even shortened (loaded) radials elevated over seawater work as
near-perfect based on N6LF's NEC-4 modeling. Objections to radials are

The objections are they are wholly unnecessary when ground is so
easily achieved by conventional means. You would need 120 radials to
shield against the loss you perceive, and that loss doesn't matter

What loss is it that I perceive? N6LF's results show near lossless
results with only four shortened radials over seawater.

when you stand to gain so much in propagation. You couldn't even
field a tenth of these radials. At HF, and maintaining their tune
and symmetry, you would be lucky to fit in 2.

Other studies have shown a single elevated radial over land to lose less
than one dB over a perfect ground plane.

At that stage of the
game, there is absolutely no match advantage over conventional
techniques aboard a small craft (and at HF you don't qualify for any
thing other).

4) Counterpoise (i.e., mast, forestay, shrouds, lifelines, engine, metal
tanks, 100 square feet of copper, keel, rudder, etc. bonded together)

This type of
counterpoise is also the approach recommended by both Icom and SGC.

Only because it is already available and doesn't ask you to go any
further for no obvious advantage.


Well, what makes life interesting is that to advocates of the other
approaches, there are obvious advantages.

5) OCF dipole w/horizontal component along deck

Not commonly used,

Who would choose a complicated design over so many simple ones?


Multiple resonant radials that cover the popular marine and ham bands on
a small boat are not seen by all as simple. One might ask the same
question of those who advocate the counterpoise approach, since the wire
in the water is simpler. I think choosing the best system (broadly
defined to also consider operation over fresh water and near-vertical
radiation when important) will be easy if we can only get some
objective, reproducible data and/or analysis.


Is that where it stands, folks?

If you want a dipole, make a VERTICAL dipole, even a lousy one.


Certainly worthy of consideration. Many backstay antennas are probably
operated as half-wave vertical dipoles (end-fed, of course) above 10 MHz
or so.

Finally, and to repeat, learn the distinction between matching and
propagation. Your focus on matching issues is like seeing your glass
3/4ths empty. Looking at the propagation advantages in comparison is
like seeing a pitcher of water nearby that will fill that glass a
dozen times.

I didn't address any matching issues at all that I can see, Richard.
Sorry if I misled you.

All of the alternatives utilize the same seawater for propagation and
the same vertical radiator. They differ in whether there is any
high-angle radiation from a horizontal radiator, and possibly in the
magnitude of their "ground return losses."


Appreciate your comments.

73,

Chuck


73's
Richard Clark, KB7QHC

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I would also add that sea waters conductivity is not a consistent as
some seem to think. The salinity of salt water varies with temperature.
NASA has surveyed most of the world oceans using microwave radar and
salinity if far from consistent. This fact combined with tidal flows,
man made pollution from storm water drains and other factors makes
"connecting" to sea water seem dubious.

If we assume you can connect to sea water, do you want to place most of
your current in such a small area? I doubt someone could keep this
connection clean enough in seawater to be efficient. This fact combined
with electrolysis will lay waste to any connection very quickly. Maybe a
gold plated conductor might be able to survive in a salt water environment.

The way most people install radials in yacht would make them elevated,
rather than buried below skin depth. N6LF has indicated in his modeling
that short radials as long as .1 wavelength work just as effectively as
0.5 wavelength radials over sea water. Since you not trying to combat
ground loss whats the point of trying to build a radial field when 2 or
4 .1 wavelength radials will do the job? Besides building a elevated
radial system will have some capacitance to ground. A single radial
should over sea water capture most of not all of the antenna return
currents

Besides from all the posts i have read burying something like a
Dynaplate below skin depths is akin to burying your rf current below a
copper plate. I also believe there is a rule of thumb that 5 skins
depths is the maximum return on investment in using the available
conductive depth of any material. Its probably that its only ever the
piece of wire to the dynaplate thats working as a short radial. I dont
see how anyone can say a dynaplate could ever work when below skin depth?

One thing i am curious about is that if you suspend a radiator or
conductor well below skin depth in air whats the radiation efficiency
like of that conductor? To me on a yacht it looks like a conductor
suspended in a U channel suspended in air with the top open and
exposed. Maybe it will operate like a waveguide with some cut off
frequency, this is a wild guess.Maybe someone who can model conductors
below ground can model this. Most yachts have at least 3ft of freeboard
above water to play with.

But who knows there seems to conflicting advice on several points.
Maybe Roy can clarify all these issues with his models.

Bob

Reg, G4FGQ wrote:
"Anything you toss into the sea water makes a good ground."

Certainly correct if "anything" is a low-impedance RF path.

If "skin effect" prevents penetration to a copper plate on the hull,
fine. RF has then made the transfer to the sea at a shallow depth.
That`s the goal.

Best regards, Richard Harrison, KB5WZI

In article ,
Richard Clark wrote:

If they all utilize the same seawater for propagation and the same
vertical radiator, they all suffer equally - it stands to reason there
is no difference given all the "sameness." It also stands to reason
by your assertion that they differ, that they do not all use the same
seawater or vertical.... Which is it? Let's skip that and cut to the
heart of the matter. How MUCH different?

Start with a conventional untuned vertical using a dynaplate and tell
me, in dB, how much better any other scheme is. Let's confine this to
a practical situation where the rig is under cover and inside the boat
and that you need two leads, one from the tuner antenna connection,
and another from the tuner ground connection.

73's
Richard Clark, KB7QHC

This is exactly right. If they all use the same water for RF Ground,
and vertical, for the antenna, then the only difference is, "How much
coupling from the ground stud on the antenna tuner does each system give
to the water?" And that is the Thousdan Dollar question. DynaPlate,
Bonded RF Ground System, wires, radials, whatever, all, just make up one
side of the capacitor, with the water as the otherside and the distance
between is the dielectric. More effective coupling equals lower
impedance RF Ground. All this talk of Modelling is just so much FuFurrR,
for anyone who has installed MF/HF Marine Antenna Systems on these type,
wood or plastic vessels. Anyone with much experience in the field will
tell you, simply, get as much surface area as possible, bonded with
low impedance connections, (Copper Strap) and get it as close to the
water as possible. The Physics of building a bigger capacitor is:
Have as much surface area as possible, with the least space between the
plates. This isn't Rocket Science, it is just basic physics, and all the
crap about tuned counterpoises, and copper screens in the overhead, and
the like is just that...... crap...woun't work, never has, and never
will.
It doesn't take a NEC Modelling Software Package to figure this out, it
just takes some common sense and a bit of OJT Experience....

Bruce in alaska
--
add a 2 before @

In article ,
(Richard Harrison) wrote:

If "skin effect" prevents penetration to a copper plate on the hull,
fine. RF has then made the transfer to the sea at a shallow depth.
That`s the goal.

Bull****, where do you guys come up with this stuff....Skin Effect is a
a Boundry Thing, and the hull of the vessel is the "Boundry of the Sea
Water" even if it is 10 feet below the sea surface.

You wrote:
In article ,
(Richard Harrison) wrote:

If "skin effect" prevents penetration to a copper plate on the hull,
fine. RF has then made the transfer to the sea at a shallow depth.
That`s the goal.

Bull****, where do you guys come up with this stuff....Skin Effect is a
a Boundry Thing, and the hull of the vessel is the "Boundry of the Sea
Water" even if it is 10 feet below the sea surface.

Finally someone gets it! This is what Roy said way back in his first
report of his modeling, that the ground plate if fastened to the hull
will be on the surface of the water even if it happens to be several
feet below. The other side of the ground plate is air. In other words
the hull is displacing the water. Unless of course the boat has sunk.

For the guys that are referencing the N6?? Article about very short
elevated radials over sea water; please note that he is saying those
short elevated radials are tuned with loading coils.
Elevated radials will not work unless they are 1/4 wave resonant or
tuned with a loading coil.

73
Gary K4FMX

wrote:
You wrote:
In article ,
(Richard Harrison) wrote:

If "skin effect" prevents penetration to a copper plate on the hull,
fine. RF has then made the transfer to the sea at a shallow depth.
That`s the goal.
Bull****, where do you guys come up with this stuff....Skin Effect is a
a Boundry Thing, and the hull of the vessel is the "Boundry of the Sea
Water" even if it is 10 feet below the sea surface.

Finally someone gets it! This is what Roy said way back in his first
report of his modeling, that the ground plate if fastened to the hull
will be on the surface of the water even if it happens to be several
feet below. The other side of the ground plate is air. In other words
the hull is displacing the water. Unless of course the boat has sunk.

It is interesting to speculate about the
proportion of displacement currents passing
through the air to the inside of the hull and then
through the hull to the grounding plate, vs. the
proportion passing from the surface along the
water-hull interface to the Dynaplate.

As Roy pointed out, one reason seawater "works"
despite its low conductivity relative to copper is
that a high percentage of the "ground" return
current is concentrated very close to the antenna
where path conductance is high. If the water path
from the surface to the Dynaplate is vertical
(four feet) does that mean return currents must
pass through four additional feet of seawater and
thus will encounter greater losses than if the
Dynaplate were at the surface?

Or will the vertical water path "collect" the same
or even greater return currents than a horizontal
water path? I've heard of radials sloping up and
away from the antenna at 45 degrees, but 90
degrees? (Assumes tuner ground terminal directly
adjacent to Dynaplate on other side of hull) Ought
to be easy to model.

Interesting, no?


For the guys that are referencing the N6?? Article about very short
elevated radials over sea water; please note that he is saying those
short elevated radials are tuned with loading coils.


Yes. That is what he reported on his modeling.

Elevated radials will not work unless they are 1/4
wave resonant or
tuned with a loading coil.

This is not at all obvious to me except at a
semantic level. And lest anyone misunderstand,
Gary is not suggesting that N6LF made that statement.

Is an automobile body (on land) conceptually
analogous to non-resonant, elevated radials? Does
it work? Would it work less well over seawater
(let it levitate or make very quick QSOs)?

Would a random length whip on HF work with a tuner
and a single, non-resonant wire about 25 feet
long, in lieu of the auto body? Would it work less
well over seawater?

If you're with me this far, the next question is
"how much better or worse?". And then on to the
other tradeoffs: radiation patterns, safety,
simplicity, RF coupling, etc.

Alternatively, we can explore why it won't work.


73
Gary K4FMX


73,
Chuck
NT3G

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chuck wrote:


As Roy pointed out, one reason seawater "works" despite its low
conductivity relative to copper is that a high percentage of the
"ground" return current is concentrated very close to the antenna where
path conductance is high. If the water path from the surface to the
Dynaplate is vertical (four feet) does that mean return currents must
travel along four additional feet of seawater (at the hull-water interface)
and thus will encounter greater losses than if
the Dynaplate were at the surface?

OOPS!

"pass through" should be changed to "travel along"
and the parenthetical expression (at the
hull-water interface) should be added for
clarification. Text above has been so edited.

Sorry about that.

Chuck

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Chuck wrote:
"If thee water parh from the surface to the Dynaplate is vertical (four
feet) does that mean return currents must pass through four additional
feet of seawater and thus encounter greater losses than if the Dynaplate
were at the surface?"

Well, the Dynaplate is at the surface of the water in contact with the
hull. That surface makes a turn to the horizontal at the sea surface.

The Dynaplate could also be connected by copper strap(s) on the
extertior of the insulated hull so as to contact the sea at a shallower
depth depending on the list (tilt) and trim of the boat. Capacitive
coupling through an insulated hull is usually comparatively easy at RF.

Best regards, Richard Harrison, KB5WZI

bob wrote:
. . .
One thing i am curious about is that if you suspend a radiator or
conductor well below skin depth in air whats the radiation efficiency
like of that conductor? To me on a yacht it looks like a conductor
suspended in a U channel suspended in air with the top open and
exposed. Maybe it will operate like a waveguide with some cut off
frequency, this is a wild guess.Maybe someone who can model conductors
below ground can model this. Most yachts have at least 3ft of freeboard
above water to play with.

But who knows there seems to conflicting advice on several points.
Maybe Roy can clarify all these issues with his models.

There's no good way to model this situation with the tools I have.
Conceptually, though, you can get a fair idea by imagining the sea to be
made of metal. The boat makes a depression in the surface, and you can
connect to the metal at the bottom of the depression just as you can
anywhere else on its surface.

Imagine that the depression is perfectly round and symmetrical, with a
grounded vertical extending up from its center. The current flowing into
the "ground" connection at the bottom of the depression will flow along
the conductor's surface, up the sides of the "dish" to the flat water
surface. The total current flowing from the center of the dish upward to
the flat surface will equal the current flowing up the vertical wire
near its base. The fields from the two will nearly cancel, so there'll
be little radiation from the vertical in the region below the flat
surface of the water. The vertical above that point should radiate
normally. This simplification will of course be modified by the reality
of a non-symmetrical hull, but it helps in getting a general idea of
what will happen.

Another way to look at the situation is to view the depression as the
outer conductor of a shorted coaxial cable, with the "ground wire"
extending down to its center as its center conductor, and the shorted
end the bottom of the depression. This shows you'd get some inductive
reactance in your connection to the surface of the water. A rough
calculation would probably get you in the ballpark of the actual value.
This doesn't represent loss, however.

The main thing, though, is that connection to the water requires a
conductor either in contact with or capacitively coupled to the water's
surface or only a very short distance below it (assuming salt water),
whether the surface is below the boat's hull in a depression or on the
flat surface of the ocean.

Roy Lewallen, W7EL