Michael Coslo wrote:

Back around the beginning of this thread a thought occurred to me,
and I'm surprised that no one else mentioned it.

Unless we are planning on putting out ship on the great Salt lake,
of one of the few other salt water inland lakes or seas, we're going to
be putting the thing in the ocean.

Immediately, one sees that if a ground is at the surface of the
water, at many points it will be 4 or more feet under the water. Dem
boats rock! There are moments that it will be quite a distance under
water, depending on the sea state.

Use a bare wire, and the top few inches will do the job regardless of
how much additional wire goes below the water. As I've said before,
there's no harm in having additional wire below the water; it simply
doesn't do anything useful.

The problem is that as the boat rocks, the length of the wire to the
ocean surface will vary in length, which will change the antenna's
impedance. So a plate just inside or outside the bottom of the hull (or
someplace that's always below the water line) would seem to me a better
idea from a practical standpoint. Surely some boater who understood
basic electromagnetics has thought about this and devised a method
that's both practical and effective.

Depending on the load, the water line is going to be different, and
will be changing constantly as fuel and food is used.

Certainly any capacitive coupling through the hull makes for a
variable capacitor? Does this have an effect?

What will cause it to vary? In any case, just make the capacitance large
enough so the reactance is always small compared to the ground
impedance, then it won't matter.

Will we eventually come to the conclusion that we can't put radios on
ships?? ;^)

It wouldn't surprise me if some folks reach that conclusion. Millions
firmly believe much more ridiculous things.

Roy Lewallen, W7EL

"Roy Lewallen" wrote:
Michael Coslo wrote:
Will we eventually come to the conclusion that we can't put radios on
ships?? ;^)

It wouldn't surprise me if some folks reach that conclusion. Millions
firmly believe much more ridiculous things.

Since the feedpoint impedance of a dipole changes as it blows
in the wind, guess we also can't use them on windy days.
--
73, Cecil http://www.qsl.net/w5dxp

Roy Lewallen wrote:
Michael Coslo wrote:


Back around the beginning of this thread a thought occurred to me,
and I'm surprised that no one else mentioned it.

Unless we are planning on putting out ship on the great Salt lake,
of one of the few other salt water inland lakes or seas, we're going
to be putting the thing in the ocean.

Immediately, one sees that if a ground is at the surface of the
water, at many points it will be 4 or more feet under the water. Dem
boats rock! There are moments that it will be quite a distance under
water, depending on the sea state.


Use a bare wire, and the top few inches will do the job regardless of
how much additional wire goes below the water. As I've said before,
there's no harm in having additional wire below the water; it simply
doesn't do anything useful.

The problem is that as the boat rocks, the length of the wire to the
ocean surface will vary in length, which will change the antenna's
impedance. So a plate just inside or outside the bottom of the hull (or
someplace that's always below the water line) would seem to me a better
idea from a practical standpoint. Surely some boater who understood
basic electromagnetics has thought about this and devised a method
that's both practical and effective.

Depending on the load, the water line is going to be different,
and will be changing constantly as fuel and food is used.

Certainly any capacitive coupling through the hull makes for a
variable capacitor? Does this have an effect?


What will cause it to vary? In any case, just make the capacitance large
enough so the reactance is always small compared to the ground
impedance, then it won't matter.

Well, I could be wrong, but if one side of the capacitor is on the
inside of the hull, and the other side is the sea water, is not the
motion of the ship going to affect that? ships move up and down quite a
bit, and low draft ones can have a *lot* of that hull out of the water,
and then a few seconds later have water coming over the bow.

Will we eventually come to the conclusion that we can't put radios on
ships?? ;^)


It wouldn't surprise me if some folks reach that conclusion. Millions
firmly believe much more ridiculous things.

Hehe, I've seen that actually happen....


- 73 de Mike KB3EIA -

Mike Coslo wrote:
Roy Lewallen wrote:
. . .

What will cause it to vary? In any case, just make the capacitance
large enough so the reactance is always small compared to the ground
impedance, then it won't matter.

Well, I could be wrong, but if one side of the capacitor is on the
inside of the hull, and the other side is the sea water, is not the
motion of the ship going to affect that? ships move up and down quite a
bit, and low draft ones can have a *lot* of that hull out of the water,
and then a few seconds later have water coming over the bow.

Well, I was envisioning a plate on some part of the hull which always
had water on the other side. If the hull on the other side of the plate
comes out of the water, you'll of course effectively lose coupling to
the water from that part of the plate. But again, if you make the plate
large enough so that enough of the plate always has water on the other
side of the hull to make a low impedance, the variation won't matter.

Sounds like you might have to make the plate cover a fair portion of the
hull to insure that there's always water on the other side of some of
it. If the entire hull comes out of the water, just remember to say
"mayday" really quick every time the hull hits the water. Other than
that, seems to me you'll probably be too busy to be playing with the
radio anyway.

Roy Lewallen, W7EL

In article ,
Mike Coslo wrote:

Well, I could be wrong, but if one side of the capacitor is on the
inside of the hull, and the other side is the sea water, is not the
motion of the ship going to affect that? ships move up and down quite a
bit, and low draft ones can have a *lot* of that hull out of the water,
and then a few seconds later have water coming over the bow.


We are not talking about 16 foot dingys here, we are talking about
vessels mostly over 30 feet in length, and usually with over 3 or 4 feet
of draft. Just how much coupling to the seawater you have is a function
of area of the inside capacitive plate, and the distance between it and
the seawater. If the dielectric distance is a few inches, and the inside
plate is below the waterline, then coupling will not change apperciably,
just because the water is sloshing around a bit on the hull. Even if
a bit of the surface area of the inside plate did come above the
waterline for a little while, say on a hard tack in a sail rig, the
coupling still wouldn't be appreciably reduced by loosing 5% of the
surface area. These are not really valid problems that one sees, when
operating MF/HF Marine Radios that have a decent, Low Impedance RF
Ground System installed in the first place. doing it right the first
time solves a lot of ills down the road, and skimping on the RF Ground,
is a presciption for disaster.


Bruce in alaska long time Marine RadioMan.......
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Bruce in Alaska wrote:
In article ,
Mike Coslo wrote:


Well, I could be wrong, but if one side of the capacitor is on the
inside of the hull, and the other side is the sea water, is not the
motion of the ship going to affect that? ships move up and down quite a
bit, and low draft ones can have a *lot* of that hull out of the water,
and then a few seconds later have water coming over the bow.



We are not talking about 16 foot dingys here, we are talking about
vessels mostly over 30 feet in length, and usually with over 3 or 4 feet
of draft.

I'm not so sure the exact size ship we speak of. But if you recall back
a long time ago when the original poster spoke of a hypothetical wire
not working at 4 feet underwater. I even suspect that a 30 foot vessel
might take greater than a 4 foot excursion, especially in your neck of
the woods!



Just how much coupling to the seawater you have is a function
of area of the inside capacitive plate, and the distance between it and
the seawater. If the dielectric distance is a few inches, and the inside
plate is below the waterline, then coupling will not change apperciably,
just because the water is sloshing around a bit on the hull. Even if
a bit of the surface area of the inside plate did come above the
waterline for a little while, say on a hard tack in a sail rig, the
coupling still wouldn't be appreciably reduced by loosing 5% of the
surface area. These are not really valid problems that one sees, when
operating MF/HF Marine Radios that have a decent, Low Impedance RF
Ground System installed in the first place. doing it right the first
time solves a lot of ills down the road, and skimping on the RF Ground,
is a presciption for disaster.

I don't doubt that the problem has been solved (if it exists in the
first place).

- 73 de Mike KB3EIA -

On Sun, 11 Jun 2006 21:33:51 -0400, Mike Coslo
wrote:
the original poster spoke of a hypothetical wire
not working at 4 feet underwater.

Hi Mike,

This hypothesis was a home-grown and hand rolled fantasy.

I don't doubt that the problem has been solved (if it exists in the
first place).

Oh, there is a problem alright: Making the lesson penetrate a quarter
inch of skull with more success than RF struggling through an
imaginary 4 foot skin depth of water problem.

73's
Richard Clark, KB7QHC

Richard Clark wrote:
On Sun, 11 Jun 2006 21:33:51 -0400, Mike Coslo
wrote:
the original poster spoke of a hypothetical wire
not working at 4 feet underwater.

Hi Mike,

This hypothesis was a home-grown and hand rolled fantasy.

I don't doubt that the problem has been solved (if it exists in the
first place).

Oh, there is a problem alright: Making the lesson penetrate a quarter
inch of skull with more success than RF struggling through an
imaginary 4 foot skin depth of water problem.

Which won't happen until we discuss this into showing how it is
impossible to put a radio on a ship! hehehe 8^)



- 73 de Mike KB3EIA -

In article ,
Mike Coslo wrote:

I'm not so sure the exact size ship we speak of. But if you recall back
a long time ago when the original poster spoke of a hypothetical wire
not working at 4 feet underwater. I even suspect that a 30 foot vessel
might take greater than a 4 foot excursion, especially in your neck of
the woods!

It really doesn't matter if the vessel has a draft of 4 feet or 24
feet,as the coupling to the seawater is to the hull/water boundry
which is the same as the surface of the water from the RF point of
view. Skin Effect, or Skin Depth @ any frequency is a Surface Effect
and that surface is the hull/water boundry, for any hull material.

Bruce in alaska
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