Roy Lewallen wrote:
chuck wrote:
. . .
2. What would the ohmic losses be over a one square foot by 33 foot
path through salt water?

Let's see, salt water conductivity is about 5 S/m, which is 1.524 S/ft.
So the *DC* resistance of that piece of sea water would be 1.524 * 33 /
(1 * 1) ~ 50 ohms. . .

Oops. The DC resistance would be 33 / (1 * 1) / 1.524 ~ 22 ohms.

Roy Lewallen, W7EL

Roy Lewallen wrote:
Roy Lewallen wrote:
chuck wrote:
. . .
2. What would the ohmic losses be over a one square foot by 33 foot
path through salt water?

Let's see, salt water conductivity is about 5 S/m, which is 1.524
S/ft. So the *DC* resistance of that piece of sea water would be 1.524
* 33 / (1 * 1) ~ 50 ohms. . .

Oops. The DC resistance would be 33 / (1 * 1) / 1.524 ~ 22 ohms.

Roy Lewallen, W7EL

Thank you for the detailed response, Roy.

A couple of issues still trouble me however.

If the skin depth at 14 MHz is about 2.4 inches, can we roughly assume
that the RF resistance of that path is no less than 52.8 ohms (2.4*22
ohms)? This assumes most of the RF current would occur in the top one
inch (attenuation at one inch would be about 15 dB), and that the
resistance at 14 MHz is equal to the DC resistance.

A path one inch deep by 16 feet long (1/4 wavelength at 14 MHz) would
then have no less than 26.4 ohms resistance at 14 MHz.

Now imagine a system of multiple one foot wide by 16 feet long copper
radials on the ground with 26.4 ohm resistance distributed uniformly in
each radial. Obviously such a system will be lossy, with an average
radial resistance of 13.2 ohms.

While the analogy is a stretch, it illustrates the difficulty I am
having in understanding how seawater can be considered more efficient
than even a single slightly elevated radial, which is reported to be
less than 1 dB worse than 120 quarter wavelength buried radials
(ignoring slight pattern distortion). So even if seawater does
constitute a less lossy ground plane than a single radial (yeah, apples
and oranges, but we can weigh their juices I think) it would be better
by less than 1 dB. .

Then there is the issue of the one foot long "grounding rod" immersed in
the sea. If the above back-of-the-envelope analysis is valid, it would
seem that a even one inch long rod would be more than sufficient. If we
were dealing with a pool of liquid mercury or silver, this would have
considerable intuitive appeal for me. But the seawater model is
troubling. I imagine seawater to be a lot like earth, except more
homogeneous and with orders of magnitude higher conductivity. And I
imagine a perfect ground plane to have conductivity orders of magnitude
higher than seawater. I imagine even a modest system of copper radials
to appear more like liquid mercury than seawater does.

Where am I going astray?

73,

Chuck
NT3G

Icom needs to modernize their thinking and get rid of their "old school"
installation guides. Wire radials are the way to go on your sailboat. Not
copper foil or wide copper strips, just plain old 14 gauge wire radials. I
suggest you read some of the threads about this on the Maritime Mobile Ham
Forum from people with real world experience with marine HF installations.
You'll find the answers to your questions the

http://cruisenews.net/cgi-bin/mmham/webbbs_config.pl

Eric

"Will" wrote in message
...
I want to set up a hf antenna for my sailboat.

I have read various guides from Icom etc.

They suggest running copper foil to a Dynaplate and use sea water as the
ground. How can this work when the Dynaplate is below sea water?

Is sea water equal to copper wire radials as a RF ground system?

Does sea water make a good enough ground without radials?

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

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

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.

All ideas and comments appreciated.

Will

You mean the "Maritime" mis information forum? Looks like some real
world BS artists on there.

Would you make those radials on the boat resonant or not?
If resonant, how would you know?

How much more inductance would a ground wire have than copper foil.

73
Gary K4FMX


On Tue, 23 May 2006 21:11:29 -0400, "Eric Fairbank"
wrote:


Icom needs to modernize their thinking and get rid of their "old school"
installation guides. Wire radials are the way to go on your sailboat. Not
copper foil or wide copper strips, just plain old 14 gauge wire radials. I
suggest you read some of the threads about this on the Maritime Mobile Ham
Forum from people with real world experience with marine HF installations.
You'll find the answers to your questions the

http://cruisenews.net/cgi-bin/mmham/webbbs_config.pl

Eric

"Will" wrote in message
...
I want to set up a hf antenna for my sailboat.

I have read various guides from Icom etc.

They suggest running copper foil to a Dynaplate and use sea water as the
ground. How can this work when the Dynaplate is below sea water?

Is sea water equal to copper wire radials as a RF ground system?

Does sea water make a good enough ground without radials?

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

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

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.

All ideas and comments appreciated.

Will

In article ,
"Eric Fairbank" wrote:

Icom needs to modernize their thinking and get rid of their "old school"
installation guides. Wire radials are the way to go on your sailboat. Not
copper foil or wide copper strips, just plain old 14 gauge wire radials. I
suggest you read some of the threads about this on the Maritime Mobile Ham
Forum from people with real world experience with marine HF installations.
You'll find the answers to your questions the

http://cruisenews.net/cgi-bin/mmham/webbbs_config.pl

Eric


Radials are the WORST type of RF Ground for ANY MF/HF Marine Antenna
System. Anyone who has any sense at all can understand this, just
thinbk about it. First, they have to be very long when dealing with
frequencies below 4 Mhz, and unless you have a BIG vessel, you don't
have room for 1/4 wave radials. Second, Radials need to be resonant
to do any good, and that limits them to one or two frequencies, where
Marine Radios need to have antennas that can operate on many Bands,
which is why non-resonate, low impedance, RF Grounds, are used
by most all Commercial Marine Antenna Systems. I suggest that you
go out and get 30 Years of Commercial Marine Radio Installation and
Operation Experience, and then come back and explain it all to us,
again.......in detail.....if you live that long....

Me been there, done that......

Eric Fairbank wrote:
Icom needs to modernize their thinking and get rid of their "old school"
installation guides. Wire radials are the way to go on your sailboat. Not
copper foil or wide copper strips, just plain old 14 gauge wire radials. I
suggest you read some of the threads about this on the Maritime Mobile Ham
Forum from people with real world experience with marine HF installations.
You'll find the answers to your questions the

http://cruisenews.net/cgi-bin/mmham/webbbs_config.pl

Eric

"Will" wrote in message
...
I want to set up a hf antenna for my sailboat.

I have read various guides from Icom etc.

They suggest running copper foil to a Dynaplate and use sea water as the
ground. How can this work when the Dynaplate is below sea water?

Is sea water equal to copper wire radials as a RF ground system?

Does sea water make a good enough ground without radials?

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

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

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.

All ideas and comments appreciated.

Will



As others have pointed out in other contexts, it is more useful to think
about an HF "radial" on a boat as the "other half" of a vertical dipole,
rather than as an "RF ground". Even with substantial asymmetry (which is
almost a necessity, given the proximity of the horizontal "radial" to
the sea), most autotuners can match an off-center-fed, L-shaped
configuration easily. It is not necessary that the horizontal "radial"
be resonant for good performance.

Disregarding the balanced, center-fed dipole, the most common
alternative approaches to a vertical antenna are 1) the use of the sea
as a large ground plane, usually with a Dynaplate, and 2) the use of a
large conducting surface (traditionally specified as a minimum of 100
square feet) inside the hull. This surface can also be thought of as the
other half of an asymmetrical dipole. It is often connected to the sea
through under water metal parts such as the keel, in which case it
constitutes a kind of hybrid involving both 1 and 2.

Comparative test data on these systems are quite difficult to obtain and
virtually all of the information available is anecdotal, rarely
reproducible, and often contradictory. Analytical studies of these
systems, particularly as applied to fiberglass yachts, are also scarce.

Unless you really know what you are doing, I second Me's advice to find
someone with a lot of experience for assistance. Of course,
experimentation is a good thing, too.

Good luck.

Chuck

Will writes:

I want to set up a hf antenna for my sailboat.

I have read various guides from Icom etc.

They suggest running copper foil to a Dynaplate and use sea water as
the ground. How can this work when the Dynaplate is below sea water?

Is sea water equal to copper wire radials as a RF ground system?

Does sea water make a good enough ground without radials?

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

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

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.

All ideas and comments appreciated.

Well, I don't have personal experience with this. There is a chapter
in the ARRL antenna book, and it basically agrees with ICOM. As to
radials - two comments. First - how do you make sure that they don't
get in the way. And that RF currents won't be a hazard to
people. Second - there are plenty of wires on a yacht. How do the
wires know whether or not they are supposed to act as radials?

*If* there is a better alternative to the traditional backstay using
seawater as ground, it might be the vertical dipole. Feeding would be
tricky, but for single band operation, you could probably feed it
like a J-Pole. I don't see how to make a multiband variant. And you
get the high voltage points close to the deck, which doesn't sound
like a good idea in a damp and salty environment.

There are also people who hoist a horizontal dipole when needed. OK
for recreational radio, not if you need to be able to communicate in
rough weather.

Of course, square riggers are beautiful, and you could use the
yard-arms as a stacked yagi.

73
LA4RT Jon

I was told, years ago, that sea water is a very good conductor of radio
signals..... Sooo, take your ground wire and simple drop it into the
water was a bit of a weight.. and see, or should I say, hear what
happens... the length should not matter as the water is your
conductor...
Of course make sure your swr is low...
Larry ve3fxq


Will wrote:
I want to set up a hf antenna for my sailboat.

I have read various guides from Icom etc.

They suggest running copper foil to a Dynaplate and use sea water as
the ground. How can this work when the Dynaplate is below sea water?

Is sea water equal to copper wire radials as a RF ground system?

Does sea water make a good enough ground without radials?

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

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

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.

All ideas and comments appreciated.

Will

Will wrote:
"How can this work when the Dynaplate is below seawater?"

In the old days, an Apelco radio, a Webster antenna, and a Dynaplate
ground put you in the marine radio business just fine.

Best regards, Richard Harrison, KB5WZI

On Tue, 23 May 2006 23:44:50 +1000, Will
wrote:

I want to set up a hf antenna for my sailboat.

I have read various guides from Icom etc.

They suggest running copper foil to a Dynaplate and use sea water as
the ground. How can this work when the Dynaplate is below sea water?

Is sea water equal to copper wire radials as a RF ground system?

Does sea water make a good enough ground without radials?

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

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

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.

All ideas and comments appreciated.

Will

First, radials on a boat are not usually better than a good ground to
seawater.
If you do use radials they need to be resonant which means they need
to be ¼ wavelength long at each frequency of operation or they need to
be tuned with a loading coil to make them resonant. The reason is that
if they are not resonant you will get little current into them. Your
antenna system will be unbalanced and being that the radials will
usually be closer to other wires etc. on the boat they will couple
into them before they couple to the sea. That will make the tuner coax
and control cables radiators as well, because of the higher impedance
of the radials.

If the radials are mounted in the bottom of the hull right near the
water they have a chance of coupling to the sea. But if you go to that
trouble it is much easier to couple directly to the seawater with some
metal under the boat. (dynaplate, through hulls etc.)

Radials that do not couple the energy to the sea act as part of the
antenna. That wouldn't be bad if that radiation went where you wanted
it to go but a large part of it will get into all sorts of things on
the boat that you don't want it to.

Radials on a boat are different than when laid over earth. When laid
over earth there is tight coupling to the earth and length is not
important. When they are elevated above earth they need to be resonant
in order to work. Short radials do little good in this situation.
A boat installation is similar to an elevated installation on land.

I see some guys on the Maritime mis-information forum spouting about
using radials on a boat.

You are much better off getting a connection to the sea for your
ground. It is one of the best ground planes available. To do so you
need a very short ground lead from the tuner to the sea connection.
The best way to accomplish that is to mount the tuner down in the hull
right next to the sea ground connection within a foot or so. Then run
your antenna lead from the tuner to the antenna as much in the clear
as you can.

Remember that no matter where the tuner is mounted the antenna starts
at the ground connection. If you have a 10 foot lead from the tuners
ground connection to the sea water connection that 10 feet will
radiate like the antenna. Problem is so will the coax and tuner
control lines radiate and couple into all sorts of places you don't
want it to.

By placing the tuner at the ground connection you have control over
what radiates and what does not.

Copper foil for the ground lead to the tuner makes a lower impedance
path than doe's wire. You want the lowest impedance path you can get
for the ground lead.

73
Gary K4FMX