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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