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"Doc" == w5lz writes:

Doc Jack, Depending on how difficult errecting the thing would be,
Doc why not give it a try anyway? The water may not 'help' a signal,
Doc but the antenna being away from nearby 'stuff' might. If you
Doc have the wire, a pond, a boat(?), etc...? 'Doc

I plan on bringing along the bits just in case I feel extra
motivated. Should anything be learned from the experience, rest
assured that I will post. :-)

Jack.
- --
Jack Twilley
jmt at twilley dot org
http colon slash slash www dot twilley dot org slash tilde jmt slash
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Richard,

Are you sure you meant the statements quoted below?

Horizontal polarization bounces just fine from "horizontally conducting
surfaces". Indeed, when a mixed polarization wave hits a conducting
surface the horizontal polarization in the reflected wave is enhanced,
not "short-circuited". This is the same phenomenon that is the related
to Brewster's angle.

Perhaps you really meant to say that a special guided wave mode, namely
the ground wave, does not support horizontal polarization.

73,
Gene
W4SZ



Richard Clark wrote:

[Lots of more or less correct stuff snipped]


Well, this is where you are in over your head (water metaphors are
abundant in this topic). This, again, requires presumptions insofar
as the original observation was driven by the AM example. However, at
this point we will depart from the low frequency mandate to examine
another mandate: polarization and your presumption of conductivity.

A horizontally polarized antenna seeing a horizontally conducting
surface is a scenario that describes a self-short-circuit.
Horizontally polarized waves meeting the earth (a conductive one)
immediately snuff themselves (how long would your car battery last
with a screwdriver held across its poles?).

On the other hand, vertical antennas do not suffer this fate - and for
the same reason: it is a current wave (or at least the magnetic
component inducing such a current, in a conductive earth) that spans
earth making a perfectly reasonable relationship to continued
propagation.

[More snip]

On Wed, 05 May 2004 22:38:06 GMT, Gene Fuller
wrote:

Richard,

Are you sure you meant the statements quoted below?

Horizontal polarization bounces just fine from "horizontally conducting
surfaces". Indeed, when a mixed polarization wave hits a conducting
surface the horizontal polarization in the reflected wave is enhanced,
not "short-circuited". This is the same phenomenon that is the related
to Brewster's angle.

Perhaps you really meant to say that a special guided wave mode, namely
the ground wave, does not support horizontal polarization.

73,
Gene
W4SZ

Richard Clark wrote:

[Lots of more or less correct stuff snipped]

A horizontally polarized antenna seeing a horizontally conducting
surface is a scenario that describes a self-short-circuit.
Horizontally polarized waves meeting the earth (a conductive one)
immediately snuff themselves (how long would your car battery last
with a screwdriver held across its poles?).


Hi Gene,

Vertical polarization is the only mode that the Brewster Angle works
for (that's why polarized sunglasses work so well, they are
contra-polarized for what DOES reflect).

To test your hypothesis, use EZNEC over a perfect ground and note the
distinct difference at low angles (less than 5 degrees). The
horizontal radiation lobe is an example of Lambertian (another Optics
term) distribution where the maximal gain is observed directly
overhead, and only when phases positively combine (due to the high
surface conduction presenting a second source). Other phases give
rise to this Lambertian distribution which is much like the lobe
characteristics of a headlight glowing in the fog.

73's
Richard Clark, KB7QHC

On Thu, 06 May 2004 00:01:19 GMT, Richard Clark
wrote:

To test your hypothesis, use EZNEC over a perfect ground and note the
distinct difference at low angles (less than 5 degrees).

I might add, compare this horizontal's low angle performance to its
free space performance (a world of difference from that nearby
"conductivity" and none of it remarkably "good" even for the most
perfect of grounds). You have to hoist your horizontal pretty high to
bring the phase gains into play.

73's
Richard Clark, KB7QHC

Richard,

Is that you, or did your evil twin steal your role on RRAA?

Try reading my comment again. If you still disagree, then perhaps you
should crack open any elementary physics or optics textbook.

I did not mention antennas or lobes. I was commenting on your assertion
that the horizontal polarization is "shorted out" at a conducting
surface. Utter nonsense.

73,
Gene
W4SZ



Richard Clark wrote:
On Wed, 05 May 2004 22:38:06 GMT, Gene Fuller
wrote:


Richard,

Are you sure you meant the statements quoted below?

Horizontal polarization bounces just fine from "horizontally conducting
surfaces". Indeed, when a mixed polarization wave hits a conducting
surface the horizontal polarization in the reflected wave is enhanced,
not "short-circuited". This is the same phenomenon that is the related
to Brewster's angle.

Perhaps you really meant to say that a special guided wave mode, namely
the ground wave, does not support horizontal polarization.

73,
Gene
W4SZ

Richard Clark wrote:

[Lots of more or less correct stuff snipped]


A horizontally polarized antenna seeing a horizontally conducting
surface is a scenario that describes a self-short-circuit.
Horizontally polarized waves meeting the earth (a conductive one)
immediately snuff themselves (how long would your car battery last
with a screwdriver held across its poles?).



Hi Gene,

Vertical polarization is the only mode that the Brewster Angle works
for (that's why polarized sunglasses work so well, they are
contra-polarized for what DOES reflect).

To test your hypothesis, use EZNEC over a perfect ground and note the
distinct difference at low angles (less than 5 degrees). The
horizontal radiation lobe is an example of Lambertian (another Optics
term) distribution where the maximal gain is observed directly
overhead, and only when phases positively combine (due to the high
surface conduction presenting a second source). Other phases give
rise to this Lambertian distribution which is much like the lobe
characteristics of a headlight glowing in the fog.

73's
Richard Clark, KB7QHC

Gene, W4SZ wrote:
"---I was commenting on your assertion that the horizontal polarization
is "shorted out" at a conductive surfacce."

Richard Clark`s description may be indelicate but as I recall, Terman
says rouighly the same in several instances. Wish I had a copy at hand.
Terman says that a horizontally polarized low-angle wave suffers a phase
reversal upon reflection and as the difference in path length is
negligible between incident and reflected waves at low angles, the waves
being of opposite phase add to zero.

Best regards, Richard Harrison, KB5WZI

Richard Clark wrote:
"Salt water is miserable as a conductor, and its special place in the
pantheon of noble applications has little to do with conductivity."

I praise the god of conductivity for the ocean`s behavior as a beniign
enabler of medium wave propagation over extraordinary distances as
compared with ordinary earth. The reason the ocean`s surface allows long
distance propagation is explained in part on page 15 by Ed Laport in
"Radio Antenna Engineering":

"Nothing can be done about the electrical characteristics of the grouind
or topography between transmitting and receiving antennas. By choice, it
is possible to locate the antennas in areas of the best available soil
conductivity, thus to increase the terminal efficiency to some extent,
and to increase this efficiency still further by proper design of the
grounding system. (For ground waves vertical systems are imperative as
there is zero horizontally polarized ground wave propagation.)

Optimum ground-wave propagation is obtained over salt water because of
its conductivity (many times that of the best soils to be found on the
land) and uniform topography."

Laport has a ground-wave propagation table on page 17 of "Radio Antenna
Engineering". It is for low frequencies which best exploit ground-waves.

At 1000 miles over seawater, a wave at 400 KHz is attenuated by 98 dB.
Over good soil, 111 dB. Over poor soil, 160 dB.

Soil resistance determines penetration depth nto the soil and loss that
the soil extracts from a wave, especially if the frequency isn`t too
high. At 10 MHz and above, over real earth, the earth`s capacitance
offers so much less opposition than the earth`s resistance that the
earth`s resistive opposition really does have very little to do with
conductivity. However low the soil conductivity is, it is effectively
bypassed by the earth`s susceptance.

Sea water is so good at limiting medium-wave penetration and loss that
broadcast stations can be heard far out at sea during daylight hours.
This range is much greater than over any type of land. I recall hearing
the steel guitars of Hawaiian music when we were approaching from the
U.S.A. during WW-2. We were still days away and the sun could be high in
the sky. It wasn`t all that far as we only traveled about 250 miles a
day in good seas. Field strength increases by 6 dB every time you cut
the remaining distamnce by half as you approach the station. At half the
distance the volts per meter double.

Best regards, Richard Harrison, KB5WZI

Richard Harrison wrote:

Richard Clark wrote:
"Salt water is miserable as a conductor, .....

I praise the god of conductivity for the ocean`s behavior as a beniign
enabler of medium wave.....

Great info again Richard,
I recall during my early days in the Navy of
being able to listen to AM radio stations from Victoria B.C. all the way to
Hawaii. I always attributed it to the salt medium, but never really knew
enough about antennas and propagation other than to tell myself that salt
water was a better conductor.

When you think in terms of 'salt water because of its
conductivity (many times that of the best soils)' and then show the differences
in terms of Db attenuation it all makes sense.

This applies in many areas of discussion on this newsgroup. One worries
about ideal height above ground, transmission line losses, radiation pattern, etc,.
whereas the main objective is to get a signal out in the ether one way or
another, and damn the technical naysayers, full speed ahead.

Even with a limited knowledge of antennas and propagation, which thanks
to the knowledge gained on this newsgroup, I have always managed to get a signal
out of the shack and into the air without regard to the warnings of the pundits,
and thoroughly enjoyed making contacts -- many DX -- blissfully unaware of
how effective or efficient my antenna system may have been!

It frequently troubles me that when a novice asks a simple question
about antennas they are often distracted and possibly prevented from trying
something because of theoretical albeit often practical arguments against.
If you don't get the wire out there, you don't get the signals out either.
60db attenuation still beats infinity, and on a clear day you can hear
forever!

By golly, maybe I should rethink salting the back 40! :-)

Irv VE6BP


--
--------------------------------------
Diagnosed Type II Diabetes March 5 2001
Beating it with diet and exercise!
297/215/210 (to be revised lower)
58"/43"(!)/44" (already lower too!)
--------------------------------------
Visit my HomePage at http://members.shaw.ca/finkirv/
Visit my Baby Sofia website at http://members.shaw.ca/finkirv4/
Visit my OLDTIMERS website at http://members.shaw.ca/finkirv5/
--------------------
Irv Finkleman,
Grampa/Ex-Navy/Old Fart/Ham Radio VE6BP
Calgary, Alberta, Canada

Every time I see a post that begins "-----BEGIN PGP SIGNED MESSAGE-----", I
can't help but think of a kid saying "hey, you want to see my secret decoder
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"Jack Twilley" wrote in message
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I have seen what appear to be AM broadcast towers in or on the edges
of salt marshes, and it seems pretty obvious to me why that's a good
place to go. However, the environmentalists being a little more
noticeable than they were once upon a time, this particular method of
siting is probably a little more challenging than it used to be.

I recognize that salt water is far more conductive than fresh water,
but fresh water's still superior to sand and the like. That being
said, I am wondering about using a pond as a ground screen and
mounting the antenna itself on an island (or a raft) in the middle of
the pond.

What I don't know is just how large a pond do I need in order for
something like this to work? Obviously it depends on type of antenna
and band and a bunch of other things, but even a wild-ass guess (with
some math or physics behind it) will help make the difference between
whether I bother trying or not.

For those who absolutely require less variables in their equations,
imagine a standard dipole tuned for 20m strung roughly 45 feet above
ground level between two trees, one on either side of a fresh water
pond. How wide does the pond have to be at that point (and others)
for it to work right? Even answers like "the pond will have to be
wider than the dipole is long" or "there will be no noticeable impact
on performance" are fine if they're based in reality, and ideally in
math and physics I can understand.

Oh, and another question: what difference, if any, would frozen
versus liquid water make in this situation?

Jack.
(exploring new antenna options.)
- --
Jack Twilley
jmt at twilley dot org
http colon slash slash www dot twilley dot org slash tilde jmt slash
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