On Wed, Apr 1, 2015 at 12:17 PM, <donovanf@starpower.net> wrote:
>
> Its not practical to place a vertical closer than 1/4
> wavelength of an ocean beachfront except in a temporary installation
> such as a DXpedition.
Also w2re@hudsonvalleytowers.com wrote:
>>... "Is there any scientific data in print to prove the theory that ocean
front property is better than a location inland about a mile or so on a
ridge overlooking salt water for HF. ... I understand the theory that
verticals literally in or on the water have a huge advantage."...
>>
It is not a theory that there is a remarkable increase in MF transmission
when closely approaching saltwater waterline. It has been observed over at
least a half century by what must now be millions of observers, certainly
the vast majority not hams, observed at least since inexpensive
transistorized portable radios were available around 1960.
The 1960 date sticks in my mind because of a story that circulates among
Berea College alumni to this day about transistor radios scattered among
1200 students stuck in a terribly boring required general assembly lecture.
Some 15 or 20 of these new all-the-rage radios were scattered all over the
assembly hall, and were tuned in to the 7th game of the 1960 world series
between Pittsburgh and the Yankees. Back then there were no earbuds to go
stealth. Volumes were low, but loud enough to hear without the giveaway of
the radio resting upon the ear. The winning run in the bottom of the ninth
resulted in barely suppressed cheers and moans and the cumulative uproar of
whispers mercifully brought the lecturer to a bewildered halt. We received
an outraged dressing down from the college president who, to his credit,
was the first up on the stage to figure out what was going on, and who
apparently was not a baseball fan. I won't get into why I know it was
terribly boring. But I digress...
These and millions of others took these radios everywhere with them, and it
was soon common knowledge that you could hear the New York AM stations all
day long if you took the radio out over the salt water at east coast ocean
beaches as far south as Cape Hatteras. Not a bit of theory involved, just
undeniable observation.
The wow factor of this has severely diminished since the internet, and
nobody except hams thinks that hearing NYC AM stations during the day down
the east coast is the least interesting. The question now is why can't the
complainer text high definition video to anywhere in the world over the
internet in five seconds or less. But transistor radios were really neat
new affordable stuff in 1960.
The depth of the drop off walking away from the beach, the inverse of the
improvement walking toward it, exposes the answer to your question.
Whatever the theory, the fact remains of an often reported sharp change in
signals across several hundred meters, sometimes in significantly less
distance.
The "mysteries" of near-to-ocean propagation or losses become less foggy if
one always carefully considers ground media loss in discussions. Ground
losses continue to be the "undiscovered country" of top band transmitting
antenna discussions, remarkably ignored in many discussions about 160 meter
antennas that require a counterpoise. These ignored counterpoise issues can
take back expensive amplifier gain with losses as large.
Models depend on a monolithic uniform ground all the way to and beyond the
horizon and uniform to deep depth. Models need this to simplify computer
computations so they can run on ordinary PC's in times that are measured in
minutes rather than months or years. Accurate 160m modeling of what goes on
from 100 meters out in the water, across a sandy beach to 10 kilometers
inland cannot be accomplished with available resources and program code.
Some investigators have set up carefully at a site with antenna and serious
commercial measuring equipment, and have simply been unable to get
measurements to match a model, regardless of the ground characteristics
specified in the model.
At the water line, the remaining difficulty at this point would be support
of a vertical. An FCP above and parallel to the water line or out over the
water would be a very efficient counterpoise and quite easy to erect with
inexpensive materials. A shortened aluminum vertical with large gauge
appropriately located loading coils could do very well in the short term.
It would have a narrow bandwidth, not being weighed down and broadbanded by
ground losses invoked by the antenna and the counterpoise. But the reality
of salt spray, wind, etc easily renders temporary anything other than a
tower and guys on piers ala the San Francisco station mentioned earlier.
And even that would require ongoing maintenance.
The sea view cliffside location, with steps taken to minimize losses
directly underneath the antenna, seems best all band all around. Some argue
there is a surface wave phenomenon right over the water, demonstrated gone
after a few hundred meters inland. Such an actual propagation mechanism
will not be had at cliffside, however excellent the site otherwise.
Perhaps someone who actually owns beachfront, including the sand or rocks
down to the salt water, lacking contrary legislation, will be able to put
up something measurable right over the salt water and and keep it up and
efficient long enough to report results.
And even if a cliffside sea view location was worth an S unit or two,
nothing overmatches the dB between the ears. A LID operating QRO at an
excellent northeastern US sea view site with excellent antennas -- is still
only a *loud* LID, who is able to cause a lot more interference and
consternation than a weak LID.
73, Guy
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