On Wed, Apr 1, 2015 at 12:17 PM, <[email protected]> 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 [email protected] 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 _________________ Topband Reflector Archives - http://www.contesting.com/_topband
