Hi Frank, Thank you for your detailed answer. I appreciate your valuable time in responding.
After a few emails and a phone call it looks like we need to be within the fresnel zone, which is five wavelengths according to the ON4UN book. Yes! I know Peter K3ZM location all too well. We put up his 190’ R25 support for his 4SQ in 30+ mph winds a few years back. Great location on a marsh about 1/4 mile from the Ocean. Thanks for the input, we looking forward to start building the contest station! :) 73, Ray W2RE On Apr 1, 2015, at 12:17 PM, donov...@starpower.net wrote: > Hi Ray, > > Two primary factors affect sky wave signal strength from Topband > verticals close to salt water: > > 1. ground loss in the immediate vicinity of the feed point. The feed > point must be much closer than 1/4 wavelength from salt water > or a salt marsh to significantly reduce ground loss. > > 2. ground reflection loss, especially close to the near edge of the > Fresnel Zone > > Perhaps the most practical solution to achieving very low ground loss > is to place the base of the vertical in a salt marsh such as at W1KM. > There is an AM broadcast tower on a pier extending well into San > Francisco Bay but this would be exceptionally difficult to duplicate in > a ham installation. 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. > > Most ground reflection loss within the Fresnel Zone of a vertical with > the feed point at ground level occurs within one wavelength of the feed > point for low angle sky wave signals. This requires that a Topband > vertical be located within several hundred feet of salt water or a salt > marsh. > > For horizontally polarized antennas, the only significant factors are > ground reflection efficiency within the Fresnel zone and blockage > of the horizon by terrain. For very tall towers and very low angles, > the Fresnel Zone extends out at least several miles but much closer > than the horizon except in mountainous terrain that blocks the visual > line of sight to the distant horizon. For horizontally polarized antennas, > salt water isn't significantly more efficient for Fresnel Zone reflection > than average soil on very flat terrain. > > Perhaps the biggest improvement for horizontal polarization at an ocean > front location derives from its exceptionally flat Fresnel Zone, especially > for VHF EME where the full 6 dB ground gain is very difficult to achieve > over typical urban and densely populated suburban location. An > exceptionally flat Fresnel Zone can be a significant improvement compared > to locations where the Fresnel Zone encompasses many large buildings or > any location with sharp elevation changes (greater than 1/4 wavelength) > close to the near edge of the Fresnel Zone. > > Don't forget to consider the many serious maintenance problems of an > ocean front location, not only antenna maintenance but also resolution of > RFI from power lines for many miles around. K3ZM had serious RFI > very efficiently propagated across the Chesapeake Bay from power lines > nearly 20 miles away. This could be a significant problem in an area with > power lines near the ocean. > > 73 > Frank > W3LPL > > > > > > > > > > From: "HVT" <w...@hudsonvalleytowers.com> > To: topband@contesting.com > Sent: Wednesday, April 1, 2015 12:47:23 PM > Subject: Topband: Salt-Water Qth! > > This is my first post to the Top-Band Reflector, so please excuse my > ignorance if this topic has been discussed in the past. > > 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 had this heated debate over the weekend with > two ham friends of mine while we traveled to Maine looking at real-estate > along the coast. I understand the theory that verticals literally in or on > the water have a huge advantage. The debate was about how far away from the > water does it become a diminishing effect. I made the claim that the > Ocean-Front property would be a better location than anything inland > including a location on a ridge within a mile. This heated debate went on for > about 500 miles while we were driving back to NY. It was a very interesting > conversation and made the long drive back much quicker! :) > > Additional information about the debate: > > In the State of Maine there is a setback regulation on shoreline property > regarding structures including radio towers. To play it safe with the > shoreline protective rules, the proposed array system would be setback > minimum 500’ from the water or as far back as 2000'. At these distances on > 80/160 meter will a vertical antenna system see any positive effects with > additional gain from the salt water? > > What about horizontal antennas? Do they see any effects from Salt-Water? > > I'm sure I can use HFTA to model the terrain, which I have done in the past > with great accuracy. However, I'm not sure if it calculates Salt-Water. Maybe > it does. > > We are anxious to start building in Maine ASAP. Any input would be > appreciated. > > Thanks, > > Ray W2RE > W2RE.com > > > Sent from my iPhone > _________________ > Topband Reflector Archives - http://www.contesting.com/_topband _________________ Topband Reflector Archives - http://www.contesting.com/_topband