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, donovanf@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" <w2re@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
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