[TowerTalk] [Bulk] Vertical Antennas near salt-water

[Grant Saviers]

Having used several "verticals on the beach" for three DXpeditions, we 
verified they work extremely well.  This is because the pattern in the 
direction of the salt water goes to near the horizon, at least as close 
as EZNEC can model it.  In "take off angle" parlance, think less than 10 
degrees.  Thus, for the 10KM paths or longer from the South Pacific to 
ROW, they were the best choice on a north facing beach, ie they are 
directive antennas.  All were with 1 or 2 raised radials, tuned for the 
band of interest.  Since then I've extensively modeled verticals on the 
beach and found that 2 radials parallel to the tide line that are 
elevated at least 0.05 and preferably up to 0.15 wavelengths maximize 
the seaward gain as long as the vertical is less than 0.4 wavelength or 
so from the water. The verticals on the beach with elevated radials have 
a resonance Z around 35 ohms, which indicates very low ground losses.

To get an omni pattern with your vertical on a dock, it needs to be 
about 1.5 wavelengths from land and a single radial is ok.  The 
directivity gain is lost, but the very low angle pattern is preserved.

Using an "electrical" connection directly to salt water is a very 
interesting question which I only have anecdotal information about from 
the sailing community.  From a DC resistance perspective it takes very 
little surface area to make a low resistance connection. From an RF 
perspective what I've seen recommended is in the several sq ft of 
surface area and then within the top few inches of the water as that is 
the skin depth at multi MHz.  If any towertalkians have data on this, 
I'd sure appreciate getting a copy.

What is proven, as other DXpeditioners have documented, is that elevated 
radials for a vertical close to the tide line work extremely well.  
Also, Al Christman K3LC modeled this extensively in a NCJ 3 part series 
published in 2005.

Grant KZ1W

On 2/3/2016 11:08 AM, Gary K9GS wrote:
> I had an interesting discussion with a friend over the weekend and 
> wanted to get some input from the TowerTalk community.
>
> Imagine a 1/4 wavelength wire hanging down from a tree with the bottom 
> end attached to a post set into the salt water.  The antenna wire 
> would be 3 or 4 feet above the water.  What should be done with the 
> radial/counterpoise wires?  Should those wires go into the water?
>
> Or imagine a similar hanging wire that has the bottom end attached to 
> the top of a seawall.  Again, the bottom of the antenna would be 3-4 
> feet above the water.  Should the radials run on the ground parallel 
> to the seawall or run into the water?
>
> A third situation would be a vertical antenna mounted at the end of a 
> pier.  Run the radials back toward shore along the pier or run all of 
> the radials into the water?
>
> Finally, if the radials are in the water does it make any difference 
> if the wire is insulated or not?
>
>