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

[Roger (K8RI) on TT]

I ask the following as a serious question.
Given the verticals appear to work well in these instances, yet salt 
water is not a low a resistivity as copper radials, but it is "flat" 
compared to most land, much lower resistivity compared to wet dirt and 
it is the equivalent of an infinite number of radials that extend 
through effectively an infinite  far field.  Is it the conductivity over 
a wide area and how does this relate or react in the near  field and far 
field ?  How does this compare with a copper disk (flat plate) with a 
radius matching typical radial lengths in the simulations?

We've all heard the claim, "I had the vertical over a 150 ft deep well 
and it really played". Yes it was a great safety ground, but the RF saw 
very little of it/
In this case the verticals work, but why?

73

Roger (K8RI)


On 2/4/2016 Thursday 1:20 AM, Grant Saviers wrote:
> 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 
<snip>

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