The vertical near the sea will benefit from in-phase reflection (which is
additive) of the vertically polarized radiation. That is probably worth 3 to
6 dB, depending on the angle, etc. Ground losses, however, will still depend
on the ground and the ground system. Those losses can be high with a poor
ground and a poor ground system. If the antenna is electrically short (less
than 1/4 wave), the losses will be especially high. If the sand is saturated
with salt-water below, that will sure help, probably because of capacitive
coupling from the radials.
But nothing will beat standing the antenna in the water and using the
salt-water (via a low resistance connection) as your ground. Think of it
like this: if half of your backyard was covered by a copper sheet and the
other half was just regular dirt, where would you put your vertical? Near or
right over the copper sheet?
I actually tested the difference between beach and water (unintentionally)
in the Bahamas. I set up a 62 foot tall vertical standing in about a foot of
salt-water. The antenna had a aluminum-base whose four legs stuck out about
10 feet under-water in each direction. The braid of the coax was connected
directly to the aluminum base. There were no radials. For three nights I was
getting good reports from EU on 160. Then next morning a storm blew down the
antenna. I relocated it onto the beach, to about 40 feet from the water's
edge at high tide. I also added 32 radials, each between 1/8 and 1/4 wave
long and about 2 feet above the sand. The next few nights I was getting
comments like "your signal is way down from before". So another three nights
later, I moved the antenna back into the water (with better guys this time),
but, again with no radials. Reports indicated that my signal was back to
"normal". Now, this is purely anecdotal, and I don have any numbers to back
it. But subsequent DXpeditions bore out my belief that antennas that are
standing in salt-water perform better than antennas near the salt-water.
Here is another piece of info: Recently, I was testing the new 160 vertical
for the KH1 DXpedition. It is a 43 foot "fat" vertical with top loading
wires. I installed it standing in salt-water in the Bahamas (same metal
base). I measured the feed-point impedance at 9 -120 Ohms. I installed the
same antenna at my home QTH, where it is standing 4 feet from the water's
edge and is connected to the sea-water via a 4 foot wide stainless steel
sheet that goes about 6 foot into the water. Additionally, there are 20
radials of various lengths on the land side. The antenna measures 12 -120
Ohms. I believe that the 3 Ohms difference is all in the ground system.
An important point to note: the "return" (braid of the coax) must be
connected to the sea-water via a low impedance path. Otherwise, there will
be a loss-making resistance in series with the "return". So the chicken wire
will help, but it will help more when it is connected.
73,
George,
AA7JV/C6AGU
On Mon, 4 Jun 2018 19:59:57 -0700
Grant Saviers <grants2@pacbell.net> wrote:
It is well known by DXpeditioners and an EZNEC analysis demonstrates that
verticals within 1 wavelength of the sea have greatly enhanced gain at low
elevation angles in the seaward direction. There is no need for the antenna to
be over water for that benefit. In the opposite direction the pattern is that
of a vertical over whatever that direction ground properties are.
The conductivity of sea water saturated sand is closer to 1 S/m and seawater is
usually modeled as 4 S/m.
See my paper "Verticals on the Beach - Some Modeling Results" in QST June 2016 and Al
Christman K3LC "Verticals by the Sea" series in NCJ 2005.
A conductive plate football field size will reduce ground losses in its direction if connected as "radials".
It will have essentially no influence on the far field elevation pattern.
Grant KZ1W
........snip.....
The soil surface conductivity is vey low. If you think about a cooper plate large as a
football field or salt water, a vertical near it will perform very poor, it only will
perform well "on it" , connect with the plate and on top of the plate. That's
way AA7JV vertical antennas works so well, George install them inside the water. Near the
salt water does not work. Conductivity wet ground (beach) is 0.02, sea water 5. The same
with radials and mesh wire if you don't connect it, it does not work! 73's N4IS JC
Why would bonding the added matting be required if it is laid over or
beneath an existing radial field? It reduces ground losses regardless.
Peter
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N6VR
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