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Re: Topband: Adding chicken wire or mesh on top of radial field

To: Grant Saviers <grants2@pacbell.net>, <n4is@n4is.com>
Subject: Re: Topband: Adding chicken wire or mesh on top of radial field
From: GEORGE WALLNER <aa7jv@atlanticbb.net>
Date: Wed, 06 Jun 2018 21:51:55 -0400
List-post: <mailto:topband@contesting.com>
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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