Hi guys
>> Why would bonding the added matting be required if it is laid over or
>> beneath an existing radial field? It reduces ground losses regardless
>> I would like to read some research or documentation on this subject.
These are interesting question about ground or should I say "ground" . The
answer for both question is the same.
First we need to clearly understand what ground means, here some basic
stuff.
# 1- Earth surface
# 2- Point or place where all points are in the same voltage we refer as
"zero".
It looks very simple to understand #1, but #2 requires some complex
explanation.
There is no short answer.
I will try to make it easy to understand avoiding equations and complex
calculations. This is a ball park estimation.
Imagine a 2.5m ( 8.2 Ft) conductor. When we pass a current on a conductor
with no drop in voltage we say zero loss. The voltage on one end is the
same on the other end. That is true but only for zero Hertz or direct
current DC. The same 2.5m conductor will behave very different is the
frequency is 28 MHz or 10m. The conductor has a 1/4 wave length and the
voltage at the end will be very high and the current very low, like a 1/4
wave vertical for 10m, the conductor has 10/4 m long.
Measuring the conductivity of the ground on DC or 60 Hz has nothing to do
with RF. Even the surface conductivity in SIEMENS is frequency dependent and
most of the time referred only as HF.
Why surface conductivity is important, Because it reflects radio waves and
allow propagation to bounce waves between ground and the ionosphere
reflecting radio waves . Conducting media provide the optimum surfaces for
reflecting radio waves. Metal surfaces, and other conducting areas provide
the best reflections. It is noticeable that for HF ionospheric propagation,
when signals are returned to earth and are reflected back again by the
Earth's surface, areas of good conductivity provide the best reflections.
Desert areas give poor reflected signals, but the sea is much better and the
differences are very noticeable despite the variations in the ionosphere and
overall propagation path.
SURFACE CONDUCTIVITY (SIEMENS)
Dry ground & desert 0.001
Average ground 0.005
Fresh water 0.01
Wet ground 0.02
Sea water 5
The interaction of fields and matter, HF and ground, also depends of the
properties of the matter, permittivity ,permeability, and conductivity.
Part of the wave is reflected, and what is not reflected is reflated though
the matter and it is attenuated.
When the HF wave reach the ground surface, the field penetrates the ground
surface and the RF keep going down.
That's why the BOG, or beverage over ground or underground works. Even if
you bury the wire several feet underground it will receive HF signals. On
Very Low Frequencies the waves propagates inside the earth.
On average ground only 10% of the energy is reflected. The other 90% keep
going reflated inside the soil and attenuated as it propagate down.
The integration between field and matter depends on the polarization too.
Horizontal waves are reflected 180 degree out of phase and vertical is
reflect in phase.
For vertical antennas the reflected signal can be understood using an
imaginary extension of the vertical antenna inside the ground, like a
vertical dipole with the feed point at the surface.
Making it simple.
The energy from the feed point is split between the element above ground and
the element below ground. So the energy of the element below ground will be
attenuated.
To avoid that loss we use a "ground plane", the function is to avoid the
energy to penetrate the ground surface and be reflected back increasing the
radiation power. Using several radials close to each other we can reflect
the RF and reduce the loses. The efficiency of the radials depend how close
they are from each other. When the wire is more than wave/100 apart, 1.6 m
for a 160m antenna the energy reflected is very low. There is not
improvement above that distance apart between the radials.
The ground plane can be improved reducing the distance between the wires,
mesh wire does help to increase the reflection.
Here is the hard part to understand, for RF there is no ground surface on
your back yard. The RF penetrate very deep and the earth can be seen as
translucid matter for RF.
Burying our cable does not shield it from RF or "ground it", common mode
noise is present even several feet below the surface. If the wires are not
connected to the feed line it is not part of the antenna, if the mesh is not
connected to the feed line it is not part of the antenna as well. Both the
wires and the mesh are not resonant or 1/2 wave long to reflect the RF by
itself. 1/4 wave elevated radials works because is become resonant adding
the 1/4 wave long vertical part of the antenna. It's not the case for short
radials or mesh wires. If you disconnect the 1/4 elevated wires from the
feed line it does not work as well.
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
-----Original Message-----
From: Topband <topband-bounces@contesting.com> On Behalf Of Raymond Benny
Sent: Monday, June 4, 2018 3:05 AM
To: Peter Bertini <radioconnection@gmail.com>
Cc: 160 <topband@contesting.com>
Subject: Re: Topband: Adding chicken wire or mesh on top of radial field
Peter:
Is this a question or what you are saying is a known fact?
I am very interested in this outcome since I will a installing a TX 4SQ
system where some existing ground radials. Over time, I have heard both pros
and cons on this subject. I would like to read some research or
documentation on this subject.
Tnx,
Ray,
N6VR
Near Prescott, AZ
On Sun, Jun 3, 2018 at 1:14 PM, Peter Bertini <radioconnection@gmail.com>
wrote:
> 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
> _________________
> Topband Reflector Archives - http://www.contesting.com/_topband
>
--
Ray,
N6VR
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