Can anyone tell me if to model ground accurately where I live, what I
should use as the data. IE if poor ground will suffice. I live in
Yellowknife, NWT. The soil here, oh wait there really isn't any!
That's the problem, there is bedrock of granite everywhere here. For
miles out and miles down! What figures could I plug into EZNEC say ,
to get accurate results?
Thanks
73
Andrew VE8AE

Another property of rock, granite and like is that they "eat" RF. Experienced
that when driving around and operating from areas in OK3 and VE3 (Kingston).
Just like ocean gives you 10 -15 dB plus, seems that rocky areas take away
about as much. Like driving into an anechoic chamber vs. into amplifier at the
ocean beach.
Looks like perhaps absence of good reflecting?
As far as modeling, use it to compare various designs in similar conditions and
perhaps try them in real life, see how they reflect the modeling.
I would use radials or ground screens under antennas, perhaps good verticals
will perform better than horizontals?

Yuri, oK3BU, VE3BMV, VE1BY

Andrew, Just enter in EZNEC :

Conductivity = 0.1 milli-Siemens,

( Or Resistivity = 10,000 ohm-metres. )

Permittivity, or dielectric constant K = 4,

and you will get results just as accurate as EZNEC is able
to provide with more usual values of ground 'constants'.

At HF, in the case of granite, as discussed below, the
controlling factor is permittivity K and any reasonable
very high value for resistivity will suffice. Granite is a
fairly low-loss material. Roy, you should have more
confidence in your 'baby'.

----------------------------------------------

Soil, or whatever you are blessed with, has an
impedance Zs = Rs - jXs. It can be modelled to the
first order of accuracy by a resistance in parallel
with a capacitance.

Rs and jXs are the equivalent series components.

Soil resistivity is that measured between opposite
faces of a 1-metre cube of the material. Easy to
visualise and understand.

Capacitance is that measured between a pair of
1-metre square plates spaced 1-metre apart,
multiplied by the permittivity of the material.

Unless iron filings or crushed ferrite are mingled with the soil, the
permeabilty of this 1-metre cube of space will be unity and can be ignored.
Such mixtures are not known in the natural world.

Soil loss occurs due to current flowing in the soil
through Rs. Note carefully that Rs, a series
component, reduces as frequency increases. And
so soil loss decreases with increasing frequency.

Permittivity K increases fast with water content. In
solid rock moisture content is negligible and K is
that of the material itself, crudely 3 to 7. Mica is
a rock, K = 7. Quartz, another rock, K = 4.
Sahara sand has a lot of dry air in it, K = 3.

Lumping all sorts of backyards together, soil impedance is resistive below 1
or 2 MHz with a small -ve angle. Around 5 to 12 MHz impedance has an angle
around 45 degrees. At 30 MHz impedance is that of a lossy capacitor, but
low in value and therefore a good reflector. At VHF soil impedance is very
low, has a high negative angle, and is an efficient low-loss reflector.

The best reflectors are those with a small impedance magnitude relative to
377 ohms combined with an impedance angle approaching -90 degrees. The
angle of incidence is also in there somewhere. But don't forget skin depth
in the soil is quite shallow at VHF and only the top thin surface layer may
be involved.

If anybody intends to do any calculations it's far more convenient and
meaningful to work in practical terms of ohm-metres. Milli-Siemens sounds
pseudo-scientific and is not particularly impressive.

The capacitance between two 1-metre square plates, spaced 1-metre apart, is
8.8 picofarads. Doesn't seem very much. But with an ordinary garden soil
permittivity of 15, the impedance at 7 MHz is - j170 ohms. And with an
ordinary garden soil resistivity of 170 ohms-metres we have an angle of -45
degrees.

Two programs, EARTHRES and RADIOETH may be of interest. Download in a few
seconds from the following website and run immediately. In addition,
program SOILSKIN, as may be expected, calculates skin depth in soil.

=======================
Regards from Reg, G4FGQ
For Free Radio Design Software
go to http://www.g4fgq.com
=======================

Thank you for the replies Gents. I am trying to get a handle on this
modeling stuff and this helps. I will ask another!
Quote--
"Unless iron filings or crushed ferrite are mingled with the soil, the
permeabilty of this 1-metre cube of space will be unity and can be
ignored.
Such mixtures are not known in the natural world." -- unquote

I was in Iqaluit last year and when I put the Globalstar antenna on
the ground the magnets picked up a huge amount of filings, like in
high school when you did that magnet class. How would that affect your
antenna? Having such a conductive ground would be good would it not?
Better ground plane? Of note the rock all around that area was like
that, huge iron content as it was orange like in it's colour.
Brings me to another question. To operate from a fjord like area on
the bottom would really kill your signal would it not? The rocks would
suck up all your sig with their high iron content would they not, and
you would have a devil of a time getting over the top right?

Andrew VE8AE

"Reg Edwards" wrote in message ...
Andrew, Just enter in EZNEC :

Conductivity = 0.1 milli-Siemens,

( Or Resistivity = 10,000 ohm-metres. )

Permittivity, or dielectric constant K = 4,

and you will get results just as accurate as EZNEC is able
to provide with more usual values of ground 'constants'.

At HF, in the case of granite, as discussed below, the
controlling factor is permittivity K and any reasonable
very high value for resistivity will suffice. Granite is a
fairly low-loss material. Roy, you should have more
confidence in your 'baby'.

----------------------------------------------

Soil, or whatever you are blessed with, has an
impedance Zs = Rs - jXs. It can be modelled to the
first order of accuracy by a resistance in parallel
with a capacitance.

Rs and jXs are the equivalent series components.

Soil resistivity is that measured between opposite
faces of a 1-metre cube of the material. Easy to
visualise and understand.

Capacitance is that measured between a pair of
1-metre square plates spaced 1-metre apart,
multiplied by the permittivity of the material.

Unless iron filings or crushed ferrite are mingled with the soil, the
permeabilty of this 1-metre cube of space will be unity and can be ignored.
Such mixtures are not known in the natural world.

Soil loss occurs due to current flowing in the soil
through Rs. Note carefully that Rs, a series
component, reduces as frequency increases. And
so soil loss decreases with increasing frequency.

Permittivity K increases fast with water content. In
solid rock moisture content is negligible and K is
that of the material itself, crudely 3 to 7. Mica is
a rock, K = 7. Quartz, another rock, K = 4.
Sahara sand has a lot of dry air in it, K = 3.

Lumping all sorts of backyards together, soil impedance is resistive below 1
or 2 MHz with a small -ve angle. Around 5 to 12 MHz impedance has an angle
around 45 degrees. At 30 MHz impedance is that of a lossy capacitor, but
low in value and therefore a good reflector. At VHF soil impedance is very
low, has a high negative angle, and is an efficient low-loss reflector.

The best reflectors are those with a small impedance magnitude relative to
377 ohms combined with an impedance angle approaching -90 degrees. The
angle of incidence is also in there somewhere. But don't forget skin depth
in the soil is quite shallow at VHF and only the top thin surface layer may
be involved.

If anybody intends to do any calculations it's far more convenient and
meaningful to work in practical terms of ohm-metres. Milli-Siemens sounds
pseudo-scientific and is not particularly impressive.

The capacitance between two 1-metre square plates, spaced 1-metre apart, is
8.8 picofarads. Doesn't seem very much. But with an ordinary garden soil
permittivity of 15, the impedance at 7 MHz is - j170 ohms. And with an
ordinary garden soil resistivity of 170 ohms-metres we have an angle of -45
degrees.

Two programs, EARTHRES and RADIOETH may be of interest. Download in a few
seconds from the following website and run immediately. In addition,
program SOILSKIN, as may be expected, calculates skin depth in soil.

=======================
Regards from Reg, G4FGQ
For Free Radio Design Software
go to http://www.g4fgq.com
=======================

Andrew, Just enter in EZNEC :

Conductivity = 0.1 milli-Siemens,

( Or Resistivity = 10,000 ohm-metres. )

Permittivity, or dielectric constant K = 4,

and you will get results just as accurate as EZNEC is able
to provide with more usual values of ground 'constants'.

At HF, in the case of granite, as discussed below, the
controlling factor is permittivity K and any reasonable
very high value for resistivity will suffice. Granite is a
fairly low-loss material. Roy, you should have more
confidence in your 'baby'.

----------------------------------------------

Soil, or whatever you are blessed with, has an
impedance Zs = Rs - jXs. It can be modelled to the
first order of accuracy by a resistance in parallel
with a capacitance.

Rs and jXs are the equivalent series components.

Soil resistivity is that measured between opposite
faces of a 1-metre cube of the material. Easy to
visualise and understand.

Capacitance is that measured between a pair of
1-metre square plates spaced 1-metre apart,
multiplied by the permittivity of the material.

Unless iron filings or crushed ferrite are mingled with the soil, the
permeabilty of this 1-metre cube of space will be unity and can be ignored.
Such mixtures are not known in the natural world.

Soil loss occurs due to current flowing in the soil
through Rs. Note carefully that Rs, a series
component, reduces as frequency increases. And
so soil loss decreases with increasing frequency.

Permittivity K increases fast with water content. In
solid rock moisture content is negligible and K is
that of the material itself, crudely 3 to 7. Mica is
a rock, K = 7. Quartz, another rock, K = 4.
Sahara sand has a lot of dry air in it, K = 3.

Lumping all sorts of backyards together, soil impedance is resistive below 1
or 2 MHz with a small -ve angle. Around 5 to 12 MHz impedance has an angle
around 45 degrees. At 30 MHz impedance is that of a lossy capacitor, but
low in value and therefore a good reflector. At VHF soil impedance is very
low, has a high negative angle, and is an efficient low-loss reflector.

The best reflectors are those with a small impedance magnitude relative to
377 ohms combined with an impedance angle approaching -90 degrees. The
angle of incidence is also in there somewhere. But don't forget skin depth
in the soil is quite shallow at VHF and only the top thin surface layer may
be involved.

If anybody intends to do any calculations it's far more convenient and
meaningful to work in practical terms of ohm-metres. Milli-Siemens sounds
pseudo-scientific and is not particularly impressive.

The capacitance between two 1-metre square plates, spaced 1-metre apart, is
8.8 picofarads. Doesn't seem very much. But with an ordinary garden soil
permittivity of 15, the impedance at 7 MHz is - j170 ohms. And with an
ordinary garden soil resistivity of 170 ohms-metres we have an angle of -45
degrees.

Two programs, EARTHRES and RADIOETH may be of interest. Download in a few
seconds from the following website and run immediately. In addition,
program SOILSKIN calculates skin depth in soil.

=======================
Regards from Reg, G4FGQ
For Free Radio Design Software
go to http://www.g4fgq.com
=======================

Andrew, VE8AE wrote:
"To operate from a fjord like area on the bottom would really kill your
signal would it not?"

Assumining Andrew does not mean the bottom of the water, it depends on
the width, length, and depth of the crevice.

I once rafted down the Colorado River between the walls of the Grand
Canyon. It is between 4 and 13 miles wide at its brim. It is from 4000
to 5,500 ft. deep and over 200 miles long with lots of twists and turns.

Medium Wave reception was near zero, but shortwave reception was just
fine in most places along the canyon floor.

Best regards, Richard Harrison, KB5WZI

It seems iron, in its magnetic form, is a little more common in soil than I
thought.

As just described, our 1-metre cube of space containing garden soil has
higher values of conductivity and permittivity than an empty space. When
associated with a grounding system the effect of increased permittivity is
to much reduce the velocity of propagation of em waves through the soil and
along any wires buried in it.

A quarter-wave of buried wire may have a physical length only 1/6th of a
quarter-wave of wire in free space. The velocity along a radial wire just
lying on the surface of good soil is reduced to only 1/2 of the free-space
value and should be pruned accordingly. Old-wives and Handbook editors
please note.

A high content of magnetic iron in the soil would reduce propagation
velocity further still in the proportion 1/Sqrt( Mu ). How this would change
the loss-distributing effectiveness of radial wires I have no idea. My back
yard contains no iron and I have no intention to dig in 10 or 20 tons of
iron filings just to see what happens on the S-meter.
----
Reg, G4FGQ