On 29 Jan 2004 05:45:02 -0800, (Maurizio) wrote:

Hi Richard,
I know that some studies have been done in the past using NEC4 to find
the ground wave/space wave fields, but my primary interest is in the
near zone modelling of such MF antennas, in particular in presence of
non-flat ground.
The scope is to make a tool to evaluate the radiated fields in
inhabited regions with limits in the maximum field amplitude.
A tool dedicated to this task would be very useful for the site
evaluation.

I have some idea on based on recent studies, but maybe (as often
happen) that others have already done something interesting.

Are these FCC resources dealing with such issues ?
And if so are they freely available?

Thanks in advance


Maurizio

Hi Maurizio,

Very few here have experience with the expensive NEC4, but I have
heard of such capabilities. Sounds like you want to investigate near
fields against complex terrain - that is going to take a lot of
modeling and a lot of CPU horsepower.

I am sure we would all be interested in the product of your effort.

The FCC does not like complexity, and as such you find a very common
and ordinary sameness to nearly every installation; unless they happen
to have a downtown location elevated above the street (there is one
like that in Spokane WA). Even there, the station conformed to the
slavish 120 radials strung out to neighboring buildings.

73's
Richard Clark, KB7QHC

Hi Richard,
my feeling is that in the past some studies have tried to find out the
structure and relative strenght of the ground/space wave fields.
Experience has then given rules to evaluate the losses due to the high
reactive fields near the antenna with the lossy ground (i have seen a
paper using a 6 dB factor to take into account antenna mismatch and
such nearby losses).
It maybe that this is almost all that has been done.
Do you agree?


Maurizio

On 30 Jan 2004 02:16:09 -0800, (Maurizio) wrote:

Hi Richard,
my feeling is that in the past some studies have tried to find out the
structure and relative strenght of the ground/space wave fields.
Experience has then given rules to evaluate the losses due to the high
reactive fields near the antenna with the lossy ground (i have seen a
paper using a 6 dB factor to take into account antenna mismatch and
such nearby losses).
It maybe that this is almost all that has been done.
Do you agree?


Maurizio

Hi Maurizio,

I worked on this a couple of years ago:
http://home.comcast.net/~kb7qhc/ante...elds/index.htm

It deals not so much with the variation of ground proximity with a
standard antenna, instead it works against the standard ground with a
variety of antennas.

Due to the intricacy of geometry afforded by a fractal form, this:
http://home.comcast.net/~kb7qhc/ante...atic/index.htm
is the most interesting. Unfortunately, the legacy of academic
fractal research (sic) has offered no more interest than the morbid
study of Down's Syndrome among the Armadillo population.

73's
Richard Clark, KB7QHC

Richard Clark wrote in message . ..
On 30 Jan 2004 02:16:09 -0800, (Maurizio) wrote:

Hi Richard,
my feeling is that in the past some studies have tried to find out the
structure and relative strenght of the ground/space wave fields.
Experience has then given rules to evaluate the losses due to the high
reactive fields near the antenna with the lossy ground (i have seen a
paper using a 6 dB factor to take into account antenna mismatch and
such nearby losses).
It maybe that this is almost all that has been done.
Do you agree?


Maurizio

Hi Maurizio,

I worked on this a couple of years ago:
http://home.comcast.net/~kb7qhc/ante...elds/index.htm

It deals not so much with the variation of ground proximity with a
standard antenna, instead it works against the standard ground with a
variety of antennas.

Due to the intricacy of geometry afforded by a fractal form, this:
http://home.comcast.net/~kb7qhc/ante...atic/index.htm
is the most interesting. Unfortunately, the legacy of academic
fractal research (sic) has offered no more interest than the morbid
study of Down's Syndrome among the Armadillo population.

73's
Richard Clark, KB7QHC

Hi Richard,
It seems that you have tried to shorten somewhat these cumbersome
antennas with the fractal approach.
I have seen recently an interesting paper on antennas & propagation
proceedings/magazine that was comparing the performance of fractal and
non-fractal designs.
Regarding the graphs you show in the web pages, if I have well
understood, you compare the E/H local fields (amplitudes) with the
free space impedence.
It is an alternative way to look at the near reactive fields.
However, the antenna that was simulated in the paper I was talking
about is a real antenna that has been modellized with a dedicated MOM
program and with the correct antenna geomety, and results have been
compared with measurements.
From this comparison it has been necessary the introduction of such
factor.
It seems to me that the 6 dB factor had to take into account all
losses from the transmitter to the radiated fields.
My concern is how this factor can be justified.
6 dB is a lot in terms of antenna usefull coverage distance.


Maurizio

On 31 Jan 2004 07:42:00 -0800, (Maurizio) wrote:

However, the antenna that was simulated in the paper I was talking
about is a real antenna that has been modellized with a dedicated MOM
program and with the correct antenna geomety, and results have been
compared with measurements.
From this comparison it has been necessary the introduction of such
factor.
It seems to me that the 6 dB factor had to take into account all
losses from the transmitter to the radiated fields.
My concern is how this factor can be justified.
6 dB is a lot in terms of antenna usefull coverage distance.


Maurizio

Hi Maurizio,

I am a trained Metrologist with advanced studies in Microwaves. The
measure of power (which is intimately tied to any expression of dB) is
very difficult to achieve with great accuracy. This means that
measurements are always suspect when they purport to confound theory.

The logic of the MOM program that works at one wavelength expresses
that it will work at all wavelengths. There is no scale determinacy
whereby results in HF are corrupted in SHF. There is every potential
for human error and measuring power reveals that quicker than any
other effort.

A 6dB discrepancy is a human problem, and glaringly evident.

73's
Richard Clark, KB7QHC

Richard Clark wrote in message . ..
On 31 Jan 2004 07:42:00 -0800, (Maurizio) wrote:

However, the antenna that was simulated in the paper I was talking
about is a real antenna that has been modellized with a dedicated MOM
program and with the correct antenna geomety, and results have been
compared with measurements.
From this comparison it has been necessary the introduction of such
factor.
It seems to me that the 6 dB factor had to take into account all
losses from the transmitter to the radiated fields.
My concern is how this factor can be justified.
6 dB is a lot in terms of antenna usefull coverage distance.


Maurizio

Hi Maurizio,

I am a trained Metrologist with advanced studies in Microwaves. The
measure of power (which is intimately tied to any expression of dB) is
very difficult to achieve with great accuracy. This means that
measurements are always suspect when they purport to confound theory.

The logic of the MOM program that works at one wavelength expresses
that it will work at all wavelengths. There is no scale determinacy
whereby results in HF are corrupted in SHF. There is every potential
for human error and measuring power reveals that quicker than any
other effort.

A 6dB discrepancy is a human problem, and glaringly evident.

73's
Richard Clark, KB7QHC

Hi Richard,
I agree that the human factor can be the problem for this discrepancy,
however, it would be also very interesting to know about other
experiences with such type of measurements, just to narrow the
expected uncertainty window.
(Better if in presence of complex environments)

Maurizio

On 4 Feb 2004 00:36:07 -0800, (Maurizio) wrote:

A 6dB discrepancy is a human problem, and glaringly evident.

73's
Richard Clark, KB7QHC

Hi Richard,
I agree that the human factor can be the problem for this discrepancy,
however, it would be also very interesting to know about other
experiences with such type of measurements, just to narrow the
expected uncertainty window.
(Better if in presence of complex environments)

Maurizio

Hi Maurizio,

This is best achieved by establishing a standard with as few variables
as possible, then varying them to determine their range of error
contribution. I am sure this is already evident to you, however
experience in going through the tests can reveal how probable those
sources of error may be.

You can quickly accumulate 3dB error in simply not providing the
correct load to the power (dB) determining measurement. Temperature
too can upset readings, but often as not, the simple presence of the
observer disrupts many things. The source is all to often taken for
granted, and all too often has frequency products that add to the
power reading, but are not in the bandwidth of interest. The list
goes on....

73's
Richard Clark, KB7QHC