On Wed, 2 Mar 2011 12:56:23 -0800 (PST), Wimpie
wrote:

When a noise source is about 5..10m away from an 3.6 MHz antenna, the
coupling of that noise source towards a "magnetic" loop antenna may be
different from the coupling towards an "electric" antenna, though
both antennas may produce the same far field radiation. This is not
from a textbook, but from experience (I am also working in power
electronics).

Text books would enlarge that volume to one half to several
wavelengths for the "near field." The text books would further
clarify this with math (yes, I know, professional and academic
discussion in light of this being an amateur forum is anathema) and
define the difference with the terms Fresnel diffraction (near-field)
and Fraunhofer diffraction (far-field). The operative physical length
of the antenna becomes meaningful, but this is getting ahead of what I
call the "benchmark" method below.

To give the magnetic loop aficionados the benefit of this, all local
noise within 100 feet would be susceptible to interfering and it
wouldn't be nullable (which is a characteristic only observed in the
far-field) except by polarization which is very haphazard in the
near-field. I have never seen a magnetic loop mount with the
necessary degrees of freedom to employ this method of "nulling." As
such, the vaunted characteristic is elusive and thus becomes legendary
rather than fulfilled.

However, the term "near-field" is rather vague. The more appropriate
discussion is found in "reactive near field" and "radiative near
field." The discussion of loop coupling to magnetic (while ignoring
electric) fields would suggest "reactive near field." In this regard,
the 80M volume of reactive interference is still roughly 100 feet in
all directions. The "radiative near field" would encompass a volume
out to 80 meters (roughly 250 feet). In either case, apartment living
finds no panacea in loop antennas.

There is another, non-textual (at least to the casual reader),
benchmark that such issues are measured by the physical spread of the
antenna itself (this usually attends discussion of capture area to
many's frustration). Here, I am returning to the allusion above of
Fresnel diffraction (near-field) and Fraunhofer diffraction
(far-field). The math (non-techs, turn your eyes away) is as simple
as:
2·D²/lambda

Let's work some examples from the sublime to the ridiculous on 80M.

The traditional half-wave dipole antenna that exhibits the traditional
usage for distinguishing between near and far:
2·40²/80 = 40 meters
a smaller quarter-wave dipole antenna
2·20²/80 = 10 meters
a tenth wave dipole antenna
2·8²/80 = 1.6 meters
a fortieth wave dipole antenna
2·2²/80 = 10 centimeters

Let's see where discussion follows in this regard.

73's
Richard Clark, KB7QHC

Hello Richard,

On 2 mar, 23:10, Richard Clark wrote:
On Wed, 2 Mar 2011 12:56:23 -0800 (PST), Wimpie
wrote:

When a noise source is about 5..10m *away from an 3.6 MHz antenna, the
coupling of that noise source towards a "magnetic" loop antenna may be
different *from the coupling towards an "electric" antenna, though
both antennas may produce the same far field radiation. *This is not
from a textbook, but from experience (I am also working in power
electronics).

Text books would enlarge that volume to one half to several
wavelengths for the "near field." *The text books would further
clarify this with math (yes, I know, professional and academic
discussion in light of this being an amateur forum is anathema) and
define the difference with the terms Fresnel diffraction (near-field)
and Fraunhofer diffraction (far-field). *The operative physical length
of the antenna becomes meaningful, but this is getting ahead of what I
call the "benchmark" method below.

To give the magnetic loop aficionados the benefit of this, all local
noise within 100 feet would be susceptible to interfering and it
wouldn't be nullable (which is a characteristic only observed in the
far-field) except by polarization which is very haphazard in the
near-field. *I have never seen a magnetic loop mount with the
necessary degrees of freedom to employ this method of "nulling." *As
such, the vaunted characteristic is elusive and thus becomes legendary
rather than fulfilled.

However, the term "near-field" is rather vague. *The more appropriate
discussion is found in "reactive near field" and "radiative near
field." *The discussion of loop coupling to magnetic (while ignoring
electric) fields would suggest "reactive near field." *In this regard,
the 80M volume of reactive interference is still roughly 100 feet in
all directions. *The "radiative near field" would encompass a volume
out to 80 meters (roughly 250 feet). *In either case, apartment living
finds no panacea in loop antennas.

There is another, non-textual (at least to the casual reader),
benchmark that such issues are measured by the physical spread of the
antenna itself (this usually attends discussion of capture area to
many's frustration). *Here, I am returning to the allusion above of
Fresnel diffraction (near-field) and Fraunhofer diffraction
(far-field). *The math (non-techs, turn your eyes away) is as simple
as:
* * * * 2 D /lambda

Let's work some examples from the sublime to the ridiculous on 80M.

The traditional half-wave dipole antenna that exhibits the traditional
usage for distinguishing between near and far:
* * * * 2 40 /80 = 40 meters
a smaller quarter-wave dipole antenna
* * * * 2 20 /80 = 10 meters
a tenth wave dipole antenna
* * * * 2 8 /80 = 1.6 meters
a fortieth wave dipole antenna
* * * * 2 2 /80 = 10 centimeters

Let's see where discussion follows in this regard.

73's
Richard Clark, KB7QHC



where is your square?

Fraunhofer region starts at (22.5 degrees phase shift):

r = 2*D^2/lambda

D = largest antenna size (excluding structures that doesn't carry
current).

Formula is only valid for electrically large structures, so not an
electrically small loop or dipole.

For electrically small loops, reactive fields are dominant for:

r 0.16*lambda

Smaller loop size does not result in smaller reactive field zone. The
correct formulas you can find everywhere. To make it easy for you:
http://www.conformity.com/past/0102reflections.html shows the
complete formulas for the electric and magnetic case, and a graph at
the end.


Best regards,

Wim
PA3DJS
www.tetech.nl

On Wed, 2 Mar 2011 15:29:55 -0800 (PST), Wimpie
wrote:

Formula is only valid for electrically large structures, so not an
electrically small loop or dipole.

"Large" or "small" are not quantities.

For electrically small loops, reactive fields are dominant for:
and how small (quantifiable) is small (qualifiable)?
r 0.16*lambda
given that I have already demonstrated that, and more, what importance
do you attach to this that hasn't already been shown?

Smaller loop size does not result in smaller reactive field zone.

What a curious defense for magnetic antennas's noise immunity.

However, the magnetic antenna is not immune from the reactive fields
of noise emitters that are very much larger than any loop discussed
here. It is the field of the emitter that is important. I thought I
would wait and see if anyone cottoned on to that aspect of the
discussion. If we proceed with the assumption (repeated here):
Smaller loop size does not result in smaller reactive field zone.
then the magnetic antenna is doomed to noise in the same sense as an
electric antenna is. Offhand I would speculate that in an apartment
situation, a magnetic antenna on the balcony is saturated with
reactive noise fields.

73's
Richard Clark, KB7QHC

On 3/2/2011 6:50 PM, Richard Clark wrote:
On Wed, 2 Mar 2011 15:29:55 -0800 (PST),
wrote:

Formula is only valid for electrically large structures, so not an
electrically small loop or dipole.

"Large" or "small" are not quantities.

For electrically small loops, reactive fields are dominant for:
and how small (quantifiable) is small (qualifiable)?
r 0.16*lambda
given that I have already demonstrated that, and more, what importance
do you attach to this that hasn't already been shown?

Smaller loop size does not result in smaller reactive field zone.

What a curious defense for magnetic antennas's noise immunity.

However, the magnetic antenna is not immune from the reactive fields
of noise emitters that are very much larger than any loop discussed
here.

Very much larger is not a quantity. How much larger?

It is the field of the emitter that is important. I thought I
would wait and see if anyone cottoned on to that aspect of the
discussion. If we proceed with the assumption (repeated here):
Smaller loop size does not result in smaller reactive field zone.
then the magnetic antenna is doomed to noise in the same sense as an
electric antenna is. Offhand I would speculate that in an apartment
situation, a magnetic antenna on the balcony is saturated with
reactive noise fields.

73's
Richard Clark, KB7QHC

On Wed, 02 Mar 2011 19:01:55 -0600, John - KD5YI
wrote:

Very much larger is not a quantity. How much larger?

Twice - at least.

73's
Richard Clark, KB7QHC

On 3/3/2011 1:35 AM, Richard Clark wrote:
On Wed, 02 Mar 2011 19:01:55 -0600, John -
wrote:

Very much larger is not a quantity. How much larger?

Twice - at least.

73's
Richard Clark, KB7QHC


So from twice to infinity. Still not a quantity. You seem to have the
same problem for which you berate others.

On Thu, 03 Mar 2011 11:17:40 -0600, John - KD5YI
wrote:

So from twice to infinity. Still not a quantity. You seem to have the
same problem for which you berate others.

2 (twice) is not a number? The antenna most frequently discussed is a
40th wave or 2 meters across. These are two more numbers (40th and
2). Twice that yields to more numbers (20th and 4).

Infinity is not a number.

73's
Richard Clark, KB7QHC

Hello Richard,

What a curious defense for magnetic antennas's noise immunity.

Where did I mention that this relates to noise immunity? I only tried
to point you to a misconception regarding the use of the 2*D^2/lambda
formula.

[start quote]
The traditional half-wave dipole antenna that exhibits the traditional
usage for distinguishing between near and far:
2 40 /80 = 40 meters
a smaller quarter-wave dipole antenna
2 20 /80 = 10 meters
a tenth wave dipole antenna
2 8 /80 = 1.6 meters
a fortieth wave dipole antenna
2 2 /80 = 10 centimeters

Let's see where discussion follows in this regard.
[end quote]

You want to believe us that a usable antenna with size=2m and
lambda=80m satisfies far field conditions at 10 cm, I really hope I
understood you wrong.

However, the magnetic antenna is not immune from the reactive fields
of noise emitters that are very much larger than any loop discussed
here. It is the field of the emitter that is important. I thought I
would wait and see if anyone cottoned on to that aspect of the
discussion. If we proceed with the assumption (repeated here):



The dominant reactive field from a small "magnetic" loop or "electric"
antenna at lambda=80m extends to somewhat more then 10cm, think of
about 5m. Though the far fields may be similar, the reactive fields
are completely different in orientation, strength and E/H ratio. See
for example the link posted earlier:
http://www.conformity.com/past/0102reflections.html

This will result in complete different coupling to conductors present
in the reactive field zone. When using reciprocity, this will also
affect the coupling from noise current in the conductors towards the
antenna. So I can't follow your statement below:

wimpie: Smaller loop size does not result in smaller reactive field zone.
then the magnetic antenna is doomed to noise in the same sense as an
electric antenna is.

Of course I agree with you for the case the noise source extends over
large distance.

What antenna is better, you cannot say beforehand and is food for the
experimenter (as I mentioned earlier).

This topic becomes lengthy. Do you think that it will result in better
statements from other people on there websites (that was the subject
of my first contribution)? The second part was just to show that the
3% claim for a 4 m loop (circumference) at 80m isn't bad.

I have real doubts about it, so I decided to send PM to Norbert some
days ago to setup a more constructive discussion.

With kind regards,

Wim
PA3DJS
www.tetech.nl

On Wed, 2 Mar 2011 18:34:12 -0800 (PST), Wimpie
wrote:

http://www.conformity.com/past/0102reflections.html

This will result in complete different coupling to conductors present
in the reactive field zone. When using reciprocity, this will also
affect the coupling from noise current in the conductors towards the
antenna.

Reciprocity does not appear in the text at your link and the concept
you are offering appears to be an invention that is unsupported. Let's
stick with unraveling one thing at a time.

So, working with your link's assertions give me a simple quantified
indicator of a reactive field.

73's
Richard Clark, KB7QHC

On 3 mar, 09:27, Richard Clark wrote:
On Wed, 2 Mar 2011 18:34:12 -0800 (PST), Wimpie
wrote:

http://www.conformity.com/past/0102reflections.html
This will result in complete different coupling to conductors present
in the reactive field zone. When using reciprocity, this will also
affect the coupling from noise current in the conductors towards the
antenna.

Reciprocity does not appear in the text at your link and the concept
you are offering appears to be an invention that is unsupported. Let's
stick with unraveling one thing at a time.

So, working with your link's assertions give me a simple quantified
indicator of a reactive field.

73's
Richard Clark, KB7QHC

Hello Richard,

As I assume you understand complex calculus, that link (
http://www.conformity.com/past/0102reflections.html ) was just to help
you to figure out field orientation and strength versus distance for
the magnetic and electrical case.

If you still believe in the 2*D^2/lambda far field formula for
electrically small antennas, I doubt whether it is useful to continue.

Best regards,


Wim
PA3DJS
www.tetech.nl