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

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, 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 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

On 03/02/2011 03:56 PM, Wimpie wrote:

If in your opinion there do not exist antennas that generate a
dominant magnetic or electric field (in the near field), then you are
contradicting yourself, as you can't transfer energy with a magnetic
field or electric field only. So your transformer also involves
electric fields. Maybe you should look into the Poynting theorem.

Hello, and that is correct. The Maxwell equations apply in all these
cases. When solving such problems, especially when dealing with
antennas, the total E-M field contains both reactive
(electric/capacitive & magnetic/inductive) and radiative components,
although certain components predominate depending on distance from the
excited structure.

When dealing with A.C. circuit problems where dimensions are a fraction
of a wavelength, one can usually ignore the the radiative/propagation
components. Why solve a problem with a sledgehammer when a small claw
hammer is adequate? Wouldn't you rather use Ohm's law in such case
rather than dealing with E and H fields? For example, the behavior of
A.C. power power distribution lines operating a 60 Hz can certainly be
modeled using transmission line equations but unless they're very long
(implying a propagation delay), a lumped-element/circuit approach is
much more easily dealt with (lumped lines. And yes, I'm intimately
familiar with the Poynting theorem and its derivation. (The designers of
the CFA obviously weren't).

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).

There's no such thing as "magnetic" and "electric" antennas. The
marketing departments of antenna vendors or others can call these
whatever they want but they can't change the laws of physics. Now, if
one dimensions a loop antenna or dipole antenna small enough (compared
to a wavelength, one obtains a magnetic or electric dipole,
respectively. Such dipoles (note the absence of the word "antenna") are
a theoretical concept but can be applied in practice to those structures
having electrically small radiators/interceptors.

I fully agree with you on the far field statements, but when you live
in an apartment (where significant spurious emission from home
equipment are in the near field of your 3.6 MHz antenna), a so-called
magnetic loop antenna may behave different (w.r.t. a short "electric"
dipole). It can be worse or better. Many radio amateurs know this from
experiments, without knowing the EM theory behind it.

Hey, I'm a fellow Ham and well aware of the contributions over the years
by hams to antenna design. Many times, however, established
electromagnetic theory is distorted to match the perceived observation.
In the case of noise immunity I would discuss the size of the victim
antenna, the antenna type (e.g. loop or dipole), antenna dimensions,
orientation and proximity wrt the offending noise source, and whether
the victim antenna is shielded and balanced. Unless one is referring to
an electrically small antenna treated as a magnetic or electric dipole,
typing an antenna as "magnetic" or "electric" is meaningless.

--
J. B. Wood e-mail:

Hello John,

On 3 mar, 13:30, "J.B. Wood" wrote:
On 03/02/2011 03:56 PM, Wimpie wrote:

If in your opinion there do not exist antennas that generate a
dominant magnetic or electric field (in the near field), then you are
contradicting yourself, as you can't transfer energy with a magnetic
field or electric field only. So your transformer also involves
electric fields. Maybe you should look into the Poynting theorem.

Hello, and that is correct. The Maxwell equations apply in all these
cases. When solving such problems, especially when dealing with
antennas, the total E-M field contains both reactive
(electric/capacitive & magnetic/inductive) and radiative components,
although certain components predominate depending on distance from the
excited structure.

When dealing with A.C. circuit problems where dimensions are a fraction
of a wavelength, one can usually ignore the the radiative/propagation
components. Why solve a problem with a sledgehammer when a small claw
hammer is adequate? Wouldn't you rather use Ohm's law in such case
rather than dealing with E and H fields? For example, the behavior of
A.C. power power distribution lines operating a 60 Hz can certainly be
modeled using transmission line equations but unless they're very long
(implying a propagation delay), a lumped-element/circuit approach is
much more easily dealt with (lumped lines. And yes, I'm intimately
familiar with the Poynting theorem and its derivation. (The designers of
the CFA obviously weren't).

Whoops, we have to be careful to not getting involved in a new
discussion, but I agree on your statement regarding that "special"
antenna and the statements regarding whether or not to use distributed
versus lumped circuit approach.


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).

There's no such thing as "magnetic" and "electric" antennas.

That is why I added the word "dominant", as you can't transfer energy
with H or E only and we were discussing small antennas as shown on
Norberts website.

One may imagine the electrically small magnetic loop antenna as the
primary of a transformer where there is no secondary coil in the
reactive field. The RF leakage (far field radiation) by accident hit
the antenna of another amateur.

The
marketing departments of antenna vendors or others can call these
whatever they want but they can't change the laws of physics. Now, if
one dimensions a loop antenna or dipole antenna small enough (compared
to a wavelength, one obtains a magnetic or electric dipole,
respectively. Such dipoles (note the absence of the word "antenna") are
a theoretical concept but can be applied in practice to those structures
having electrically small radiators/interceptors.

I fully agree with you on the far field statements, but when you live
in an apartment (where significant spurious emission from home
equipment are in the near field of your 3.6 MHz antenna), a so-called
magnetic loop antenna may behave different (w.r.t. a short "electric"
dipole). It can be worse or better. Many radio amateurs know this from
experiments, without knowing the EM theory behind it.

Hey, I'm a fellow Ham and well aware of the contributions over the years
by hams to antenna design. Many times, however, established
electromagnetic theory is distorted to match the perceived observation.

I agree on the above. Let I mention the two letters "EH" in addition
to your three-letter combination to avoid a new discussion...

In the case of noise immunity I would discuss the size of the victim
antenna, the antenna type (e.g. loop or dipole), antenna dimensions,
orientation and proximity wrt the offending noise source, and whether
the victim antenna is shielded and balanced. Unless one is referring to
an electrically small antenna treated as a magnetic or electric dipole,
typing an antenna as "magnetic" or "electric" is meaningless.


With kind regards,

Wim
PA3DJS
www.tetech.nl

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, 3 Mar 2011 02:37:34 -0800 (PST), Wimpie
wrote:

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


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.

OK, so you cannot present a simple quantified indicator of a reactive
field from your own source.

It is quite apparent without going into math (I thought that appeals
to professionalism and academics like complex calculus were verboten
here) and I see it quite plainly ILLUSTRATED in Figure 3.

However, if you cannot vouchsafe for this source and agree to what it
represents, you are right, there is no basis for discussion.

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.

I wish you wouldn't interpret beliefs and simple stick to what I've
written.

73's
Richard Clark, KB7QHC

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