On 3/2/2011 8:40 AM, Wimpie wrote:
On 2 mar, 13:58, "J.B. wrote:
On 02/23/2011 10:00 AM, RadioWaves wrote: Today I have put my homepage online with information about the Magnetic Loop
Antenna.

http://www.qsl.net/pa7nr/

PA7NR

Hmmm. A "magnetic" loop antenna. Must be some other types of loop
antennas as well. Maybe there are also "electric" loop antennas.

Guess they left something out of all those antenna textbooks I have ;-)
Sincerely, and 73s from N4GGO,

--
J. B. Wood e-mail:

Hello John,

When you cut the loop at two opposite positions, yes, you can make
your "electric" loop.

It will generate lots of E-field, you may need another coil for
matching, and it is probably less efficient then a short straight
dipole with massive capacitive disks to get larger I*delta(le)
product.

Best regards,


Wim
PA3DJS
www.tetech.nl
In case of PM, please remove abc first.

Hello, and the not-so-subtle point is that there aren't magnetic,
electric, or any other such "types" of loop antennas. There are just
loop antennas that can further be described as shielded/unshielded,
balanced/unbalanced, electrically small or large. Just like we don't
transmit (propagate) electric (E) or magnetic (H) fields by themselves.

The purpose of an antenna is to radiate and/or intercept an
electromagnetic field. By definition energy radiated by a transmitting
antenna is not temporarily stored in the antenna's local electric or
magnetic field. It's been released into free space subject to
interception by a receiving antenna(s) or any other parasitic
structures. The receiving antenna transfers part the intercepted energy
to the load (receiver and other dissipative losses) and scatters the
rest back into free space.

By contrast, a transformer, for example, is a "magnetic" device that is
intended to transfer energy by a localized means (induction) other than
the propagation/interception of electromagnetic radiation.

To further confuse the issue, a conductor in the near (reactive) field
of a transmitting antenna will have current induced in it by the
antenna's local electric and/or magnetic fields. However, that's not
the usual purpose for which we design antennas. An exception might be
the immoboliser (PATS) system used in late-model motor vehicles that
incorporates a ring antenna embedded in the steering column that is
closely coupled at RF frequencies to the transponder chip and loop
antenna embedded in the vehicle ignition key. So is it a
transmit-receive antenna configuration or a primary coil-secondary coil
transformer configuration? Given the proximity of the inserted key to
the steering column I would guess the latter. Sincerely,

--
J. B. Wood e-mail:

On 3/2/2011 12:14 PM, J.B. Wood wrote:
On 3/2/2011 8:40 AM, Wimpie wrote:


To further confuse the issue, a conductor in the near (reactive) field
of a transmitting antenna will have current induced in it by the
antenna's local electric and/or magnetic fields. However, that's not the
usual purpose for which we design antennas.

Hello, all. I should also add that in stating the above I was only
considering nearby conductors (towers, metal on buildings, etc) and
wasn't including the local directors/reflectors that may be incorporated
into an antenna to provide the desired radiation pattern
characteristics. Sincerely,


--
J. B. Wood e-mail:

Hello John,

On 2 mar, 18:14, "J.B. Wood" wrote:
On 3/2/2011 8:40 AM, Wimpie wrote:



On 2 mar, 13:58, "J.B. *wrote:
On 02/23/2011 10:00 AM, RadioWaves wrote: *Today I have put my homepage online with information about the Magnetic Loop
Antenna.

http://www.qsl.net/pa7nr/

PA7NR

Hmmm. *A "magnetic" loop antenna. *Must be some other types of loop
antennas as well. *Maybe there are also "electric" loop antennas.

Guess they left something out of all those antenna textbooks I have ;-)
Sincerely, and 73s from N4GGO,

--
J. B. Wood * * * * * * * * *e-mail:

Hello John,

When you cut the loop at two opposite positions, yes, you can make
your "electric" loop.

It will generate lots of E-field, you may need another coil for
matching, and it is probably less efficient then a short straight
dipole with massive capacitive disks to get larger I*delta(le)
product.

Best regards,

Wim
PA3DJS
www.tetech.nl
In case of PM, please remove abc first.

Hello, and the not-so-subtle point is that there aren't magnetic,
electric, or any other such "types" of loop antennas. *There are just
loop antennas that can further be described as shielded/unshielded,
balanced/unbalanced, electrically small or large. *Just like we don't
transmit (propagate) electric (E) or magnetic (H) fields by themselves.

The purpose of an antenna is to radiate and/or intercept an
electromagnetic field. *By definition energy radiated by a transmitting
antenna is not temporarily stored in the antenna's local electric or
magnetic field. *It's been released into free space subject to
interception by a receiving antenna(s) or any other parasitic
structures. *The receiving antenna transfers part the intercepted energy
to the load (receiver and other dissipative losses) and scatters the
rest back into free space.

By contrast, a transformer, for example, is a "magnetic" device that is
intended to transfer energy by a localized means (induction) other than
the propagation/interception of electromagnetic radiation.

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.

To further confuse the issue, a conductor in the near (reactive) field
of a transmitting antenna will have current induced in it by the
antenna's local electric and/or magnetic fields. *However, that's not
the usual purpose for which we design antennas. *An exception might be
the immoboliser (PATS) system used in late-model motor vehicles that
incorporates a ring antenna embedded in the steering column that is
closely coupled at RF frequencies to the transponder chip and loop
antenna embedded in the vehicle ignition key. *So is it a
transmit-receive antenna configuration or a primary coil-secondary coil
transformer configuration? *Given the proximity of the inserted key to
the steering column I would guess the latter. *Sincerely,

--
J. B. Wood * * * * * * * * *e-mail:

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).

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.

I have no problems when people talk about a "magnetic loop antenna".
It shows me that they are discussing an antenna with a circumference
0.2 lambda. When people talk about a "loop antenna", it can be
anything.

Best regards,


Wim
PA3DJS
www.tetech.nl

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

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