On 8/23/2016 6:22 AM, J.B. Wood wrote:
On 08/20/2016 04:39 PM, rickman wrote:
I've been studying loop antennas for some time now and I don't recall a
mention of polarization. I would think that a loop antenna mounted
vertically would provide a vertically polarized signal. Is that right?


Finally, someone on the ng said "loop antennas". You can't be a ham
because you didn't say "magnetic loop" ;-). Sincerely, and 73s from N4GGO,

Not sure what you mean. You are aware that magnetic loops and loops are
not the same thing. Magnetic loops are a subset of loop antennas.

--

Rick C

On Tue, 23 Aug 2016 13:14:32 -0400, rickman wrote:

Not sure what you mean. You are aware that magnetic loops and loops are
not the same thing. Magnetic loops are a subset of loop antennas.

To add a little confusion, the convention is for the polarization to
be that of the E-field (electric field) and not that of the H-field
(magnetic field), even if the communications ocurrs using the H-field
as in a shielded loop antenna.
https://en.wikipedia.org/wiki/Loop_antenna#Radiation_pattern_and_polarization
Small loops (0.1 wavelength circumference) are also a subset of loop
antennas.
http://www.antenna-theory.com/antennas/smallLoop.php

Loop antenna users are also polarized. Some users hate them, while
other users swear by them. There is some middle ground, but not in
public forums.


--
Jeff Liebermann
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558

On 8/23/2016 2:09 PM, Jeff Liebermann wrote:
On Tue, 23 Aug 2016 13:14:32 -0400, rickman wrote:

Not sure what you mean. You are aware that magnetic loops and loops are
not the same thing. Magnetic loops are a subset of loop antennas.

To add a little confusion, the convention is for the polarization to
be that of the E-field (electric field) and not that of the H-field
(magnetic field), even if the communications ocurrs using the H-field
as in a shielded loop antenna.
https://en.wikipedia.org/wiki/Loop_antenna#Radiation_pattern_and_polarization
Small loops (0.1 wavelength circumference) are also a subset of loop
antennas.
http://www.antenna-theory.com/antennas/smallLoop.php

Loop antenna users are also polarized. Some users hate them, while
other users swear by them. There is some middle ground, but not in
public forums.

I've been told that the term "magnetic" loop is the same as "small"
loop. It refers to the facts that the near field of a small loop is
mostly magnetic ( 1/10 lamda) and that they respond to the magnetic
component of the EM wave. I'm not sure how that matters in real world
use though as all antenna transmit both E and M in the far field.

--

Rick C

On Tue, 23 Aug 2016 15:57:27 -0400, rickman wrote:

I've been told that the term "magnetic" loop is the same as "small"
loop.

Dunno. As I understand it, a magnetic loop is really a "shielded
electrostatic loop", where E-field operation is blocked by the shield.
It would seem that removing the E-field, and leaving the H-field,
would make it a "magnetic loop":
https://www.google.com/search?q=shielded+magnetic+loop+antenna&tbm=isch
At some point, some clever person decided to do away with the E-field
shield and tolerate the increased noise pickup, but still called it a
"magnetic loop". I don't know if this is really true, but it seems
possible.

It refers to the facts that the near field of a small loop is
mostly magnetic ( 1/10 lamda) and that they respond to the magnetic
component of the EM wave. I'm not sure how that matters in real world
use though as all antenna transmit both E and M in the far field.

A small loop is different. It's where the circumference of the loop
is sufficiently small, that the current through the loop is
essentially constant at all points around the circumference. This
results in something that operates like a dipole, but with the E and H
fields interchanged.

Real world? Well, we had some kind of discussion a few years ago in
S.E.D. about WWVB polarization. I ran this study of how a loopstick
antenna in a commodity WWVB receiver responds to different
orientations:
http://802.11junk.com/jeffl/WWVB%20test/

If you look at the WWVB antenna construction, it looks like a really
big dipole:
http://802.11junk.com/jeffl/WWVB%20test/WWVB-antenna-lowered.jpg
Yet, the signal is vertically polarized:
https://softsolder.com/2010/01/02/wwvb-groundwave-signal-is-vertically-polarized/
Ok, that seems counter-intuitive, so it might be useful to prove it
experimentally:
End of the loopstick pointed at Denver (lousy signal):
http://802.11junk.com/jeffl/WWVB%20test/end-pointed-at-WWVB.jpg
Loopstick perpendicular to Denver and oriented up/down (lousy signal):
http://802.11junk.com/jeffl/WWVB%20test/loopstick-vertical.jpg
Loopstick perpendicular to Denver and oriented left/right (good
signal):
http://802.11junk.com/jeffl/WWVB%20test/loopstick-perpendicular-to-WWVB.jpg
Yep, it's vertically polarized.

--
Jeff Liebermann
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558

On 08/23/2016 01:14 PM, rickman wrote:
On 8/23/2016 6:22 AM, J.B. Wood wrote:
On 08/20/2016 04:39 PM, rickman wrote:
I've been studying loop antennas for some time now and I don't recall a
mention of polarization. I would think that a loop antenna mounted
vertically would provide a vertically polarized signal. Is that right?


Finally, someone on the ng said "loop antennas". You can't be a ham
because you didn't say "magnetic loop" ;-). Sincerely, and 73s from
N4GGO,

Not sure what you mean. You are aware that magnetic loops and loops are
not the same thing. Magnetic loops are a subset of loop antennas.


Sorry, guys but it ain't so. It's either a loop (shielded or
unshielded) or something else. This "magnetic" stuff appears to have
originated with hams. A receiving antenna (be it a loop or something
else) in the far (radiated) field of a transmitter samples an incident
electromagnetic (EM) wave. That EM wave has a magnetic and electric
component but you can't have one without the other. J.C. Maxwell (and
others) says so. Anyone, ham or other, who claims that an antenna in
the far (several wavelengths from the transmitter) field "receives" (or
favors) an E-field or an H-field is demonstrating a lack of
understanding of basic electromagnetic theory.

Now, consider two loops, one transmitting and one receiving. If the
receiving loop is in the near field of the radiating loop then it can be
magnetically coupled. In this instance the loop behaves more like a
mutually coupled inductor than an antenna. Perhaps this is where the
"magnetic" loop idea had its genesis. (Just like the immobilizer system
in your motor vehicle that has a loop embedded around the ignition
switch and which couples to the loop in the capsule inside your
transponder key.)

Textbooks on EM and antenna theory do talk about "magnetic" and
"electric" dipoles as theoretical constructs but that's another
discussion. Sincerely, and 73s from N4GGO,


--
J. B. Wood e-mail:

On 8/24/2016 6:43 AM, J.B. Wood wrote:
On 08/23/2016 01:14 PM, rickman wrote:
On 8/23/2016 6:22 AM, J.B. Wood wrote:
On 08/20/2016 04:39 PM, rickman wrote:
I've been studying loop antennas for some time now and I don't recall a
mention of polarization. I would think that a loop antenna mounted
vertically would provide a vertically polarized signal. Is that right?


Finally, someone on the ng said "loop antennas". You can't be a ham
because you didn't say "magnetic loop" ;-). Sincerely, and 73s from
N4GGO,

Not sure what you mean. You are aware that magnetic loops and loops are
not the same thing. Magnetic loops are a subset of loop antennas.


Sorry, guys but it ain't so. It's either a loop (shielded or
unshielded) or something else. This "magnetic" stuff appears to have
originated with hams. A receiving antenna (be it a loop or something
else) in the far (radiated) field of a transmitter samples an incident
electromagnetic (EM) wave. That EM wave has a magnetic and electric
component but you can't have one without the other. J.C. Maxwell (and
others) says so. Anyone, ham or other, who claims that an antenna in
the far (several wavelengths from the transmitter) field "receives" (or
favors) an E-field or an H-field is demonstrating a lack of
understanding of basic electromagnetic theory.

Now, consider two loops, one transmitting and one receiving. If the
receiving loop is in the near field of the radiating loop then it can be
magnetically coupled. In this instance the loop behaves more like a
mutually coupled inductor than an antenna. Perhaps this is where the
"magnetic" loop idea had its genesis. (Just like the immobilizer system
in your motor vehicle that has a loop embedded around the ignition
switch and which couples to the loop in the capsule inside your
transponder key.)

Textbooks on EM and antenna theory do talk about "magnetic" and
"electric" dipoles as theoretical constructs but that's another
discussion. Sincerely, and 73s from N4GGO,

Perhaps you can explain what the shield does on a receiving loop
antenna? Your explanation clearly says an antenna can be magnetic in
the near field. That is what the term means for receiving antennas. At
lower frequencies much interference is in the near field and is electric
rather than magnetic I am told. Think 100 kHz and household appliances.

The term "magnetic" is usually used in context of a transmitting antenna

--

Rick C

On 08/24/2016 01:12 PM, rickman wrote:


Perhaps you can explain what the shield does on a receiving loop
antenna? Your explanation clearly says an antenna can be magnetic in
the near field. That is what the term means for receiving antennas. At
lower frequencies much interference is in the near field and is electric
rather than magnetic I am told. Think 100 kHz and household appliances.

The term "magnetic" is usually used in context of a transmitting antenna


Hello, and before we get too far afield, I submit that well-respected
EM/Antenna theory textbooks (e.g. those by Jackson, Stratton,
Kraus,Jasik, Terman) don't use the term "magnetic loop antenna" just as
they don't use "electric dipole" antenna". EEs who design antennas
don't either. Hams seem to coin their own terms but not always for
valid theoretical reasons IMO. EM theory says if we make the area of a
single loop of conductor carrying uniform current very small then it can
be considered to function as a "magnetic dipole". But EM texts would
call this a small loop vice magnetic loop antenna. Likewise we consider
an "electric dipole" to be a straight conductor of very small length
(compared to a wavelength) carrying uniform current.

Finally, it's not my intent to imply one has to have an EE degree to
enjoy ham radio and build and experiment with various types of antennae.
Just like you don't have to understand all the nuances of fluid
dynamics to enjoy sailing or flying an airplane. Sincerely, and 73s
from N4GGO,

--
J. B. Wood e-mail:

Just to note that halo antennas were/are dipoles, not loop antennas.

https://en.wikipedia.org/wiki/Halo_antenna

In article ,
says...

Just to note that halo antennas were/are dipoles, not loop antennas.

https://en.wikipedia.org/wiki/Halo_antenna

Loop antennas are usually a full wavelength around, and the halos are
about a half wavelength like a dipole, just bent in a circle. As always
there can be several variations on this.


---
This email has been checked for viruses by Avast antivirus software.
https://www.avast.com/antivirus

J.B. Wood clip: " ... Anyone, ham or other, who claims that an antenna in
the far (several wavelengths from the transmitter) field "receives" (or
favors) an E-field or an H-field is demonstrating a lack of
understanding of basic electromagnetic theory. ..."
_____________

For far-field conditions, it is a given that the E field and the H field of an e-m wave are orthogonal to each other. Neither field can exist without the other.

A simple experiment will illustrate that a single antenna can favor one field but not other, even though that other field exists.

AM broadcast stations transmit using vertical polarization (polarization is defined as the physical orientation of the E-field vectors with respect to the horizontal plane). Vertical polarization maximizes their groundwave coverage areas.

A conventional AM broadcast band receiver (other than in an automobile) uses a loopstick antenna consisting of a close-wound loop of wire wound along a ferrite core. It responds to the H field of the arriving e-m wave, and for maximum r-f output it must be oriented in the horizontal plane -- even though that arriving wave is "vertically polarized."

Such a receiver can work very well when the axis of its loopstick lies in the horizontal plane, and normal to the direction of the arriving e-m wave. But when that receiver is vertically rotated 90° around the bearing to the transmit site so that the loopstick axis is vertical, reception is much poorer than before.

So the loopstick does not respond well to the E field, even though the E field is present at the receive site.

My experiment using a Tecsun PL-880 portable receiver had about s 30 dB reduction in the value of the signal strength shown on its front-panel display, when changing its loopstick orientation from horizontal to vertical.

Richard Fry, CPBE