On 8/24/2016 9:29 AM, Richard Fry wrote:
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.

I do not agree that your explanation holds water at all. The loopstick
antenna will respond to a vertically polarized EM wave maximally when
horizontal. That says nothing about whether it is responding to the E
field or the H field.

To determine that you need to generate a calibrated E field without the
H field (or very low) and an H field with small E field (obviously only
possible in the near field) and compare the results.

Polarization is an entirely different matter.

--

Rick C

Rick C (rickman) clips:

I do not agree that your explanation holds water at all. The loopstick
antenna will respond to a vertically polarized EM wave maximally when
horizontal. That says nothing about whether it is responding to the E
field or the H field.

RESPONSE: Actually it does, because the maximum H field of a vertically-polarized, far-field, e-m wave always lies in the horizontal plane. So if the maximum r-f output of a loopstick receive antenna occurs when its axis lies in the horizontal plane, that output necessarily was produced by the H field.

To determine that you need to generate a calibrated E field without the
H field (or very low) and an H field with small E field (obviously only
possible in the near field) and compare the results.

RESPONSE: This was an assumption made by the developers of the E-H and Cross-field antennas --which was disproven in their field trials, as well as by theory. Neither the E field or the H field component of a far-field e-m wave can be produced or radiated independently. If one field exists, they both exist, and are related to the radiated power by the 377-ohm impedance of free space.

RF

On 8/24/2016 2:50 PM, Richard Fry wrote:
Rick C (rickman) clips:

I do not agree that your explanation holds water at all. The loopstick
antenna will respond to a vertically polarized EM wave maximally when
horizontal. That says nothing about whether it is responding to the E
field or the H field.

RESPONSE: Actually it does, because the maximum H field of a vertically-polarized, far-field, e-m wave always lies in the horizontal plane. So if the maximum r-f output of a loopstick receive antenna occurs when its axis lies in the horizontal plane, that output necessarily was produced by the H field.

The part you are missing is that you have no basis to assume the antenna
responds in any particular way to the E field or the H field. You
*assume* that a horizontal loop stick antenna is responding to the H
field because the ferrite is horizontal. How do you know which
orientation of the antenna makes it sensitive to which field?


To determine that you need to generate a calibrated E field without the
H field (or very low) and an H field with small E field (obviously only
possible in the near field) and compare the results.

RESPONSE: This was an assumption made by the developers of the E-H and Cross-field antennas --which was disproven in their field trials, as well as by theory. Neither the E field or the H field component of a far-field e-m wave can be produced or radiated independently. If one field exists, they both exist, and are related to the radiated power by the 377-ohm impedance of free space.

The E and H fields are always present in the far field. Not so in the
near field where one can dominate over the other.

You have a weird way of replying to a post.


--

Rick C

rickman: I've responded to you twice now with accurate information, but you haven't shown that you understood it. Suggest that you give the subject more thought and study using antenna engineering textbooks. Regards,

RF

On 8/24/2016 4:18 PM, Richard Fry wrote:
rickman: I've responded to you twice now with accurate information, but you haven't shown that you understood it. Suggest that you give the subject more thought and study using antenna engineering textbooks. Regards,

Dude, I get what you are saying, but you don't have a clear basis for
your statements. The results are clear... your reasoning is *not*.

--

Rick C

On 8/24/2016 3:18 PM, Richard Fry wrote:
rickman: I've responded to you twice now with accurate information,
but you haven't shown that you understood it. Suggest that you give
the subject more thought and study using antenna engineering
textbooks. Regards,

RF


Richard: I understood all you posted and found it accurate. rickman is a
troll. It does not matter what you post to him, he will argue with you.

J.B Wood clip: ... Likewise we consider an "electric dipole" to be a straight conductor of very small length (compared to a wavelength) carrying uniform current.
________

Just note that while the currents along the two sides of a dipole can be equal, they can never be uniform. Essentially no r-f current exists at the far ends of a dipole, no matter how short or long it is in terms of wavelengths.

On 08/25/2016 08:23 AM, Richard Fry wrote:
J.B Wood clip: ... Likewise we consider an "electric dipole" to be a
straight conductor of very small length (compared to a wavelength)
carrying uniform current. ________

Just note that while the currents along the two sides of a dipole can
be equal, they can never be uniform. Essentially no r-f current
exists at the far ends of a dipole, no matter how short or long it is
in terms of wavelengths.


It's a theoretical (textbook) construct but finds practical antenna
modeling use in method-of-moments software such as the Numerical
Electromagnetics Code (NEC). The idea is if we take smaller and smaller
sections (say about 1/20 wavelength) of a conductor carrying alternating
current we can consider the current to be uniform in that small
conductor. Of course an actual antenna would consist of a series of
these small conductors each carrying its respective value of uniform
current. Programs like NEC also consider, in addition to conducted
current the capacitive and inductive interactions between all the
segments comprising an antenna model.

Similarly we can build a transmission line using a number of identical
tee or pi sections connected ladder-fashion. The currents and voltages
associated with a section depend on its position along the length of the
line. Sincerely, and 73s from N4GGO,

--
J. B. Wood e-mail:

On 8/25/2016 10:54 AM, J.B. Wood wrote:
On 08/25/2016 08:23 AM, Richard Fry wrote:
J.B Wood clip: ... Likewise we consider an "electric dipole" to be a
straight conductor of very small length (compared to a wavelength)
carrying uniform current. ________

Just note that while the currents along the two sides of a dipole can
be equal, they can never be uniform. Essentially no r-f current
exists at the far ends of a dipole, no matter how short or long it is
in terms of wavelengths.


It's a theoretical (textbook) construct but finds practical antenna
modeling use in method-of-moments software such as the Numerical
Electromagnetics Code (NEC). The idea is if we take smaller and smaller
sections (say about 1/20 wavelength) of a conductor carrying alternating
current we can consider the current to be uniform in that small
conductor. Of course an actual antenna would consist of a series of
these small conductors each carrying its respective value of uniform
current. Programs like NEC also consider, in addition to conducted
current the capacitive and inductive interactions between all the
segments comprising an antenna model.

Similarly we can build a transmission line using a number of identical
tee or pi sections connected ladder-fashion. The currents and voltages
associated with a section depend on its position along the length of the
line. Sincerely, and 73s from N4GGO,


Richard is correct. The current at the feed point diminishes linearly
(on a short dipole) from the feed point to the open end of the antenna
as it must. Look at the current distribution using your NEC modelling
program.

On 08/25/2016 12:07 PM, John S wrote:
Richard is correct. The current at the feed point diminishes linearly
(on a short dipole) from the feed point to the open end of the antenna
as it must. Look at the current distribution using your NEC modelling
program.

No one said he wasn't. Did you read my last post? The uniform currents
in each segment aren't the same value. Of course the end segments would
be minimum. Sincerely,
--
J. B. Wood e-mail: