On 10/24/2013 08:10 AM, W5DXP wrote:
On Thursday, October 24, 2013 5:54:05 AM UTC-5, J.B. Wood wrote:
So the above statements don't make sense.

I agree that the E/M ratio for far field signals in space is a constant. That doesn't prohibit a receiving antenna from creating its own unique near-field conditions and altering that ratio just as there is nothing prohibiting a load from altering the E/M ratio that exists in a transmission line. In fact, the E/M ratio must necessarily be altered at impedance discontinuities.

Example: Two different antennas are receiving the same signal and indicating the same signal level. As a human walks close to the two antennas, the received signal strength of one antenna changes radically while the received signal strength of the other is affected by only a small amount. If both antennas were *accepting* the same fixed far-field E/M ratio, a human body should have the same effect on both antennas but we can demonstrate that it doesn't.
--
73, Cecil, w5dxp.com


No

--
J. B. Wood e-mail:

On 10/24/2013 08:10 AM, W5DXP wrote:
On Thursday, October 24, 2013 5:54:05 AM UTC-5, J.B. Wood wrote:
So the above statements don't make sense.

I agree that the E/M ratio for far field signals in space is a
constant. That doesn't prohibit a receiving antenna from creating its
own unique near-field conditions and altering that ratio just as
there is nothing prohibiting a load from altering the E/M ratio that
exists in a transmission line. In fact, the E/M ratio must
necessarily be altered at impedance discontinuities.

Example: Two different antennas are receiving the same signal and
indicating the same signal level. As a human walks close to the two
antennas, the received signal strength of one antenna changes
radically while the received signal strength of the other is affected
by only a small amount. If both antennas were *accepting* the same
fixed far-field E/M ratio, a human body should have the same effect
on both antennas but we can demonstrate that it doesn't. -- 73,
Cecil, w5dxp.com


Don't have argument with the above, Cecil, but these phenomena appear to
be in addition to what I think was being discussed. Sincerely,
--
J. B. Wood e-mail:

On 10/24/2013 8:02 AM, J.B. Wood wrote:
On 10/24/2013 08:10 AM, W5DXP wrote:
On Thursday, October 24, 2013 5:54:05 AM UTC-5, J.B. Wood wrote:
So the above statements don't make sense.

I agree that the E/M ratio for far field signals in space is a
constant. That doesn't prohibit a receiving antenna from creating its
own unique near-field conditions and altering that ratio just as
there is nothing prohibiting a load from altering the E/M ratio that
exists in a transmission line. In fact, the E/M ratio must
necessarily be altered at impedance discontinuities.

Example: Two different antennas are receiving the same signal and
indicating the same signal level. As a human walks close to the two
antennas, the received signal strength of one antenna changes
radically while the received signal strength of the other is affected
by only a small amount. If both antennas were *accepting* the same
fixed far-field E/M ratio, a human body should have the same effect
on both antennas but we can demonstrate that it doesn't. -- 73,
Cecil, w5dxp.com


Don't have argument with the above, Cecil, but these phenomena appear to
be in addition to what I think was being discussed. Sincerely,

J.B. -

I have always understood EMF to be exactly as you have explained. I did
not know how to refute the misunderstanding by others on this topic.
Thanks for handling this discussion.

On Thursday, October 24, 2013 7:57:52 AM UTC-5, J.B. Wood wrote:
On 10/24/2013 08:10 AM, W5DXP wrote:
... a human body should have the same effect on both antennas but we can demonstrate that it doesn't.

No

I'm sorry, but that is a non-answer. Please explain, within what you have been asserting, how a human body can have a completely different effect on two antennas that receive identical EM waves.
--
73, Cecil, w5dxp.com

On 10/24/2013 02:15 PM, W5DXP wrote:
On Thursday, October 24, 2013 7:57:52 AM UTC-5, J.B. Wood wrote:
On 10/24/2013 08:10 AM, W5DXP wrote:
... a human body should have the same effect on both antennas but
we can demonstrate that it doesn't.

No

I'm sorry, but that is a non-answer. Please explain, within what you
have been asserting, how a human body can have a completely different
effect on two antennas that receive identical EM waves. -- 73, Cecil,
w5dxp.com

I would like to think this is an easy one: Say we have a receiving
antenna such as a loop that isn't operating in the presence of nearby
(close in coupling) objects such as metal, ferromagnetic cores, or human
skin. If we introduce these objects, we see that compared to operation
in their absence we have in general altered the antenna's gain, pattern
and feedpoint impedance. IOW, the nearby structures are now part of the
antenna.

Suppose we setup a dipole antenna and a loop antenna of appropriate
dimensions such that both are responding to the same E-M wave and
produce the same available receive power at their feedpoints. Just to
keep things simple, assume both antennas are low in resistive losses and
they are operating free of nearby objects of the type I mentioned.
Either antenna could produce the same power dissipated in an conjugately
matched load at its feedpoint.

If we now place objects near either antenna, anything goes, depending on
the objects and how they're oriented with respect to either the loop or
dipole.

None of this, however, can be used to assert that the E field is
favored/more responsive than the H field or vice-versa for a particular
antenna structure. Sincerely,

--
J. B. Wood e-mail:

On Thursday, October 24, 2013 2:15:11 PM UTC-5, J.B. Wood wrote:
None of this, however, can be used to assert that the E field is
favored/more responsive than the H field or vice-versa for a particular
antenna structure.

Next time you have an MRI, please try to convince the doctors that an ERI would work just as well.
--
73, Cecil, w5dxp.com

On 10/24/2013 10:07 PM, W5DXP wrote:
On Thursday, October 24, 2013 2:15:11 PM UTC-5, J.B. Wood wrote:
None of this, however, can be used to assert that the E field is
favored/more responsive than the H field or vice-versa for a particular
antenna structure.

Next time you have an MRI, please try to convince the doctors that an ERI would work just as well.
--
73, Cecil, w5dxp.com


I wouldn't view the huge MRI coil as a transmitting antenna insofar as
its intended usage. It's more akin to the primary of transformer with
the human body serving as the "secondary".

Cecil, I've done my best to point out the difference between a close-in
coupling (capacitive and/or inductive) situation and that involving two
(decoupled electrically but in the same medium) antennas separated by
many wavelengths. I can't think of anything else to say at this point.
Sincerely, and 73s from N4GGO,

--
J. B. Wood e-mail:

On Friday, October 25, 2013 5:32:34 AM UTC-5, J.B. Wood wrote:
I can't think of anything else to say at this point.

I don't know what the disagreement is. A small loop operates with a high magnetic field (high current) and a low electric field (low voltage) on both transmit and receive as required by the laws of physics. It seems reasonable to me to call it a "magnetic" loop. A small dipole operates with a high electric field (high voltage) and a low magnetic field (low current) on both transmit and receive as required by the laws of physics. It seems reasonable to me to call it an "electric" dipole.

I also cannot think of anything else to say. There was never any disagreement that all coherent far-field ExB photons are identical. The remaining question is: Given identical capture areas, why does a human body have such a large effect on an electric dipole and such a small effect on a magnetic loop?

I see the same thing with my indoor TV antenna. The VHF section is an electric dipole and I can affect VHF signal strength by walking between the transmitting station and the TV antenna. The UHF section is a magnetic loop and walking between the transmitting station and the TV antenna has very little effect on signal strength. My converter box has both an audible and visual signal strength indicator.
--
73, Cecil, w5dxp.com

In article W5DXP writes:
On Thursday, October 24, 2013 5:54:05 AM UTC-5, J.B. Wood wrote:
So the above statements don't make sense.

I agree that the E/M ratio for far field signals in space is a constant. Th=
at doesn't prohibit a receiving antenna from creating its own unique near-f=
ield conditions and altering that ratio just as there is nothing prohibitin=
g a load from altering the E/M ratio that exists in a transmission line. In=
fact, the E/M ratio must necessarily be altered at impedance discontinuiti=
es.


Example: Two different antennas are receiving the same signal and indicatin=
g the same signal level. As a human walks close to the two antennas, the re=
ceived signal strength of one antenna changes radically while the received =
signal strength of the other is affected by only a small amount. If both an=
tennas were *accepting* the same fixed far-field E/M ratio, a human body sh=
ould have the same effect on both antennas but we can demonstrate that it d=
oesn't.

Of course, if the antennas are accepting the signal from different directions,
they will be affected differently by people walking around them. My point is
that other factors could cause the antennas to have different results when
a person moves near them.

Alan
wa6azp