As I understand it a shielded loop (non-magnetic shield) favors the
magnetic field. If I wanted to measure the difference between the 2 fields
how would I measure the electric field? A loop shielded with magnetic
material would probably reject both fields. The 3.5 foot loop for my old HP
comparator for WWVB is totally non-magnetic.
Can I generate and transmit each field separately? If so how would I do
it?
tnx

--

73
Hank WD5JFR

"Henry Kolesnik" wrote in message
...
As I understand it a shielded loop (non-magnetic shield) favors the
magnetic field.
Correct.

If I wanted to measure the difference between the 2 fields how would I
measure the electric field?
Any antennna can measure the electric field, you simply have to know the
antenna factor.
Antenna factors can be calculated for various structures; for example the
aperture of a half wave dipole is given by: 0.13*lambda^2. Simple
calculations can then provide the antenna factor, and relate the E field (in
V/m) to the received signal. The electric and magnetic fields are related
by a constant -- the impedance of free space, 377 ohms. i.e. E/H = 377.
In the vicinty of an antenna (the near field) the impedance of free space
becomes a complex number.

A loop shielded with magnetic material would probably reject both fields.
Probably true, but have never experimented with such antennas.

The 3.5 foot loop for my old HP comparator for WWVB is totally
non-magnetic.

Can I generate and transmit each field separately? If so how would I do
it?
No. The E field cannot exist without the H field. See the relationship
above. Some people claim to have invented antennas that seperately generate
E and H fields. Such antennas are known as "EH" and "Crossed-field", and
have largely been rejected by the engineering comunity as bogus. The
designers claim that they do not conform to Maxwell's Equations, but some
other indefinable mathematics.

Regards,

Frank

tnx

--

73
Hank WD5JFR

Frank
If I have two parallel plates seperated by an air space and the plates are
connect to a batttery I have a capacitor with an E field between the plates
and squeezing out the sides. In steady state there's no current flow so I
have no H field.
If I have a coil or a solenoid and connect it to a battery I have a current
flow with a strong H field but I'm not certainabout the E field.
Can this be taken to the next step to answer my original question?
tnx
--

73
Hank WD5JFR

"Frank" wrote in message
news:4Pyie.68625$tg1.4151@edtnps84...
"Henry Kolesnik" wrote in message
...
As I understand it a shielded loop (non-magnetic shield) favors the
magnetic field.
Correct.

If I wanted to measure the difference between the 2 fields how would I
measure the electric field?
Any antennna can measure the electric field, you simply have to know the
antenna factor.
Antenna factors can be calculated for various structures; for example the
aperture of a half wave dipole is given by: 0.13*lambda^2. Simple
calculations can then provide the antenna factor, and relate the E field
(in V/m) to the received signal. The electric and magnetic fields are
related by a constant -- the impedance of free space, 377 ohms. i.e. E/H
= 377. In the vicinty of an antenna (the near field) the impedance of free
space becomes a complex number.

A loop shielded with magnetic material would probably reject both fields.
Probably true, but have never experimented with such antennas.

The 3.5 foot loop for my old HP comparator for WWVB is totally
non-magnetic.

Can I generate and transmit each field separately? If so how would I do
it?
No. The E field cannot exist without the H field. See the relationship
above. Some people claim to have invented antennas that seperately
generate E and H fields. Such antennas are known as "EH" and
"Crossed-field", and have largely been rejected by the engineering
comunity as bogus. The designers claim that they do not conform to
Maxwell's Equations, but some other indefinable mathematics.

Regards,

Frank

tnx

--

73
Hank WD5JFR

Henry Kolesnik wrote:
"If I have a coil or solenoid and connect it to a battery I have a
current flow with a strong H field but I`m not certain about the E
field."

Resistance somewhere is limiting the current. The E field accompanies
the resistive voltage drop. Static fields don`t make waves. Only the
rate of change makes a disturbance which propagates in waves, E&M, which
generate each other.

Best regards, Richard Harrison, KB5WZI

Henry Kolesnik wrote:
"If I wanted to measure the difference between the two fields how would
I measure the electric field?"

If this is the radiation field, not the reactive field, it would make no
difference if you measured the electric field or the magnetic field, as
they contain the same quantity of energy. In fact, the energy is
identical as one field begets the other field. That`s "The Secret of
Propagation".

That does not mean the fieldfs can`t be separated. It is easy. Enclose
your loop in an effective Faraday screen. This screen prohibits
electrostatic coupling to the loop, but freely allows magnetic coupling.

Faraday screens are not rare. Nearly every medium wave broadcast station
uses a Faraday screen at every tower between the primary and secondary
of an air-core coupling transformer. Because, without the screen,
capacitive coupling to the tower would favor harmonics of the broadcast
frequency over its fundamental frequency and make compliance with FCC
rules difficult. The Faraday screen is also an excellent lightning
protector.

It`s just as easy to allow only capacitive coupling. Simply put a
circuit to be kept from magnetic coupling in an enclosure which is
completely enclosed in a metal structure (sealed like an expensive
signal generator except for one small hole). Use a capacitor through the
small hole to couple to the outside world. Only the electric field via
the capacitor will influence the circuit in the box.

R-F will not penetrate a metal shield, unless it`s special like the
sliced-up Faraday screen. Then, it`s only the magnetic field which
penetrates. Skin effect requires r-f to flow only on the surface of good
conductors to any appreciable depth.

Best regards, Richard Harrison, KB5WZI

Hank, and Richard, For a good explanation of this subject I always liked the
book: "Introduction to Electromagnetic Fields" by Paul and Nasar. The first
two chapters of mathematical review are excellent. I see barnesandnoble.com
has the 3rd edition, used, for as low as $66. John D. Kraus' book;
"Electromagnetics" is also a very good text.

73,

Frank

Isn't Kraus "Electromagnetics" a little heavy on the math for the
average Ham ??

Frank wrote:

Hank, and Richard, For a good explanation of this subject I always liked the
book: "Introduction to Electromagnetic Fields" by Paul and Nasar. The first
two chapters of mathematical review are excellent. I see barnesandnoble.com
has the 3rd edition, used, for as low as $66. John D. Kraus' book;
"Electromagnetics" is also a very good text.

73,

Frank

"Ham op" wrote in message
...
Isn't Kraus "Electromagnetics" a little heavy on the math for the average
Ham ??

I guess it depends on how interested they are. A good grounding in advanced
calculus is certainly a prequesit for either of those texts. Even
elementary calculus, combined with chapters 1 and 2, of Paul and Nasar,
should be sufficient.

73,

Frank


Frank wrote:

Hank, and Richard, For a good explanation of this subject I always liked
the book: "Introduction to Electromagnetic Fields" by Paul and Nasar.
The first two chapters of mathematical review are excellent. I see
barnesandnoble.com has the 3rd edition, used, for as low as $66. John D.
Kraus' book; "Electromagnetics" is also a very good text.

73,

Frank

Ham Op:

Yes, it is... mostly, people who are NOT gifted in explanations that the
"layman" can understand--gravitate to such extreme mathematics (and turn
them off, effectively silencing them).... let me give you my views...

.... it is somewhat obvious that when a wave sent forth from our antennas
encounters a metallic object that is close to resonate freq, and a very good
to EXCELLENT conductor, that a LARGE current flows in the metallic structure
encountered--what E and what H wave are then products are debatable (the
energy absorbed is re-radiated)--however--probably of a very different
nature than that of wave which encountered the metallic object in
question--and here is where this debate is ongoing... at an extreme is a
"tesla coil", ultimate voltage and virtually NO current (very minimal
current to generate the nice purple coronas)--yet an excellent transmitting
"antenna"--and that is ALL "E-wave." (well, mostly...)

Warmest regards,
John

"Ham op" wrote in message
...
Isn't Kraus "Electromagnetics" a little heavy on the math for the average
Ham ??

Frank wrote:

Hank, and Richard, For a good explanation of this subject I always liked
the book: "Introduction to Electromagnetic Fields" by Paul and Nasar.
The first two chapters of mathematical review are excellent. I see
barnesandnoble.com has the 3rd edition, used, for as low as $66. John D.
Kraus' book; "Electromagnetics" is also a very good text.

73,

Frank

"John Smith" wrote in message
...
Ham Op:

Yes, it is... mostly, people who are NOT gifted in explanations that the
"layman" can understand--gravitate to such extreme mathematics (and turn
them off, effectively silencing them).... let me give you my views...

I thought that my explanations were very non-mathematical, requiring only
minimal use of very simple calculations. My response was not complete as I
did not want to go overboard, but try to give very easy examples that could
be expanded on if any interest was shown. Perhaps you could be more
specific as to where I went wrong in my response. My mention of a couple of
textbooks was only to provide references for those interested in trying to
understand concepts in more detail. While it is true that some people are
capable of rigorous mathematical analysis, they cannot explain it in
non-mathematical terms. Those people, then, do not really understand their
subject. It is also true that such complex subjects cannot be fully
understood without in-depth math (Which is something I wish I had).
..
... it is somewhat obvious that when a wave sent forth from our antennas
encounters a metallic object that is close to resonate freq,

Not sure that resonance is important.
and a very good to EXCELLENT conductor, that a LARGE current flows in the
metallic structure encountered--

Current will flow in the surface.

what E and what H wave are then products are debatable (the energy
absorbed is re-radiated)--however--probably of a very different nature
than that of wave which encountered the metallic object in question--and
here is where this debate is ongoing...

If the conducting surface is perfect, no absorbtion takes place. The
reflected EM wave is planar, and identical to the incident plane wave --
with the exception of direction of propagation, and a phase reversal. A
(spatial) standing wave pattern is set up, and the analysis is identical to
that of a shorted transmission line.

at an extreme is a "tesla coil", ultimate voltage and virtually NO current
(very minimal current to generate the nice purple coronas)--yet an
excellent transmitting "antenna"--and that is ALL "E-wave." (well,
mostly...)

A Tesla coil is not an antenna, although some radiation will take place from
its conductors -- which will probably be damped sinusoidal pulses similar to
a spark transmitter. The radiation will not be all "E", but will have the
same E/H ratio of any radiated signal. i.e. E/H = 377 (ohms) in the far
field.

73,

Frank


Warmest regards,
John

"Ham op" wrote in message
...
Isn't Kraus "Electromagnetics" a little heavy on the math for the average
Ham ??

Frank wrote:

Hank, and Richard, For a good explanation of this subject I always liked
the book: "Introduction to Electromagnetic Fields" by Paul and Nasar.
The first two chapters of mathematical review are excellent. I see
barnesandnoble.com has the 3rd edition, used, for as low as $66. John
D. Kraus' book; "Electromagnetics" is also a very good text.

73,

Frank