"Richard Harrison" wrote
The Faraday screen is common in radio stations. It was put there not to
affect the antenna match but only to eliminate capacitive coupling to
the antenna. It also serves as a path to earth for many antenna
lightning strikes as evidenced by numerous pits and metal hrom them
splashed about the enclosure.
______________

This must be a very dated observation. In my experience, and as confirmed
to me this morning by colleagues and consultants who design such networks,
MW broadcast Antenna Coupling Units commonly do not contain Faraday screens.

Lightning protection for most MW broadcast antenna systems is provided by
some combination of a small inductance in series with the tower feed (copper
tubing with a helical loop or two in it to connect the ACU output to the
tower feedpoint), an arc gap across the tower base to ground adjusted to
flash over at the lowest practical peak voltage, and a static drain choke
(path with high Z for RF, but low DC resistance to ground).

RF

Richard Hry wrote:
"---MW broadcast Antenna Coupling Units commonly do not contain Faraday
screens."

My observation is from a previous century. Faraday screens were used in
stations in which I worked.

My response was to the question: Can the E and H fields be separated?
Yes they can, and the Faraday screen is a way to eliminate coupling the
E field while coupling the H field. On the decoupled side of the shield,
induced magnetic lines immediately produce electric potential
differences and E fields. Little changes and nothing has been lost
except for capacitive coupling between circuits on opposite sides of the
Faraday screen. Breaks in the screen prevent circulating current which
would generate opposition to magnetic coupling. This is demonstrated as
effective since ancient times in electricity. Electric lines find a
ground return in the Faraday screen and go no further.

A shield without breaks allows current circulation which generates an
opposing force (Lenz`s law) and nullifies the induction. The continuous
conducting screen also provides a grounded termination for the electric
lines and blocks their passage too.

Capacitive coupling through a hole in a continuous shield can allow the
E field to be coupled while eliminating magnetic coupling.

This does not say there is any merit to the E/H Antenna, about wehich I
am ignorant.

Best regards, Richard Harrison, KB5WZI

"Richard Harrison" wrote
Richard Fry wrote:
"---MW broadcast Antenna Coupling Units commonly
do not contain Faraday screens."

My observation is from a previous century. Faraday screens were used in
stations in which I worked. My response was to the question: Can the
E and H fields be separated? Yes they can, (etc)
_____________

No dispute about the nature and effectiveness of Faraday screens where
appropriately used -- only about your statements that "Nearly every medium
wave broadcast station uses a Faraday screen," and as to the virtual
requirement that they MUST be used in MW ACUs to suppress harmonics to legal
levels and to prevent lightning damage. None of that is accurate.

RF

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

Excellent logic Richard, I applaud you....

Warmest regards,
John

"Richard Harrison" wrote in message
...
Richard Hry wrote:
"---MW broadcast Antenna Coupling Units commonly do not contain Faraday
screens."

My observation is from a previous century. Faraday screens were used in
stations in which I worked.

My response was to the question: Can the E and H fields be separated?
Yes they can, and the Faraday screen is a way to eliminate coupling the
E field while coupling the H field. On the decoupled side of the shield,
induced magnetic lines immediately produce electric potential
differences and E fields. Little changes and nothing has been lost
except for capacitive coupling between circuits on opposite sides of the
Faraday screen. Breaks in the screen prevent circulating current which
would generate opposition to magnetic coupling. This is demonstrated as
effective since ancient times in electricity. Electric lines find a
ground return in the Faraday screen and go no further.

A shield without breaks allows current circulation which generates an
opposing force (Lenz`s law) and nullifies the induction. The continuous
conducting screen also provides a grounded termination for the electric
lines and blocks their passage too.

Capacitive coupling through a hole in a continuous shield can allow the
E field to be coupled while eliminating magnetic coupling.

This does not say there is any merit to the E/H Antenna, about wehich I
am ignorant.

Best regards, Richard Harrison, KB5WZI

"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

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

Just checked http://home.wtal.de/herbs_teslapage/theory.html The Tesla coil
is a spark transmitter without an antenna connected.

Frank

Shield the coil, the coronas effect is still as powerful on florescents,
vtvms detecting voltage... that voltage may well be inducing a magnetic
field as it is conducted by air/ether/ground... but it looks to me like the
voltage is the main force... rfi will tear up a neighborhood too...

Warmest regards,
John

"Frank" wrote in message
news:GVbje.7002$wr.3522@clgrps12...

"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

"John Smith" wrote in message
...
Shield the coil, the coronas effect is still as powerful on florescents,
vtvms detecting voltage... that voltage may well be inducing a magnetic
field as it is conducted by air/ether/ground... but it looks to me like
the voltage is the main force... rfi will tear up a neighborhood too...

Warmest regards,
John

Since I have never had experience with a Tesla coil, this is all relatively
new to me. After a little research I found the following information,
which may be of interest.

The Tesla coil design reference at
http://home.wtal.de/herbs_teslapage/design.html provides an Excel spread
sheet showing all the appropriate parameters. The spread sheet example
shows a single gap spark transmitter, of input power 375 W at a frequency of
322 kHz. Since the wavelength is relatively long, at 932 m, the near
field/far field transition is very close to the radiating structure, which
will include the conductive arc plasma.

Near field/far field transition is approximated as (2D^2)/lambda, where D is
the largest dimension of the radiating structure, and lambda is the
wavelength.

The observable effects you mention are therefore most likely due to far
field effects. The E/H ratio is still a constant at 377 ohms. From the
above formula you can see that you would have to be very close to the souce
for any inductive or capacative coupling to occur.

Having heard of Tesla coils I never realized they were only simple spark gap
transmitters.

73,

Frank

First tesla coils I ever made were spark gaps using a 15,000 volt neon sign
transformer, large caps out of aluminum foil, xfrmr oil and polyethylene
sheeting... later on friends and I built units around 50Khz-150Khz which
used push-pull circuits to drive the primary coil of the tesla (no noise
from the spark gap which is almost deafening!)--I think the first used 811
(825's?) tubes from old gov't surplus equip (I remember the tubes were about
the size of coke bottles)....

Warmest regards,
John

"Frank" wrote in message
news:EWkje.7026$wr.338@clgrps12...

"John Smith" wrote in message
...
Shield the coil, the coronas effect is still as powerful on florescents,
vtvms detecting voltage... that voltage may well be inducing a magnetic
field as it is conducted by air/ether/ground... but it looks to me like
the voltage is the main force... rfi will tear up a neighborhood too...

Warmest regards,
John

Since I have never had experience with a Tesla coil, this is all
relatively new to me. After a little research I found the following
information, which may be of interest.

The Tesla coil design reference at
http://home.wtal.de/herbs_teslapage/design.html provides an Excel spread
sheet showing all the appropriate parameters. The spread sheet example
shows a single gap spark transmitter, of input power 375 W at a frequency
of 322 kHz. Since the wavelength is relatively long, at 932 m, the near
field/far field transition is very close to the radiating structure, which
will include the conductive arc plasma.

Near field/far field transition is approximated as (2D^2)/lambda, where D
is the largest dimension of the radiating structure, and lambda is the
wavelength.

The observable effects you mention are therefore most likely due to far
field effects. The E/H ratio is still a constant at 377 ohms. From the
above formula you can see that you would have to be very close to the
souce for any inductive or capacative coupling to occur.

Having heard of Tesla coils I never realized they were only simple spark
gap transmitters.

73,

Frank