Ed Price wrote:

"Robert Baer" wrote in message
...
Ed Price wrote:

"Watson A.Name - "Watt Sun, the Dark Remover""
wrote
in message ...

"Some Guy" wrote in message
...
What a load of horse ****.

You guys are acting as if the engines and flight control surfaces of
an aircraft are intimately tied to the plane's radio receiver, and the
slightest odd or out-of-place signal that it receives is enough to
send any plane into a tail spin.

No, the laws say that you can be arrested for breaking them, and one
way
to break them is to use a FM radio while the aircraft is flying.

All this while the air travel industry is considering allowing
passengers to use their own cell phones WHILE THE PLANES ARE IN FLIGHT
by adding cell-phone relay stations to the planes and allowing any
such calls to be completed via satellite. So I guess the feeble
radiation by my FM radio (powered by 2 AAA batteries) is enough to
cause a plane to dive into the ocean, but the guy next to me putting
out 3 watts of near-microwave energy is totally safe.

You don't know what you're talking about. With the attitudes of the
air
marshals nowadays, making airliners turn around and go back to their
departure point just because a passenger is unruly, there is a high
probability that one of them is flying along on your flight, and if he
sees an earphone hanging out of your ear, you might be that unruly
passenger they arrest at the departure point. Especially with your
nasty attitude!

What about my hand-held GPS unit? Any chance me using it (during all
phases of a flight, which I do routinely) will result in a one-way
ticket to kingdom come?

Geez, what a TWERP! You can't add two and two without jumping to
conclusions! A rational conversation with you is nearly impossible.

Getting back to the original question (poor to non-existant AM
reception), I understand the idea of aperature and long wavelenths of
AM radio and the size of airplane windows - but what about the effect
of ALL the windows on a plane? Don't they create a much larger
effective apperature when you consider all of them? And since the
plane isin't grounded, isin't the exterior shell of a plane
essentially transparent to all RF (ie it's just a re-radiator) because
it's not at ground potential?

You're even dumber than I had thought. Look up Faraday Shield.
Here, try this: http://www.physlink.com/Education/AskExperts/ae176.cfm
You don't have to worry about a ground for it to work. Duh.


He's not dumber than "I" thought!

Ed
wb6wsn

"Faraday shield" to some degree is a myth.
I have seen radars inside quonset huts track a *bird* flying a few
miles away (thru the metal wall)!

You must have some strange buddies. Who in the world would set up a radar
within a metal hut? And even if they did, who would think it's a good idea
to stay inside with it if it were on?

There's nothing mythical about the Faraday shield; it works really well, so
long as there are no discontinuities (apertures) and sufficient thickness
and conductivity. Under real-world conditions, steel works pretty good, and
any thickness sufficient to support itself will yield great shielding
effectiveness. So the only real performance variable left is the holes in
the conductive surface. How many, maximum dimension, proximity of radiating
source to the shield, etc.

While I would expect a Quonset hut to really mess up the accuracy of a
radar, it likely wouldn't be a good shield, as the floor isn't metal, I
don't think the ends are metal, and the various skin panels are rather
poorly RF bonded.

Ed
wb6wsn


I do not think your objections concerning the floor or the bonding of
the panels are too relevant.
The ends are metal and not relevant either.
The radar was pointing right at the wall (no windows nearby); any
presumed leakage via remote holes that you assumed might allow the
transmitted signal to leak, but would then not be focused on the bird(s)
and the path lengths would vary.
But the reflected signal from the bird or birds would be rather weak
and could not possibly be received via the same wild path(s) to a very
directional antenna.

My point is that a Farady shield is a good attenuator, but not
"perfect" as ASSuMEd.
And it sure is not "flat" in attenuation characteristic as a function
of frequency.

"Watson A.Name - \"Watt Sun, the Dark Remover\"" wrote:

"Robert Baer" wrote in message
...
Ed Price wrote:

"Watson A.Name - "Watt Sun, the Dark Remover""
wrote
in message ...

"Some Guy" wrote in message
...
What a load of horse ****.

You guys are acting as if the engines and flight control surfaces
of
an aircraft are intimately tied to the plane's radio receiver,
and the
slightest odd or out-of-place signal that it receives is enough
to
send any plane into a tail spin.

No, the laws say that you can be arrested for breaking them, and
one way
to break them is to use a FM radio while the aircraft is flying.

All this while the air travel industry is considering allowing
passengers to use their own cell phones WHILE THE PLANES ARE IN
FLIGHT
by adding cell-phone relay stations to the planes and allowing
any
such calls to be completed via satellite. So I guess the feeble
radiation by my FM radio (powered by 2 AAA batteries) is enough
to
cause a plane to dive into the ocean, but the guy next to me
putting
out 3 watts of near-microwave energy is totally safe.

You don't know what you're talking about. With the attitudes of
the air
marshals nowadays, making airliners turn around and go back to
their
departure point just because a passenger is unruly, there is a
high
probability that one of them is flying along on your flight, and
if he
sees an earphone hanging out of your ear, you might be that unruly
passenger they arrest at the departure point. Especially with
your
nasty attitude!

What about my hand-held GPS unit? Any chance me using it (during
all
phases of a flight, which I do routinely) will result in a
one-way
ticket to kingdom come?

Geez, what a TWERP! You can't add two and two without jumping to
conclusions! A rational conversation with you is nearly
impossible.

Getting back to the original question (poor to non-existant AM
reception), I understand the idea of aperature and long
wavelenths of
AM radio and the size of airplane windows - but what about the
effect
of ALL the windows on a plane? Don't they create a much larger
effective apperature when you consider all of them? And since
the
plane isin't grounded, isin't the exterior shell of a plane
essentially transparent to all RF (ie it's just a re-radiator)
because
it's not at ground potential?

You're even dumber than I had thought. Look up Faraday Shield.
Here, try this:
http://www.physlink.com/Education/AskExperts/ae176.cfm
You don't have to worry about a ground for it to work. Duh.


He's not dumber than "I" thought!

Ed
wb6wsn

"Faraday shield" to some degree is a myth.

You use weasel words like 'to some degree' to avoid talking about the
truth. Radio waves don't go thru a sheet of metal.

I have seen radars inside quonset huts track a *bird* flying a few
miles away (thru the metal wall)!

No, not thru a metal wall. I saw the radar go thru the wooden walls of
the bldg when I was in radar repair school in the army. But that was
wood. Your so-called metal quonset hut was probably wood or fiberglass.

If you saw anything, it was probably your own reflection off the metal
walls, IF it didn't fry you like a porkchop in a microwave oven!

Nope; it was a metal quonset hut; Army Signal Corps Fort Huachuca
AridZona.

"Robert Baer" wrote in message
...
Ed Price wrote:

"Robert Baer" wrote in message
...
Ed Price wrote:

"Watson A.Name - "Watt Sun, the Dark Remover""
wrote
in message ...

"Some Guy" wrote in message
...
What a load of horse ****.

You guys are acting as if the engines and flight control surfaces
of
an aircraft are intimately tied to the plane's radio receiver, and
the
slightest odd or out-of-place signal that it receives is enough to
send any plane into a tail spin.

No, the laws say that you can be arrested for breaking them, and one
way
to break them is to use a FM radio while the aircraft is flying.

All this while the air travel industry is considering allowing
passengers to use their own cell phones WHILE THE PLANES ARE IN
FLIGHT
by adding cell-phone relay stations to the planes and allowing any
such calls to be completed via satellite. So I guess the feeble
radiation by my FM radio (powered by 2 AAA batteries) is enough to
cause a plane to dive into the ocean, but the guy next to me
putting
out 3 watts of near-microwave energy is totally safe.

You don't know what you're talking about. With the attitudes of the
air
marshals nowadays, making airliners turn around and go back to their
departure point just because a passenger is unruly, there is a high
probability that one of them is flying along on your flight, and if
he
sees an earphone hanging out of your ear, you might be that unruly
passenger they arrest at the departure point. Especially with your
nasty attitude!

What about my hand-held GPS unit? Any chance me using it (during
all
phases of a flight, which I do routinely) will result in a one-way
ticket to kingdom come?

Geez, what a TWERP! You can't add two and two without jumping to
conclusions! A rational conversation with you is nearly impossible.

Getting back to the original question (poor to non-existant AM
reception), I understand the idea of aperature and long wavelenths
of
AM radio and the size of airplane windows - but what about the
effect
of ALL the windows on a plane? Don't they create a much larger
effective apperature when you consider all of them? And since the
plane isin't grounded, isin't the exterior shell of a plane
essentially transparent to all RF (ie it's just a re-radiator)
because
it's not at ground potential?

You're even dumber than I had thought. Look up Faraday Shield.
Here, try this:
http://www.physlink.com/Education/AskExperts/ae176.cfm
You don't have to worry about a ground for it to work. Duh.


He's not dumber than "I" thought!

Ed
wb6wsn

"Faraday shield" to some degree is a myth.
I have seen radars inside quonset huts track a *bird* flying a few
miles away (thru the metal wall)!

You must have some strange buddies. Who in the world would set up a radar
within a metal hut? And even if they did, who would think it's a good
idea
to stay inside with it if it were on?

There's nothing mythical about the Faraday shield; it works really well,
so
long as there are no discontinuities (apertures) and sufficient thickness
and conductivity. Under real-world conditions, steel works pretty good,
and
any thickness sufficient to support itself will yield great shielding
effectiveness. So the only real performance variable left is the holes in
the conductive surface. How many, maximum dimension, proximity of
radiating
source to the shield, etc.

While I would expect a Quonset hut to really mess up the accuracy of a
radar, it likely wouldn't be a good shield, as the floor isn't metal, I
don't think the ends are metal, and the various skin panels are rather
poorly RF bonded.

Ed
wb6wsn


I do not think your objections concerning the floor or the bonding of
the panels are too relevant.
The ends are metal and not relevant either.
The radar was pointing right at the wall (no windows nearby); any
presumed leakage via remote holes that you assumed might allow the
transmitted signal to leak, but would then not be focused on the bird(s)
and the path lengths would vary.
But the reflected signal from the bird or birds would be rather weak
and could not possibly be received via the same wild path(s) to a very
directional antenna.

My point is that a Farady shield is a good attenuator, but not
"perfect" as ASSuMEd.
And it sure is not "flat" in attenuation characteristic as a function
of frequency.


Those weren't objections, they were speculations on my part as to how you
boys could have been finessing the generally applicable laws of physics.

But truly, the story stinks. So you and your army buddies are in this metal
hut, with a fairly high-power radar, and somebody comes up with the bright
idea to turn the thing on. Apparently no thought about RF personnel hazards
and no concern about strong reflections cooking your detector. Did you test
your M16's in a Quonset hut too?

Next point. "The radar was pointing right at the wall..." Now tell me, in a
semi-circular Quonset hut, how do you point anything "right at the wall"?
Maybe straight up?

Now, a bird doesn't have a very big radar cross section, maybe only about
0.01 square meters, so the return loss is really big. And to resolve a
single bird, I'm gonna guess that you had an X or K band radar. So let's run
some numbers. Let's say you had a 100kW radar, with a 30 dBi antenna of 1
square meter aperture. At 1500 meters, your detector power would be about 1
picowatt, or -60 dBm. Well hey, that's pretty decent, I'll bet you could see
a bird at one mile.

But that's assuming no loss at all due to the metal hut skin. Let's see what
happens if we say that the metal hut walls give us only 40 dB of shielding
(by absorption or reflection, it doesn't matter). That bites 80 dB out of
your path budget, putting your detector signal down to -140 dBm. I think
your story just ran out of luck.

Now you can argue about the 40 dB shielding effectiveness of the metal wall,
but I'll say that I was being very generous about that. At 10 GHz, I know
(How? Easy, I do it everyday. Just 3 days ago, I was keeping some 1.3 GHz
from radiating off of some cables, and it was common old Reynolds Wrap to
the rescue.), I can get 100 dB out of a sheet of aluminum foil. The SE is
so damn high from the material that the only significant factor is when the
energy finds a path around the shield.

Don't try to argue that a Faraday cage leaks; you appear to be trying to
build a general case based on your experience of always having observed
leaky structures. Sure, I know that shielding varies with lots of factors,
conductivity, permeability, thickness, frequency, angle of incidence,
distance from source, and then there's the problem of apertures. But your
hut, with plain old galvanized steel about 1/16" thick, would make a great
shielded enclosure, as long as the joints didn't leak.

BTW, I don't like using the term "Faraday cage". Despite all due respect to
Mr. Faraday, calling it a shielded enclosure is a clearer description.

Ed
wb6wsn

Robert Baer wrote:
"So the only real performance variable left is the holes in the
conductive surface."

A plane window, like the fuselage itself, acts as apipe below cutoff
frequency. Minimum size for low attenuation is 1/2-wavelength.

The thicker the window frame, the longer the waveguide and the greater
the attenuation at frequencies below cutoff. See page 277 of
"Transmission Lines, Antennas, and Wave Guides" by King, Mimno, and Wing
to quantify the attenuation. It`s big below cutoff.

Best regards, Richard Harrison, KB5WZI

Ed Price wrote:

"Robert Baer" wrote in message
...
Ed Price wrote:

"Robert Baer" wrote in message
...
Ed Price wrote:

"Watson A.Name - "Watt Sun, the Dark Remover""
wrote
in message ...

"Some Guy" wrote in message
...
What a load of horse ****.

You guys are acting as if the engines and flight control surfaces
of
an aircraft are intimately tied to the plane's radio receiver, and
the
slightest odd or out-of-place signal that it receives is enough to
send any plane into a tail spin.

No, the laws say that you can be arrested for breaking them, and one
way
to break them is to use a FM radio while the aircraft is flying.

All this while the air travel industry is considering allowing
passengers to use their own cell phones WHILE THE PLANES ARE IN
FLIGHT
by adding cell-phone relay stations to the planes and allowing any
such calls to be completed via satellite. So I guess the feeble
radiation by my FM radio (powered by 2 AAA batteries) is enough to
cause a plane to dive into the ocean, but the guy next to me
putting
out 3 watts of near-microwave energy is totally safe.

You don't know what you're talking about. With the attitudes of the
air
marshals nowadays, making airliners turn around and go back to their
departure point just because a passenger is unruly, there is a high
probability that one of them is flying along on your flight, and if
he
sees an earphone hanging out of your ear, you might be that unruly
passenger they arrest at the departure point. Especially with your
nasty attitude!

What about my hand-held GPS unit? Any chance me using it (during
all
phases of a flight, which I do routinely) will result in a one-way
ticket to kingdom come?

Geez, what a TWERP! You can't add two and two without jumping to
conclusions! A rational conversation with you is nearly impossible.

Getting back to the original question (poor to non-existant AM
reception), I understand the idea of aperature and long wavelenths
of
AM radio and the size of airplane windows - but what about the
effect
of ALL the windows on a plane? Don't they create a much larger
effective apperature when you consider all of them? And since the
plane isin't grounded, isin't the exterior shell of a plane
essentially transparent to all RF (ie it's just a re-radiator)
because
it's not at ground potential?

You're even dumber than I had thought. Look up Faraday Shield.
Here, try this:
http://www.physlink.com/Education/AskExperts/ae176.cfm
You don't have to worry about a ground for it to work. Duh.


He's not dumber than "I" thought!

Ed
wb6wsn

"Faraday shield" to some degree is a myth.
I have seen radars inside quonset huts track a *bird* flying a few
miles away (thru the metal wall)!

You must have some strange buddies. Who in the world would set up a radar
within a metal hut? And even if they did, who would think it's a good
idea
to stay inside with it if it were on?

There's nothing mythical about the Faraday shield; it works really well,
so
long as there are no discontinuities (apertures) and sufficient thickness
and conductivity. Under real-world conditions, steel works pretty good,
and
any thickness sufficient to support itself will yield great shielding
effectiveness. So the only real performance variable left is the holes in
the conductive surface. How many, maximum dimension, proximity of
radiating
source to the shield, etc.

While I would expect a Quonset hut to really mess up the accuracy of a
radar, it likely wouldn't be a good shield, as the floor isn't metal, I
don't think the ends are metal, and the various skin panels are rather
poorly RF bonded.

Ed
wb6wsn


I do not think your objections concerning the floor or the bonding of
the panels are too relevant.
The ends are metal and not relevant either.
The radar was pointing right at the wall (no windows nearby); any
presumed leakage via remote holes that you assumed might allow the
transmitted signal to leak, but would then not be focused on the bird(s)
and the path lengths would vary.
But the reflected signal from the bird or birds would be rather weak
and could not possibly be received via the same wild path(s) to a very
directional antenna.

My point is that a Farady shield is a good attenuator, but not
"perfect" as ASSuMEd.
And it sure is not "flat" in attenuation characteristic as a function
of frequency.

Those weren't objections, they were speculations on my part as to how you
boys could have been finessing the generally applicable laws of physics.

But truly, the story stinks. So you and your army buddies are in this metal
hut, with a fairly high-power radar, and somebody comes up with the bright
idea to turn the thing on. Apparently no thought about RF personnel hazards
and no concern about strong reflections cooking your detector. Did you test
your M16's in a Quonset hut too?

Next point. "The radar was pointing right at the wall..." Now tell me, in a
semi-circular Quonset hut, how do you point anything "right at the wall"?
Maybe straight up?

Now, a bird doesn't have a very big radar cross section, maybe only about
0.01 square meters, so the return loss is really big. And to resolve a
single bird, I'm gonna guess that you had an X or K band radar. So let's run
some numbers. Let's say you had a 100kW radar, with a 30 dBi antenna of 1
square meter aperture. At 1500 meters, your detector power would be about 1
picowatt, or -60 dBm. Well hey, that's pretty decent, I'll bet you could see
a bird at one mile.

But that's assuming no loss at all due to the metal hut skin. Let's see what
happens if we say that the metal hut walls give us only 40 dB of shielding
(by absorption or reflection, it doesn't matter). That bites 80 dB out of
your path budget, putting your detector signal down to -140 dBm. I think
your story just ran out of luck.

Now you can argue about the 40 dB shielding effectiveness of the metal wall,
but I'll say that I was being very generous about that. At 10 GHz, I know
(How? Easy, I do it everyday. Just 3 days ago, I was keeping some 1.3 GHz
from radiating off of some cables, and it was common old Reynolds Wrap to
the rescue.), I can get 100 dB out of a sheet of aluminum foil. The SE is
so damn high from the material that the only significant factor is when the
energy finds a path around the shield.

Don't try to argue that a Faraday cage leaks; you appear to be trying to
build a general case based on your experience of always having observed
leaky structures. Sure, I know that shielding varies with lots of factors,
conductivity, permeability, thickness, frequency, angle of incidence,
distance from source, and then there's the problem of apertures. But your
hut, with plain old galvanized steel about 1/16" thick, would make a great
shielded enclosure, as long as the joints didn't leak.

BTW, I don't like using the term "Faraday cage". Despite all due respect to
Mr. Faraday, calling it a shielded enclosure is a clearer description.

Ed
wb6wsn

I was not alluding to leakage; a more accurate term would be
re-radiation.
Take an ordinary transformer; it radiates a magnetic field, despite
the fact that the core is a closed loop.
In fact, one could get nasty and say the same thing about a toroid
transformer.
Now add a shorted copper turn around the outside of the ordinary
transformer's core (i have seen this on many TV power transformers and
others as well).
What happens? That magnetic field induces a current in that shorted
turn, making an opposing magnetic field - thereby reducing the net
radiated magnetic field greatly - but not to zero.
Now, instead of using that closely wrapped copper shoted turn, put
that transformer inside that shielded room you love.
Results: great reduction, but not to zero.
Increase the frequency to something one might consider RF.
Now one has an RF transmitter inside that shielded room, inducing
currents in the wall(s).
Those currents create opposing fields, and greatly attenuate the
signal outside the walls.
But they are not zero.
BW, radar is usually pulsed, and in the megawatt to multi-megawatt
region for the pulse.
Also, the quonset huts i saw had relatively vertical walls; the
rounded curvature was more so near the top.
And it might help to ask the bird(s); they even dislike those pesky
jets getting in their way.

FAR more likely that the antenna for the radar was outside the hut.
There may have been one slaved to it, inactive, inside the hut to
demonstrate what's going on upstairs.

There are plenty of good reasons why such a demo wouldn't work as described,
from killing the detector with strong reflections, to massive
re-re-reflections inside the building, to the fact that radar relies on a
"pencil" beam that wouldn't survive through those walls in any rational way,
and so on.

"Robert Baer" wrote in message
...


SNIP

"Faraday shield" to some degree is a myth.
I have seen radars inside quonset huts track a *bird* flying a few
miles away (thru the metal wall)!

You must have some strange buddies. Who in the world would set up a
radar
within a metal hut? And even if they did, who would think it's a good
idea
to stay inside with it if it were on?

There's nothing mythical about the Faraday shield; it works really
well,
so
long as there are no discontinuities (apertures) and sufficient
thickness
and conductivity. Under real-world conditions, steel works pretty
good,
and
any thickness sufficient to support itself will yield great shielding
effectiveness. So the only real performance variable left is the holes
in
the conductive surface. How many, maximum dimension, proximity of
radiating
source to the shield, etc.

While I would expect a Quonset hut to really mess up the accuracy of a
radar, it likely wouldn't be a good shield, as the floor isn't metal,
I
don't think the ends are metal, and the various skin panels are rather
poorly RF bonded.

Ed
wb6wsn


I do not think your objections concerning the floor or the bonding of
the panels are too relevant.
The ends are metal and not relevant either.
The radar was pointing right at the wall (no windows nearby); any
presumed leakage via remote holes that you assumed might allow the
transmitted signal to leak, but would then not be focused on the
bird(s)
and the path lengths would vary.
But the reflected signal from the bird or birds would be rather weak
and could not possibly be received via the same wild path(s) to a very
directional antenna.

My point is that a Farady shield is a good attenuator, but not
"perfect" as ASSuMEd.
And it sure is not "flat" in attenuation characteristic as a function
of frequency.

Those weren't objections, they were speculations on my part as to how you
boys could have been finessing the generally applicable laws of physics.

But truly, the story stinks. So you and your army buddies are in this
metal
hut, with a fairly high-power radar, and somebody comes up with the
bright
idea to turn the thing on. Apparently no thought about RF personnel
hazards
and no concern about strong reflections cooking your detector. Did you
test
your M16's in a Quonset hut too?

Next point. "The radar was pointing right at the wall..." Now tell me, in
a
semi-circular Quonset hut, how do you point anything "right at the wall"?
Maybe straight up?

Now, a bird doesn't have a very big radar cross section, maybe only about
0.01 square meters, so the return loss is really big. And to resolve a
single bird, I'm gonna guess that you had an X or K band radar. So let's
run
some numbers. Let's say you had a 100kW radar, with a 30 dBi antenna of 1
square meter aperture. At 1500 meters, your detector power would be about
1
picowatt, or -60 dBm. Well hey, that's pretty decent, I'll bet you could
see
a bird at one mile.

But that's assuming no loss at all due to the metal hut skin. Let's see
what
happens if we say that the metal hut walls give us only 40 dB of
shielding
(by absorption or reflection, it doesn't matter). That bites 80 dB out of
your path budget, putting your detector signal down to -140 dBm. I think
your story just ran out of luck.

Now you can argue about the 40 dB shielding effectiveness of the metal
wall,
but I'll say that I was being very generous about that. At 10 GHz, I know
(How? Easy, I do it everyday. Just 3 days ago, I was keeping some 1.3 GHz
from radiating off of some cables, and it was common old Reynolds Wrap to
the rescue.), I can get 100 dB out of a sheet of aluminum foil. The SE
is
so damn high from the material that the only significant factor is when
the
energy finds a path around the shield.

Don't try to argue that a Faraday cage leaks; you appear to be trying to
build a general case based on your experience of always having observed
leaky structures. Sure, I know that shielding varies with lots of
factors,
conductivity, permeability, thickness, frequency, angle of incidence,
distance from source, and then there's the problem of apertures. But your
hut, with plain old galvanized steel about 1/16" thick, would make a
great
shielded enclosure, as long as the joints didn't leak.

BTW, I don't like using the term "Faraday cage". Despite all due respect
to
Mr. Faraday, calling it a shielded enclosure is a clearer description.

Ed
wb6wsn

I was not alluding to leakage; a more accurate term would be
re-radiation.
Take an ordinary transformer; it radiates a magnetic field, despite
the fact that the core is a closed loop.
In fact, one could get nasty and say the same thing about a toroid
transformer.
Now add a shorted copper turn around the outside of the ordinary
transformer's core (i have seen this on many TV power transformers and
others as well).
What happens? That magnetic field induces a current in that shorted
turn, making an opposing magnetic field - thereby reducing the net
radiated magnetic field greatly - but not to zero.
Now, instead of using that closely wrapped copper shoted turn, put
that transformer inside that shielded room you love.


My shielded enclosure only asks that I respect it; I don't think it would
provide better SE even if I told it that I loved it.


Results: great reduction, but not to zero.


Nothing ever goes to zero; I'll usually settle for "great" reductions.


Increase the frequency to something one might consider RF.
Now one has an RF transmitter inside that shielded room, inducing
currents in the wall(s).
Those currents create opposing fields, and greatly attenuate the
signal outside the walls.


You're getting a little fuzzy here. The propagating wave induces surface
currents on the metal barrier. The currents "sink" into the metal,
decreasing to about 37% (1/e) in what's called a "skin depth". At 10 GHz, a
"skin depth" in steel is really thin. After even 10 skin depths, the current
is down to only about 1/100,000 of what was on the surface. And there's a
whole lot of more skin depths to go before the current is presented to the
far surface of the steel barrier. And only then does the surface current on
the far side of the barrier get to launch a propagating wave.

Note that the "opposing fields" you mentioned are on the INSIDE, the near
surface, of the barrier. The reflected field is 180 degrees out of phase
with the incident field, so, real close to the metal surface, the E-field
nulls. OTOH, that reflected wave now goes marching back at you, creating
lots of fun with out-of-phase energy pumped back into the original radiating
element. Everybody sees bad, bad VSWR. And, since you guys were inside a
metal hut, there's even more fun in store for you. Not all that energy goes
back into the originating antenna. A lot of it just keeps bouncing around
inside the hut, creating 3-D variations in power density. Think of yourself
as a potato, slowly cooking.

So, to keep this straight, the current that survives Ohmic losses to make it
to the far side of the barrier doesn't "greatly attenuate the signal outside
the walls". It actually creates the signal (the propagating wave) on the far
side of the barrier.

We can talk about aperture leakage and re-radiation from barrier impedance
discontinuities some other time.


But they are not zero.
BW, radar is usually pulsed, and in the megawatt to multi-megawatt
region for the pulse.


Multi-megawatt? Hmm, 10 MW? OK, and maybe a duty cycle of 0.01%? Isn't that
1 kW average? I own a 250 kW X-band radar that will do up to 0.1% duty
cycle. I sure wouldn't sit in a metal box with that thing running! I
wouldn't even want to be in the boresight of the antenna within a few
hundred feet. I was trying to be charitable in assuming that nobody would be
so dumb as to fire up a multi-megawatt radar INSIDE a metal hut. Looks like
you guys proved me wrong!

Ed
wb6wsn


Ed
wb6wsn

What's with all the recipe bull**** posts?

Who's posting these?

Ed Price wrote:

oil.
Add a little water, season, then add the carcass.
Simmer for half an hour keeping the stock thick.
Remove the carcass and add the vegetables slowly to the stock,
so that it remains boiling the whole time.
Cover the pot and simmer till vegetables are tender
(2 hours approximately).
Continue seasoning to taste.
Before serving, add butter and pasta,
serve piping with hot bread and butter.

On Tue, 28 Dec 2004 09:32:21 -0500, Julia Child
wrote:

ignore

What's with all the recipe bull**** posts?

Who's posting these?

Well, this is the info I received. I don't really understand it, but
this is what I was told:

Hello,

this message is never sent unsolicited. Don't panic.
You - or more precisely someone using your mail address - have
posted a test message to the following Newsgroups:

de.alt.test,bit.listserv.test,rec.radio.amateur.an tenna

Your message was sent

Sat, 25 Dec 2004 21:01:30 GMT

travelling from your location to the news.karlvalentin.de (Germany).
Your article arrived here at Sun Dec 26 2004 00:40:05 +0100 (CET)
and this is the way it went (read from back to front):


news.karlvalentin.de!news.qymp.de!tarantoga!auth.d e.news.easynet.net!spool3.bllon.news.easynet.net!e asynet-quince!easynet.net!news.glorb.com!transit1.nntp.hc cnet.nl!transit.nntp.hccnet.nl!transit2.nntp.hccne t.nl!feeder.news-service.com!psinet-eu-nl!news.satx.rr.com!149.52.149.150.mismatch

Reflector Mail is sent to anybody posting into a group ending with
the
word ".test". If you don't want to receive reflector mails, include
e.g.
the words 'ignore' at the top of your articles.

For obvious reasons, mails to are directed
into /dev/null. If you feel to write us, send your mail to
instead.

Full headers plus the first 20 lines of your original message we
| Path: news.karlvalentin.de!news.qymp.de!tarantoga!auth.d e.news.easynet.net!spool3.bllon.news.easynet.net!e asynet-quince!easynet.net!news.glorb.com!transit1.nntp.hc cnet.nl!transit.nntp.hccnet.nl!transit2.nntp.hccne t.nl!feeder.news-service.com!psinet-eu-nl!news.satx.rr.com!149.52.149.150.mismatch
| From: Bob Miller
| Subject: Modification of G5RV - need help on this
| Approved: Bob Miller
| Newsgroups: de.alt.test,bit.listserv.test,rec.radio.amateur.an tenna
| References:
| Date: Sat, 25 Dec 2004 21:01:30 GMT
| Message-ID:
| X-Newsposter: AtomicPost/32 (http://149.52.149.150) Registered
| NNTP-Posting-Host: 149.52.149.150
| X-Trace: satx.rr.com 5830402087 149.52.149.150 (25 Dec 2004 21:01:30 GMT)
| Followup-To: news.admin.net-abuse.email
| Lines: 49
| Xref: news.karlvalentin.de de.alt.test:11560
|
| soften.
| In skillet, brown the meat in a little olive oil,
| then add onions, peppers, and celery (all chopped finely)
| and season well.
| Place in a large bowl and cool.
| Add seasoned breadcrumbs and a little of the tomato gravy,
| enough to make the mixture pliable.
| Divide the stuffing among the cabbage leaves then roll.
| Place seam down in a baking pan.
| Ladle tomato gravy on top,
| and bake at 325¦ for 30 - 45 minutes.
|
|
|
| Umbilical Cordon Bleu
|
| Nothing is so beautiful as the bond between mother and child,
| so why not consume it?
| Children or chicken breasts will work wonderfully also.
|



Ed Price wrote:

oil.
Add a little water, season, then add the carcass.
Simmer for half an hour keeping the stock thick.
Remove the carcass and add the vegetables slowly to the stock,
so that it remains boiling the whole time.
Cover the pot and simmer till vegetables are tender
(2 hours approximately).
Continue seasoning to taste.
Before serving, add butter and pasta,
serve piping with hot bread and butter.

Bob Miller wrote:
Julia Child wrote:
What's with all the recipe bull**** posts?

Who's posting these?

Well, this is the info I received. I don't really understand it, but
this is what I was told:

this message is never sent unsolicited. Don't panic.
You - or more precisely someone using your mail address - have
posted a test message to the following Newsgroups:

de.alt.test,bit.listserv.test,rec.radio.amateur.an tenna

That's just a side-effect of the message having been posted to a 'test'
newsgroup - basically irrelevant to the real issue.

Look up 'hipcrime' in google for more info about what went on with the baby
recipes.

miguel
--
Hit The Road! Photos from 32 countries on 5 continents: http://travel.u.nu