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.