RadioBanter - Faraday Cage Grounded Or Ungrounded

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Faraday Cage Grounded Or Ungrounded

I am assuming that a microwave oven is a Faraday cage. Since it keeps
the radiation trapped, bouncing around inside to heat up the food
instead of you. I am betting you would loose signal on a cell phone
completley if it were placed inside of a microwave with the door
closed. This should work even with the oven unplugged from the wall
outlet, which then would be ungrounded.

The electric field inside a Faraday cage is zero, regardless of what
the outside is doing or is connected to. But the reverse is also true.
The charges that are built up from components inside of the Faraday
cage are trapped to bounce around like the radiation inside of a
microwave. So that makes me think it needs to be grounded. On the
other hand, if the shell of a microwave is grounded. Then what keeps
the radiation inside from going to ground instead of bouncing around
and cooking your food?

apples and oranges.

the ( approx 1.2 cu ft ) metal space inside of a microwave oven is
a " resonant " tuned circuit .... designed to resonate the microwave
oscillator tube at it's designed operating freq. this tuned circuit
impacts the total current drawn by the tube ( out of resonance will
cause it to over heat ) ...... and promote power output into the load
placed inside the " e " field of the microwave oven . grounded or
not is not relevant ... except related to RF / emf interference
related to the microwave RF signal or the power supply.
spaces too large or too small would not work ... causing the tube
to self destruct at worse and at the least preventing too little power
to load ( flow ) into the space to cook anything. the microwave
tube doesn't care about grounding ... it's all about size
and shape to the tube.

RF proof faraday shielded rooms ...... like the ones that used to be
found in every hospital , back in the '50s , '60s and '70s ( tube
type ekg diagnostic heart monitor machines used to be particularly
susceptible to RF and EMF field interference ... this before the
advent of " balanced " , common mode , noise canceling circuitry.
( found in ALL modern EKG machines ) are most definitely grounded
to a earth ground where they are located. there used to be standards
that the copper room shield grid had to have less than 1/4 to 1/2 of
1 ohm resistance between each copper shield plate and between those
and ANY and every earth ground it was connected to. ( even the
doorway and door had to be metal and had wires connecting them to the
room walls ) these rooms are VERY RF proof and absolutely NO signals
get into them or out of them . not am radio , not FM radio , not VHF
handhelds and certainly not cellfones. the quality of the grounding ,
or said in another way , the lower the resistance between the
shielding and the earth ground ...
the more effective the shielded room works. EMF in particular ,
more than RF ..can penetrate the room more easily as the quality of
the ground of the copped shield diminishes. 20 to 50 ohms between the
shield and ground and you have a giant square , resonant RF antenna
that picks up everything.

these shielded rooms were necessary in the old days to insure the
proper function of the ekg and eeg equipment ... no longer a problem
with modern day circuit designs. these rooms have , for the most
part, been disassembled and the huge amount of copper sold off
for scrap.

resonant cavities of microwave ovens ( the inside cooking space ) and
faraday shielded rooms have practically NO technical commonality.

apples and oranges ....

k.....................

I am assuming that a microwave oven is a Faraday cage. Since it keeps
the radiation trapped, bouncing around inside to heat up the food
instead of you.

On Wed, 16 Jun 2004 14:50:47 -0500, AC/DC wrote
(in article ) :

I am assuming that a microwave oven is a Faraday cage.

Often attributed to Abraham Lincoln:

question: How many legs does a dog have it we count the dog's
tail as a leg?
answer: Four. Caliing something by a name doesn't make it
necessarily so.

No, there is no Faraday cage inside a microwave oven anymore than
coax is constructed of an inner wire, then physical insulation,
then a Faraday cage, then the outer physical insulation.

A microwave oven has shielding. Hopefully, enough shielding that
it warms your coffee rather than you.

Since it keeps
the radiation trapped, bouncing around inside to heat up the food
instead of you. I am betting you would loose signal on a cell phone
completley if it were placed inside of a microwave with the door
closed. This should work even with the oven unplugged from the wall
outlet, which then would be ungrounded.

Seems likely. But you could do the same thing with a big hunk of
shielding from that coax we were using earlier.

The electric field inside a Faraday cage is zero, regardless of what
the outside is doing or is connected to.

Not necessarily at all. A properly constructed Faraday cage (and
they are simple and very easy to construct) has only the
electrical/electronic field of any device within that generate
something or atother.

But the reverse is also true.

The original wasn't true, either.

The charges that are built up from components inside of the Faraday
cage are trapped to bounce around like the radiation inside of a
microwave.

Do what? And to whom? And,
"uh, eh, what?!?" ---- interrorbang

There aren't any charges "built-up" inside a Faraday cage. It's
not a capacitor, it's a blocktor -- joke on name. All five sides
are tied together and well-grounded to dissipate the energy from
both outside and inside.

So that makes me think it needs to be grounded. On the
other hand, if the shell of a microwave is grounded. Then what keeps
the radiation inside from going to ground instead of bouncing around
and cooking your food?

The radiation of the klystron (or whatever is being used
nowadays) radiates outward from the klystron. It strikes the
coffee cup and permeates through to the coffee. It, then, follows
the path of least resistance to the ground (because the
definition of a ground is - yep, all that stuff, including that,
also because . . . And stuff. And so forth.).

I get the suspicious feeling (grin) that your "theory" abolishes
the possibility of so-called "radio waves" ever having any useful
purpose unless the xmtr and antenna aren't grounded.

Gray Shockley
--------------------------------------------------------
If you're aligning the first stage in a receiver and,
at the same time, someone is working on a
2kw jammer in the same area, a Faraday
Case could be an asset.

Gray Shockley wrote:

"There are more people killed with unloaded microwave . . . . "

Microwaves don't grill people. People grill people..

mike (...when they pry it from my cold, uncooked hands...) II