basics: Faraday cage keeps RF energy in as well as out ?

[bxn]

if you want me to pack my basic questions somewhere else, let me know...

I know enough to know that a Faraday cage (a metal container) will do a good job of preventing RF energy from reaching its interior. Now, will placing a transmitter in a Faraday cage prevent the RF energy it emits from passing out of the cage/container ? Or would it function as an antenna/reflector ?

I'll guess that the answers vary with frequency and power. Thanks in advance for your comments,
bxn

[Amish_Bill]

That's a good question.
Hmmm...

A proper Faraday Cage has no openings for RF, so unless you have your antenna in contact with the cage itself, I don't see how any signal could get in or out. Of course, that's just a guess...

[MountainSniper]

AB makes a good argument. I believe both would be the right answer and contact between antenna and cage would be the key issue.

[3par]

Any conductor has a property called skin depth that tells you how deep an electromagnetic wave can penetrate before it is attenuated by a known proportion. Typical EM waves only need a few mm of metal to completely absorb on good conductors like copper. So in theory a farady cage with the proper thickness can completely shield your transmitter from receiving or transmitting.
However, in reality no such thing exist in the world. The container can never be completely solid and you need an opening to let things in and out. The seam/gap between your opening enclosure can never be zero and magnetosatic components vertical to the gap and electrostatic components parallel to the gap will escape.
Every electric component in the US and in EU and Asia has to be rated by FCC on its EM leakage while operating (FCC wants everyone to be able to enjoy watching TV and listening to radios and free of electromagnetic interference from other electronics). Most of them will violate the law without the shielding so everyone build some kind of ferady cage in their enclosure to make sure the FCC class A or B interference limitation. Read the label of your PC or printer and there will probably be a label saying it is FCC class B (home use).
In the peak of the cold war employees of the US embassy in Moscow were literally "cooked" by the microwave bugging device of the soviets. In order to securely talk without the fear of bugging, they actually built metal bubbles so that people can talk inside without the fear of eavesdrops. However, it was later found out soviet spies have put small leaks from the opening and the shield was compromised.

[bxn]

good stuff all, thank you !