Re: Shielded rooms, faraday cages, etc.

To: tesla-at-pupman-dot-com
Subject: Re: Shielded rooms, faraday cages, etc.
From: Terry Fritz <twftesla-at-uswest-dot-net>
Date: Thu, 13 Apr 2000 14:48:41 -0600
Approved: twftesla-at-uswest-dot-net
Cc: "Ruud de Graaf" <rdegraaf-at-daxis.nl>, jimlux-at-jpl.nasa.gov
Delivered-To: fixup-tesla-at-pupman-dot-com-at-fixme
In-Reply-To: <001001bfa39e$4bd87360$457bbc86-at-n1989>

Hi Ruud, Jim, All,

One of our engineers at work is a former cell phone engineer.  It appears
your observation is completely expected.

A microwave oven is designed to drop the signal level maybe -60dB which is
well enough to keep from frying people around a microwave oven.  However, a
modern spread spectrum cell phone can catch a signal down at -120dB and
some can reach right down into the thermal noise and snatch a ring signal
down at -180dB!!  The microwave will stop serious energy that would be a
hazard to safety, but it is no match for today's super sensitive cell phones.

Apparently, you can often ring a cell phone in a copper shielded room!  The
person I talked to had seen the best phones ring in a six layer (-200dB)
super shielded room with a close transmitter (much to the dismay of people
paying big bucks to rent to use of the room ;-)).  Those phones with the 1
inch antenna and such are just unbelievably SUPER sensitive!!

Surprisingly, a cell phone will even often ring in a copper ball.  The high
frequencies set up little eddy currents in the copper that are strong
enough to pass a sufficient signal to the other side of the copper surface.
 If you brought the copper to absolute zero (super conducting) then you
could stop the signal.  Anything less, doesn't cut it.

So the oven does work and it probably shields your cell phone perfectly
from destructive energy from the coil.  But it's shielding is simply far
too little to reduce the signal to where a cell phone will not see the ring
signal.  You may not be able to use the phone since your phone's signal
back is much lower power with a poor antenna, but incoming signal are fine.

We also tried it at work and the phones ring fine for use too.  If you are
trying to avoid some unpleasant call or something, simply turn the oven on.
;-)) 

Cheers,

	Terry

At 12:11 PM 04/11/2000 +0200, you wrote:
>Now we are on the subject of shielding, what do you think about this:  on
>the first meeting of 'The Dutch' we did put our GSM's in a discarded
>microwave to protect it from our combined TC. When we were busy to assemble
>the temporary TC, the phone of the CapMan ringed!!! When we checked the RF
>signal-strength it was only 1 or 2 S-figures lower than out of the
>microwave! We tried other microwave
>ovens I had in the garage, but they all had the same influence on the GSM's.
>
>Microwaves have an operating frequency of 1450 MHz and the level of RF that
>is allowed to pass through the oven must be very low and because the GSM's
>are working in the 800MHz  range my expectation was that the GSM's couldn't
>receive a thing in the microwave ovens.
>
>Well, as often is proven, practice is better than theory!  Anyone has a
>clue?
>
>Greetings from lovely and sunny Holland,
>
>Ruud
>
snip...