Faraday Cages

 SR> I'm familiar with the basic idea of Faraday cages, and I     
 SR> think I may know how they're designed (kinda sorta), but     
 SR> could you (or anyone who cares to contribute) provide        
 SR> information (or a good source of information) for relevant   
 SR> details in Faraday cage design, as well as a little theory.

Also Quoting Ryan Brett:

 RB> Recently a friend and I have begun building a rather large   
 RB> Tesla coil. I was wondering, would any type of shielding be  
 RB> necessary?  I have heard about a Faraday cage, what is that? 
 RB> Any advice is appreciated. Thanks in advance for any help,

A Faraday cage is a grounded enclosure with walls, floors and
ceilings made of metal, or completely covered with grounded metal
screen or hardware cloth. Devices prone to excess radiation may
be placed inside of a Faraday cage and operated without spurious
signal leaving the enclosure. Most Tesla coils do not require
Faraday cages, but some large coils, as well as coils configured
for transmission, may require Faraday cages in order to operate
legally. A microwave oven employs a small Faraday cage. The oven
contains a resonate cavity, but all six sides of the oven are
made of sheet metal or are covered in wire grid to prevent leaks. 

An "el cheapo" Faraday cage may be built in the corner of a
basement with a steel reenforced foundation. Hardware cloth
(metal mesh screening) may be stiched together with bailing wire
to form panels. Panels are hung across the ceiling in a corner
and are allowed to drape down to the floor. The two foundation
walls and the concrete floor form part of the triangular 
enclosure. The metal mesh roof and wall are grounded with strap.

Structures can be built by framing in with wood then covering the
framework with hardware cloth and/or sheet metal panels. I have
seen flattened out 55 gal. drums, old capacitor plates, etc.
nailed up for low cost coverage. The doors opening into the cage
must be close fitting, and care must be taken to ensure that all
panels and doors in the cage construction are electrically
connected and well grounded. A number of all metal storage sheds
are available "off the shelf" for a serious hobbiest.

I would stipulate that a dedicated RF ground be used for
grounding a Faraday cage. Grounding the cage to the breaker box
or water pipe would be a mistake IMHO. A proper RF ground for 
this type work would consist of several 8 - 10 foot copper pipes
driven into the ground and connected with 1 inch ground strap.

I have seen solid state Tesla coils that were base fed with 
about 15 watts of CW output from a small IC based oscillator.
These coils typically are not powerful enough to break out with
much real spark, but they do produce some corona and are capable
of lighting bulbs at some distance. A resonating coil does not
make an effective radiator or antenna, and even though the coil
is driven with a clean RF signal from a modern oscillator, the
range of any interference would be very limited. Yet this type of
project can produce unwanted RF emissions, and especially if
operated in an apartment complex or such, may represent the type
of project that would be a candidate for operation in a small
Faraday cage.

Richard Quick

... If all else fails... Throw another megavolt across it!

... If all else fails... Throw another megavolt across it!
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