Re: Preventing a REALLY expensive mistake.

["Tesla list" <tesla-at-pupman-dot-com>]

Original poster: "Ray von Postel by way of Terry Fritz <twftesla-at-uswest-dot-net>" <vonpostel-at-prodigy-dot-net>


Christopher:

> Doesn't a Faraday cage only work if it's a COMPLETELY ENCLOSED room? I don't
> mean airtight (but there is a specific maximum size hole for a given
> frequency protection limit)?

The short answer is yes.  The maximum size of allowable hole depends on the
wave length of the maximum
frequency you want to keep out  of the shielded room. It is also dependent
upon the power.

>
> And if I do spend the time/money in caging my High Voltage Lab, Computer
> labs, or both the second I plug the computers in to the AC, Ethernet, or any
> other antenna (wire) that passes outside the cage (into the wall or another
> room) haven't I just defeated the cage?

Again, yes. All leads going through the shielding have to be filtered.
Again, this is frequency dependent
because you have to design, build and/or purchase filters. You have to know
at least the frequencies
involved.  Filters are probably the least expensive of your problems.

Perhaps some one on the list has the information on the r.f. spectrum
generated by Tesla coils and will
share it with us.

The construction of a shielded room, once you know what you are shielding
against, can be expensive.  My
recollection, which probably is wrong, is that the Andrews Co. who
specialized in broadcast, FM, and TV
antennas systems also built shield rooms.  I am reasonably sure that the
"Proceeding of the Institute of
Radio Engineers", or  Proc. of Electrical Engineers" will have construction
details for shielded room for
various purposes.

The magazine, "Electronics" published by McGraw-Hill is an other possible
source. There is a book which has
selected articles from "Electronics".   Vin Zeluff and John Markus,
"Electronics Manual for Radio
Engineers", 1st. Ed. 1949, McGraw-Hill Book Co. Inc. See page 430-432
"Construction Shielded Room in VHF
Field".  While this deals primarily with the VHF band who is to say how
much energy your experiments with
Tesla coils might generate.

A possible problem, which is largely dependent on power level and the
proximity of transistorized equipment,
such as meters, scopes, and computers is that of magnetic pulses.  Faraday
screens are ineffective for this.
It is even more difficult to shield against.  It may or may not be a
problem.  Hopefully someone has done
some research on this.  Yes, I know that Hertzian waves have both an
electrostatic and electromagnetic
component.  Faraday screens work for the electrostatics but not the magnetics.



> I know the math Gods can help on this. :)

Even the math Gods can't help unless they have something to go on.

The rule of thumb for holes in shielding  r.f. is that any opening in the
screen be much less than 1/4 wave
length in its largest dimension at the frequency of interest.  That is why
shielded rooms are normally built
out of copper fly screen with all edges soldered together, all doors are
weather stripped usually using
silver plated beryllium copper finger stock and all electrical connections
filtered.  And that is just for
starters.

My advice?  It depends on your resources, but I would plan on doing my
calculations with a slide rule and
taking notes using a manual typewriter or paper and a quill pen.
This may be over kill, but until you really know more about the nature of
the problem I would error on the
cautious side.

It seems to me that researching your problem could lead to the development
of  a whole body of valuable
knowledge.

Summary:  I don't think enough is known about the problem.  Therefore,
until you can state the exact problem
no one can give you anything but a "try it and see it worked for me" answer.