RE: faraday cage questions (fwd)

["High Voltage list" <hvlist@xxxxxxxxxx>]

Original poster: Steven Roys <sroys@xxxxxxxxxx>



---------- Forwarded message ----------
Date: Tue, 26 Dec 2006 01:32:25 -0800
From: Jim Mora <jmora@xxxxxxxxxxx>
To: 'High Voltage list' <hvlist@xxxxxxxxxx>, 'Parkinen' <parkinen@xxxxxxx>
Subject: RE: faraday cage questions (fwd)

Hi Steve,

I built a satellite dish years ago (before military level scrambling) and I
am "assuming" (key word) this is the reverse of what your needs are. As I
remember, 1/4" mesh was all that was needed to reflect 4 Ghz.

Seemingly, calculate the primary wavelength you will be running at, and
adjust as needed. I would think 1 inch chicken wire would work; way cheaper.

The pass-through is a whole different issue. I'll defer to our HV RF friends
how to do this as it is again and again stated as problematic.

You clearly want a very good EMI filter outside the box to catch the any
stray leakage and high frequency harmonics.

The only Faraday cage I have ever been in was copper mesh screen, and that
was to keep EMI out...no money spared. 

Regards,
Jim Mora

-----Original Message-----
From: High Voltage list [mailto:hvlist@xxxxxxxxxx] 
Sent: Monday, December 25, 2006 8:28 PM
To: hvlist
Subject: faraday cage questions (fwd)

Original poster: Steven Roys <sroys@xxxxxxxxxx>



---------- Forwarded message ----------
Date: Sat, 23 Dec 2006 14:43:15 -0600
From: Steve Ward <steve.ward@xxxxxxxxx>
To: High Voltage list <hvlist@xxxxxxxxxx>
Subject: faraday cage questions

Hello all,

Ive recently moved most of my "HV" lab out of my parents house and
into the house i live at when going to school.  Having 5 other room
mates who could really care less about what im doing in the basement
offers a great opportunity for me to take advantage of that space.
BUT, they are all highly dependent on their electronics still
functioning after ive had my fun!  Since i would still love to work on
my HV projects at school, i have considered building a faraday cage.
The design has to be easily collapsable for when im done experimenting
and need the space again.  Anyway, enough background, and onto the
questions.

Mesh size:  Is it safe to assume that any frequency with a wavelength
greater than the mesh opening will be completely attenuated?  Or is
there some function that describes the attenuation of radiated energy
through such a mesh size?  I was planning on either using 1/2" or 1/4"
square heavy duty mesh, but i could resort back to something like
aluminum window screen, which is something like .08" squares i think.
I need to avoid interference with our WiFi connection (~2.4GHz).

Power feed-through:  What would be the best approach?  I was thinking
of just using normal line filters, but locating them "mid-way" into
the mesh and connecting the case to the screen.  But, im not sure how
effective line filters really are.  Also, what if i wanted to simply
feed HV into the cage (from a HVDC power source), i suppose i would
need to design some sort of feed-through filter for that as well
(ideally id avoid this situation).

I plan on running small tesla coils and possibly my marx generators
inside this cage to give you an idea of what im dealing with.  Id
assume that i can just connect the cage to mains ground simply for
safety reasons, but no RF current will be present on this connection
as the RF circuit is completely enclosed within the cage.

Any tips or comments are appreciated.  Im also looking for a cheap
source for the screening, if anyone has a suggestion.

Steve Ward