RE: faraday cage questions (fwd)

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Original poster: Steven Roys <sroys@xxxxxxxxxx>



---------- Forwarded message ----------
Date: Thu, 28 Dec 2006 18:11:55 +1300
From: G. Tyler <gtyler@xxxxxxxxxxxxxxx>
Reply-To: georgetyler@xxxxxxxxxx
To: 'High Voltage list' <hvlist@xxxxxxxxxx>
Subject: RE: faraday cage questions (fwd)

I have made one with 12 X 24mm (approx) weld mesh. Attenuation was about 15
db at 300Mz, will be less as the frequency increases. Why not build it out
of copper sheet, it could be thin and will be more effective? 

-----Original Message-----
From: High Voltage list [mailto:hvlist@xxxxxxxxxx] 
Sent: Thursday, 28 December 2006 5:54 p.m.
To: hvlist
Subject: Re: faraday cage questions (fwd)

Original poster: Steven Roys <sroys@xxxxxxxxxx>



---------- Forwarded message ----------
Date: Wed, 27 Dec 2006 01:12:45 +0900
From: Peter Terren <pterren@xxxxxxxxxxxx>
To: High Voltage list <hvlist@xxxxxxxxxx>
Subject: Re: faraday cage questions (fwd)

I have experience with 3 different Faraday cages.
The first is a $20,000 dollar one at a science museum.
 http://tesladownunder.com/Tesla%20display.htm#Scitech
Uses fairly fine mesh (?1 1/2 inch square) with special care to avoid long 
thin gaps between panels and the door. I recall some springy coiled strip. 
Out of your price range but works and has been "certified" by professionals.

The second is my 8 foot cube made such that each of the faces of 8x8 will 
fold into a 4x8 to be able to fit through doors. It is simple but still a 
pain to set up and takes an hour or two. I use this for all my public 
displays. It is made of chicken wire with the hexagonal holes of about 2 
inches. Does it work? I think so.  Certainly the fluorescent light fitting 
12 inches above it did not light up at all and I have runs audio and 
computer stuff not far away. I join the RF earth to the cage and also the 
mains earth which grounds the box that my Terry filter is in. The Terry 
filter is just inside the cage.  Run all your earths to the cage.  I was a 
bit careless about this and was getting some potential between my controller

box and the cage last time I used it.
http://tesladownunder.com/tesla_coil_sparks.htm#4%20inch%20coil

The third one I used is simply a roll of 4inch square hole ringlock fencing.

There is enough to make about a 6 foot diameter cylinder and there is a bit 
for the top. The idea is that it is adjustable and can fit through doors 
etc. The TC base has a counterpoise of a 2 foot square aluminium plate with 
extensions to support whatever diameter you choose.
http://tesladownunder.com/Tesla%20display.htm#Tesla%20coil%20(Physics%20Dept
)%202006

So what would I do in your situation? None of these.  Just line one corner 
of your basement up to the roof with chicken wire on a simple wooden frame 
tacking it on with a wood stapler. Make some sort of door sized flap. Have 
something on the floor as well so that all six sides are covered.  How 
collapsible and clever you make it depends on you.

Peter

> ---------- 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