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EMR min. mesh aperature

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Robert Davis

Jan 1, 1970
0
I need to build a walk-in Faraday cage for noise-free EMR
measurements. It must exclude all practical EMR from external power
and communications systems. For lowest cost I am considering
galvanized mesh stapled to a wooden frame.

1. What is a practical upper bandwidth limit? IOW what is the highest
frequency interference likely to be encountered in a modern urban
setting?

2. How small a mesh aperature would be required to screen it?

Thank you for any advice along these lines.

Robert Davis
 
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Martin Riddle

Jan 1, 1970
0
Robert Davis said:
I need to build a walk-in Faraday cage for noise-free EMR
measurements. It must exclude all practical EMR from external power
and communications systems. For lowest cost I am considering
galvanized mesh stapled to a wooden frame.

1. What is a practical upper bandwidth limit? IOW what is the highest
frequency interference likely to be encountered in a modern urban
setting?

2. How small a mesh aperature would be required to screen it?

Thank you for any advice along these lines.

Robert Davis

Rule of thumb is to use Lamba/20 for antenna effect of slots or holes.
so 1Ghz yields 1.5cm hole. 10ghz- 1.5mm.
I've seen old screen rooms made of copper screen, maybe 3-5mm square.
The problem is making sure the mesh is electrically connected at every
cross.

For a real 3 meter chamber the price isnt that awful.

EMC pre-screening?


Cheers
 
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Robert Davis

Jan 1, 1970
0
The problem is making sure the mesh is electrically connected at every
cross.

Hmm ... every cross. I didn't consider that. So woven galvanized mesh
would not work? I thought all that was required was a path to ground
from every strand. Or, in some cases, I have seen it in use just
floating and OK for screening higher frequencies.

Can you please clarify, if possible?

Welded mesh is not common in small aperatures. Otherwise, maybe one of
the expanded steel meshes would be better. But difficult to
electrically join the seams.

Robert Davis
 
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Ecnerwal

Jan 1, 1970
0
I need to build a walk-in Faraday cage for noise-free EMR
measurements. It must exclude all practical EMR from external power
and communications systems. For lowest cost I am considering
galvanized mesh stapled to a wooden frame.

You can use sheet metal for infinitely small holes in the "mesh", and
you can solder the seams if you use galvanized steel or copper - but you
will have the common problems that keep commercial screen rooms
expensive - doors (getting a good electrical connection for the door is
difficult) and power (and/or signal, if any) feeds leaking. You can use
a steel door - but the door-to-doorframe gap is going to be a problem
you'll have to solve. If you can run all your measurements from battery
power, that would solve the power feedthrough issues.
 
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Ecnerwal

Jan 1, 1970
0
I need to build a walk-in Faraday cage for noise-free EMR
measurements. It must exclude all practical EMR from external power
and communications systems.

Forgot to add: a good estimate of whether your screen room is working
effectively can be obtained by taking a broadcast radio receiver into
the room and closing the door - if you can still pick up radio stations,
it needs work. I suppose a cell phone or wireless network connection
would allow evaluating the effectiveness at higher frequencies these
days.
 
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Paul Keinanen

Jan 1, 1970
0
You can use
a steel door - but the door-to-doorframe gap is going to be a problem
you'll have to solve.

Fingerstock is quite usable in many situations.

If the Fingerstock is destroyed, you may have to replace both the door
and as well as the door frame.

Paul
 
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