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Faraday cage, shielding and grounding

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ricko_uk:
Thank you Greybeard! Very interesting, the conductive gasket too, that could be a possible solution!

Ahbushnell,
what is chem filmed aluminium? I googled it and it looks like some process, is it possible to somehow apply it to a standard enclosure too?

Thank you :)

ahbushnell:

--- Quote from: ricko_uk on June 12, 2020, 11:30:14 pm ---Thank you Greybeard! Very interesting, the conductive gasket too, that could be a possible solution!

Ahbushnell,
what is chem filmed aluminium? I googled it and it looks like some process, is it possible to somehow apply it to a standard enclosure too?

Thank you :)

--- End quote ---
chem film is slang.
Trade name is Alodine.  You can get clear and yellow.  I like yellow because it shows it's been treated.  Plus it looks better.  :) 

You can buy kits and do it yourself or have it done.  We normally spec the coating the sheet metal house. 

https://usglassmag.com/bonding/alodine-aluminum-the-brand-versus-the-finish/


ricko_uk:
Thank you ahbushnell :)

rhb:
There are two issues:  electric field and magnetic field.  Copper will not block magnetic fields whereas low carbon steel sheet is fairly effective above 1 MHz.  Screen drops in effectiveness as the frequency goes up. Low frequency magnetic fields require mumetal which is quite expensive as it is nearly pure nickel.  Galvanized steel sheet is a good enough conductor to be effective for the electric field.

A friend who is a retired  level II certified TEMPEST tech told me that the commercial rooms he dealt with used plywood with galvanized steel sheet on both sides and a custom rib that held the panels together with bolts every few inches.

I'm building a lab room approximately 15' x 11' which will have all the surfaces covered with 26 gauge galvanized steel sheet riveted to metal studs with all seams soldered.  The door will use metal weather stripping on  all edges.

For a small shielded enclosure I spot welded piano hinge on a pair of steel radio chassis along with a trunk latch.  Later it will get a layer of thermal insulation and a Peltier junction to control the temperature.

https://www.eevblog.com/forum/metrology/shielded-test-chamber/msg1471450/#msg1471450

A lot depends upon how big you need the chamber to be, whether there is significant heat being generated that needs to be removed and what type and  level of environmental noise you have.

I lived a mile or two from a 250 kW FM transmitter when I was in grad school.  Drove me nuts!  While I don't have that problem where I live now, it made me want a shielded room.

A reasonably inexpensive option for a quiet bench would be a 5 sided steel box holding your test gear and a copper screened front panel that allowed you to see the displays and provide air circulation.

You should make or buy an H field probe.  Dave did a video on them and there are some really cheap ones from China.  There is *no* justification for the $$$$ versions.  It's nothing special, just a shielded loop so it only responds to magnetic fields.  Combine it with an SDR to do spectrum analysis.

For a small low cost enclosure with good magnetic shielding consider a large diameter section of threaded steel pipe with malleable iron caps.  Thoroughly annealed if possible.

You will need to *very* carefully filter all lines passing through the walls.  The details of that depend very much on the signal. For fast signals make opto-isolators that send the signal through a hole in the enclosure and then put a metal cover over both sides.

It can get very gnarly.  So measure often and keep at it.

Have Fun!
Reg


ricko_uk:
Thank you Reg and all :)

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