The $20 desktop faraday cage - Page 1
Forum section: electronics / beginners

author: cellularmitosis
author_rank: Unknown
timestamp: January 17, 2014, 05:23:06 am
content: After reading Jim Williams' app note AN83, I was inspired to make my own cookie tin faraday cage for taking low noise measurements.Unfortunately, the only cookie tins which my local grocery store carried were pathetically small.But I found something way better! An all aluminum Dutch oven, big enough to easily fit a 4x6 copper clad board and still have room for several other smaller boards (battery boxes, small instruments, etc). And it was only $20, so I snagged it.The handle in the middle of the lid unscrews, leaving a nice pilot hole to drill out a hole for a BNC fitting.I've been experiencing a 90 MHz noise problem with my DSO, and the best-case scenario I was able to finagle out of this setup was roughly a 10x reduction in noise with the lid closed vs open (60ish mv open, 6ish mv closed). Unfortunately this didn't solve my noise mystery (leaving the DSO disconnected yields a 0.5mv noise floor), but that's the subject of another thread

author: Rerouter
author_rank: Super Contributor
timestamp: January 17, 2014, 06:56:05 am
content: Based on the frequencies it could well be your coax picking up a radio station,

author: Bored@Work
author_rank: Super Contributor
timestamp: January 17, 2014, 07:03:20 am
content: There is only so much a cookie tin can do. I still use one at home. But at work mobile phone networks and some EMI turned out to be a problem for us. So, long ago we changed from cookie tins to what we call "sandwich toasters" in lab slang.http://www.rohde-schwarz.com/en/product/cmwz10-productstartpage_63493-10816.htmlTo check your oven you can try the following experiment. Be in a place with good mobile phone coverage, e.g. near a transmitter. Get a modern mobile phone with good RF reception sensitivity (i.e. not any Apple iPhone). Make sure it is connected to the phone network. Check if you can call it from a second phone. Put it in the tin can. Try to call the phone every half a minute or so. If it still rings, even after being in the can for minutes, the shielding isn't good enough. Works best (or worst, depending on your goal) if you are near a mobile phone transmitter.

author: Joule Thief
author_rank: Regular Contributor
timestamp: January 17, 2014, 07:40:34 am
content: Nice! This should help folks who might be "panning" for a solution in hopes of putting a "lid" on some of their RF interference issues.Thanks

author: cellularmitosis
author_rank: Unknown
timestamp: January 17, 2014, 04:06:17 pm
content: Quote from: Bored@Work on January 17, 2014, 07:03:20 amWow, that looks cool, are those modular plug interfaces in the front, so that you can pass as few or as many cables through as needed?I'll have to invite a friend over and play faraday phone tag

author: Bored@Work
author_rank: Super Contributor
timestamp: January 17, 2014, 06:05:15 pm
content: Quote from: cellularmitosis on January 17, 2014, 04:06:17 pmTwo connector modules in the front and two connector modules in the back. You have a limited choice of expensive connector modules, but they are well shielded. A typical problem is that you can't get as many cables, probes, power supply, etc. through as you would like to. So you end up constantly changing your measurement setup. But on the other hand, every cable going in is a potential problem.

author: Rigby
author_rank: Super Contributor
timestamp: January 20, 2014, 07:55:25 pm
content: Quote from: cellularmitosis on January 17, 2014, 05:23:06 amMake sure your BNC is of good quality and that (if possible) your faraday cage cookware is grounded. You may also need some sort of RF gasket around the lid, depending on how well that seals/closes. This is probably why JW used cookie tins; they have a good 0.5" overlap between tin & lid when they're fully closed.

author: Rick Law
author_rank: Super Contributor
timestamp: January 20, 2014, 08:05:22 pm
content: Quote from: cellularmitosis on January 17, 2014, 05:23:06 amOne should also consider empty PC case also. They are reasonably well shielded, with openings for a fan, DB9/DB25 openings. and others - and you can block the unused ones with aluminum foil. Bonus -they come equipped with many nice grounding post ready to receive screws.

author: mtdoc
author_rank: Super Contributor
timestamp: January 20, 2014, 08:07:01 pm
content: Years ago when I was doing a lot of electrophysiology, we made faraday cages out of common window screens wired together.Very inexpensive and effective.

author: Rick Law
author_rank: Super Contributor
timestamp: January 20, 2014, 08:08:59 pm
content: Quote from: mtdoc on January 20, 2014, 08:07:01 pmTrouble is, today window screens are mostly synthetic plastic of some sort instead of metal.

author: mtdoc
author_rank: Super Contributor
timestamp: January 20, 2014, 08:17:21 pm
content: Quote from: Rick Law on January 20, 2014, 08:08:59 pmGood point though it looks like you can still get aluminum ones:LINKI would bet you could find cheap used ones at a typical used/recycled building material store as well.