Shielding, Van Eck, and Faraday Cages

[Tim May]

On Thursday, August 23, 2001, at 01:43 AM, Eugene Leitl wrote:

> On Wed, 22 Aug 2001, Faustine wrote:
>
>> Have you happened to have seen any good papers on constructing do-it-
>> yourself cheap, effective, portable shielding? Probably might as well
>> ask for the moon too while I'm at it, but it's worth a shot!
>
> Using cast aluminum cases, copper foil shielding, tight glands which
> preferably transport only optical signals or coax, using low power parts
> which don't clock too many Hz, and the like.
>
> Even if you don't have access to a testing facility, careful work and 
> some
> thinking will eventually make you very, very silent.
>


Even without spectrum analyzers and the like, it's relatively easy to 
test shielding: use a portable radio. Tune it to a couple of stations, 
loud. Put in inside the Faraday cage. If you can still hear it, not very 
effective. (Sound muffling should be second-order, but easy to take into 
account.)

To get fancier, instrument the radio. Put a meter on the speaker 
outputs.  Tune to several frequencies.

What can't get in can't get out. Though this RF method is mostly working 
in the RF spectrum, it gives a good indication of overall shielding. Can 
push this up in frequency in the obvious ways.

We used this method to test the Faraday cage I worked in when I was 
doing Josephson Junction stuff.

And using the same principle, one can listen to equipment with radios 
and t.v.s and gauge the effectiveness of shielding. (A signal that is 
attenuated by 90 db a few inches away will of course be hard for even 
trucks with large antennas to pick up a block away.)

There is much out there on building Faraday cages, either large ones or 
small ones. Search engines will turn up suppliers and papers.

The "heads up" displays of a couple of vendors are the likely long-term 
solution to a lot of supposed Van Eck radiation snooping.


--Tim May