Originally Posted by exploziv
I have a lead lined box in my car just for that.
Lead sheet is good. You can fold it over at the edges.
In general, a Box within a Box within a Box helps.
On one occasion in the past I had access to a proper EMI lab (about the size of a football field), the old TRW/NGC plant where "Falcon & a Snowman" (the original historical incident) happened.
Working with an EE, we tested a fixture I brought with me.
It was designed in conjunction with Nokia's 2.5 G base stations (2001).
It was Box (with the RF source) within a Box within a Box, next to a Box (with the antenna signal trace) within a Box within a Box.
I got 130+ dB of shielding from 10 MHz to 2+ GHz. Very cool, you could see the coupled signal crawling out of the noise floor at 2.5 GHz (might sound complicated, but with some bar room paper napkins and some good pot, it would be easy to explain.)
Long story short, RF shielding is like with keeping warm - Layering helps.
You get 20+ dB out of each layer.
If you're designing for long term use, you have to be careful about surface finishes. When corrosion starts, you lose shielding.
If you are at a house with a bunch of Stainless steel bowls, put your cell phone in the mid-size one - then put that in a bigger one, with a smaller one on top. etc.
There are a lot of ways to get the shielding you need.