In high school I worked with an Electrical Engineer to do EMI/RFI testing. We had to build a 10'x10'x10' shielded test box. Had to be that size for propagation he said. Something to do with a mathematical/harmonic of the actual range that the FCC would do EMI/RFI testing at.

Amazing all the stuff we had to do. And it would boil down to something as simple as not having copper wool (not steel) properly sealing the cracks in the walls. We'd seal the room, fire up the antenna array, find noise on the floor, then spend hours crawling around with probes that had maybe a 2" detection cone. Grueling stuff but once we were done the business paid well.