When we say “EMI testing,” we are usually referring to measuring the electromagnetic fields emitted by an electronic product and then deciding if the measured values are too high. That is to say whether or not they will cause interference to other devices. These emissions may be radiated through the air or conducted through a product's power leads or input/output ports. One of the big challenges in EMI testing is that there are many different military and commercial standards that you may have to test to, including FCC, CISPR, EN, ETS, TELCO (BELLCORE), VDE, ANSI, VCCI, MIL-STD, VG, DEF-STAN, and others. So, one criterion to keep in mind when setting up an EMI test facility or choosing a vendor for doing EMI testing is that it will need to run tests called out in all of the standards that are applicable to your product.