The Technician's EMI Handbook

Chapter 5

Shielding Electronic Circuits

It is almost an article of religion in electronics that shielding electronic circuits prevents EMI problems. A good shield will keep undesired signals inside in the case of a transmitter, or outside in the case of other forms of circuits. All transmitters generate harmonics and other spurious signals. If these signals are radiated, they will interfere with other services. Signals that go out through the antenna terminal usually pass through either tuning or filtering networks, which tend to clean up the emission. But if the circuits are not shielded, direct radiation from the chassis will defeat the effects of the filtering.

Shields are good. Unfortunately, many shields are essentially useless. In some ...