Designers pride themselves on their imaginationstheir ability to visualize a signal path through a circuit or a system and how it is affected by the various "junctions" along the way. Particularly when dealing with sensitive radio receiver front ends and low-level signals, unanticipated signal flows or leakage can wreak havoc with a design, or even that dreaded last resort: the addition of shielding gaskets to an enclosure. Shielding is that one component that no one wants, but often needs, in order to effectively contain signals within an enclosure, or to prevent signals from outside the enclosure from getting into it.

Shielding is often added to a design as an afterthought, after the thought that the initial design was sound had to be discarded. That original design might have been considered leak proof or grounded well enough to minimize the effects of interference. But reality often punches holes in the best paper or computer-aided circuits. Then it is time to search for help, usually in the form of a shielding product. One of the leading suppliers of such products, Tech-Etch, has made that search a little easier by developing an interactive catalog in PDF form, available for free. It includes electromagnetic-interference (EMI) and radio-frequency-interference (RFI) shielding, and makes the task of adding a late fix to a "perfect" design all that less painful.