Interesting times

Richard A. Quinnell, Technical Editor -- Test & Measurement World, 9/1/2004

EMC test is facing challenges on all fronts. Advances in product design are requiring the continual revision of specifications. Meanwhile, test engineers are struggling to apply existing methods where they do not belong, and to make educated guesses as to new requirements that may arise.

Most radiated emissions specifications limit themselves to the 30- to 1000-MHz range. When these specs were developed, digital clocks were running at a few tens of megahertz, and the upper limit represented a comfortable estimate of the signals and harmonics that equipment might be expected to generate at significant power levels. Similarly, signals below 30 MHz were typically tested only as conducted emissions, under the expectation that far-field radiation of these signals would be weak.

Technology has a way of running past assumed limits, however. Now, processor chips routinely run with clock rates at 2 GHz and above, making the 1000-MHz upper bound woefully inadequate. The advent of broadband Internet traffic is causing near-field radiation from DSL modems to be a concern, forcing a need for radiated emissions testing below the 30-MHz lower bound.

The tendency for technology to force changes in regulatory requirements will only increase. But the process of developing specifications will probably not improve, so EMC test engineers should be prepared for increased turmoil as new requirements evolve. We're all experiencing the old Gypsy curse, "May you live in interesting times."

Contact Richard A. Quinnell at richquinnell@att.net.