Timing Is Everything

There comes a time in the design of many an electronic product when it is taken to a certified laboratory for EMC testing. The result of this test determines whether the product can be shipped or needs to be redesigned in order to comply with the regulations. Such a time comes at the worst possible moment in the schedule - the product is fully designed and debugged, the prototype is assembled, materials for inventory have been ordered, production is planned, Marketing and Sales are loitering in the Engineering quarters trying to glean how soon they can begin selling the product, and time is running out.

Every day of delay can cost a company thousands (or even millions) of dollars in revenues. It is inconceivable for upper management that such an insignificant engineering procedure as an EM compliance test can actually bring the whole operation to a halt, should the product fail the test. It is even more surprising to many that the last minute "quick fix" for the compliance problems may raise the cost of the product several dollars, ruining revenue plans, profit objectives, etc.

Since EM compliance is almost never considered to be among the prime objectives of product development, it is seldom given enough attention. Typically, an EMC test is not a part of the plan, but rather a scheduled event somewhere at the end of the project. Yet, if one were to calculate the damage non-compliance could bring to a business, surely the bright minds in a reasonable company would assign it a very high priority from the very beginning. The wasted time due to "unforeseen" EMC problems could be weeks, if not more.

The thousands of dollars spent on unnecessary tests and revisions of the prototype at the last moment fades in comparison to the lost revenues due to a schedule slip and the cost of added unplanned EMC protection parts to every shipped unit. As Wall Street Journal reports in its Aug. 5/94 issue, Compaq had to delay shipment of their Elite line of notebook computers from March to June due to the FCC compliance problems. How many companies can absorb such impact on revenues? Smooth and timely passing of the EM compliance test without "emergency" expenses is almost never an accident; it is a result of a good planning.

The earlier electromagnetic compliance enters the scene, the fewer surprises will be waiting at the end. Most of the factors determining the EMC fate of the product are decided upon at the earliest stages of design: the product's physical architecture, the number of the PC boards in the product, the required cable interconnects, the number of layers in each board, the number of different clocks and the clock frequencies, the type of enclosure and its material, etc. Most of these decisions will be made far ahead of having a fully working system that is testable for compliance. Some large percent of guesswork is unavoidable. But having the right tools for the job can dramatically reduce the pure guesswork down to educated estimates, and further, to some level of confidence.

The standard far-field compliance test for radiated emission is not well suited for the early stages of product development. The first prototype board is seldom the same as its final version; cable assemblies are spaghetti-like; and the enclosure is nowhere in sight. Furthermore, the far field test cannot tell where to look for the problems. The near field test can become the perfect tool for early pre-compliance work. Performing a near-field scan on the very first revision of the PC board can reveal future "hot" spots at the time they can be made harmless at the lowest cost. Traces can be re-routed, ground planes added, filter components, such as ferrite beads, etc. can be accommodated.

Early knowledge of the radiation patterns can tell the mechanical engineer exactly where to prepare to accommodate shielding, should it become necessary. This alone can save hundreds of thousands of dollars in last-minute tooling changes. Early detection can not be achieved with only the far-field test. No one would be able or willing to take early prototypes to the EMC laboratory for routine diagnostics. As for the financial aspects, a full-blown far-field setup on site may cost a prohibitive amount of money. On the other hand, ScanEM near-field probes are affordable, and can and should be as common for an electronics engineer as a multimeter or an oscilloscope.

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