EMC Pre-Compliance Testing: Practical Design Insights for Engineers

Webinar timeline 

 Total runtime is about 49 minutes. Use the timestamps to jump to a topic in the recording below.

0:00 – Introduction

Jeff Markham opens the session and explains his background: EMC Principal Engineer at Element’s Burton, Michigan lab, with nearly four decades in automotive and defense EMC. He sets out what the webinar covers, from what pre-compliance realistically reveals to the design decisions that drive a first-time pass. 

2:09 – What pre-compliance testing is, and what it is not 

Pre-compliance flags EMC risk early, supports design iterations, and cuts the cost of late failures, but it does not guarantee full compliance, and it cannot get a product to market on its own. Jeff is clear that it complements, and never replaces, the formal testing required to meet standards such as FCC Part 15. Treat it as a diagnostic tool, not a cheaper rehearsal of the chamber. 

3:55 – What pre-compliance realistically reveals 

The measurements reveal where the schematic and board need work, from a switch-mode supply with runaway harmonics to conducted and radiated emissions exceeding the limit. Jeff shows how a bench setup with an oscilloscope FFT and near-field probes locates hot spots on a PCB or harness and provides a workable approximation of the compliance limit before you book chamber time at an accredited EMC testing laboratory. 

7:32 – How setup and correlation affect result quality 

Result quality depends more on the setup than on the instrument. Jeff walks through the variables that drive correlation with a formal chamber: the test environment, ground plane and harness layout, equipment calibration, and correction factors for probes and antennas. Skip these, and the data skews toward one extreme, which is why he stresses mimicking the harness lengths and ground-plane size specified by the standard. 

10:52 – How to improve correlation 

The practical fix is to design against an internal target set below the published limit, so the margin absorbs the uncertainty you cannot measure on a bench. Jeff also argues for reading trends across six or eight design iterations rather than chasing an absolute number you cannot yet trust. Repeatability and a known measurement uncertainty are what separate a development bench from an accredited lab. 

14:25 – Effective pre-compliance techniques 

Jeff runs through the techniques that give the most return for the least spend: conducted emissions by the voltage method with a LISN or the current method with a clamp, near-field scanning with sniffer probes to find magnetic-field hot spots, bulk current injection for immunity, and time-domain FFT on an oscilloscope. Much of this equipment can be rented or built, so a small team can start without capital investment. 

20:03 – Where pre-compliance falls short 

Pre-compliance cannot answer everything. Jeff covers the limits: a non-ideal test site near a transmitter, the bandwidth and pre-selection gaps of a spectrum analyzer against a compliance-grade EMI receiver, immunity fields you cannot generate without a chamber, and an EMC test plan that is not ready. A missing or generic plan is a common failure point, which is why he points teams to build a proper EMC test plan and checklist before they start. 

25:04 – Where electromagnetic interference comes from 

Jeff ranks the internal sources he sees most in the lab: switch-mode power supplies first, then microcontrollers and high-speed digital logic, then bus protocols and Ethernet transceivers that radiate off cabling. External sources include EV and hybrid charging systems that couple noise between the vehicle and the grid, and electrostatic discharge that leaves latent damage months before a part fails. For vehicle programs, this maps directly to automotive EMC testing. 

30:10 – Techniques for identifying risk early 

The cheapest risk reduction happens before layout. Jeff recommends a system-level EMC review of the block diagram, time on the schematic to add debug pads and zero-ohm jumpers, and simulation tools with near-field and far-field solvers, which Element supports through electromagnetic simulation and modeling. He also flags the RF section that shares a board with switching supplies as an early risk to identify, relevant to radio and wireless testing.

37:12 – Design decisions that drive compliance 

Jeff lists the decisions that determine the outcome: system architecture planning, choosing a linear regulator over a switcher where speed is not needed, PCB stack-up and ground-plane continuity, high-speed signal routing and decoupling, and mechanical enclosure grounding. His line is blunt. Design because you need fast, not because you want fast, and slow every rise and fall time you can. 

40:49 – Common causes of EMC failures during development 

The recurring failures are grounding strategy, excessive loop areas from poor routing, decoupling errors, and breaks in shield termination that must run a full 360 degrees. Jeff corrects a common myth that more decoupling capacitors are always better and warns that skipping pre-compliance almost guarantees a six- to eight-week return to the chamber for a new design iteration. 

43:31 – When to use an external EMC lab 

Move to a lab when the team lacks the knowledge, equipment, or a shielded environment; when the design freeze is approaching without pre-compliance data; or when measurement uncertainty is suspected, and correlation cannot be trusted. Full compliance ultimately requires an accredited lab, and Element runs accredited EMC facilities across North America and Europe for automotive, medical, industrial, aerospace, and defense EMC testing. 

45:39 – Practical takeaways 

Jeff closes the technical section with his rules. Pre-compliance reveals risk, not a pass or fail. Setup quality determines the value of the data. EMC issues come from design decisions, not a lack of planning. Early diagnostics reduce late redesigns. EMC success is a design activity, not a test event. 

47:47 – About Element’s EMC capabilities 

Jeff gives a short overview of Element’s testing, inspection, certification, and calibration services, an EMC laboratory network spanning automotive, medical device, industrial, aerospace, and defense, and how to reach the team for test plan support or development testing. The Burton, Michigan lab runs three shifts for EMC work. 

If you are preparing for formal EMC testing, our accredited EMC testing laboratories support programmes across automotive, aerospace, medical device, industrial and connected technology applications. To discuss your specific EMC challenge, speak to one of our experts.