1. The Best Value in Electronic Test & Measurement

2. Pre-compliance Basics
How to get through compliance quickly

3. What is EMC Testing? EMC = Electromagnetic Compatibility
Moving electrons create electromagnetic waves
For an intentional radiator (radios, WiFi, etc.) these are desirable.. But..
Unintentional radiators:
The waves interfere with other intentional radiators or cause issues (jamming, lock up, failure).. This undesirable radiation is known as Electromagnetic Interference (EMI)
Governments regulate the amount of EMI allowed (RF or other)
Guidelines in the US are created and enforced by the FCC (Federal Communications Commission)
Compliance is self-determined… but the testing can be complex.
End result – you have to rely on special test houses (Compliance Labs) to perform the required testing.

4. Basic EMC tests
Radiated Emissions – How much RF is flying off of a product
Conducted Emissions – How much RF is sent back down the power line
Susceptibility - How much RF can your product take before failure

5. Radiated Emissions Must isolate the DUT from the environmental RF
Open air or special chamber (anechoic or semi-anechoic) = $$
Physical and electrical test setup is critical
Averages $2000/day.. for testing. Consultation can cost more

6. Radiated Emissions Basic Setup

7. Radiated Emissions: Pre-compliance
Difficult without a chamber, but possible
Consistent, repeatable, and well understood environmental RF (background scans)
Physical layout should not change (people, equipment, desks, etc..)
Reflections (Hot/cold spots) should be understood
Still relative measurements.. So, you can get meaningful data..
Use a fixed physical layout (measured distances and angles), pictures of the tests, etc..
Perform an environmental RF test immediately before and after DUT testing (DUT off)
If you have a failed test report, you can use this to help “key in” on specific frequencies

8. Near field probes Near field = close proximity measurements
Far field measurement antennas ~ 1 m or more away from DUT
Near field ~ an inch or two
Magnetic (H) and Electric (E) field probe types
Can ignore environmental effects due to weak coupling
Simple setup
Fixturing can minimize variations and make better relative measurements
Can use with a failed report to help find root cause of issues

9. Near field probes

10. Current clamp
Cabling can radiate and cause failures.. Especially poorly shielded cables
Can make relative measurements using a current clamp

11. Conducted Emissions
Measures DUT energy directed towards the power grid
Interference on power lines causes AM radio interference
Much more repeatable than radiated.. And easier

12. Susceptibility Irradiate DUT and check performance
Must shield to prevent exceeding FCC regulations for unlicensed transmissions
Can use near field probes to inject signals onto boards and traces

13. Tools Spectrum analyzer – The “eyes” of the EMC Engineer
Oscilloscope with FFT
Sequencing software
Near field probes
Antennas (rabbit ears and bowties can be useful in some situations)
Current clamps
Aluminum foil
Conductive tape
Line Impedance Stabilization Network (LISN) and transient limiter
RF Source with AM modulation capability probe can easily find leaks
AM Radio (can be used to troubleshoot radiated issues)

14. SIGLENT Tools
SIGLENT SSA3021X/32X – 2.1 GHz/3.2 GHz Spectrum analyzer (Start at $1395)
SIGLENT SVA1015X – Spectrum and vector network analyzer (Start at $1395)
EasySpectrum software (free)
SIGLENT SDS series of scopes (Start at $299)
SRF5030 and SRF5030T near field probes
More to come…

15. Common failure root causes
Harmonics- What is the rise time of digital signals within your enclosure?
Faster rise times = higher frequency harmonics = potential for trouble
Shield terminations on connectors – Are they really shielded 360°?
Small common mode currents (a few uA) can radiate.. And will find an antenna
LCDs – Rarely shielded well and have high data rates
Unintentional antennas (cutouts/holes are physically identical to “solid” antennas)
Splits in ground planes .. time varying currents follow path of least impedance, not just resistance..
Control current return paths, or the electrons will find their own way “home”
Enclosure shielding/gasketing – Nearfield probe can easily find leaks

16. Resources Application Notes: Books: Pre-compliance basics:
Pre-compliance Near Field:
Pre-compliance Conducted Emissions:
EasySpectrum software:
Books:
EMI Troubleshooting Cookbook: Andre’ and Wyatt
Electromagnetic Compatibility Engineering: Ott

17. Resources, con’t Useful sites: FCC subpart 15 limits: www.fcc.gov
The EMC Blog:
Ken Wyatt:
Doug Smith:
IEEE EMC Society:

18. SIGLENT—The Best Value in Electronic Test & Measurement
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SIGLENT—The Best Value in Electronic Test & Measurement
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