FCC Test Equipment & Facilities Requirements 1 — Questions and Answers
Question 1: What is the minimum shielding effectiveness typically required for an RF shielded room used in FCC testing?
- 100 dB attenuation from 10 kHz to 10 GHz (Correct answer)
- 10 dB attenuation across all frequencies
- 50 dB attenuation at 1 GHz only
- No minimum is specified; it depends on the ambient RF environment
Correct answer: 100 dB attenuation from 10 kHz to 10 GHz
High-performance RF shielded rooms for FCC testing typically provide at least 100 dB of shielding effectiveness across the measurement frequency range to ensure that external RF signals do not corrupt emission measurements.
Question 2: What type of absorber material is placed on the walls, ceiling, and floor of an anechoic chamber for FCC EMC testing?
- Pyramidal carbon-loaded polyurethane foam absorbers (Correct answer)
- Concrete with embedded steel mesh
- Copper foil lining with no absorbers
- Fibreglass panels with air gaps
Correct answer: Pyramidal carbon-loaded polyurethane foam absorbers
Pyramidal carbon-loaded polyurethane foam absorbers are used in anechoic chambers to convert incident RF energy into heat, preventing reflections that would distort the free-space measurement environment.
Question 3: What is the purpose of a spectrum analyzer or EMI receiver in FCC radiated emissions testing?
- To measure the amplitude of electromagnetic emissions at each frequency across the test range (Correct answer)
- To generate calibrated RF signals for testing device immunity
- To measure the impedance of the device under test
- To control the automated test turntable
Correct answer: To measure the amplitude of electromagnetic emissions at each frequency across the test range
An EMI receiver or spectrum analyzer measures the level of electromagnetic emissions radiated by the device under test across the specified frequency range, providing the data that is compared against FCC emission limits.
Question 4: What is a 'pre-scan' in FCC radiated emissions testing and why is it performed?
- A fast sweep to identify peak emission frequencies before conducting the slower, definitive final scan (Correct answer)
- A preliminary review of the test setup checklist before beginning measurements
- A calibration check performed on the EMI receiver before each test
- A review of the device's technical documentation before testing begins
Correct answer: A fast sweep to identify peak emission frequencies before conducting the slower, definitive final scan
A pre-scan uses a peak detector in fast sweep mode to quickly identify candidate frequencies where emissions are highest, allowing the time-consuming final measurement to focus on those specific frequencies rather than scanning the entire range.
Question 5: What power supply conditions must be verified when setting up a device for FCC conducted emissions testing?
- The device must be powered from a nominal AC line voltage with the LISN inserted, operating under its worst-case emission configuration (Correct answer)
- The device must be battery powered only during conducted emissions testing
- The device must be powered from a DC supply to avoid power line effects
- The power supply condition is irrelevant if the LISN is properly installed
Correct answer: The device must be powered from a nominal AC line voltage with the LISN inserted, operating under its worst-case emission configuration
The device under test must be powered from a regulated AC source at nominal line voltage through the LISN, and must be placed in its worst-case operating mode (typically maximum processing load) to ensure the highest emission levels are measured.
Question 6: What is the purpose of a ground plane in a radiated emissions test setup?
- To provide a reference conducting plane that simulates installation on a typical metallic surface and ensures measurement repeatability (Correct answer)
- To prevent static electricity from damaging the device under test
- To provide a return current path for the LISN
- To shield the receive antenna from low-frequency magnetic fields
Correct answer: To provide a reference conducting plane that simulates installation on a typical metallic surface and ensures measurement repeatability
The metallic ground plane (typically 2m × 2m or larger) provides a defined reflective surface beneath the equipment under test, ensuring repeatable measurement conditions and simulating typical deployment on a metallic surface such as a desk or floor.
FCC Test Equipment & Facilities Requirements 1
What is the minimum shielding effectiveness typically required for an RF shielded room used in FCC testing?