FCC Test Equipment & Facilities Requirements 2 — Questions and Answers
Question 1: What is a 'log-periodic dipole array' (LPDA) antenna and what frequency range does it cover in FCC testing?
- A wideband antenna used for radiated emissions measurements typically from 200 MHz to 1 GHz (Correct answer)
- A high-gain directional antenna used only above 10 GHz
- An omnidirectional antenna used for the 30–200 MHz range
- A resonant dipole used for calibration purposes only
Correct answer: A wideband antenna used for radiated emissions measurements typically from 200 MHz to 1 GHz
An LPDA is a broadband directional antenna whose element lengths and spacings are scaled logarithmically, providing relatively flat gain and impedance characteristics across a wide frequency range, typically used from 200 MHz to 1 GHz in FCC emissions testing.
Question 2: What is the function of a preamplifier in an FCC radiated emissions test setup?
- To boost weak signals from the receive antenna above the noise floor of the spectrum analyzer/EMI receiver (Correct answer)
- To amplify the signal from the device under test for easier detection
- To increase the power output of the transmit antenna during calibration
- To filter harmonics from the signal before measurement
Correct answer: To boost weak signals from the receive antenna above the noise floor of the spectrum analyzer/EMI receiver
A preamplifier placed close to the receive antenna amplifies the incoming signal before it travels through the coaxial cable to the receiver, improving the overall system sensitivity and ensuring that weak emissions above the noise floor can be measured accurately.
Question 3: What safety consideration must be addressed before placing personnel inside a shielded chamber during active RF testing?
- RF exposure must be evaluated and personnel must not be present when transmit power levels exceed safe exposure limits (Correct answer)
- Personnel must wear anti-static wrist straps at all times
- The chamber door must remain open during any measurement
- All metallic objects must be removed from the chamber before power is applied
Correct answer: RF exposure must be evaluated and personnel must not be present when transmit power levels exceed safe exposure limits
RF energy levels inside a shielded chamber can exceed FCC maximum permissible exposure (MPE) limits when transmit antennas are in use, so personnel must not enter the chamber or must be protected when RF fields above safe levels are present.
Question 4: What is the required height range for a receive antenna during FCC semi-anechoic chamber radiated emissions testing at 3 meters?
- 1 to 4 meters above the ground plane (Correct answer)
- 0 to 2 meters above the ground plane
- 3 to 6 meters above the ground plane
- Fixed at 1.5 meters, no scanning required
Correct answer: 1 to 4 meters above the ground plane
ANSI C63.4 requires the receive antenna to be scanned in height from 1 to 4 meters above the ground plane (in a semi-anechoic chamber at 3-meter separation) to find the height that maximizes the received signal level.
Question 5: What is a 'hybrid chamber' or 'giga-cell' in the context of FCC testing above 1 GHz?
- A test facility that combines shielded room construction with partial absorber lining to perform measurements above 1 GHz according to ANSI C63.4-2014 or similar standards (Correct answer)
- A chamber that simultaneously tests radiated and conducted emissions
- A reverberation chamber modified to produce uniform fields above 1 GHz
- A portable shielded tent used for on-site FCC compliance verification
Correct answer: A test facility that combines shielded room construction with partial absorber lining to perform measurements above 1 GHz according to ANSI C63.4-2014 or similar standards
A hybrid or giga-cell chamber uses absorber on portions of the chamber walls to reduce unwanted reflections for measurements above 1 GHz where a fully anechoic environment is required, allowing testing per ANSI C63.4-2014 above 1 GHz in an indoor facility.
Question 6: What is the purpose of a 'signal generator' or 'RF source' in FCC test equipment immunity testing?
- To generate calibrated RF interference signals to test how well the device under test withstands electromagnetic interference (Correct answer)
- To measure the emission levels from the device under test
- To calibrate the receive antenna factor
- To provide a reference frequency for the spectrum analyzer
Correct answer: To generate calibrated RF interference signals to test how well the device under test withstands electromagnetic interference
In immunity (susceptibility) testing, a signal generator produces a controlled RF field that stresses the device under test to verify it continues to function correctly when exposed to electromagnetic interference, complementing the emissions test.
FCC Test Equipment & Facilities Requirements 2
What is a 'log-periodic dipole array' (LPDA) antenna and what frequency range does it cover in FCC testing?