ANSI C63.4
American National Standard for Methods of Measurement of Radio-Noise Emissions from Low-Voltage Electrical and Electronic Equipment in the Range of 9 kHz to 40 GHz — the primary test method standard for FCC Part 15 Subpart B unintentional radiator compliance. Part of the Compatible Electronics Learning Center.
What is ANSI C63.4?
ANSI C63.4 is an American National Standard published by the Accredited Standards Committee C63® on Electromagnetic Compatibility. It specifies the methods of measurement of radio-noise emissions from low-voltage electrical and electronic equipment — specifically, the conducted and radiated emission measurement procedures used to demonstrate compliance with the FCC's technical regulations for unintentional radiators.
Unintentional radiators are devices that generate RF energy as a byproduct of their operation — computers, tablets, printers, monitors, switching power supplies, LED drivers, and virtually any digital electronic product. These devices must comply with FCC Part 15 Subpart B emission limits, measured according to ANSI C63.4 procedures, before they can be marketed in the United States.
Compatible Electronics is NVLAP-accredited to test to ANSI C63.4 (2014) and provides dedicated ANSI C63.4 testing services at our Lake Forest/Silverado, Brea, and Newbury Park locations.
Scope and Application
ANSI C63.4 covers low-voltage electrical and electronic equipment operating from AC or DC power sources at voltages up to approximately 600 V. It specifies measurement methods for:
- Conducted emissions — disturbances conducted onto the AC mains supply or DC power input, measured from 150 kHz to 30 MHz using a Line Impedance Stabilization Network (LISN)
- Radiated emissions — electric field strength radiated from the equipment and its associated cables, measured from 30 MHz to 40 GHz (with the upper frequency determined by the device's highest internal frequency)
- Discontinuous interference — click noise and other intermittent disturbances from equipment with motors, thermostats, or other switching elements
The standard is most commonly applied to FCC Part 15 Subpart B digital devices — any device that uses digital techniques and generates and uses timing signals or pulses at a rate in excess of 9,000 pulses per second. This covers an enormous range of consumer and commercial electronics.
Class A vs. Class B Equipment
A
Class A Digital Devices
Equipment that has been tested and found to comply with the Class A limits in FCC Part 15 Subpart B. Class A is intended for commercial, industrial, or business environments — not marketed for use in the home. Class A limits are 10 dB or more less stringent than Class B limits in key frequency ranges. A Class A device that is marketed for home use must comply with the more stringent Class B limits.
B
Class B Digital Devices
Equipment that is marketed for use in the home environment, regardless of where it is actually used. Class B limits are the most protective in the FCC framework, designed to ensure that products sold to the general public do not cause interference to broadcast television, radio, and other services received in residential locations. Most consumer electronics require Class B compliance.
Key Measurement Procedures
ANSI C63.4 provides detailed specifications for every aspect of the measurement process to ensure reproducibility across different laboratories:
1
Test Site Requirements
Radiated emission measurements are performed on an Open Area Test Site (OATS) or in an accredited alternative test site — typically a semi-anechoic chamber (SAC) validated to produce equivalent results to an OATS. The standard specifies site validation procedures using a normalized site attenuation (NSA) measurement. Compatible Electronics' semi-anechoic chambers are validated to ANSI C63.4 requirements.
2
Antenna Height Scanning
For radiated emission measurements, the receive antenna is scanned vertically (typically 1 m to 4 m above the ground plane) while the equipment under test (EUT) is rotated through 360°. The maximum emission in any direction and at any antenna height is recorded and compared to the applicable limit. This scan procedure ensures that the worst-case radiation geometry is captured.
3
Detector Functions
ANSI C63.4 specifies the use of quasi-peak (QP) and average (AVG) detectors, consistent with CISPR 16 measurement receiver specifications. For FCC Part 15 Subpart B, the quasi-peak detector is the primary measurement detector for most frequency ranges, though average limits also apply in certain bands for conducted emissions.
4
EUT Configuration and Operating Modes
The standard specifies how the EUT must be configured during testing — including cable arrangements, peripheral connections, and operating modes. The EUT must be exercised in the configuration that produces the maximum emissions, which requires understanding the product's internal clock frequencies and data activity patterns.
FCC Authorization Methods for Subpart B Devices
Products tested to ANSI C63.4 may be authorized through two FCC mechanisms:
1
FCC Certification
Required for certain Class B devices including personal computers, peripherals, and other specified products. A test report demonstrating compliance to ANSI C63.4 is submitted to an FCC-authorized Telecommunications Certification Body (TCB). Compatible Electronics is an FCC-authorized TCB (CETCB), enabling us to both test and certify qualifying devices. See our FCC certification and FCC certification testing pages.
2
Supplier's Declaration of Conformity (SDoC)
Used for most Class A devices and certain Class B devices including peripherals not requiring certification. The responsible party tests the device (to ANSI C63.4 procedures), affixes an FCC label, and maintains test records. No TCB submission is required, but test records must be retained and made available to the FCC on request. See our FCC SDoC authorization guide.
ANSI C63.4 Accreditation at Compatible Electronics
Compatible Electronics holds NVLAP accreditation (Lab Code 200527-0) for ANSI C63.4 across multiple versions and applications:
| Standard / Application | Locations Accredited |
|---|
| ANSI C63.4 (2014) — Unintentional Radiators, FCC Part 15 Subpart B | Lake Forest/Silverado, Brea, Newbury Park |
| ANSI C63.4 (2009) — Unintentional Radiators, FCC Part 15 Subpart B | Brea |
| ANSI C63.4 (2003) — Unintentional Radiators, FCC Part 15 Subpart B | Brea |
| ANSI C63.4 (2003) — Intentional Radiators, FCC Part 15 Subpart C | Brea |
ⓘ Combined US/Canada testing: Many products require compliance testing for both the FCC (US) and Industry Canada / ISED (Canada). ANSI C63.4 measurements can often be used to support both FCC and ICES-003 compliance in a combined test campaign, minimizing time and cost. Ask our engineering team about combined testing strategies.
Ready to Test Your Product?
Compatible Electronics is an NVLAP-accredited EMC testing laboratory (Lab Code 200527-0) and FCC-authorized TCB with three Southern California locations. Fast turnaround, combined FCC/ICES campaigns available.
www.celectronics.com
