Meaning
Federal regulations in the United States specify maximum allowable electromagnetic field strength levels for unlicensed radio frequency devices. Engineers design wireless products to operate within FCC Part 15 radiated limits to prevent harmful interference with licensed spectrum users. Section 15.247 and Section 15.249 govern intentional radiators operating in industrial and medical frequency bands.
Spectral Threshold
Field strength boundaries vary according to frequency band and device classification. Intentional radiators operating at two point four gigahertz must not exceed fundamental field strengths of fifty millivolts per meter measured at three meters. Unintentional emissions from digital logic circuitry fall under subpart B, which enforces strict quasi-peak limits between thirty megahertz and one gigahertz.
Higher harmonic emissions must satisfy peak and average field strength restrictions to ensure electromagnetic compatibility with adjacent receivers.
Compliance Distance
Compliance measurements occur at prescribed distances of three meters or ten meters inside semi-anechoic test chambers.
Out-of-band Suppression
Radiated emissions outside designated frequency bands must be attenuated by at least twenty decibels relative to fundamental carrier power. Automated measurement software adjusts raw spectrum analyzer readings using antenna factors and cable loss tables. Test documentation recorded during certification proves that final product assemblies maintain required field strength attenuation under maximum RF output settings.
Adherence to FCC Part 15 radiated limits forms a mandatory prerequisite for legal distribution of radio equipment in American commercial markets.
