Code of Federal Regulations, Title 47, Part 15 (47 CFR 15) is an oft-quoted part of Federal Communications Commission (FCC) rules and regulations regarding unlicensed transmissions. It is a part of Title 47 of the Code of Federal Regulations (CFR), and regulates everything from spurious emissions to unlicensed low-power broadcasting. Nearly every electronics device sold inside the United States radiates unintentional emissions, and must be reviewed to comply with Part 15 before it can be advertised or sold in the US market.
Subpart A includes 21 sections from 15.1 to 15.38.
47 CFR 15.1 states that any radiator (that which emits radio energy), whether or not intentional, must be licensed unless it meets 47 CFR 15 or is otherwise exempted by the FCC.
47 CFR 15.3 the definitions are defined by the definition given.
47 CFR 15.5 contains a general provision that devices may not cause interference and must accept any interference received. You are cautioned that any changes or modifications to devices not expressly approved by the party responsible for compliance may void your authority to operate devices.
47 CFR 15.5 prohibits intentional damped wave transmissions such as spark-gap transmitters which were common before the 1920s but occupy a needlessly wide range of frequencies.
47 CFR 15.9 prohibits operating a device under Part 15 for the purpose of eavesdropping, except when under lawful authority of law enforcement or when all parties in a conversation consent.
Subpart B deals with unintentional radiators—devices for which the purpose is not to produce radio waves, but which do anyway, such as computers. There are 16 sections between 15.101 and 15.123.
Subpart C deals with devices that are specifically designed to produce coherent radio waves, such as small transmitters. Specific to broadcasting, 15.221 (and 15.219) deal with the AM band; & 15.239 deals with the FM band. 15.247 covers most Wi-Fi frequencies that aren't U-NII.
Sections 15.301 to 15.323 deal with unlicensed PCS devices from 1.91 to 1.93 GHz.
Cordless telephones using DECT 6.0 standards use this unlicensed PCS band.
15.401 to 15.407 deal with unlicensed National Information Infrastructure (U-NII) devices
15.501 to 15.525 deal with ultra-wideband (UWB) devices, including ground-penetrating radar.
15.601 to 15.615 deal with broadband over power lines (BPL) devices operating in the 1.705–80 MHz band over medium- or low-voltage lines.
15.701 to 15.717 deal with (TVBDs), TV-band devices that operate on an available television channel in the broadcast television band. An available channel is a 6 megahertz television channel that is not being used by an authorized service in a given geographical location, and thus may be used by unlicensed devices under the provisions of this rule part.
Unintentional radiators are designated in two major classes:
The emission limits for Class B devices are about 10 dB more restrictive than those for Class A devices since they are more likely to be located closer to radio and television receivers.
These devices include personal computers and peripheral devices, and electrical ballasts for fluorescent lights.
On the standard AM broadcast band, under 15.219, transmission power is limited by 100 milliwatts of DC input power to the final RF stage (with restrictions on size, height of, and type of antenna), or alternatively, under 15.221, if the AM transmission originates on the campus of an educational institution, the transmission can theoretically be any power so long as it does not exceed the field strength limits stated in 15.209 at the perimeter of the campus, 24,000/fkHz μV/m.
Unlicensed broadcasts on the FM broadcast band (88 to 108 MHz) are limited to a field strength of 250 microvolts per meter (~48 dBμ) measured at a distance of 3 meters. This corresponds to a maximum effective radiated power of 0.01 microwatts. Emissions must be kept within the 88.0 to 108.0 MHz band under 15.239 rules.
Unlicensed broadcasts on the TV broadcast bands are prohibited, except for certain medical telemetry devices and other low power auxiliary stations. 87.5 to 88.0 MHz is considered part of the VHF TV low band. For TV, 15.241 and 15.242 deal with high VHF (channels 7 to 13), 15.242 also deals with UHF (band IV and band V).
Frequently encountered types of "Part 15" transmitters include:
Electronic equipment from computers to intentional transmitters can produce unwanted radio signals and are subject to FCC regulation. For digital devices including computers and peripherals, FCC Class B is the more stringent standard, applying to equipment marketed for use in the home, even if it could be used elsewhere. Home users are likely to be annoyed by interference to TV and radio reception. Class A is a looser standard for equipment intended only for business, industrial and commercial settings.
Transmitters also must adhere to a spectral mask, to prevent adjacent-channel interference, intermediate frequency interference, and intermodulation.