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.
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Subpart A includes 21 sections from 15.1 to 15.38.
47 C.F.R. 15.1b 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 C.F.R. 15.3 contains definitions.
47 C.F.R. 15.5 contains a general provision that devices may not cause interference and must accept interference from other sources. It also prohibits the operation of devices once the operator is notified by the FCC that the device is causing interference. 47 C.F.R. 15.5d prohibits intentional damped wave transmissions, which were common before the 1920s but cut across large sections of frequencies.
47 C.F.R. 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, 15.239 deals with the FM band, while 15.221 (and 15.219) deal with the AM band.
Sections 15.301 to 15.323 deal with unlicensed PCS devices from 1910 to 1930MHz.
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.
Unintentional radiators are designated into two major classes:[1]
These devices include personal computers and peripheral devices, and electrical ballasts for fluorescent lights.
Unlicensed broadcasts on the FM broadcast band (88 to 108 MHz) are limited to a field strength of 250 µV/m at a distance of 3 meters from the antenna. This is equivalent to 0.01 microwatts.[2] Emissions must be kept within the 88.0 to 108.0 MHz band under Part 15 rules.
The FM broadcast band is limited but not restricted to 87.9 MHz (but see note below on TV) to 107.9 MHz. There are two class D FM stations on 87.9 MHz.[3] Any unlicensed 88 to 108 MHz broadcasting with a signal strength greater than 250 µV/m at a distance of 3 m from the antenna is punishable by law and confiscation of all broadcast equipment. Low power station licenses are available to noncommercial educational entities and public safety/travellers information entities, but not individuals or commercial operations. .[4]
Unlicensed broadcasts on the TV broadcast bands are prohibited, except for certain medical telemetry devices, wireless microphones, and other 'low power auxilliary' stations with an output or 50 mW or less. 87.5 to 88.0 MHz is considered part of the VHF TV low band (channel 6 analog audio is on 87.75), though it shows up on most FM tuners. 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).
On the standard AM broadcast band, transmission power is limited by 100 milliwatts of DC input power to the final RF stage, (with restrictions on size, height 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, 24000/fkHz µV/m.
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.