FCC Rules and Regulations For Part 15 Unlicensed Wireless Equipment

FCC Rules for Unlicensed Wireless Equipment operating in the ISM bands

The ISM radio bands were originally set aside for electromagnetic radiation produced by industrial, scientific and medical (ISM) equipment. In the early 1990's the Federal Communcations Commission (FCC) allowed using three of the ISM bands for unlicensed communication equipment. These three ISM bands are:

  • 902 to 928 MHz
  • 2.400 to 2.4835 GHz
  • 5.725 to 5.875 GHz

In the United States the use of these bands for communication purposes is regulated by part 15 of the FCC rules.

Maximum Transmit Output Power in the ISM bands

Several of the FCC part 15 rules govern the transmit power permited in the ISM bands. Here is a summary of those rules:

  1. Maximum transmitter output power, fed into the antenna, is 30 dBm (1 watt).
  2. Maximum Effective Isotropic Radiated Power (EIRP) is 36 dBm (4 watt).
    You can obtain the EIRP by simply adding the transmit output power, in dBm, to the antenna gain in dBi.
  3. If your equipment is used in a fixed point-to-point link, there are two exceptions to the maximum EIRP rule above:
  4. In the 5.8 GHz band the rule does not apply, i.e., in a fixed point-to-point link you can use antennas with any gain (although the transmit power fed into the antenna is still limited to 30 dBm).
  5. In the 2.4 GHz band you can increase the antenna gain to get an EIRP above 36 dBm but for every 3dBi increase of antenna gain you must reduce the transmit power by 1 dBm. The table below shows the combinations of allowed transmit power / antenna gain and the resulting EIRP.

Maximum = See FCC Special Rule *2

Maximum Power from Intentional Radiator *1 / Maximum Antenna Gain (dBi) / EIRP (dBm) *3 / EIRP (watts) *3
30dBm or 1 watt / 6 / 36 / 4
29dBm or 800mW / 9 / 38 / 6.3
28dBm or 630mW / 12 / 40 / 10
27dBm or 500mW / 15 / 42 / 16
26dBm or 400mW / 18 / 44 / 25
25dBm or 316mW / 21 / 46 / 39.8
24dBm or 250mW / 24 / 48 / 63
23dBm or 200mW / 27 / 50 / 100
22dBm or 160mW / 30 / 52 / 158

*1 The FCC terminology of Intentional Radiator is the transmitter power of the wireless equipment, such as a wireless access point, router or bridge. *2 The FCC ruling states that for every 1dBi the Intentional Radiator is reduced below the initial 30dBm that the antenna gain may be increased from the initial 6dBi by 3dB. *3 Equivalent Isotropically Radiated Power (EIRP) is terminology for the total RF power radiated by the antenna.
The responsibility for staying within these power limits falls on the operator (or, if professionally installed, on the installer).

Maximum Transmit Output Power in the UNII bands

Band / Frequency / Max Intentional
Radiation *1 / EIRP *2
U-NII Low (U-NII-1) Indoor Only / 5150-5250 MHz / 50 mW / 200 mW
U-NII Mid (U-NII-2) Indoor/Outdoor / 5250-5350 MHz / 250 mW / 1 Watt
U-NII Worldwide Indoor/Outdoor DFS / 5470-5725 MHz / 250 mW / 1 Watt
U-NII Upper (U-NII-3) / 5725-5825 MHz / 1 Watt / 200 Watt

*1 The FCC terminology of Intentional Radiator is the transmitter power of the wireless equipment, such as a wireless access point, router or bridge. *2 Equivalent Isotropically Radiated Power (EIRP) is terminology for the total RF power radiated by the antenna.

FCC Rules Applicable to ISM-Spread Spectrum Radios

The FCC regulates not only the "intentional radiation" of radio transmitters, but also the "unintentional radiation" of noise from all sorts of electrical equipment. The FCC regulations appear in title 47 of the United States Code of Federal Regulations (47CFR), The FCC part 15 rules that affect operation of communication equipment in the ISM bands are listed below:

FCC 15.107 / Conducted Emissions including AC Line
FCC 15.109 / Unintentional radiation from ITE
FCC 15.205 / Restricted bands of operation
FCC 15.207 / Conducted emissions from intentional radiators
FCC 15.209 / Radiated emission limits, general requirements
FCC 15.247 / ISM Band Communication Equipment

FCC Rules Applicable to U-NII

U-NII is an FCC regulatory domain for 5- GHz wireless devices. U-NII power limits are defined by the United States CFR Title 47 (Telecommunication), Part 15 - Radio Frequency Devices, Subpart E - Unlicensed National Information Infrastructure Devices, Paragraph 15.407 - General technical requirements.