FCC §15.247

FCC §15.247 sets technical requirements for frequency-hopping and digitally modulated intentional radiators operating in the 902–928 MHz, 2400–2483.5 MHz and 5725–5850 MHz bands. It is one of the principal rule sections used for licence-exempt wireless devices under 47 CFR Part 15.

Common applications include Wi-Fi in the 2.4 GHz band, Bluetooth, Zigbee and other proprietary or standards-based data links. The applicable limits depend on the operating band, modulation method, hopping configuration and antenna system.

Systems Covered by §15.247

• Frequency Hopping Spread Spectrum (FHSS)

• Digitally modulated systems, including DSSS and OFDM implementations

As with other Part 15 devices, operation is subject to the condition that the device does not cause harmful interference and must accept interference received. Our FCC requirements overview explains the wider US equipment-authorization framework.

Digital Modulation Requirements

Digitally modulated systems may operate in all three §15.247 bands. Their minimum 6 dB bandwidth is 500 kHz. The maximum conducted output power is 1 W, subject to the antenna-gain provisions described below. Power spectral density may not exceed 8 dBm in any 3 kHz band.

Frequency-Hopping Requirements

The minimum number of hopping channels, bandwidth limit and permitted conducted power are band-specific:

• 902–928 MHz: At least 50 channels below 250 kHz 20 dB bandwidth, with up to 1 W conducted power; at least 25 channels from 250 kHz to the 500 kHz maximum, with up to 0.25 W when 25–49 channels are used.

• 2400–2483.5 MHz: At least 15 channels; up to 1 W with at least 75 non-overlapping channels, otherwise up to 0.125 W.

• 5725–5850 MHz: At least 75 channels, a maximum 20 dB bandwidth of 1 MHz and up to 1 W conducted power.

Hopping-channel carrier frequencies are generally separated by at least 25 kHz or the full 20 dB bandwidth, whichever is greater. In the 2.4 GHz band, systems operating at no more than 125 mW may instead use 25 kHz or two-thirds of the 20 dB bandwidth, whichever is greater.

Antenna Gain and Point-to-Point Operation

The conducted-power limits are based on antennas with directional gain not exceeding 6 dBi. Under the general rule, each decibel of gain above 6 dBi requires an equal reduction in conducted power. Where the 1 W base limit applies, this maintains an EIRP of approximately 4 W.

Different provisions apply to systems used exclusively for fixed point-to-point operation:

• In the 2.4 GHz band, conducted power is reduced by 1 dB for every 3 dB of antenna gain above 6 dBi.

• In the 5.8 GHz band, directional gain above 6 dBi does not require a corresponding reduction in conducted power.

These exceptions do not apply to point-to-multipoint systems, omnidirectional applications or multiple co-located transmitters carrying the same information.

Unwanted Emissions

Outside the operating band, radio-frequency power in any 100 kHz bandwidth must generally be at least 20 dB below the highest in-band level. A 30 dB attenuation requirement applies when compliance with the conducted-power limit is based on the permitted RMS-averaging method. Emissions in restricted bands must also comply with §§15.205 and 15.209.

Certification and Compliance

Equipment operating under §15.247 is authorized through the FCC Certification procedure. Testing covers the applicable power, bandwidth, hopping, spectral-density and unwanted-emission requirements, and certification is granted by the FCC or an FCC-recognized Telecommunications Certification Body (TCB).

The resulting FCC ID combines the grantee code assigned to the responsible party with the product code. The approved equipment must be identified and accompanied by the information required by the applicable FCC rules.

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