RF Safety and Regulatory Spectrum Regulation Informational

What are the ISM bands and what are the rules for operating RF equipment in them?

ISM (Industrial, Scientific, and Medical) bands are frequency bands designated by the ITU for non-communication uses of RF energy. However, many of these bands are also heavily used for short-range wireless communication (Wi-Fi, Bluetooth, Zigbee): (1) Major ISM bands: 2.4-2.5 GHz: the most heavily used ISM band worldwide. Used for: Wi-Fi (802.11b/g/n/ax), Bluetooth, Zigbee, microwave ovens, and cordless phones. Available worldwide (harmonized globally). FCC power limit: 1 W (30 dBm) conducted power with 6 dBi antenna gain (total EIRP = 4 W for point-to-multipoint). 5.725-5.875 GHz: used for Wi-Fi (802.11a/n/ac/ax), and ISM applications. FCC power limit: 1 W conducted, 36 dBm EIRP for point-to-point. 902-928 MHz: used for ISM and unlicensed communication in the Americas. Used for: LoRa/LoRaWAN, Z-Wave, some RFID systems. Not available in Europe (the 868 MHz band is the EU equivalent, with different rules). FCC power limit: 1 W (30 dBm) conducted. 5.8 GHz: a sub-band of the 5 GHz ISM band. Used for some dedicated ISM applications and short-range radar. 24.0-24.25 GHz: ISM band used for short-range radar (automotive, industrial), ISM heating, and some data links. 61.0-61.5 GHz: ISM band within the 60 GHz unlicensed spectrum. (2) Rules for operation: ISM devices must accept any interference from licensed services and other ISM users (ISM devices have no protection from interference). ISM devices must not cause harmful interference to licensed services. Specific technical requirements depend on the frequency band and the regulatory domain (FCC Part 15 in the US, ETSI EN 300 328 in the EU). Spread spectrum or frequency hopping is typically required for higher power operation (FCC Part 15.247). Digital modulation with minimum 6 dBi processing gain may be used instead of frequency hopping (Part 15.247). (3) Communication in ISM bands: although ISM bands were originally intended for non-communication uses (industrial heating, medical diathermy): regulatory agencies (FCC, ETSI) have allowed communication devices to operate under specific rules. The huge success of Wi-Fi and Bluetooth is built on ISM band access.

Category: RF Safety and Regulatory

Updated: April 2026

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ISM Band Operations

The ISM bands are the foundation of the wireless revolution, enabling billions of Wi-Fi and Bluetooth devices to operate without individual frequency coordination or licensing.

FCC Part 15.247 Rules (2.4 & 5.8 GHz)

(1) Frequency hopping spread spectrum (FHSS): must hop across at least 15 channels (for 2.4 GHz). Maximum dwell time on any channel: 0.4 seconds. Transmit power: up to 1 W (30 dBm) conducted. Antenna gain: allowed up to 6 dBi without power reduction. Above 6 dBi: reduce conducted power by 1 dB for every 3 dB of antenna gain above 6 dBi. (2) Direct sequence spread spectrum (DSSS) / digital modulation: minimum 6 dB processing gain (the digital bandwidth must be at least 4× the data rate). Transmit power: up to 1 W (30 dBm) conducted. Antenna gain: same rules as FHSS. (3) 5.8 GHz point-to-point exception: for fixed point-to-point systems at 5.725-5.850 GHz: antenna gain up to 23 dBi with only 1 dB power reduction per dB of gain above 23 dBi. This allows high-EIRP links for wireless backhaul. Maximum EIRP: not explicitly capped, but practical limits are ~36-40 dBm.

Global Variations

(1) 2.4 GHz band: US (FCC): 2.400-2.4835 GHz, 1W EIRP, 4W EIRP with directional antenna. EU (ETSI): 2.400-2.4835 GHz, 100 mW (20 dBm) EIRP. The EU limit is 20× lower than the US limit. This is why some consumer Wi-Fi products have different power settings for different countries. Japan: 2.400-2.497 GHz (wider band), 10 mW/MHz. (2) 5 GHz band: split into multiple sub-bands with different rules: UNII-1 (5.150-5.250 GHz): indoor only, 200 mW EIRP (US, EU). UNII-2 (5.250-5.350 GHz): indoor/outdoor with DFS (dynamic frequency selection, to avoid interference with weather radar). UNII-2 Extended (5.470-5.725 GHz): same as UNII-2. UNII-3 (5.725-5.850 GHz): outdoor allowed, higher power, ISM band. Wi-Fi 6E adds: UNII-5 through UNII-8 (5.925-7.125 GHz): 1.2 GHz of new spectrum. (3) 60 GHz band (57-71 GHz): very high power allowed (FCC: up to 40 dBm average EIRP, 43 dBm peak). The high atmospheric absorption at 60 GHz (10-15 dB/km from oxygen) limits the range, enabling dense frequency reuse. Used for: WiGig (802.11ad/ay), 5G backhaul, and short-range data links.

ISM Band Power Limits

2.4 GHz FCC: 1W conducted, 4W EIRP max
2.4 GHz ETSI: 100 mW (20 dBm) EIRP
5.8 GHz: up to 36 dBm EIRP (P2P)
ISM: no interference protection
FHSS: ≥15 hopping channels

Common Questions

Frequently Asked Questions

Do I need certification for an ISM band device?

Yes. Even though the ISM bands are "unlicensed" (no user license is needed to operate): the device itself must be certified (FCC Part 15 equipment authorization). Requires: the device must be tested by an accredited test lab to verify it meets the Part 15 technical requirements (power limits, spurious emissions, frequency stability). The test results and application are submitted to the FCC (or to a Telecommunication Certification Body, TCB). Upon approval: the device receives an FCC ID, which must be labeled on the device. Cost: $5,000-$20,000 for testing and certification (depending on the complexity). No certification is needed for: devices that fall under FCC Part 15 Subpart B (unintentional radiators, like computer equipment) and meet the limits without intentional transmission.

Can I use the ISM bands for commercial products?

Yes. The ISM bands are universally used for commercial products: Wi-Fi routers and access points (billions of devices). Bluetooth headphones, speakers, and peripherals. Zigbee and Thread (smart home devices). Industrial IoT sensors (LoRa at 915 MHz). Microwave ovens (2.45 GHz ISM, not a communication device). There is no restriction on commercial use. The only requirements: the device must be certified (FCC Part 15), and the device must accept interference and not cause interference to licensed services.

What is DFS and why does it matter?

DFS (Dynamic Frequency Selection): in the 5 GHz UNII-2 and UNII-2 Extended bands (5.250-5.350 and 5.470-5.725 GHz): there are co-frequency radar systems (weather radar, military radar). To coexist: Wi-Fi devices must implement DFS: the device scans the channel for radar pulses before transmitting. If a radar pulse is detected: the device must vacate the channel within 10 seconds. The device must not return to the channel for at least 30 minutes. The device must select a different channel (that is free of radar). DFS was mandated by the ITU to allow spectrum sharing between Wi-Fi and radar. Without DFS: Wi-Fi devices would interfere with critical weather radar systems. The DFS requirement adds complexity: the Wi-Fi chipset must include a radar pulse detector (which consumes die area and power). Channel switching introduces brief connectivity interruptions. Some consumer access points disable DFS channels to avoid the interruptions.

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