ISM Band
Understanding ISM Bands
ISM bands were originally designated for non-communication uses such as microwave ovens (2.45 GHz), industrial heating, and medical diathermy equipment. Because they are unlicensed (anyone can use them without a license), they were adopted for short-range wireless communications, leading to the explosive growth of Wi-Fi, Bluetooth, and IoT devices.
Major ISM Bands
| Band | Range | Primary Uses |
|---|---|---|
| 433 MHz | 433.05-434.79 MHz | Remote controls, key fobs (Region 1) |
| 915 MHz | 902-928 MHz | LoRa, RFID, IoT (Americas only) |
| 2.4 GHz | 2.400-2.4835 GHz | Wi-Fi, Bluetooth, Zigbee, microwave ovens |
| 5.8 GHz | 5.725-5.875 GHz | Wi-Fi, FPV drones, radar detectors |
| 24 GHz | 24.00-24.25 GHz | Short-range radar, motion sensors |
| 60 GHz | 57-71 GHz | WiGig, wireless VR (varies by region) |
Frequently Asked Questions
What are ISM bands?
ISM bands are unlicensed radio frequency allocations originally designated for industrial, scientific, and medical equipment. The most well-known are 2.4 GHz (Wi-Fi, Bluetooth) and 915 MHz (IoT). No license is required to transmit in ISM bands, subject to power limits.
Why is 2.4 GHz so congested?
The 2.4 GHz ISM band has only 83.5 MHz of bandwidth shared by Wi-Fi, Bluetooth, Zigbee, baby monitors, wireless mice, cordless phones, and microwave ovens. Its worldwide availability and unlicensed status attracted massive adoption, resulting in severe congestion in urban environments.
What power limits apply in ISM bands?
In the US, FCC Part 15 limits EIRP to 1 watt (30 dBm) in the 2.4 GHz ISM band. The 5.8 GHz ISM band allows up to 4 watts EIRP. Other regions have different limits. Higher power is allowed with spread-spectrum or frequency-hopping techniques.