The industrial, scientific, and medical (ISM) bands are radio frequency ranges freely available for industrial, scientific and medical applications, although there are also many devices aimed at private users that operate in these bands. ISM devices require only general type approval and no individual testing.
The radio communication sector of the International Telecommunication Union (ITUR) defines the ISM bands at an international level. Wi-Fi and Bluetooth operate in ISM bands, as do many radio headphones and remote cameras, although these are not usually described as ISM devices. These devices are responsible for considerable radio communications interference (especially at 433 MHz and at 2.4 GHz).
ITU-R defines the following bands, not all of which are available in every country:
- 6.765 to 6.795 MHz
- 13.553 to 13.567 MHz
- 26.957 to 27.283 MHz
- 40.66 to 40.70 MHz
- 433.05 to 434.79 MHz
- 902 to 928 MHz
- 2.400 to 2.500 GHz
- 5.725 to 5.875 GHz
- 24 to 24.25 GHz
Some countries allocate further ISM bands in addition to those above. ISM applications have the lowest priority within any given band. Many bands available for ISM are shared with other spectrum users: for example the 433 MHz ISM band is shared with 70 cm amateur radio communications.
ISM users must not interfere with other users, but must be able to tolerate the interference to their own communications caused by higher-priority users in the same band. The band from 868 MHz to 870 MHz is often mistakenly characterized as an ISM band. It is nevertheless available to short-range radio devices, such as RFID tags, remote switches, remote alarm systems, and radio modules.
For more information, refer to Wolfgang Rudolph & Burkhard Kainka’s article, “ATM18 on the Air,” 080852, Elektor, 1/2009.