The ISM Band Frequency Dilemma: Which One is Right for You?

January 23, 2014 at 10:00 AM


The FCC allocates different frequencies for different purposes, and each has its own advantages. In the US, 900, 2400 and 5000 MHz frequency bands are set aside by the FCC for unlicensed Industrial, Scientific and Medical (ISM) applications. The lack of licensing requirements has greatly encouraged the growth of the wireless industry. These bands are used for consumer and commercial WiFi and WLAN applications as well as for commercial Radio Frequency Identification (RFID) and Supervisory Control and Data Acquisition (SCADA) applications. Here are some highlights of each ISM band frequency for you to consider:

900 MHz

900 MHz 9 dBi Yagi Antenna

The 900 MHz ISM band is known to be very narrow, thus limiting the maximum data rates. Typically applications such as SCADA and RFID use the 900 MHz ISM band since their data rate requirements are lower than applications found in the 2.4-5 GHz frequency bands. Many times the type of data packets being sent in these types of applications is a simple on /off command to something like a motor or value.


When obstructions such as trees and leaves are in the Line of Sight (LOS), the 900 MHz frequency will fare better than 2.4 GHz. The 2.4 GHz frequency is absorbed by water found in trees and leaves, which then causes path loss of the 2.4 GHz transmission. 900 MHz is often used in Non-Line-Of-Sight (NLOS) applications.



2.4 GHz

WiFi Grid Antenna

For the home user and commercial businesses, 2.4 GHz ISM Band is the primary band used for WiFi, Bluetooth, cordless phone, printer, keyboard, mouse and gaming controller applications. Voice, video and data communications are also typically used in 2.4 GHz systems where higher data rates are required (up to 300 Mbps for 802.11n applications).


2.4 GHz is the most widely used frequency (especially since it includes devices like microwave ovens, baby monitors, cordless phones etc.) and in some cases may even be overcrowded. When too much overcrowding occurs, your WiFi network signal may be weak or not work at all. In some cases it's best to use 5 GHz backhaul links to connect 2.4 GHz WiFi networks as 5 GHz is a less crowded frequency.



5 GHz

5.8 GHz Sectorized Antenna Array with four 90°  Sectorial Antennas

The 5 GHz frequency is often used in commercial WiFi applications. As mentioned above, it is often used as a backhaul link connecting two 2.4 GHz systems over some distance. 5 GHz is also the frequency used for the emerging standard 802.11ac which will provide up to 1.3 Gbps of wireless data throughput. Additionally, 802.11n can also use the 5 GHz frequency.





For more information about US Frequency Allocations, click here.


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