Pros and Cons of the ISM Band Frequencies

November 26, 2015 at 8:00 AM


900, 2,400, 5,000 – these are not factors in an algebraic algorithm.  These are the unlicensed frequency bands that have helped propel the growth of the wireless industry.


In the US, the 900, 2,400 and 5,000 MHz frequency bands are set aside by the FCC for unlicensed Industrial, Scientific and Medical (ISM) applications. Each ISM band frequency is allocated for a different purpose. They are used for consumer and commercial Wi-Fi and WLAN applications as well as commercial Radio Frequency Identification (RFID) and Supervisory Control and Data Acquisition (SCADA) applications.


Here, we take a closer look at the pros and cons of each frequency.


900 MHz

What the 900 MHz band lacks in bandwidth, it makes up for in distance. This frequency is very narrow which limits its maximum data rates, though it is able to penetrate obstructions such as tree and leaves in the Line-of-Sight (LOS).


The 900 MHz band is commonly used by applications such as SCADA and RFID which have lower data rate requirements than applications found in the 2.4-5 GHz frequency bands. The type of data packet usually sent in these applications is a simple on/off command to a motor or a valve, for instance.


The 900 MHz frequency surpasses other bandwidths with its ability to penetrate obstructions such as trees and leaves in the Line-of-Sight.  For example, the 2.4 GHz band is absorbed by water found in trees and leaves which causes path loss of the transmission. Thus, 900 MHz is often used for Non-Line-Of-Sight (NLOS) applications.


2.4 GHz

2.4 GHz is the frequency of choice for the home user and commercial businesses. It is the primary band used for cordless phones, microwave ovens, baby monitors, Wi-Fi, Bluetooth, printers, keyboards and gaming controller applications. Voice, video and data communications are typically used in 2.4 GHz systems requiring higher data rates of up to 300 Mbps for 802.11n applications.


As the most widely used frequency, the 2 .4 GHz band can become overcrowded. When excessive overcrowding occurs, Wi-Fi network signal may be weak or not work at all. In some cases, it's best to connect 2.4 GHz Wi-Fi networks using backhaul links on the less crowded 5 GHz frequency.


5 GHz

The 5 GHz frequency is often used in commercial Wi-Fi applications. It is also the frequency used for the emerging 802.11ac standard which will provide up to 1.3 Gbps of wireless data throughput.  802.11n can also use the 5 GHz frequency. On the flip side, this super-speed band has the shortest range of all three ISM frequency options.


There you have it, the good and the bad of each ISM frequency.  Now you know all the factors to consider when choosing the best band for your application.




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