Radios communicate by creating and detecting electromagnetic waves. Radios that are designed to communicate with each other are usually tuned to transmit and receive waves of a particular frequency or group of frequencies. Most countries have certain frequencies set aside for use as license-free bands for Industrial, Scientific and Medical (ISM) use. Using an approved module, like those that Digi offers, the ISM bands are convenient because no additional government licensing is necessary. The disadvantage of these bands is that anyone can install a radio at any location that may interfere with any other transmitters/receivers that are already in the area.

Radios within the ISM bands are required to use some form of spread spectrum to help avoid interference. Usually, communication and throughput may degrade if two systems are in the same area, but normally it will not be entirely eliminated because of the spread spectrum techniques.

If you are designing a system, it is important to remember that interference is bound to happen and so you’ll want to make sure any protocol you use can tolerate the loss of some data and retry any lost data packets. If you are installing in an environment where interference already exists, placing the antennas as far away as possible from the interfering source can help reduce the negative effects and improve performance.