As radio waves travel the radio signals gradually lose energy. The higher the frequency of transmission, the quicker the radio wave will lose energy down to a point where it cannot be detected by a receiver. Higher frequency waves also lose energy quicker when trying to penetrate walls, trees, or other obstructions. If both a 900 MHz radio and a 2.4 GHz radio had the same output power and receive sensitivity and were compared side by side, the 900 MHz radio would get almost twice the range of the 2.4 GHz radio.
If deploying systems in the United States or Canada, either 900 MHz or 2.4 GHz can be used without additional government agency approvals. The European union and most of the Asian countries do not allow 900 MHz systems, so normally 2.4 GHz systems are deployed in those countries. However, there are some countries which allows limited channels on 900 MHz band. They are Australia, New Zealand, Singapore and Brazil. Whether your preference is 900 MHz or 2.4 GHz, Digi has a variety of solutions to meet the needs of your application.