Three types of systems are in use - this link describes them but doesn't list freqs for FM system. http://www.access-board.gov/publications/9-als/bulletin-c.htm Freq range and new band here http://www.zak.co.il/deaf-info/old/ald.html ALT72 System Features and Specifications: Selectable Frequencies: 10 channels available: 72.1 to 72.9, 74.7, and 75.5 to 75.9 MHz. http://www.rldrake.com/al/alt72system.html -