The SA1401 Infrared Transmitter is designed for professional applications (classrooms, board rooms, small meeting and conference rooms) as well as for home personal use and is compatible with most infrared receivers currently in use. The drop-in charger is designed only to recharge Sound Associates SA1520 series receivers. It is designed with a new industrial-strength chassis for added durability in commercial applications. Its advanced mechanical design ensures years of trouble-free use, while making the headset comfortable to wear. The SA1401 single channel, selectable transmitter is designed to emit a frequency modulation of 2.3MHz, 2.8MHz or 95kHz (via selector switch located on the back of the unit.) The SA1401 uses infrared light to transmit audio to the receiver. As it is a “line of sight” technology, the receiver (headset) must be used in direct line of sight with the transmitter. The receiver must be free of any obstructions that would block the infrared light from the receiver.