The atw-t902a system 9 frequency-agile VHF wireless handheld transmitter and mic from Audio-Technica is a frequency-agile, Single-Channel transmitter with a unidirectional dynamic Capsule. This means that you can select any one of the four frequencies (169.505, 170.245, 171.045, and 171.905 MHz) and use up to four system 9 wireless systems at the same time, if each system is set to a different channel frequency.