The ATW-T901a System 9 Frequency-Agile VHF Bodypack Transmitter from Audio Technica is a single-channel transmitter, although it is a frequency agile system, which means 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 frequency.

The ATW-T901a bodypack transmitter can be used when paired with an optional System 9 receiver and a 4-pin lavalier microphone, headset microphone, or AT-GcW guitar/instrument input cable (sold separately) to capture audio for presentation, ENG, and sound reinforcement applications.