The Electro-Voice Telex SoundMate PST-170 Belt Pack Transmitter may be set to any one of the 17 channels which is displayed on the backlit LCD, and operates on frequencies in the 72-76 MHz band. It is lightweight, battery operated and includes a small lapel microphone for convenient portable use. The PST-170 has two audio input jacks. The Auxiliary input is designed to allow the use of audio devices such as teacher’s aids or tape players. The second jack is normally used with a microphone and is located on the top panel. The PST-170 is also compatible with the E.D.R. feature of the SR-400.