RS603 TW Dual Listen Monaural Beltpack

The RS-603 is a 2-channel 3-pin dual-listen monaural beltpack with a
4-pin male headset connector and 3-pin female/male loop through
intercom line connectors. It also has a 2.5mm AUX headset connector
and an RS-232 data connector for programming.  Two channels of audio
are passed down a single 3-pin...