RTS 4030 Portable 2-Channel IFB Listening Station for Series 4000 IFB & TW Intercom SystemsTwo Wire IFB Beltpack with (6. 3 mm) Jack The RTS model 4030 is a portable two channel listening station. It permits a user to monitor one audio channel in each ear with independent volume adjustment for each channel. The model 4030 may be used as a component of the RTS Series 4000 IFB system, or it may be used as a listen only user station in an RTS TW intercom system. In IFB applications, talent, such as newscasters, musicians, sportscasters, etc.,