Clear-Com EF-701M - Four Wire RS-422 Interface with Call Signal for Encore Series4 Wire Interface with Call Signal, Matrix to Party line. The EF 701M interface connects one channel of standard or TW party line intercom to four wire audio, and simultaneously converts either the DC voltage call signal or 20kHz call signal to RS 422 data (and back). The resulting four wire audio plus RS 422 data can then be sent to a fiber optic converter (modem) or transmitted over twisted pair cable such as CAT 5. Excellent stand alone two to four