A vehicle mounted mobile transceiver (11) communicates via a secondary mobile unit (51) with a short range portable unit (10). The portable unit (10) can be either a cordless microphone or a transceiver. The portable unit (10) allows a remotely positioned operator to transmit messages to a base station (13). To ensure security and reliable operation, the portable and vehicle mounted units use digitized codes for ID and instruction purposes. These codes are newly generated from time to time by the vehicle mounted unit and are imparted to the portable unit via a battery charging interface by modulating the battery charging signal with the reset and digital data signals. An improved remote squelch detect is also provided.