Radio telephone interface linking to public telephone - has automatic transmit or receive switching performed by modulation frequency detectors in interface unit

摘要

An interface unit enables a bidirectional link to be established between a mobile radio telephone and a public or private telephone network. Switching for transmit or receive is automatically performed by detecting modulation frequencies. The radio telephone transmitter receiver is connected to a two wire telephone line via an interface unit which contains modulation frequency detectors for the receive and transmit directions. The detectors connect to logic circuits and to relays which effect switching of the transmit and receive circuits and ringing circuits to the transmission channel. Sequentially connected integrated circuit monostables are connected to acoustic frequency oscillator and amplifier circuits whose outputs are routed to the modulation terminals on the radio transmitter to provide tone signals.