Caller identification in private telephone system - has call signals followed by identifying frequency during fixed period, counted for numerical display

摘要

A personal telephone system is fitted with a receiver that enables the caller to be identified before the receiver is lifted to make the connection. The incoming signal is represented by two distinct periods, the initial one containing the frequency multiplexed dialling signal to identify the required subscriber and a second period containing frequency information relating to the caller. The high frequency amplifier (4) receives incoming signals (3) that are discriminated (5) and processed through a filtered amplifier (6) to identify a dialling tone signal (7) at the end of the first period. A gating circuit (19) allows all signals through during the second fixed interval period and these are converted (13) and decoded (17) to provide an identifying display (18).