FERNSPRECHLEITUNGSPRÜFEINHEIT MIT EINEM LAUTFERNSPRECHER FÜR KOMMUNIKATION

摘要

A telephone test set that performs dry loop testing of telephone lines has a passive speech network, a speakerphone circuit, and an amplifier and a speaker coupled to the speakerphone circuit. The passive speech network and the speakerphone circuit area isolated by the use of latching relays which are switched by a relay driver circuit that provides a short current burst. Line power can be used to power the speakerphone, so as to extend battery life of a battery which can augment the line power as needed.