Abstract: The potential impedance mismatch of digital terminal equipment and a line test unit that has been equipped to conform with the Bellcore standard of terminating the line with a 600-900 ohm impedance during data reception is addressed by modifying the craftsman's test unit to include a controllably disabled AC impedance, which is operative to normally bridge the tip and ring leads of the telephone circuit under test with the required (600-900 ohm) impedance during data reception and, under direct control by the craftsman's keypad or software control resident in the test set's microcontroller, to selectively remove the AC matching impedance that would otherwise bridge the line. The AC impedance is comprised of a D.C. blocking capacitor and a resistor coupled in series with a controllable solid state relay which is normally rendered conductive during data reception to bridge the tip and ring leads.

Abstract: 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.