| 摘要 |
<p>A telephone test set that performs dry loop testing of telephone lines has a passive speech network (38), a speakerphone circuit (50), and an amplifier (30) and a speaker (32) coupled to the speakerphone circuit. The passive speech network and the speakerphone circuit are isolated by the use of latching relays (17) which are switched by a relay driver circuit (31) 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.</p> |
