Quick Start Guide

page 29
Monitoring an Outgoing Phone Call
This slide outlines an observation of an outgoing call.
In the beginning, the loop is closed, the phone is on-hook and -
50V are displayed.
When the handset is picked up, loop current flows and the line
voltage drops to -9V.
Subsequently the DTMF tones dialed by the caller are put out.
Thus one can examine numbers dialed by fax machines or
analog least cost routers.
The conversation can be listened to afterwards.
off-hook (-9V)
phone number dialed
on-hook (-50V)