User`s manual

A feature available on the ES/QS-100M revision B and newer is the
ability to input the carrier detect (DCD) signal from the RJ-11 connector.
When shipped from the factory, the ES/QS-100M is configured for
compatibility with revision 'A' of the adapter as shown in Figure 14(A)
below. In this configuration, pin 3 of the RJ-11 is connected to chassis
ground i.e. the frame of the PC.
For applications requiring the carrier detect signal, pin 3 of the
RJ-11 connector may be configured to input DCD in place of the chassis
ground connection. The decision to connect pin 3 to chassis ground or
DCD may be made on a per channel basis using jumpers J11 through J18.
Figure 14 --- Output connector configuration.
Chassis Ground
Carrier Detect (DCD)
Quatech QS-100M/ES-100M User's Manual 13