S-COM 7K, Manual

Page: 153 / 400

Telephone Interface Functions
7-59
Reverse Patch
The Reverse Patch feature allows users to dial a number for the repeater site,
and be connected to a repeater user. The reverse patch can be used in two
ways. The controller can signal via a CW message that a user has dialed the
site, or the controller can wait for a command from the telephone party before
signalling via CW.
In the first mode, the telephone party never has access to the DTMF decoder.
The only function that a call to the site number possesses is to trigger a
reverse patch signal.
In the second mode, the telephone party is similar to a control operator. He/she
will be able to enter any command. To trigger a reverse patch, the proper
command will have to be entered from a Touch Tone™ telephone.
The first mode may be necessary in several situations. For example, in areas
without Touch Tone™ service, the controller will have to be configured to
trigger a reverse patch without requiring a command. Other exchanges reverse
the polarity of the telephone line loop voltage going to the telephone set after
the dialing process; this disables the DTMF encoder in the telephone. These
situations can be fixed by using a separate DTMF encoder in the first case, and
using a bridge rectifier to feed unipolar DC to the DTMF encoder in the second
case. However, it will still be difficult to trigger the Reverse Patch from a pay
phone, or a phone not equipped with DTMF capability, in rotary exchanges.