44443-1098 <90-00059>
P
AGE
5
RCV and XMT Attenuator Circuits
The attenuator circuits are made up of resistance T-pads. The
pads are designed to be switched into the 4-wire RCV and XMT
lines. Refer to Fig. 2, in the
Installation
section.
Front Panel Test Jack Circuits
The four front panel test jacks provide internal connections for test
and calibration of the Term Set.
44443-01
This module includes the basic Term Set network circuits of the
44443-00, plus selectable strap connections for engaging an Idle
Line Termination (ILT) branch or Echo Suppression Override (ES)
branch across the 4-wire XMT port. Refer to Fig. 1.
The branch circuit selected in is controlled by relay K1. K1 is
energized by an external battery supply (-21 VDC to -56 VDC)
applied to pin 25 (-) and pin 29 (+). Relay K1 is protected from
excessive current flow by transistor Q1. Using Q1 to limit current
eliminates the need for a resistive voltage drop for -24 or -48 VDC
supplies.
Idle Line Termination Circuit
When K1 is energized, the normally closed side of K1A opens and
the 600 ohm ILT branch is disconnected. At the same time, the
normally open side of K1A closes, establishing the transmission
path to pin 49.
When K1 is released at the end of the call, the normally closed side
of K1A closes, reconnecting the 600 ohm termination across the 4-
wire XMT line. At the same time, the normally open side of K1A
re-opens, isolating the 600 ohm termination branch.
NOTE
: For the idle state to exist, the ILT bypass strap option should
not be used. Refer to Fig. 1
Echo Suppression Override Circuit
If K1 is energized, contact K1B is closed and connects a 50 ohm
load resistor across the 4-wire XMT line. This allows an override to
occur. If K1 is not energized, K1B remains open, disallowing an
override response.
NOTE
: Since the K1A (normally open) contact would normally open the
XMT line, the ILT bypass strap must be installed to prevent
interruption. Refer to Fig. 1
CIRCUIT DESCRIPTION
