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TM11-5895-932-14&P
diagram prior to performing patching for testing.
b. Isolator Substitution (fig. 3-2). Isolator
The types of tests, the performance standards and
substitution involves the multicircuit (12-wire)
procedures to be used for these tests are contained
patch cords. In this case, it is assumed that
in various DCA manuals, listed in appendix A.
operational spares for the isolators are connected
to circuit 19. On the black patch, the MODEM
jack of circuit 2 is connected to the COMP jack of
Patching for fault location includes loopback by
circuit 19. On the other side of the isolator cabinet
use of special test cords and plugs and use of the
(red dc unsecure patch), the MODEM jack of
BERT for troubleshooting.
circuit 19 is connected to the COMP jack of circuit
a. Loopback Loopback is a method for con-
number 2 to complete the patch.
necting the transmitting lines of a communication
device to its received lines. The purpose of the
loopback is so that a standard, or test message
Testing patches, as described here, are defined as
those patches which connect the analog test
may be sent from and to the communication device
equipment (noise measuring set, transmission
for comparison of the transmitted to the received
measuring set) into the vf lines. The patching
message for testing purposes. At the PTF, request
arrangements for these patches are shown on
for loopback comes from either the AMME or the
figure 3-3. A schematic a n d a d r a w i n g
remote terminals. Two special loopback cables and
representing the way the actual patch cords are set
one special plug are provided at the PTF. The use
up are shown. PTF personnel should study this
of the cables and plug is illustrated in figure 3 -4.
3-4
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