Lesson 1/Learning Event 5
Learning Event 5: DC CIRCUIT AREA
The DC circuit area of the typical TCF handles digital communication
circuits operating in the DC mode. These circuits exist in a wide variety
of configurations, transmission speeds, and operating levels. The two major
categories of DC circuits are those operating at speeds up to 1 megabite per
second (Mb/s) and those operating at speeds above 1 Mb/s.
The first
category, comprises standard teletypewriter communications circuits and low-
and medium-speed digital data circuits. These circuits are connected on the
user side to digital data output instruments, or submultiplexers and on the
transmission side to multiplexing equipment.
Generally, digital circuits
from the user terminals make their first appearance in the DC circuit area
at the DC primary patch bay. The other major category of patch bays in the
area is the DC circuit patch bay, at which all circuits are configured for
low-level polar operation.
Accordingly, circuits appearing at the DC
primary patch bay in some other form must be converted before routing to the
DC circuit patch bay.
Figure 1-16 shows the common types of DC circuits
encountered in military communications and the routing through patch bays
and conversion equipment in the DC circuit area.
a. DC Primary Patch Bay.
(1) Function and Designations. All high-level and nonstandard DC user
circuits access the TCF through the DC primary patch bay. Circuits that are
unbalanced to ground enter through a primary patch designated as a D patch.
Balanced circuits enter through a K patch. The DC patching logic employed
in the DC primary patch bay (and in the DC circuit patch bay) is arranged
for the following:
(a) Provision
of
a
normal-through
connection
for
signal
and
timing
leads.
(b) Monitoring on at least the line side of DC circuits.
(c) Patching of any line to any piece of equipment.
(2) Send and Receive Patching Modules.
Separate patching modules are
used for sending and receiving DC circuits. These modules contain LINE and
EQ (Equipment) patching jacks, LINE MON jacks, and EQ MON jacks which are
optional. They may also contain cut keys as an option. A cut key is used
to disconnect a sending or receiving device from the line and usually is
mounted with an indicator lamp to show if the device is connected. Figure
1-17 shows the front panel of the standard Army patching module used
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