Figure 3-4.—Mark XII IFF system interrogator station.
The Computer, KIR-1A/TSEC, encodes mode 4
challenges for transmission by the interrogator. It also
decodes the received mode 4 transponder replies. The
code changer key, TSEC/KIK-18, inserts the mode 4
code into the computer.
The Video Decoder, AN/UPA-59(), has various
configurations. The most common configuration uses a
video decoder, an intra-target data indicator, and an
alarm monitor.
The video decoder provides control signals that the
interrogator uses to display challenges in the various
modes. It also decodes and processes reply video (mode
4 video goes directly through without processing) and
provides video output to the indicator. The video
decoder will accept radar video from an associated radar
and route it, with or without IFF video, to the indicator
for display. An intratarget data indicator plugs into a
receptacle in the decoder’s front panel. It provides
readouts of reply codes for modes 1, 2, and 3/A and
direct altitude readouts for mode C. The alarm monitor
contains a loud speaker and indicator lights to provide
audible and visual alarms when IFF emergency signals
are decoded.
The defruiter can be one of two types of
interference blankers. The MX-8757/UPX is a
four-channel type, using one channel per mode for
modes 1, 2, 3/A, and C. The MX-8758/UPX is a
one-channel type, using one channel for all modes.
Both units remove nonsynchronous transponder replies
(fruit) and receiver noise from IFF video.
The control monitor functions as a remote
control and remote monitor for the interrogator
section. The front panel of the control monitor is
shown in figure 3-5.
The Switch and Driver, AN/UPA-61, provides
ISLS operation for the Mark XII system. Targets at
close range may reply to side and back lobes, as well as
to the main antenna beam. This could cause a target to
appear for nearly 360 degrees close to the origin of the
display, a phenomenon known as “ring-around.” ISLS
prevents ring-around by inhibiting transponder replies
to side lobes.
The Antenna Pedestal Group, AN/UPA-57, can
operate in any of three modes: slaved to a radar system,
self-synchronous, or manually. It consists of a manual
pedestal control unit, a control power supply unit, an
antenna pedestal assembly, and a pedestal disconnect
mast switch.
The manual pedestal control is usually located at
the ppi. The front panel controls allow the selection of
free run, slave, or manual operation. The control power
supply unit, located below decks, develops all power
required for the antenna pedestal group. In the free run
operation mode, the power supply unit can rotate the
pedestal assembly at up to 15 rpm. When slaved to a
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