Volume 1
MIL-HDBK-162A
Section 3
15 December 1965
ITEM NAME: DECODER GROUP
TYPE: AN/UPA-49(XN-1)
of IFF displayed targets.
TECHNICAL DESCRIPTION
The decode functions of the decoder group are (1)
Inputs
to check a target reply code for parity with a preset code
IFF Video: Mode 1, 2, or 3 SIF code
(passive decode); (2) to check the reply code for
train replies
bracket-pulse coincidence (bracket decode); and (3) to
Polarity: Pos
translate the reply code, which is in a binary coded octal
Pulse Amplitude: 2v plus or minus 0.5v
form, into its equivalent decimal number (active
Pulse Width: 0.30 to 1.0 usec (0.45
decode). As a result of these functions, output signals
usec nom)
are provided for display as the IFF target on an
Pulse Spacing: 1.45 or 2.90, usec
associated radar indicator, and a decimal number is
plus or minus 0.50 usec, as measured
read out on 1 amp indicating devices. The IFF target
from pulse leading edges.
display and the code readout are performed in
Azimuth Signal: A nom 15v neg pola-
synchronism. A three channel device, the code readout
rity, rectangular pulse
presents instantaneously the reply codes of three
Radar Video: 0.30 to 1500 usec dura-
discreate targets. In addition, a delayed code video
tion of individual pulses; 2v (min)
output is provided for display and, when interconnected,
amplitude
the surveillance radar video is passed or mixed with IFF
Outputs
video as an output. Selecting an IFF, radar, or mixed
Radar Video: Output supplied identical
output, establishing a preset code and an IFF mode of
to input; or as a mixed output w/IFF
operation, and enabling the interrogator challenge are
video
functions of operating controls located on the front panel
Bracket Decode: A single 1.5 usec
of the video decoder.
(nom) pulse
A sector gate generated by the decoder indicator
Polarity: Pos
unit of the decoder group provides a means of selecting
Amplitude: Adjustable between 1.5 to
and segregating targets for active readout. This gate is
4.0v
applied externally to the video sweep of the associated
Passive Decode: A single 1.5 usec
radar indicator and internally to the code translation
(nom) pulse
circuits. As displayed on a PPI type indicator the sector
Polarity: Pos
gate is defined by azimuth radials and range arcs which
Amplitude: Adjustable between 1.5 to
appear as brightened traces to form essentially a
4.0v
rectangular shape on the screen. This defined area
Bracket Decode: Normal bracket pulse;
represents in range and azimuth the time during which
stretched passive decode pulse (10
target replies are enabled for active readout. The
usec nom)
placement of the sector gate is a function of the
Passive Decode: Passive decode pulse
associated radar indicator controls; the area delimited
(10 usec nom)
by the gate is adjustable within limits by means of
Code Video: Same form as IFF input
azimuth and range controls on the video decoder unit.
video, but delayed approx 40.B usec
The sector gate is also useable for delimiting target
Polarity: Pos
challenge to the gated area.
Amplitude: Adjustable between 1.5 to
RELATION TO SIMILAR EQUIPMENT
4 .0v
Target Sector Gate: Series of pulses;
Decoder Group AN/UPA-49(XN-1) and Decoder
pos polarity; amplitude adjustable from
Group AN/UPA-50(XN-1) are functionally identical units.
0 to 4v
They differ only in their application to particular system
Power Requirements: 115v ac, 400 cyc,
complex and in minor circuit variations which are
1-ph, 50w
necessary to make each group compatible with the
characteristics of associated equipment. The AN/UPA-
INSTALLATION CONSIDERATIONS
49 is used in the Navy Tactical Data System. A Video
Related Equipment
Decoder KY-387(XN-1)UPA and a Power Supply PP-
Required but not Supplied: For Decoder
3078(XN-1) are units common to both groups. A
Group AN/UPA-49. Units of a Navy
Decoder-Indicator is the third unit in a group; the KY-
Tactical Data System are required to
386(XN-1) /UPA-49 is used. Decoder Group AN/UPA-
provide IFF video and azimuth inputs,
49 is a replacement for the Decoder Group AN/ UPA-24.
and to display decoder group outputs.
AN/UPA-49(XN-1): 2
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