Volume 1
MIL-HDBK-162A
Section 1
15 December 1965
ITEM NAME: RADAR SET GROUP
TYPE: AN/GPA-27, AN/GPA-27A, AN/GPA-57, AN/GPA-57A
AN/GPA-58, AN/GPA-58A
AN/GPA-27A is similar to Radar Set Group
a dual modulator while Radar Set AN/FPS-20A is of the single
AN/GPA-57A
and
AN/GPA-5BA
but
not
modulator type. A rotary joint in the antenna pedestal
interchangeable. The AN/GPA-27 is similar to Radar
replaces the slip rings used on the systems being converted.
Set Group AN/GPA-57, and AN/GPA-58 but not
The rotary joint permits the entire complement of electronic
interchangeable.
Radar Set Groups AN/GPA-27A,
equipment to be located away from the rotating antenna
AN/GPA-57A, and AN/GPA-5BA are similar to and
support. Therefore, the receivers, transmitters, and control
interchangeable as a whole with Radar Set Groups
equipment have been placed inside a heated shelter to
AN/GPA-27, AN/GPA-57, and AN/GPA-5B respectively,
facilitate maintenance.
This feature permits training of
but are the preferred models and differ in the four type
personnel, using the standby channel, without interrupting
1754 thyroton tubes being replaced by a single type
normal operation of the facility. In addition, preventative
1257 tube.
maintenance can be performed on one transmitter receiver
group while the other is operating, thereby reducing off-the-air
time. Control circuits are simplified since there is no longer a
TECHNICAL DESCRIPTIONS
requirement for control at both the antenna and the control
Radar Set Group AN/GPA-27:
shelter locations.
Converts Radar Set AN/FPS-3 to dual modulator
Channel switching is accomplished by a change over
Radar Set AN/FPS-20.
switch which automatically changes transmitter-receiver
Radar Set Group AN/GPA-57:
groups and controls the position of the waveguide switch.
Converts Radar Set AN/FPS-3A to dual modulator
Radar Set AN/FPS-20 (dual modulator system) and Radar
Radar Set AN/FPS-20.
Set AN/FPS-20A (single modulator system) equipment
Radar Set Group AN/GPA-58B:
employs a line feed instead of the four-horn feed used on the
Converts Radar Set AN/MPS-7 (fixed) to dual
systems being converted. The effective range for small
modulator Radar Set AN/FPS-20.
targets has been increased by an improvement in noise figure,
Radar Set Group AN/GPA-27A:
higher transmitter-power output, and a reduction in receiver
Converts Radar Set AN/FPS-3 to single modulator
bandwidth. However, the maximum range is limited by the
Radar Set AN/FPS-20A.
system prf (pulse repetition frequency).
Radar Set Group AN/GPA-57A:
The MTI (moving target indicator) system circuits reduce
Converts Radar Set AN/FPS-3A to single modulator
the scanning clutter received from fixed ground targets. This
Radar Set AN/FPS-20A.
is accomplished with two quartz delay lines in cascade with
Radar Set Group AN/GPA-58A:
feedback circuits around the delay lines. MTI performance is
Converts Radar Set AN/MPS-7 (fixed) to single
further improved by a reduction of power supply ripple in the
modulator Radar Set AN/FPS-20A.
transmitter and receiver power supplies.
Electrical Characteristics of the high-
The new receiving system uses a video enhancement
power Radar Sets AN/FPS-20 and AN/FPS-20A:
circuit which is very effective in reducing interference from
Primary Power: 3-ph, 60 plus or minus 5 cycles,
other radar equipment using a different pulse repetition
120/206 plus or minus 5v, 4-wire.
frequency. It is not necessary to have a blanking trigger from
Antenna Beam: one.
the interfering radar equipment for the video enhancement
Frequency Range: 1250 to 1350 mc
circuit to function. Interference from other radar equipment
Transmitter Power Output: 2 megw min peak
with an identical repetition rate is not a serious problem since
power, 4320 w min avg power.
it is displayed on the PPI (plan position indicator) scope as a
Transmitter R-F Pulse Width: 6 usec
single narrow ring of constant range and does not hamper, to
PA Modulator Video Pulse Width: B usec
any large extent, normal scope readings.
Pulse Repetition Frequency: 360 cps nom
The antichaff receiver, a useful antijamming device,
Noise Figure: 9 db
assists in the elimination of undesirable signals caused by
Cancellation Unit Cancellation Ratio:
chaff.
single line, greater than 40 db;
The high-power radar system utilizes a three-cavity
cascaded line, greater than 50 db
klystron in place of the magnetron employed in the medium-
Coho Cancellation Ratio Limitation: 50 db at 50 mi
power sets.
Stalo Cancellation Ratio Limitation: 40 db at 50 mi
Receiver Cabinet Sub-clutter Ratio: 36 db
RELATION TO SIMILAR EQUIPMENT
AN/GPA-27: 2
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