15 December 1965
ITEM NAME: RADAR SET GROUP
TYPE: AN/GPA-27, AN/GPA-27A, AN/GPA-57, AN/GPA-57A
AN/GPA-27A is similar to Radar Set Group
a dual modulator while Radar Set AN/FPS-20A is of the single
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
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,
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
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
requirement for control at both the antenna and the control
Radar Set Group AN/GPA-27:
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.
The antichaff receiver, a useful antijamming device,
Noise Figure: 9 db
assists in the elimination of undesirable signals caused by
Cancellation Unit Cancellation Ratio:
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
Stalo Cancellation Ratio Limitation: 40 db at 50 mi
Receiver Cabinet Sub-clutter Ratio: 36 db
RELATION TO SIMILAR EQUIPMENT