General Theory of Operation
The AN/GPN-27 is a modular, solid-state,
dual-channel, dual-beam/frequency diversity, S-band,
surveillance radar used for safe, efficient movement of
air traffic within the naval or Marine Corps Air Station
National Airspace System area.
Some of the operating features include:
Stable local oscillator (STALO)
MTI with 10-bit design
Clutter rejection
Circular polarization
Reduced side lobes
Field-programmable range azimuth gate
Configuration
The AN/GPN-27 radar includes three major groups:
an antenna group, a transmitter building group, and a
display site group.
The antenna group consists of a reflector, dual-feed
assembly, rotary joint, pedestal, and a dual-drive train
assembly. It is a dual-beam design with normal and
passive channels, including switchable linear and
circular polarization. The cosecant-squared elevation
pattern provides constant radiation altitude coverage up
to 30 degrees above peak of beam. The passive,
receiver-only feed horn is tilted upward from the normal
beam to reduce interference from ground clutter at short
ranges.
In the transmitter building group, the transmitter
has an air-cooled klystron, a solid-state modularized
modulator, and a solid-state, high-voltage power supply.
The receiver provides normal video, log video, and
moving target indicator (mti) video signals to the
processor unit. The digital processor processes the
receiver video for the radar tuning and control circuits,
the range/azimuth gate generator, the azimuth pulse
generator (APG), and the video cable-line drivers. The
system control interface and distribution unit features a
solid-state control system for radar command and status
indications. A 16-inch maintenance plan position
indicator (MPPI) aids in system alignment and
maintenance. The transmitter building group also has
two of the five stations (1 master and 1 slave) of the
intercommunication system.
The display site group at the indicator site or air
traffic control (ATC) room consists of a display site
remote unit, two system control panels, a display site
cable junction box, and an intercommunications system
with three stations (2 master and 1 slave).
SIGNIFICANT INTERFACES.— The only
interfacing is within the system itself. The control
system contains control boxes that have release and
take-control circuitry to ensure that radar command is
available only at the selected control box. Operators
scan the radar screen for incoming and outgoing aircraft,
vector aircraft to the airfield, and work with other
controllers to coordinate precision approach radars
(PAR) and land aircraft.
FOR THE MAINTAINER.— The AN/GPN-27
uses state-of-the-art design and technology. All radar
command and status signals stay in power-protected
solid-state memory, isolating the control system from
short-term power outages. The MPPI at the transmitter
building aids in system alignment and other
maintenance.
Maintenance
Maintenance of the AN/GPN-27 is performed on
demand or as scheduled and is done by Electronics
Technicians (NEC ET-1580). Organizational level
maintenance includes fault isolation, performance
testing, and alignment.
Corrective maintenance
consists of the removal and replacement of
sub-assemblies, modules, and printed circuit boards
(PCBs).
Those items not repairable at the
organizational level are returned to the depot facility
through normal Navy supply channels.
THREE COORDINATE (3D) AIR
SEARCH RADARS
Fire Control Technicians (FCs) usually
maintain the height-finding radars installed aboard
Navy ships. So, rather than cover specific
equipment, we will cover general information to
help you understand the overall radar capabilities
of your ship.
The 3D radar functions much like the 2D system,
but also provides elevation information. To do this,
the height-finding radar uses a beam that is very
narrow, both vertically and horizontally. Azimuth is
provided as the antenna rotates continuously at speeds
varying up to 15 rpm. Although the antenna usually
operates in the automatic mode, the operator may
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