RF energy from the transmitter is coupled into
antenna. The position circuits include sweep resolver
waveguide and directed to the slotted waveguide array.
B2, reed switch S2 and (in Antenna Pedestal AB-1247A
Energy is radiated from the array in a narrow
undirectional beam, so that the bearing of an object
The stator winding of resolver B2 receives the
reflecting energy can be determined to within
resolver drive input (a 900-Hz square wave) from the
approximately 1 Vertically, the beam is relatively wide
indicator via the receiver transmitter. A compensation
so that the roll and pitch of the vessel will not normally
winding on B2 provides a feedback signal back to the
impair the antenna direct line of sight to the horizon.
indicator to regulate a constant drive input to the stator
The antenna radiates the pulse of high frequency
winding. The rotor of B2 is mechanically coupled to the
energy, and receives the reflected pulse of energy when
antenna drive mechanism. Sine-modulated and cosine-
the transmitter is off.
modulated square wave outputs from rotor windings of
The slotted waveguide array is continuously
B2 are sent to the indicator to rotate the PPI sweep in
rotated by the drive system which reduces the antenna
synchronism with the antenna.
motor shaft speed to the desired antenna rotation speed.
Reed switch 52 can be mechanically adjusted
The resolver is an electro-mechanical device which
for a momentary closure when the antenna is positioned
converts the rotation and instantaneous direction of the
forward at zero degrees. Closure of S2 provides a
antenna into electrical signals that cause the PPI trace
heading flash (HF) trigger to the indicators.
to rotate in synchronism with the antenna. The heading
line is generated by means of a reed switch that
AB-1247A only) provides antenna position data to the
momentarily closes once every revolution. Figure 4-2 is
AN/SPA-25 and AN/SPA-66 indicators. Excitation
a functional block diagram of the antenna and pedestal.
voltage, 115 Vac, 60 Hz, is applied to the rotor winding
of B3. The rotor is driven by antenna shaft gearing.
4.3.1 Antenna Drive Mechanism
The outputs, used to position the AN/SPA-25 and
AN/SPA-66 indicator sweeps, are taken from stator
windings of B3.
The antenna drive mechanism consists of a
1/4horsepower drive motor and a gear reducer
4.4 AZIMUTH RANGE INDICATORS IP-1282/IP-1283
assembly. Operating power for the motor is supplied
from the receiver transmitter through safety switch S1,
the interlock switch and the normally closed thermostat
The indicator displays the video output of the receiver at
switch. The motor drives the gear reducer assembly by
the proper bearing and range. The IP1282 (12-inch) and
means of a belt to provide antenna rotation at a speed
IP-1283 (16-inch) indicators use common electronic
of approximately 33 rpm.
circuits and have identical control panels. The location
of the bezel-mounted controls differs slightly due to the
4.3.2 Radiating Characteristics
difference in cabinet size. Figure 4-3 is a functional
block diagram of the indicators. The following
description applies to both indicators.
The antenna array is horizontally polarized to
produce a horizontal beam width of approximately 1.3
4.4.1 Sweep Generation
degrees and a vertical beam width of approximately 23
degrees. The array also produces horizontal sidelobes
within 10 degrees (up to 29 dB down) of the main lobe,
188.8.131.52 North Stabilization Circuits. - The north
or more than 10 degrees (greater than 30 dB down).
stabilization circuits combine antenna position data and
When the system is in operation, the peak power
ship's compass data to enable the indicator display to be
transmitted by the antenna is approximately 20 KW (18
oriented with north appearing at the top (zero degrees)
W average) .
of the CRT. The north stabilized display is presented
when the NSK function switch on the indicator control
panel is in the GYRO STAB or HDG SET position.
When the NSK function switch is in the HD UP position,
WITH THE SYSTEM OPERATING
north stabilization is disabled and the indicator display is
AND THE ANTENNA STOPPED, A
oriented to present the ship's heading at the top of the
CRT. The NSK resolver is automatically rotated to align
WITHIN 6 FEET OF THE ANTENNA.
the display with the ship's gyro compass when the NSK
function switch is held in the HDG SET position.
4.3.3 Antenna Position Circuits
When a north-stabilized display is presented, indicator
lamps at the top of the indicator are illuminated to
The antenna position circuits provide data to the
inform the operator of the condition.
indicators to synchronize the indicator sweep with the