4.2.2 Modulator-Transmitter Circuits
The IF signal is amplified by a 45 MHz solid-
state three-stage IF amplifier. The bandwidth of the IF
The primary function of modulator V1 is to
strip is switched from 4 to 24 MHz, depending on
provide a means of pulsing the magnetron transmitter.
transmitter pulse width.
The output of a pulsewidth generator is amplified to
The input amplifier gain is controlled by the STC
drive the modulator which allows the magnetron to be
signal. The STC signal also controls the IF amplifier
brought rapidly into and out of oscillation. The
gain at close ranges. The overall gain of the IF
modulator is a hard-tube type whose pulse width
amplifier is controlled by the indicator GAIN control.
(.065,0.5, and 1 microsecond) is selected and triggered
The full-wave video detector detects the IF
by the indicator. When the magnetron fires, the
signal envelope and provides positive video signals to
modulator generates the acknowledge pulse which is
the regenerative video amplifier which supplies positive
sent to the indicator to trigger and synchronize the
video signals to the indicator.
display with the transmitted pulse.
The transmitter utilizes magnetron V2 to
4.2.5 Power Control and Power Supplies
produce a minimum peak output of 20 kilowatts for the
X-band radar. The magnetron output is coupled through
an RF duplexer to the external waveguide, which routes
(115 Vac, single phase, 60 Hz) is controlled by the
the high frequency burst of energy to the antenna via a
system enable lines which are closed when the indicator
rotary joint located in the antenna pedestal.
POWER switch is set to the ST BY or TX ON position.
During medium and long pulse operation, when
The receiver transmitter LOCAL TEST switch is
the magnetron duty cycle (PRF/pulse width) is relatively
connected in parallel with the indicator POWER switch
high, the magnetron filament voltage is lowered by
to provide independent turn-on capability to standby at
the receiver transmitter for maintenance.
4.2.3 Duplexer and Receiver RF Circuits
(115 Vac, single phase, 60 Hz) provide: antenna drive
motor power (switch-controlled by the receiver
transmitter ANT ON/OFF switch); indicator power in
The duplexer couples the transmitted RF energy
single-indicator systems (V1); and video amplifier power
from the transmitter to the antenna pedestal rotary joint.
in multiple-indicator systems (V2, V3, V4).
Reflected RF energy received by the antenna is coupled
The low voltage power supply provides the
through the duplexer to the receiver. The receiver RF
following operating voltages for the receiver transmitter
circuits process the received RF signals for use by the
IF and video amplifier circuits.
Since the transmitter and receiver use a
+5 and +12 Vdc (logic circuits)
common waveguide feed and antenna, a protective
+26 Vdc (modulator filament)
device (T/R limiter V3) is used to prevent high powered
+120 Vdc (pulse driver)
transmitter pulses from feeding into the sensitive
6.3 Vac (magnetron filament)
receiver circuits. Without this protection, the mixer
crystals would be physically destroyed, and the local
oscillator damaged. This passive limiter also provides
protection for the crystals against pulses from other
The high voltage power supply provides the
transmitters when the radar is switched off.
following operating voltages for the modulator:
The mixer crystals, CR5 and CR6, combine the
received RF signals (at the transmitter frequency) with
+9 KVdc (anode)
the signal from the local oscillator (45 MHz above the
+800 Vdc (screen grid)
transmitter frequency) to produce the 45-MHz echo
-400 Vdc (control grid)
signals for the receiver.
4.3 ANTENNA AS-3194 AND ANTENNA PEDESTAL
4.2.4 Receiver Circuits
The receiver circuits process the 45-MHz
The antenna is an X-band slotted waveguide array
received RF signals to provide video data for the
mounted on the antenna pedestal. The antenna
indicator. The receiver circuits include an IF amplifier, a
pedestal contains the antenna drive motor, drive
video detector and a video amplifier.
system, sine-cosine resolver, heading line switch and
(Antenna Pedestal AB-1247A only) synchro transmitter.