TM 11-5840-360-14-1-1
4.9.1. Pulse Generation and Receiver Control Circuits
harder for the higher power S-band magnetron. The
RT-1241
output of a pulse width generator is amplified to drive
the modulator which allows the magnetron to be brought
The pulse generation and receiver control circuits
rapidly into and out of oscillation. The modulator is a
establish the pulse width for the transmitter and select
hard-tube type whose pulse width is selected and
either narrow or wide bandwidth for the receiver. The
triggered by the indicator. When the magnetron fires,
circuits also determine STC recovery start timing to
the modulator generates the acknowledge pulse which is
control receiver short range gain.
sent to the indicator to trigger and synchronize the
Input triggers for the transmitter are normally
display with the transmitted pulse.
received from the master indicator at the proper PRF for
The transmitter utilizes magnetron V2 to produce
the selected range. For test purposes, an on-board local
a minimum peak output of 50 kilowatts for the S-band
oscillator provides the proper repetition rate. This allows
radar. The magnetron output is coupled through an RF
for complete testing of a receiver transmitter without the
circulator to the external waveguide, which routes the
use of a working display. The PRF selector lines control
high frequency burst of energy to the antenna via a
the local test oscillator and the 2-input, 3-output pulse
rotary joint located in the antenna pedestal.
width decoder to determine which of the pulse
generators (one-shot multivibrators) is triggered. The
4.9.2.2. Magnetron Heater Scheduling and
MTR trigger pulse is routed through the trigger delay
Acknowledge Pulse Detector Circuits- - Proportional
generator circuit to begin developing the STC
heater control for the magnetron is provided by the
waveform.
After the delay period, the one-shot
magnetron heater scheduling circuit. The duty cycle is
multivibrators are all triggered; however, the 2-input, 3-
sensed in the cathode of the modulator by this circuit
output pulse width decoder determines which ones are
which adjusts the filament voltage to the magnetron.
enabled to produce an output pulse.
The acknowledge pulse detector circuit, also triggered
The output of the pulse width gate is routed to the
by a pulse derived from the modulator cathode,
amplifier driver which amplifies the pulse to drive the
provides the acknowledge pulse to the indicator for
modulator. Each of the pulse widths is independently
display synchronization.
adjustable: short pulse (R28); medium pulse (R23); and
long pulse (R25).
4.9.3. Circulator and Receiver RF Circuits (RT-1241)
During short pulse operation the pulse width
decoder switches the receiver IF bandwidth to 30 MHz,
The 3-port circulator couples the transmitted RF
energy from the transmitter to the antenna pedestal
medium and long pulse operation the IF bandwidth is 3
rotary joint. Reflected RF energy received by the
MHz.
antenna is coupled through the circulator to the receiver.
The non-delayed indicator trigger is applied
The receiver RF circuits process the received RF
through the STC delay generator to the STC integrator-
signals for use by the IF and video amplifier circuits.
amplifier. The output of the integrator-amplifier, the
Since the transmitter and receiver use a common
delayed STC waveform, is applied to the IF amplifier to
waveguide feed and antenna, a TR device is used to
control short range gain of the receiver. The slope of
prevent high powered transmitter pulses from feeding
the STC waveform trailing edge is set by STC Law
into the sensitive receiver circuits.
Without this
control R57 and the ANTI-CLUTTER SEA control. The
protection, the mixer crystals would be physically
STC waveform can be adjusted to approximately an
destroyed, and the local oscillator damaged. The
eight-mile range to control short range gain.
passive limiter provides protection for the crystals
Maintenance test switches provide local control of
against pulses from other transmitters when the radar is
the receiver transmitter status (off, standby, on) and
switched off.
selection of the PRF and pulse width.
The mixer crystals, CR5 and CR6, combine the
received RF signal (at the transmitter frequency) with
4.9.2. Transmission Circuits (RT-1241)
the signal from the local oscillator (45 MHz above the
transmitter frequency) to produce the 45-MHz echo
signals for the receiver.
The local oscillator is
4.9.2.1. Modulator-Transmitter Circuits (V4). -The
mechanically adjustable and, electrically tunable from
primary function of modulator V1 is to provide a means
the indicator TUNE control.
of pulsing the magnetron transmitter. The modulator is
the same type used in the X-band radar but is driven
4-18
Previous Page
