JRC JMA-5212-4, Service Manual

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2-7
Figure 2.2 shows the functional system diagram of the scanner unit for this equipment.
When the power relay for the scanner unit in the display system is turned on and power is
supplied to the scanner unit, the power circuit starts power supply to each circuit of the
scanner unit. The CPU in the interface circuit is started by starting the power supply, and
preheating of the magnetron is started after initialization. The scanner unit waits for a
communication signal from the display system. A communication link is established when
a communication signal is received, and then the scanner unit is placed under control of the
display system.
While the magnetron is being preheated, the interface circuit sets the operation of each
circuit of the scanner unit according to the initial setting value transmitted by the display
system. After completion of preheating, the scanner unit informs the display system that
the preheating is complete. When the operator performs operation to start transmission, a
transmission start command is sent through the communication line from the display
system, and the scanner unit starts the scanner motor and the transmission.
A transmission timing pulse is generated in the interface circuit and input to the modulator
switching circuit. After high-voltage switching for the modulator, the high-voltage pulse is
further boosted by the pulse transformer and applied to the magnetron for obtaining
pulse-modulated microwave. The radar-signal pulse width and repetition frequency are
specified by a control command from the display system.
The radar signal passes through the duplexer circuit configured with the circulator and
the rotary joint and transmitted into space from the antenna.
A signal reflected from a target is input through the antenna, and then input to the
receiving block by the duplexer function. After the received signal is amplified, it is
converted to IF frequency and log-detected, and turns into a radar video signal. If the
receiving tuning function is in automatic mode, the interface circuit processes the received
signal and automatically controls the tuning voltage to obtain optimum local frequency.
The motor power circuit controlled by the interface circuit is turned on, DC power is
supplied to the motor driver circuit, and the motor starts running. The rotation control
signal output by the interface circuit is supplied to the motor driver circuit after
frequency-voltage conversion in the motor power circuit, by which the motor speed is
controlled. When the safety switch is turned off, power supply to the motor driver is
forcibly turned off, by which the motor is stopped. The radiation bearing of scanner beam
is detected by the encoder.