JRC JMR-92 Series Field Service Manual page 74

Fig. 2.3.1, Fig. 2.3.2, and Fig. 2.3.3 show the function system diagram for the scanner unit /
transmitter-receiver unit of 3-unit, 2-unit, and 2-unit solid state respectively. In the 3-unit type, the
transmitter-receiver unit is installed indoors, away from the scanner unit. In the 2-unit type, the
transmitter-receiver unit is installed inside the scanner unit.
Magnetron Scanner Unit
When the +48V power supply in the display unit starts, the power supply circuit in the
transmitter-receiver unit activates and power is supplied to the circuits in the scanner unit and the
transmitter-receiver unit. Once the power supply starts, the CPU in the interface circuit starts and
perform initial settings. Then the preheating of the magnetron begins, and the transmitter-receiver
unit waits for a communication signal to be sent from the display unit. When it receives the
communication signal from the display unit, a communication link is established, and the scanner
unit and the transmitter-receiver unit are subsequently controlled from the display unit.
While the magnetron is preheating, the interface circuit sets the operation of the various circuits
in the transmitter-receiver unit according to the initial setting values it receives from the display
unit. When the preheating is complete, the transmitter-receiver unit notifies the display unit. When
the user performs the operation to start transmission, the display unit sends the transmission start
command via the communication line and the transmitter-receiver unit starts the rotation of the
antenna motor and begins transmission.
A transmission timing pulse is generated in the interface circuit, which is input to the modulator
switching circuit for high voltage switching. The pulse transformer further increases the voltage of
the high-voltage pulse, and the high voltage is applied to the magnetron. In this way,
pulse-modulated microwaves are obtained. The pulse width of the radar wave and the
pulse-repetition frequency are specified by means of control commands from the display unit.
The radar wave passes through a duplexer circuit that uses a circulator and then through a rotary
joint, before being transmitted into the air from the antenna. A signal reflected from a target is
input from the antenna to the receiving block using the duplexer function. The received signal is
amplified before being converted to the IF frequency, after which logarithmic detection is
performed and the signal becomes a radar video signal. If the receiving tuning function is set to
the auto mode, the interface circuit processes the received signal and automatically controls the
tuning voltage so as to match the optimum local frequency.
When the interface circuit turns on the scanner unit relay, AC power is supplied to the motor
driver circuit and the antenna motor rotates. If the safety switch is off, the power supplied to the
motor driver is forcibly shut off, stopping the rotation of the antenna motor. The beam azimuth of
the antenna is detected by the encoder.
The received radar video signal, the transmission timing signal, and the antenna rotation signal
are all sent to the display unit. The radar video signal is an unprocessed log-compressed signal.
The antenna rotation signal is an incremental signal which uses the 2048 pulse/rotation pulse and
the azimuth reference pulse.
When a set period of time has elapsed after the communication signal from the display unit has
Chapter 2 System Configuration 2-16