JRC JMR-92 Series Field Service Manual page 75

stopped, the interface circuit switches to the protection mode and forcibly stops transmission and
the rotation of the antenna.
When the radiator is subjected to external force of wind (corresponding wind speed is greater
than 51.5m/s) that exceed the ability to drive the scanner unit, the scanner unit stop to drive the
motor. Because a built-in overload protection circuit is activated. If the scanner unit rotates by the
wind in a counterclockwise direction, the TXRX[Reverse] alarm will be appeared, and stop to
transmit. If the scanner unit rotates by the wind in a clockwise direction, the scanner unit stops to
drive the motor. Therefore the TXRX[AZI] alarm will be appeared when the wind is calm down.
When the corresponding wind speed is less than or equal to 51.5m/s, the break circuit (in the
scanner unit) can reduce the scanner rotation speed to 11rpm less than, therefore the radar can
transmit normally.
Solid state Scanner Unit
Fig. 2.3.3 shows the Function diagram of Solid state scanner unit.
Solid state scanner unit consists of motor drive unit, transceiver/receiver unit, and power supply
unit. It constructs 2-unit type marine radar equipment by connecting with the display unit.
When the +48V power supply in the display unit starts, the power supply circuit in the solid state
scanner unit activates and power is supplied to each circuits of it. Once the power supply starts,
the CPU in the Radar processor unit CDC-1492 starts and performs initial settings. Then it waits
for a communication signal to be sent from the display unit. Solid state scanner does not need
preheating. When it receives the communication signal from the display unit, a communication link
is established, and the scanner units are subsequently controlled from the display unit.
When the Radar processor received range table data that includes information such as the pulse
width of the radar wave and the pulse-repetition frequency, it starts the function setting sequence
corresponding to designated transmission and reception spec. When the function setting
sequence is finished, the Radar processor notifies the transmission and reception preparation
completion status to 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 scanner unit starts the rotation of
the antenna motor and begins transmission.
Since solid state scanner unit does not use a magnetron, it needs no preheating. Therefore, it
can begin transmission and reception immediately after the end of above settings. In this time, the
transmission control signals such as the transmission trigger signal that synchronized with the
transmission IF signal flow together, and perform the operation timing control of TRX module. The
transmission IF signal consists of unmodulated pulse signal P0N and frequency modulation pulse
signal Q0N.
TRX module performs time division transmission control. That allows P0N narrow pulse width
signal to be used for detection at the range scale which would be the blind echo in the main-bang
of Q0N wide pulse width signal. Transmission RF signal is amplified to approx.250W peak-power
by the power amplifier unit constituted of RF FETs, and it is outputs as the transmission signal
from TRX module via circulator. This signal is input to the antenna port via coaxial cable, and then
it is transmitted into the air from the antenna.
2-17 Chapter 2 System Configuration