Furuno FAR-2107 Series Service Manual page 417

- CR802, 803
CR802 and 803 serve to protect the Magnetron. When the trigger is switched from
ON to OFF, counter-electromotive force (overshoot) generated on the Magnetron is
released to the GND line.
- L3 (MD board)
L3 serves to protect the heater power supply circuit. L3 prevents the leakage of
high voltage generated at the pulse transformer from flowing to the heater power
supply circuit.
Circulator
The radar antenna is used commonly for sending and receiving. The circulator performs
switching between sending and receiving. The circulator has three I/O ports and has a
permanent magnet and ferrite core arranged in the center. It serves to output
electromagnetic waves coming from one port to a particular direction. For instance,
electromagnetic waves coming from a port connected to the Magnetron are outputted to
the antenna connecting port and not outputted to a port connected to the MIC to protect
the receiving circuit from a large level of electromagnetic waves. During receiving
signals, receiving waves from the antenna are outputted to the MIC connecting port to
reduce the loss of receiving waves.
Receiving circuit
Receiving waves from the circulator are inputted to the MIC via a diode limiter or TR
Note
limiter . If strong sending waves are inputted from other ship, there is a risk of the
MIC being damaged. To protect the MIC from damage, the diode limiter attenuates
strong sending waves. The MIC is comprised of a local oscillation circuit, a LNA circuit,
PIN ATT circuit and a frequency conversion circuit, which converts received signals to
IF signals of 60 MHz.
Note:
- Diode limiter: FAR-2xx7, FAR 2x37S
- TR limiter: FAR-2827W, FAR-2837SW
7-12
7.2 Antenna Unit