Furuno FAR-2107 - Manual (Page 113)

1. RADAR OPERATION
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The range scale is automatically set to 24 nm. The radar screen will show one or
two arcs. If the radar transmitter and receiver are in good working conditions in
as much as the original state when the monitor was turned up, the innermost
arcs should appear between 13.5 to 18.5 nm. The performance monitor can
observe a total of 10 dB loss in transmitter and receiver.
Transmitter: normal
Receiver: normal
Transmitter and receiver:
10 db loss
Echo is not visible
13.5 nm
18.5 nm
Display Radar State
Note: The lengths of the arcs may vary according to installation environment.
Judge the strength of the echo which appears within 90° behind own ship
to confirm if the radar is working properly or not.