Furuno FAR-28 Series Operator's Manual page 117

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.
Display
13.5 nm
to 18.5 nm
Note: The lengths of the arcs may vary according to installation environment.
Judge the strength of the echo that appears within 90° behind own ship to
confirm if the radar is working properly or not.
Radar State
Transmitter: normal
Receiver: normal
13.5 nm
to 18.5 nm
Transmitter and receiver:
No arc is indication of10 db
loss. Replacement of the
magnetron is necessary.
1. RADAR OPERATION
1-95