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2.3 SART (Search and Rescue Transponder)
A Search and Rescue Transponder (SART) may be triggered by any X-Band (3 cm) radar
within a range of approximately 8 nm. Each radar pulse received causes it to transmit a
response which is swept repetitively across the complete radar frequency band. When
interrogated, it first sweeps rapidly (0.4 µs) through the band before beginning a relatively
slow sweep (7.5 µs) through the band back to the starting frequency. This process is
repeated for a total of twelve complete cycles. At some point in each sweep, the SART
frequency will match that of the interrogating radar and be within the pass band of the
radar receiver. If the SART is within range, the frequency match during each of the 12 slow
sweeps will produce a response on the radar display, thus a line of 12 dots equally spaced
by about 0.64 nautical miles will be shown.
When the range to the SART is reduced to about 1 nm, the radar display may show also
the 12 responses generated during the fast sweeps. These additional dot responses,
which also are equally spaced by 0.64 nm, will be interspersed with the original line of 12
dots. They will appear slightly weaker and smaller than the original dots.
9500 MHz
9200 MHz
Radar antenna
beamwidth
Screen A: When SART
is distant
Screen B: When SART
is close
Lines of 12 dots
are displayed in
concentric arcs.
Echo of SART
Position of
SART
Own ship’s
position
Own ship’s
position
SART mark
length
Radar receiver
bandwidth
Sweep time
7.5 µs
95 µs
Sweep start
High speed sweep signal
Low speed sweep signal
24 NM
1.5 NM
Position of
SART
Echo of
SART
Figure 2-6 Appearance of SART signal on the radar display
2.3.1 General procedure for detecting SART response
1. Use the range scale of 6 or 12 nm as the spacing between the SART responses is
about 0.6 nm (1125 m) to distinguish the SART.
2. Turn off the automatic clutter suppression.
3. Turn off the Interference Rejector.
4. Turn off the Echo Average.