Sart (Search And Rescue Transponder) - Furuno FR-7041R-MARK-2 Operator's Manual

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.
Screen A: When SART
is distant
Position of
SART
9500 MHz
9200 MHz
Figure 2-6 Appearance of SART signal on the radar display
2. INTERPRETING THE DISPLAY
Screen B: When SART
Radar antenna
beamwidth
Position of
SART
SART mark
length
Radar receiver
bandwidth
Sweep time
7.5 µs
95 µs
is close
2-5