Furuno FR-8252 Sart Search and Rescue Transponder, Sart description, Appearance of Sart echo

2. RADAR OBSERVATION

2.3SART (Search and Rescue Transponder)

2.3.1SART description

A Search and Rescue Transponder (SART) may be triggered by any X-band (3 cm wavelength) 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 interro- gated, 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 dis- play, thus a line of 12 dots equally spaced by about 0.64 nautical miles will be shown.

When the radar to the SART is reduced to about 1 nm, the radar display my show also the 12 responses generated during the fast sweeps. These additional dot responses, which also are equally spaced by 0.64 nautical miles, 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	Screen B: When SART
is distant	is close

Echo from SART	Radar antenna
	beamwidth
24 NM	1.5 NM

Position of

SART

Lines of 12 dots are displayed in concentric arcs.

Echo from

SART

Own ship position

Own ship
position	Position of

9500 MHz

SART mark length

SART

Radar receiver

9200 MHz 7.5 μs Sweep time 95 μs

bandwidth

Low speed sweep signal Sweep start

High speed sweep signal

Appearance of SART echo

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