Furuno FR-7252, FR-7112, FR-7062 manual Sart Search and Rescue Transponder, Iii

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 n.miles. 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 μsec) through the band before beginning a rela- tively slow sweep (7.5 μsec) 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 radar to the SART is reduced to about 1 n.miles, the radar display may show also the 12 respopnses generated during the fast sweeps. These additional dot responses, which also are equaly spaced by 0.64 nautical miles, will be interspersed with the original line of 12 dots. They will appear slightly weaker and smaler than the original dots.

Screen A: When SART	Screen B: When SART
is distant	is close

Radar antenna beamwidth

Position

of SART

SART mark

length

9500 MHz

Radar receiver

9200 MHz

7.5 µsSweep time 95 µs

bandwidth

Low frequency sweep signal

Sweep starting

Fast sweep signal

Showing SART marks on the radar display

To show the SART marks only on the radar display, detune the radar receiver by the manual tuning out of best tuning condition. This erases or weakens all normal radar ech- oes, but, the SART marks are not erased because the SART response signal scans over all frequencies in the 9 GHz band. When the radar approaches the SART in operation, the SART marks will enlarge to large arcs, blurring a large part of the screen. Reduce the sensitivity and adjust the sea clutter control of the radar.

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