Furuno 1942 MARK-2 Manuel d'utilisateur télécharger pdf (Page 31)

4-3

4.5 SART (Search and Rescue

Transponder)

A Search and Rescue Transponder (SART)

may be triggered by any X-Band (3 cm) ra-

dar within a range of approximately 8 n.miles.

Each radar pulse received causes it to trans-

mit a response which is swept repetitively

across the complete radar frequency band.

When interrogated, it first sweeps rapidly (0.4

∝s) through the band before beginning a rela-

tively slow sweep (7.5 ∝s) 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 inter-

rogating radar and be within the pass band

of the radar receiver . If the SAR T 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 SAR T 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

smaler 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

s

95

s

Sweep start

High speed sweep signal

Low speed sweep signal

24 NM

1.5 NM

Position of

SART

Echo of

SART

Figure 4-5 SART display

Showing SART marks on the radar

display

To show the SART marks only on the radar

display, detune the radar receiver manualy .

This erases or weakens all normal radar ech-

oes, but, the SART marks are not erased be-

cause 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, blur-

ring a large part of the screen. Reduce the

sensitivity and adjust the sea clutter control

of the radar.

Summary to detect SART response

1. Use 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.

General remarks on receiving SART

Radar range scale

When looking for a SAR T it is preferable to

use either the 6 or 12 nautical mile range

scale. This is because the total displayed

length of the SAR T response of 12 (or 24)

dots may extend approximately 9.5 nautical

miles beyond the position of the SART and it

is necessary to see a number of response

dots to distinguish the SAR T from other re-

sponses.

SART range errors

When responses from only the 12 low fre-

quency sweeps are visible (when the SART

is at a range greater than about 1 nm), the

position at which the first dot is displayed may

be as mush as 0.64 nm beyond the true po-

sition of the SAR T. When the range closes

so that the fast sweep responses are seen

also, the first of these will be no more than

150 meters beyond the true position.

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