Furuno 1943, 1933, 1833 manual False echoes, Multiple echoes, Sidelobe echoes

2. RADAR OPERATION

2.27.2False echoes

Occasionally echo signals appear on the screen at positions where there is no target or disappear even if there are targets. False target situations may be recognized, however, if you understand why they are displayed. Typical false echoes are shown below.

Multiple echoes

Multiple echoes occur when a transmitted pulse returns from a solid object like a large ship, bridge, or breakwater. A second, a third or more echoes may be observed on the display at double, triple or other multiples of the actual range of the target as shown below. Multiple reflection echoes can be reduced and often removed by decreasing the gain (sensitivity) or properly adjusting the [A/C SEA] control.

True echo

Target

Own ship

Multiple echo

Multiple echoes

Sidelobe echoes

Every time the radar pulse is transmitted, some radiation escapes on each side of the beam. This stray RF is called a “sidelobe.” If a target exists where it can be detected by the sidelobes as well as the main lobe, the side echoes may be represented on both sides of the true echo at the same range. Sidelobes show usually only on short ranges and from strong targets. They can be reduced through careful reduction of the gain or proper adjustment of the A/C SEA control.

Target A

Target B

(Spurious) Target B

(True)

Sidelobe echoes

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