Icom MR-1220 Instruction Manual - Page 20

2 Basic operation Basic radar theory Radar finds targets by receiving electromagnetic radiation reflected from large vessels, bridges, or other nearby metal objects. Receiving unwanted reflections from some objects may cause false echoes on screens where the target does not exist. By understanding these phenomena logically and adjusting the radar function appropriately, some of these false echoes can be reduced. DDMultiple echoes Multiple echoes may be displayed when a short-range and strong echo is received from a vessel, a bridge, or a breakwater. Multiple echoes will be displayed beyond the target's true echo point on the same bearing of a large target. You can reduce them by properly adjusting SEA / control. See page 8 for more information on SEA / control. DDIndirect echoes Indirect echoes may be returned from a passing vessel or from a reflective surface such as the mast of your vessel. A target Scanner True echo Your vessel A target Multiple echoes True echo DDSidelobe echoes Radiation escapes on both sides of the beam in the sidelobe. If a target reflects this radiation, it will be displayed on the screen as an echo. Sidelobe echoes usually occur as a result of large (strongly reflecting) targets at a short distance. You can reduce them by properly adjusting SEA / control. See page 8 for more information on SEA / control. Mast or similar obstruction False echo Indirect echoes from the reflective surface appear in different orientations than direct (true) echoes, but the distance is approximately the same for both. A target True echo Your vessel Bridge Indirect reflection Mirrored image of the target Indirect echo Sidelobes Main beam True echo Sidelobe echoes 15