Indirect Echoes; Multiple Echoes; Blind Sectors Or Shadow Effect - Raymarine RL70C Owner's Handbook Manual

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Indirect Echoes

There are several types of indirect echoes or ghost images. These sometimes
have the appearance of true echoes, but in general they are intermittent and
poorly defined.
Indirect (false) echoes
False echo
Passing
ship

Multiple Echoes

Multiple echoes appear if there is a large target with a wide vertical surface at a
comparatively short range. The transmitted signal will be reflected back and
forth between the target and your own ship. Multiple echoes therefore appear
beyond the true target's echo on the same bearing (as shown below). This is not
very common.
MULTIPLE ECHOES

Blind Sectors or Shadow Effect

Funnels and masts, when located near the antenna array, may cause shadows. In
shadow areas beyond the obstruction there will be a reduction of the beam
intensity, although not necessarily a complete cut-off. However, there will be a
blind sector if the subtended angle is more than a few degrees. There may also
be multiple echoes which extend behind the obstruction. This should be
avoided by careful selection of the scanner site prior to installation (see
Chapter 8).
True echo
Mast
or funnel
True echo
Multiple echoes
HSB Series LCD Display
True echo
False echo
D1641-2
D1642-1