Identifying false echo returns, Side lobes – Raymarine Radar equipment Raychart Chartplotter RC530 PLUS User Manual

Page 75

Advertising
background image

Chapter 3: Standard Radar Operations

3-5

Id

enti

fyi

ng F

al

se E

cho

Re

tu

rn

s

.t

Identifying False Echo Returns

Not all echoes are direct returns to the radar antenna. Occasionally signals
appear at positions where there is no actual target. These are called false
echoes
, and may be caused by side lobes, ghost images, indirect echoes or
multiple echoes.

This section briefly describes the echo patterns that can be produced by false
echoes and the likely cause. It should be noted that the radar operator, through
observation, practice, and experience, can generally detect these conditions
very quickly. These effects can usually be minimized using the radar controls.

Side Lobes

A small part of the RF energy from each transmitted pulse is radiated outside
the single narrow beam. This produces side lobe patterns, shown in
Figure 3-3.

Side lobes have no effect on distant or small surface objects. However, the
echo from a large object at short range may produce an arc on the radar screen
similar to a range ring or a series of echoes forming a broken arc. Side-lobe
echoes normally occur at ranges below 3nm, and can be reduced by adjusting
the SEA control.

Figure 3-3:

Side Lobes

Table 3-3:

Controls to Adjust the Radar Picture

Control

Option

Function

Default Setting

GAIN

GAIN
SEA
RAIN
FTC

Controls the strength of the target returns
Reduces sea returns
Reduces close rain or snow returns
Reduces distant rain or snow returns

AUTO
AUTO-HARBOUR
OFF
OFF

MULTI

TUNE

Fine tunes the receive

AUTO

TARGETS
Soft Key

INT REJ
EXPANSION
WAKES

Turns interference rejection on/off
Turns target expansion on/off
Turns wakes on/off and selects wakes length

ON

OFF

OFF

True echo

Side echoes

Main lobe

Antenna

Arc

Side lobe

Side lobe

D1638-2

Advertising