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Reducing Interference
2. OPERATIONAL OVERVIEW
Reducing Interference_
Basically there are three types of interference which may hinder radar reception: sea dutter
caused by echoes reflected of waves (mentioned earlier), precipitation dutter due to
weather conditions, and radar interference from other shipbome radars operating nearby
on the same frequency band. This radar can eliminate or reduce these types of interference.
Precipitation dutter
The vertical beamwidth of the scanner is designed to see surface targets even when the ship
is rolling. However, by this design the unit will also detect rain storms, snow, or hail in the
same manner as normal targets. Precipitation dutter is easily recognizable by its wool-like
appearance on the display (see Figure 2-11). When this type of interference obscures a large
areabf the screen, you may use the
FTC
switch and/or the
A/C RAIN
control to eliminate or
reduce the interference.
The FTC (Fast Time Constant) circuit works by splitting up these unwanted echoes into a
speckled pattern, making recognition of solid targets easier. When only a slight amount of
dutter is visible on the screen, turn the
A/C RAIN
control clockwise to distinguish targets from
the dutter. In heavy storms or partial dutter, activate the FTC circuit by pressing the
A/C
RAIN
control. Then, adjust the
A/C RAIN
control to reduce the dutter. "FTC" appears at the
upper right-hand corner of the display when the FTC circuit is turned on.
In addition to reducing dutter, the
FTC
switch can be used in fine weather to clarify the
picture when navigating in confined waters. However, with the circuit activated the receiver
is less sensitive. Therefore, turn off the circuit when there is no dutter.
(A) Rain squall,
FTC OFF
c=>
FTC
f
Indication
(B) FTC
Circuit
ON,
interference
reduced
Figure 2-llEffect of FTC
2-13
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Troubleshooting
