TM 11-5840-360-14-1-1
ranges. In any event, small readjustments of the GAIN
3.7.11 ANTI-CLUTTER SEA Control
control may be necessary after adjusting the ACS knob.
The ANTI-CLUTTER SEA (ACS) control, also
3.7.12 ANTI-CLUTTER RAIN Control
known as the sensitivity time control, is an auxiliary gain
control. While the GAIN control affects echo strength
uniformly throughout all ranges, the effect of ACS is
The function of the ANTI-CLUTTER RAIN
greatest on short-range echoes, becoming progressively
(ACR) control is to reduce the displayed size of the large
less as range increases.
echoes which, because of their size, may overlap and
obscure smaller echoes in their immediate vicinity. This
The range of ACS control is variable from 0 to
is particularly true of large echo areas depicting rainfall
more than 3 miles to allow an optimum picture to be
and large land masses. The control causes only the
obtained under adverse weather conditions. Maximum
leading edges of large echoes to be displayed, but
reduction in the strength of nearby echoes occurs when
affects small echoes only slightly (see Figure 3-4).
the ACS knob is turned fully clockwise; when turned fully
counterclockwise, there is no reduction in echo strength.
ACR can be used to great advantage on short
Specifically, ACS reduces the strength of the mass of
range settings to distinguish between two very close
random echoes received from nearby waves. ACS
echoes on the same bearing which would otherwise be
should be used to reduce the strength of the echoes
merged into one echo. The control is a combined switch
such that clutter appears only as small dots, and small
and potentiometer. When fully counterclockwise (OFF)
objects can be distinguished (see Figure 3-3).
the fast-time constant circuit is switched off. As the
control is turned clockwise, the effectiveness of ACR
progressively increases.
NOTE:
3.7.13 FTE ON/FLASH OFF Switch
At short ranges, the setting of the
ACS knob should never be advanced
This is a spring-loaded 3-position (center off)
so far as to completely obliterate all
toggle switch. When held in the FTE ON position, the
clutter, since this setting could result
FTE (False Target Elimination) circuit is turned on to aid
in the loss of echoes. At long ranges
in recognition of false targets. If a target is suspected as
(8 miles and up) turning the knob
being false, its location should be noted on the PPI and
fully clockwise will reduce bloom at
verified for two or three sweeps. On the next sweep,
the CRT center without any loss of
just before the sweep line approaches the location of the
useful information. This will help to
false target, the FTE ON/FLASH OFF switch should be
extend the life of the CRT.
set and held in the FTE ON position. If the target is
true, its location will remain stationary on the PPI as the
Clutter appears on the display as a very large
previous sweeps. If the target is false, its position will
number of small echoes. The positions of these echoes
shift out toward the edge of the PPI display, and in some
vary from scan to scan, usually covering a considerable
cases, disappear completely.
area. Sea clutter is usually limited to a range of
approximately 3 to 4 miles from the vessel when the sea
When the switch is held in the FLASH OFF
is rough. The area of sea clutter is approximately oval
position, the normally displayed ship's heading line is
in shape, not centered about the vessel, and with the
switched off when its display would obscure an echo.
largest part lying to windward.
3.7.14 GAIN Control
When the ACS knob is adjusted from the
optimum setting, a crescent of clutter will probably
Rotation of the GAIN control varies receiver
remain in the windward direction. Excessive application
gain, and thus the strength of the echoes (and noise
of ACS will create a zone of darkness around and
signals) on the display. The normal setting for this
beyond the maximum range to which the clutter
control produces a light background speckle on the
extends. This may eliminate many desired echoes,
display.
The radar is most sensitive when this
particularly if the GAIN control is set so that the
background speckle is just visible; objects will then be
speckled background is not clearly visible at longer
detected at the greatest possible range (see Figure 3-5).
3-11
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