Suppressing Precipitation Clutter; Interference Rejector - Furuno FR-2125V Operator's Manual

1.15 Suppressing Precipitation Clutter

In adverse weather conditions, clouds, rain or snow produce a lot of spray-like spurious
echoes and impairs target detection over a long distance. This situation can be improved
by using a function key provided that it is so programmed. If the function key fails to offer
a favorable suppression of the rain clutter, adjust the [A/C RAIN] control on the control
head.
BRILLIANCE
#1
OFF ON
#3
EBL
The [A/C RAIN] control adjusts the receiver sensitivity as the [A/C SEA] control does but
rather in a longer time period (longer range). Clockwise rotation of this control increases
the anti-clutter effect.

1.16 Interference Rejector

Mutual radar interference may occur in the vicinity of another shipborne radar operating in
the same frequency band. It is seen on the screen as a number of bright spikes either in
irregular patterns or in the form of usually curved spoke-like dotted lines extending from
the center to the edge of the picture. This type of interference can be reduced by activating
the interference rejector circuit.
The interference rejector is a kind of signal correlation circuit. It compares the received
signals over successive transmissions and suppresses randomly occurring signals. There
are three levels of interference rejection depending on the number of transmissions that
are correlated. These are indicated by the legends IR1, IR2 and IR3 at the upper left-hand
position of the screen.
[A/C RAIN] control
A/C RAIN A/C SEA GAIN
#2
STBY
#4
RANGE
Figure 1-16 Control head, A/C RAIN effect
Figure 1-17 Interference
TX
[A/C RAIN]
off
control [A/C RAIN]
adjusted
control
1-17