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PRIMUS
r
880
Digital
W
eather
Radar
System
A28-1146-102-00
Radar Facts
5-37
VARIABLE GAIN CONTROL
The PRIMUS
â
880 Digital Weather Radar variable gain control is a
single turn rotary control and a push/pull switch that is used to control
the radar’s receiver gain. With the switch pushed in, the system is in the
preset, calibrated gain mode. In calibrated gain, the rotary control does
nothing.
When the GAIN switch is pulled out, thesystem enters the variable gain
mode. Variable gain is useful for additional weather analysis. In the WX
mode, variablegain can increase receiversensitivity over the calibrated
level to show very weak targets or it can be reduced below the
calibrated level to eliminate weak returns.
WARNING
LOW VARIABLE GAIN SETTINGS CAN ELIMINATE HAZARDOUS
TARGETS.
RAIN ECHO ATTENUATION COMPENSATION
TECHNIQUE (REACT)
Honeywell’s REACT feature has three separate, but related functions.
D Attenuation Compensation - As the radar energy travels through
rainfall, the raindrops reflect a portion of the energy back toward the
airplane. This results in less energy being available to detect
raindrops at greater ranges. This process continues throughout the
depth of the storm, resulting in a phenomenon known as
attenuation. The amount of attenuation increases with an increase
in rainfallrate and with an increase in the range traveled throughthe
rainfall (i.e., heavy rain over a large area results in high levels of
attenuation, while light rain over a small area results in low levels of
attenuation).
Storms with high rainfall rates can totally attenuate the radar energy
making it impossible to see a second cell hidden behind the first cell.
In some cases, attenuation can be so extreme that the total depth
of a single cell cannot be shown.
Without some form of compensation, attenuation causes a single
cell to appear to weaken as the depth of the cell increases.