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
theradar’sreceivergain.Withtheswitchpushedin,thesystemisinthe
preset, calibrated gain mode. In calibrated gain, therotary controldoes
nothing.
WhentheGAINswitchispulledout,thesystementersthevariablegain
mode. Variable gainis usefulfor additionalweather analysis.In theWX
mode,variablegaincanincreasereceiversensitivityoverthecalibrated
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, butrelated functions.
D Attenuation Compensation -As the radar energy travelsthrough
rainfall, the raindrops reflect aportion ofthe energyback towardthe
airplane. This results in less energy being available to detect
raindrops at greater ranges. This processcontinues throughoutthe
depth of the storm, resulting in a phenomenon known as
attenuation. The amount of attenuation increases with an increase
inrainfallrateandwithan increaseintherangetraveledthroughthe
rainfall (i.e., heavy rain over a large area results in high levels of
attenuation, while light rain over a small arearesults in low levels of
attenuation).
Stormswithhighrainfallrates cantotally attenuatetheradarenergy
makingitimpossibletoseeasecondcellhiddenbehindthefirstcell.
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.
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