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position sets the radar sensitivity to the standard calibrated reflectivity
levels and is the recommended position for normal operation. If desired,
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HOW RADAR WORKS COLLINS
Gain MultiScan™ Radar
the radar gain may be adjusted to increase sensitivity by rotating the
GAIN control clockwise from the CAL position or to decrease the
sensitivity by rotating the GAIN control counterclockwise from the CAL
position. The GAIN control settings and the corresponding sensitivity
changes are contained in the following tables.
GAIN TABLES
AIRBUS
Airbus gain settings correspond to the nomenclature on the Airbus
weather radar control panel (♦page 4-1). There is no EFIS indication
when CAL (calibrated) gain is selected. MAN GAIN is displayed
whenever gain is selected to other than the CAL position (♦page 4-4).
Airbus Gain Settings
WX, WX+T Modes
(see Notes 1 and 2 below)
Knob Position Gain Change EFIS Indication
MAX +16 dB MAN GAIN
+12 +12 dB MAN GAIN
+8 +8 dB MAN GAIN
+4 +4 dB MAN GAIN
CAL +0 dB
-3 –3 dB MAN GAIN
-6 –6 dB MAN GAIN
-9 –9 dB MAN GAIN
-12 –12 dB MAN GAIN
MIN –14 dB MAN GAIN
Note 1: Path Attenuation Compensation (PAC) is disabled for all
non-CAL gain settings.
Note 2: The CAL gain in the MAP mode is approximately 10 dB less
sensitive for weather targets than CAL gain is in the WX or WX+T
modes due to the different nature of ground and weather targets.
1st Edition, 1st Revision
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COLLINS HOW RADAR WORKS
MultiScan™ Radar Gain
BOEING
On Boeing aircraft, maximum gain is achieved when the GAIN knob is
rotated to its fully clockwise (CW) position. Minimum gain is achieved
when the GAIN knob is rotated to its fully counterclockwise (CCW)
position. CAL (calibrated) gain is selected when the black triangle (▼)
is rotated to the 12 o’clock position (♦page 4-2). Intermediate gain
positions are achieved by selecting the various detents between these
three positions. There is no EFIS indication when CAL (calibrated) gain
is selected. VAR (variable) is displayed whenever gain is selected to
other than the CAL position (♦page 4-7).
Boeing Gain Settings
WX, WX+T Modes
(see Notes 1 and 2 below)
Knob Position Gain Change EFIS Indication
Fully CW +16 dB VAR
+8 dB VAR
+4 dB VAR
CAL +0 dB
–2 dB VAR
–4 dB VAR
–6 dB VAR
–8 dB VAR
–12 dB VAR
Fully CCW –14 dB VAR
Note 1: Path Attenuation Compensation (PAC) is disabled for all
non-CAL gain settings.
Note 2: The CAL gain in the MAP mode is approximately 10 dB less
sensitive for weather targets than CAL gain is in the WX or WX+T
modes due to the different nature of ground and weather targets.
1st Edition, 1st Revision
18 Sep 03 6-7
HOW RADAR WORKS COLLINS
Gain MultiScan™ Radar
EFFECTS OF GAIN SELECTION
Figures 6-8 through 6-12 show the weather returns for each gain
position on a Boeing control panel. (Airbus control panels positions
produce similar returns.) MAX gain (+16 dB) is equivalent to an
approximately one and a half color level increase. MIN gain (-14 dB)
is equivalent to an approximately one and half color level decrease
(♦page 6-4).
Figure 6-8 Radar Displays with Gain set to MIN and –12 dB
1st Edition, 1st Revision
6-8 18 Sep 03
COLLINS HOW RADAR WORKS
MultiScan™ Radar Gain
Figure 6-9 Radar Displays with Gain set to –8 dB and –6 dB
1st Edition, 1st Revision
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HOW RADAR WORKS COLLINS
Gain MultiScan™ Radar
Figure 6-10 Radar Displays with Gain set to –4 dB and –2 dB
1st Edition, 1st Revision
6-10 18 Sep 03
COLLINS HOW RADAR WORKS
MultiScan™ Radar Gain
Figure 6-11 Radar Displays with Gain set to CAL and +4 dB
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HOW RADAR WORKS COLLINS
Antenna Characteristics MultiScan™ Radar
Figure 6-12 Radar Displays with Gain set to +8 dB and MAX
ANTENNA CHARACTERISTICS
PARABOLIC VERSUS FLAT-PLATE ANTENNAS
Older parabolic antennas used with magnetron radars produce a large
main beam and extensive side lobes. The width of the main beam
produces less precise weather returns than current generation flat-plate
antennas. The large side lobes can produce ground clutter range rings
and also make it impossible to use this type of radar for windshear
detection. However, the side lobes do have the benefit of providing
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Collins Weather Radar operator’s guide(36)
