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represent areas of downdraft where the cloud dissipates. The resulting
turbulent air can make for a bumpy ride (figure 5-36).
Figure 5-36 Popcorn-Shaped Cumulous Cloud Turbulence
1st Edition, 1st Revision
5-38 18 Sep 03
COLLINS HOW RADAR WORKS
MultiScan™ Radar Table of Contents
TABLE OF CONTENTS
Title Page
The Radar System ........................................................................... 6-1
Frequency Comparison .................................................................... 6-2
Gain .................................................................................................. 6-4
Calibrated Gain Color Scheme ..................................................... 6-4
Gain Control Settings .................................................................... 6-5
Gain Tables ................................................................................... 6-6
Airbus ........................................................................................ 6-6
Boeing ....................................................................................... 6-7
Effects Of Gain Selection .............................................................. 6-8
Antenna Characteristics ................................................................. 6-12
Parabolic Versus Flat-Plate Antennas ........................................ 6-12
Antenna Side Lobes and False Windshear Warnings ................ 6-14
Antenna Calibration .................................................................... 6-16
Antenna Stabilization .................................................................. 6-17
Radar Beam Characteristics .......................................................... 6-19
Beam Diameter ........................................................................... 6-20
Range And Azimuth Resolution .................................................. 6-21
Beam Attenuation ....................................................................... 6-23
Sensitivity Time Control (STC) ................................................ 6-24
Long-Range Color Enhancement ............................................ 6-26
Path Attenuation (Radar Shadow) .......................................... 6-27
Radome Characteristics ................................................................. 6-30
Cat’s Eyes/Ghost Targets ........................................................... 6-30
Radome Inspection ..................................................................... 6-31
Doppler Turbulence ........................................................................ 6-32
Windshear ...................................................................................... 6-33
Windshear Event ........................................................................ 6-33
Automatic Enable ........................................................................ 6-35
Collins’ Windshear Philosophy ................................................... 6-36
Alert Level Activation Regions .................................................... 6-39
Airbus ...................................................................................... 6-40
Boeing ..................................................................................... 6-42
MVD™ Windshear Recording ..................................................... 6-43
1st Edition, 1st Revision
18 Sep 03 i
HOW RADAR WORKS COLLINS
Table of Contents MultiScan™ Radar
Title Page
Alien Radar ..................................................................................... 6-44
Radiation Hazards .......................................................................... 6-44
1st Edition, 1st Revision
ii 18 Sep 03
COLLINS HOW RADAR WORKS
MultiScan™ Radar The Radar System
HOW RADAR WORKS
THE RADAR SYSTEM
The critical factor for weather detection for any radar is “loop gain”.
Loop gain is defined as the difference between the signal generated by
the transmitter and the signal processed by the receiver (figure). A
high power output combined with a sensitive receiver yields a high loop
gain, which allows the weather signal to be processed and separated
from atmospheric noise. Although many factors affect loop gain
performance, four of the primary ones are:
• R/T power output and pulse width (the more the better)
• Receiver sensitivity (the more sensitive the better)
• Flat-plate antenna technology (how well the antenna focuses the
radar beam)
• Radome performance (how transparent the radome is)
Figure 6-1 Loop Gain (Signal to Noise Ratio)
1st Edition, 1st Revision
18 Sep 03 6-1
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Collins Weather Radar operator’s guide(34)
