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 AF 121, 122; SN 351-399  CONFIG 3  01 Page 31  Apr 25/9834-43-00
 WEATHER RADAR SYSTEM - DESCRIPTION AND OPERATION
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 1.  General
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 A.  The weather radar system is a navigation system which uses the reflective effect of microwave pulses on material substances to obtain a picture of conditions ahead of the airplane. Weather radar operation is based on the fact that water particles present in the air as rainfall (generally associated with storm cells) reflect a radar beam with intensity in proportional to the moisture concentration.
 B.  AF 160, 162-171; The weather radar operates in the X-band and has a penetration range through relatively light intervening rainfall to detect distant rainfall storm areas at ranges of up to 320 miles. With the system in weather plus turbulence (WX+T) mode, four colors - green, yellow, red, and magenta - represent increasing levels of rainfall concentration are useful in identifying storm cells with heavy rainfall or steep rainfall gradients. Strong echoes may also return from other objects (such as mountains) and may also be displayed on the indicator.
 C.  AF 183, 184; The weather radar operates in the X-band and has a penetration range through relatively light intervening rainfall to detect distant rainfall storm areas at ranges of up to 320 miles. With the system in search (SCH) mode, four colors - green, yellow, red, and magenta - represent increasing levels of rainfall concentration are useful in identifying storm cells with heavy rainfall or steep rainfall gradients. Strong echoes may also return from other objects (such as mountains) and may also be displayed on the indicator.
 D.  The weather radar system consists of one control panel, two receiver/transmitter units, two indicator control units, a waveguide switch, waveguide, and an antenna assembly (Fig. 1).
 E.  Visual display of hazardous weather conditions or a display of the terrain ahead of the airplane, is presented on the indicators. The control panel switches and controls and indicator controls allows the crew to select various modes of weather operation depending upon the type of video data desired. The receiver/transmitter generates and transmits high energy radio frequency (rf) pulses which are radiated by the antenna. A small portion of the radiated energy is reflected back to the airplane by moisture laden clouds or by major terrain features. The reflected signals are received by the antenna, processed by the R/T unit, and displayed on the indicators (Fig. 1 and 2).
 F.  The weather radar systems normally operate from 400-Hz, single-phase, 115-volt ac power from electronic circuit breaker panel P7. The captain's (No. 1 system) R/T and indicator receive power from the P7 essential radio bus while the first officer's (No. 2 system) R/T and indicator receive power from the P7 radio bus No. 2.
 G.  The weather radar system has three self-test features: the
 overtemperature fault indicator on the face of the R/T unit, the
 alphanumeric failure message displayed on the indicator, and the
 self-test video pattern on the indicator in TEST mode.

 H.  The inertial reference system provides stabilization signals for the weather radar systems.
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 AF 160, 162-171, 183, 184  CONFIG 4  01 Page 1  Sep 25/9434-43-00
TRANSMITTER RECEIVER/ (2 PLACES)  SEE  B  C  (2 PLACES) TRANSMITTER RECEIVER/ 
SEE  A  C 
WAVEGUIDE 
PASSENGER R/T MOUNT) WAVEGUIDE SWITCH (PART OF DUAL  DSEE WEATHER RADAR FLAT PLATE ANTENNA  FREIGHTER  DSEE WEATHER RADAR FLAT PLATE ANTENNA 

SEE E
SEEF SEEE
Weather Radar System - Component Location
Figure 1 (Sheet 1)

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CONFIG 4AF 160,162-171,183,184799 Page 2
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Sep 25/94
 E39572
RECEIVER/
TRANSMITTER R/T COOLING FAN

RECEIVER/
NO. 2 TEST SWITCHESTRANSMITTER ON AFT SIDE
NO. 1
R/T MOUNT OF R/T MOUNT
R/T MOUNT WAVEGUIDE
WAVEGUIDE TO ANTENNA
SHELF
ASSEMBLY

FORWARD EQUIPMENT CENTER RACK
PASSENGER
A
AIRPLANE RECEIVER/ FLOOR BEAM TRANSMITTER NO. 2
RECEIVER/ TRANSMITTER NO. 1
R/T MOUNT WAVEGUIDE TO ANTENNA
FREIGHTER
B
Weather Radar System Component Location
Figure 1 (Sheet 2)

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Sep 25/94
E39574

RECEIVER/TRANSMITTER CONTROL PANEL

Weather Radar System Component Location
Figure 1 (Sheet 3)

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CONFIG 4 AF 160,162,171,183,184
799 Page 4
　
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