747飞机维护手册AMM CHAPTER 34 - NAVIGATION 第34章导航3(89)

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 8.  Waveguide Switch
________________
 A.  A waveguide switch connects the two R/T unit waveguides to the antenna, or to a dummy load (if provided) flange mounted on a switch port. The waveguide switch is a conventional RF type of switch, controlled by the system transfer switch on the control panel. It connects through the use of quick-disconnect fasteners. When a GND TEST/NORMAL switch is provided on the radar control panel, the GND TEST position causes the waveguide switch to direct rf from the R/T into the dummy load.
 9.  Reflectometer (On all GN and MD airplanes)
_____________
 A.  A reflectometer used for maintenance testing of rf power and VSWR measurements may be permanently installed in the waveguide run at the R/T units (Fig. 1). The incident and reflected wave test ports on the reflectometer have protective covers that are removed during maintenance tests.
 10. Operation
_________
 A.  Functional Description, Video Generation and Display (See figure 3.)
 (1)  The warmup cycle for the dual radar system is controlled by the mode selector switches on the radar control panel as follows:
 (a)  
If the STBY button is depressed but not latched in, both systems will be in standby mode and after approximately 3-1/2 minutes, be ready for operation in any one of the four operate modes: NORM, CONT, MAP or TEST.

 (b)  
If the STBY button is depressed and latched in, the selected system goes into standby mode and will be ready for operation in approximately 3-1/2 minutes. The other system will be off.

 EFFECTIVITY
 AF 101-120, 123-156, 158,

 159, 172-182, 185-199;  SN 301-350; IB 405; GN ALL; CONFIG MD ALL; VM ALL  02 Page 7
   Sep 25/94

34-43-00
FROM R/T 2
CIRCULATORS RECEIVER-TRANSMITTER 1

UNRESOLVED SWEEP
ANTENNA
RESOLVED SWEEP
Weather Radar System Display AND Video Generation - Block Diagram
Figure 3 (Sheet 1)

EFFECTIVITY AF 101-120,123-156,158,159,
 CONFIG 2172-182,185-199; SN 301-350, 799 Page 8 IB 405; GN ALL; MD ALL; VM ALL Sep 25/94
34-43-00

INDICATOR
Weather Radar System Schematic Figure 3 (Sheet 2)
EFFECTIVITY AF 101-120,123-156,158,159,
 CONFIG 2 172-182,185-199; SN 301-350; 799 Page 9IB 405; GN ALL; MD ALL; VM ALL Sep 25/94
34-43-00
 (c)  
When the selected system is placed into an operate mode, the other system goes into standby and will be ready for operation in approximately 3-1/2 minutes.

 (d)  
After initial warmup has taken place in both systems, either system may be selected and will operate within 3 seconds after selection.

 (2)  
The magnetron output is applied through the fixed circulator to the waveguide switch, which connects either R/T 1 or R/T 2 to the antenna, depending on the R/T selected at the control panel. During receive mode, the T-R switch and fixed circulators pass the received RF to the balanced mixer, supplying the 30 MHz difference frequency to the IF amplifier. A sample of the transmitted pulse is coupled to the AFC mixer to be compared with the local oscillator frequency, and keep the IF tuned.

 (3)  
The trigger generator is range-gated and applied to the sweep generator, supplying unresolved sweep to the antenna. The antenna furnishes the resolved X and Y sweep to the indicator sweep amplifiers, which in turn drive the deflection yoke. The trigger generator output is also supplied to the erase generator to erase the display.

 (4)  
The range gate generator is controlled by the RANGE switch, and supplies the selected gate to the range marks generator. The range marks are added to the video in the amplifier and shaping circuits, and applied to the display storage tube. During iso-echo contour operation (CONT selected on control panel), the radar video is inverted to furnish a negative display; that is, the center of the storm appears as a black spot.

 (5)  
The transmitting pulse repetition rate of 200 PPS is determined by the trigger generator, which controls modulator pulsing through a switch drive. Protective circuits monitor VSWR and power output to prevent transmissions when these monitor signals are not within tolerance; and also protect the solid-state devices against magnetron arcing, short circuits, open circuits, silicon controlled rectifier (SCR) lock-on, and loss of trigger. Recovery is automatic when the fault has been cleared.

 B. Functional Description, Antenna Stabilization (See figure 4.)
 (1)  
The antenna is driven in a split-axis dual-drive manner; that is, all drive components are duplicated such that either R/T may provide the drive signals in elevation, azimuth, and roll. The duplicated components are shown on figure 4 as double-lined circles and boxes.
　
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